Adjacent Segment Degeneration After Anterior Cervical Discectomy and Fusion With an Autologous Iliac Crest Graft: A Magnetic Resonance Imaging Study of 59 Patients With a Mean Follow-up of 27 Years

Adjacent Segment Degeneration After Anterior Cervical Discectomy and Fusion With an Autologous... Abstract BACKGROUND Anterior cervical decompression and fusion (ACDF) is a widely accepted surgical technique for the treatment of degenerative disc disease. ACDF is associated with adjacent segment degeneration (ASD). OBJECTIVE To assess whether physiological aging of the spine would overcome ASD by comparing adjacent to adjoining segments more than 18 yr after ACDF. METHODS Magnetic resonance imaging of 59 (36 male, 23 female) patients who underwent ACDF was performed to assess degeneration. The mean follow-up was 27 yr (18-45 yr). Besides measuring the disc height, a 5-step grading system (segmental degeneration index [SDI]) including disc signal intensity, anterior and posterior disc protrusion, narrowing of the disc space, and foraminal stenosis was used to assess the grade of adjacent and adjoining segments. RESULTS The SDI of cranial and caudal adjacent segments was significantly higher compared to adjoining segments (P < .001). The disc height of cranial and caudal adjacent segments was significantly lower compared to adjoining segments (P < .001, P < .01). The SDI of adjacent segments in patients with repeat cervical procedure was significantly higher than in patients without repeat procedure (P = .02, P = .01). The disc height of the cranial adjacent segments in patients with repeat procedure was significantly lower than in patients without repeat procedure (P = .01). CONCLUSION The physiological aging of the cervical spine does not overcome ASD. The disc height and the SDI in adjacent segment are significantly worse compared to adjoining segments. Patients who underwent repeat procedure had even worse findings of disc height and SDI. ACDF, Adjacent segment degeneration, Cervical spine, Long-term follow-up, Magnetic resonance imaging, MRI, Cervical disc height ABBREVIATIONS ABBREVIATIONS ACDF anterior cervical decompression and fusion ASD adjacent segment degeneration MRI magnetic resonance imaging sASD symptomatic adjacent segment degeneration SDI segmental degeneration index Aging of the society has increased during the last decades. As a consequence, degenerative cervical disorders are frequently surgically treated. Anterior cervical decompression and fusion (ACDF) is an accepted procedure for this treatment. Long-term follow-up studies have demonstrated clinical success rates of 84.2% to 86.4% after ACDF.1,2 Although there is no proof that ACDF is superior to discectomy without fusion, surgeons around the world tend to perform ACDF because of a lower postoperative kyphosis rate. Despite the high acceptance of ACDF, it is associated with several disadvantages. One of those is the acceleration of adjacent segment degeneration (ASD). ASD might become a symptomatic condition that requires repeat surgery (sASD). Following this awareness, several studies have reported data on radiographic outcome after anterior cervical fusion. The literature presents 2 different opinions on the development of ASD. One supports the hypothesis that ASD is the result of a physiological process of degeneration.2-4 Other authors believe that fusion increases the stress and strain at the 2 adjacent segments and thereby accelerate segmental degeneration.5-8 The prevalence of ASD using radiographic images has been reported to have a wide range, ie, from 18% to 96%.9,10 However, magnetic resonance imaging (MRI) is a more sensitive technique to evaluate the grade of disc degeneration.11,12 Until today, studies that have assessed ASD via MRI in long-term follow-up are rare and, to the best of the authors’ knowledge, currently there is no study with follow-up of more than 15 yr. It is unknown whether accelerated degeneration of the adjacent segments will stop at a certain time after ACDF. Further, it is unknown whether or not the degeneration of the adjoining segment will reach the level of the adjacent segment over time. The present study is unique and presents 2 important aspects. This is the first study that assessed the grade of degeneration of the 2 segments that are located cranial and caudal to the fused level (adjacent segments) using an MRI with a follow-up of 27 yr. Secondly, this study assessed and compared the grade of degeneration of the first and second segments, which are located cranial to the cranial adjacent segment (cranial adjoining segments) and located caudal to the caudal adjacent segment (caudal adjoining segments). The purpose of this study is to evaluate whether physiological aging of the adjoining segments would overcome the degeneration of the adjacent segments after ACDF in a long-term follow-up. METHODS We retrospectively reviewed all consecutive files of patients who had undergone a de novo 1- or 2-level ACDF for a minimum of 18 yr and a maximum of 45 yr previously at our neurosurgical department. Inclusion criteria were patients who underwent ACDF without adding a cervical plate for degenerative disorders with documentation of preoperative neurological status, a detailed operation report of the initial ACDF and repeat procedures, the postoperative process during hospitalization, the postoperative neurological status, and full contact detail. All patients who did not fulfill the inclusion criteria were excluded. Out of 451 patient files, 212 patients fulfilled inclusion criteria and 239 patients were excluded because the initial diagnosis was trauma or tumor, or incomplete clinical documents, or incomplete contact details. We were able to successfully contact 198 patients via the telephone (93.4%). Ninety-five patients participated in the study (48.0%) and 60 patients agreed to visit our department for a personal follow-up examination and an MRI scan of the cervical spine (63.2%). An MRI scan of the cervical spine was performed in 59 participants by the Department of Neuroradiology. In 1 case, an MRI scan could not be performed due to cochlea implant. The study was approved by the local ethical committee, and informed consent from all patients was obtained. Surgical Technique of Initial ACDF In all cases, a transverse skin incision was performed, and a combination of sharp and blunt dissection was used to identify the prevertebral fascia. The presumptive segment was identified using either a needle or a dissector with a blunt tip. A complete discectomy and decompression of both nerve roots were performed. An autologous iliac crest graft was harvest and tapped gently into position in each disc space. Before closure of the wound, the position of the graft was confirmed fluoroscopically. MRI Protocol A 3.0 Tesla MRI was used for all participants (Siemens Magnetom Skyra, Erlangen, Germany). The protocol for each scan consisted of T1 sagittal images (TR 833 ms; TE 12 ms; flip angle 150°), T2 sagittal images (TR 5110 ms; TE 96 ms; flip angle 150°), T1 axial images (TR 530 ms; TE 9 ms; flip angle 150°), T2 axial images (TR 5740 ms; TE 92 ms; flip angle 150°), and sagittal T2-SPACE images (TE 1600 ms; TR 232 ms; flip angle 100°). Evaluation of MRI The MRI imaging was independently reviewed using the Centricity PACS-system (General Electric Healthcare, Chalfont St Giles, United Kingdom) by an experienced neurosurgeon and a neuroradiologist. No information about the patients’ history was given. The reviewers assessed the 2 segments that were located cranial and caudal to the fused level. These 2 segments were defined as cranial and caudal adjacent segment (see Figure 1). FIGURE 1. View largeDownload slide SDI and disc height measurements. A, 1 = second cranial adjoining segment, 2 = first cranial adjoining segment, 3 = cranial adjacent segment, 4 = caudal adjacent segment, 5 = first caudal adjoining segment, 6 = second caudal adjoining segment, a = anterior disc height, b = middle disc height, c = posterior disc height; white ring: disc signal intensity (dark and/or speckled—1 point). B, White arrow = posterior disc protrusion (disc material protruding beyond the posterior margin of the vertebral body without compression—1 point), white arrowhead = anterior disc protrusion (disc material protruding beyond the anterior margin of the vertebral body—1 point). FIGURE 1. View largeDownload slide SDI and disc height measurements. A, 1 = second cranial adjoining segment, 2 = first cranial adjoining segment, 3 = cranial adjacent segment, 4 = caudal adjacent segment, 5 = first caudal adjoining segment, 6 = second caudal adjoining segment, a = anterior disc height, b = middle disc height, c = posterior disc height; white ring: disc signal intensity (dark and/or speckled—1 point). B, White arrow = posterior disc protrusion (disc material protruding beyond the posterior margin of the vertebral body without compression—1 point), white arrowhead = anterior disc protrusion (disc material protruding beyond the anterior margin of the vertebral body—1 point). Further, the reviewers assessed the 2 segments that were located cranial to the cranial adjacent segment and caudal to the caudal adjacent segment. These segments were defined as first and second cranial and caudal adjoining segments (see Figure 1). Depending on the location of the initial fusion, 2 adjacent segments (1 cranial and 1 caudal) and 4 adjoining segments (2 cranial and 2 caudal) were assessed. For MRI assessment of each segment, the authors used a modified 5-step grading system that was designed by Matsumoto et al13 (see Table 1). A T2-weighted sequence was used to determine the segmental degeneration on behalf of 5 categories specific for the segment (see Figures 1 and 2). For each category, points were given depending on the grade of degeneration. FIGURE 2. View largeDownload slide Foraminal stenosis measurements. A, T2-weighted sagittal and axial image of C4-5 with foraminal stenosis (1 point). B, T2-weighted sagittal and axial image of C7-Th1 without foraminal stenosis (0 point). FIGURE 2. View largeDownload slide Foraminal stenosis measurements. A, T2-weighted sagittal and axial image of C4-5 with foraminal stenosis (1 point). B, T2-weighted sagittal and axial image of C7-Th1 without foraminal stenosis (0 point). TABLE 1. Five-Step Grading System for Segmental Degeneration Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  View Large TABLE 1. Five-Step Grading System for Segmental Degeneration Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  View Large The total score for each segment ranged from 0 to 8 points. If 1 category could not be evaluated with absolute certainty, the authors did not assess this specific category and the maximum of possible points were downgraded according to the maximum points of this specific category. For better comparison of the degeneration, a segmental degeneration index (SDI) was created for each segment. The SDI was assessed as follows: the total of determined points according to the 5-step grading system divided by the maximum of possible points. The SDI might range from .0 to 1.0. An SDI of .0 describes a segment without signs of degeneration, whereas an SDI of 1.0 describes a segment that shows the most distinct signs of degeneration according to the 5-step grading system. The authors defined an SDI of <.333 as mild, an SDI of .334 to .667 as moderate and an SDI of >.667 as severe. If there was a disagreement between the raters concerning the grade of segmental degeneration, consensus was reached by evaluating the grade together again. The intervertebral disc height of each segment was defined as the mean of anterior, middle, and posterior disc height (see Figure 1). The mean value was assigned in cases of disagreement between the radiographic data. The SDI and the disc height of adjacent and adjoining segments were compared to each other. For comparison, the SDI of each segment was subtracted from one another. The frequency of positive and negative actual difference was compared to each other. Data Analysis SPSS software version 23 was used for statistical analysis (IBM, Armonk, New York). A P-value <.05 was considered to be statistically significant. A t-test, Wilcoxon test, and Mann–Whitney U-test were used to compare the index and the mean disc height of adjacent to the adjoining segments. RESULTS Patient Demographics Fifty-nine patients participated in this evaluation. The patients’ mean age at time of ACDF was 42 yr (range: 26-56 yr). At mean follow-up of 27 yr (range: 18-45 yr), the mean age was 70 yr (range: 51-79 yr). The basic surgical technique was identical in every case. A standard Smith-Robinson approach was performed with autologous iliac crest graft without adding of a cervical plate. A compilation of patient characteristics at follow-up is shown in Table 2. The result of the personal examination of these 59 patients was previously reported by Burkhardt et al.2 TABLE 2. Patient Characteristics at Follow-up Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  aOne case with ADR C4-5 and ACDF C6-7. View Large TABLE 2. Patient Characteristics at Follow-up Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  aOne case with ADR C4-5 and ACDF C6-7. View Large Patients With Repeat Procedure Twelve patients underwent repeat surgery for degenerative changes. The period from initial ACDF to repeat procedure varied from 1 to 27 yr. In all cases, repeat procedure was performed via an anterior approach. One patient had a third procedure 3 yr after repeat procedure and 11 yr after initial ACDF. Ten among those 12 repeat procedures were caused by sASD. In 4 of those 10 procedures, an ACDF was performed, and in 6 of those 10 repeat procedures, an ACDF with an autologous iliac crest with adding of a Caspar plate (ACDF+PS) was performed. In 2 cases, an ACDF+PS was performed at the cranial adjacent segment (1-level procedure), in 2 cases an ACDF+PS was performed at the cranial adjacent and the first cranial adjoining segment (2-level procedure), and in 2 cases an ACDF+PS was performed at the caudal adjacent segment (1-level repeat procedure). In 1 case each, an ACDF+PS (1-level repeat procedure) and an ADR was performed at the first cranial adjoining segment. A detailed compilation of all operated segments at initial ACDF and repeat procedures is shown in Table 3. TABLE 3. Initial ACDF and Repeat Procedures Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  View Large TABLE 3. Initial ACDF and Repeat Procedures Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  View Large Identification of the Affected Segment The following data are based on the operative reports, which were reviewed thoroughly. In 33 cases, the affected segment was identified using lateral fluoroscopy and a dissector or retractor with a blunt tip, the disc was not punctured via the dissector or retractor. In 26 cases, the presumptive segments were identified using lateral fluoroscopy and a needle. The correct disc was punctured in 21 cases, and the wrong disc was punctured in 5 cases (ie, in 4 cases, the cranial adjacent disc, in 1 case, the caudal adjacent disc). None of the patients in whom the wrong segment was punctured via a needle had to undergo a repeat procedure at the falsely punctured segment. In all repeat procedures, the affected adjacent or adjoining segment was located using the lateral fluoroscopy and a retractor. In none of these repeat procedures, a needle was used for identification. SDI and Disc Height Measurement The frequencies of positive findings of the 5-step grading system are shown in Table 4. TABLE 4. Compilation of Positive Findings According to the 5-Step Grading System Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  View Large TABLE 4. Compilation of Positive Findings According to the 5-Step Grading System Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  View Large A compilation of frequency of all SDI according to location of the segment is shown in Table 5. The disc height measures are shown in Figure 3. FIGURE 3. View largeDownload slide Disc height. FIGURE 3. View largeDownload slide Disc height. TABLE 5. Compilation of Frequency of Mild, Moderate, and Severe SDI SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  View Large TABLE 5. Compilation of Frequency of Mild, Moderate, and Severe SDI SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  View Large Comparison of SDI and Disc Height The SDI and disc height of cranial and caudal adjacent segments, first and second cranial and caudal adjoining segments were compared to each. A compilation of comparison for SDI is shown in Table 6, and a compilation of comparison for disc height is shown in Table 7. TABLE 6. Comparison of Adjacent and Adjoining SDI 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  View Large TABLE 6. Comparison of Adjacent and Adjoining SDI 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  View Large TABLE 7. Comparison of Adjacent and Adjoining Segment Disc Height 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  DH, disc height View Large TABLE 7. Comparison of Adjacent and Adjoining Segment Disc Height 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  DH, disc height View Large DISCUSSION The development of degenerative changes at the cervical spine is a physiological process. Boden et al14 evaluated the MRI scans of 63 asymptomatic volunteer and reported that volunteers over 40 yr of age had significantly more degenerative findings compared to volunteers under the age of 40. Also, Matsumoto et al15 reported that the frequency of degenerative findings on MRI of asymptomatic volunteers will increase with aging and that over 85% of asymptomatic volunteers over 60 yr of age had loss of signal intensity (grade 1 and grade 2) and about 25% of volunteers over 60 yr of age had posterior disc protrusion. The SDI is based on the 5-step grading system of Matsumoto et al,13,15 which has good interobserver agreement. However, the authors want to state that the SDI as an outcome measurement is not validated yet. The acceleration of ASD was first noticed after lumbar spinal fusion procedures.16 Since then, many studies have analyzed the clinical and radiographic outcome after ACDF. Gore et al17 evaluated the pre- and postoperative radiographs of 121 patients who underwent ACDF with a mean follow-up of 5 ± 3 yr. They reported a prevalence of 25.6% for ASD. In a 21-yr follow-up series, Gore et al10 reported a postoperative prevalence of 32.0% for ASD. Goffin et al,5 however, reported a 92.0% rate of ASD at the superior and/or inferior adjacent disc levels in a considerably shorter follow-up of over 5 yr. In these earlier studies, lateral radiographs were taken to assess the degeneration. It has to be noted that radiographs are limited in their ability to assess the degeneration of the disc itself. Since the late 1990s, MRI is frequently used in diagnostics, and it is the most sensitive technique in order to evaluate degeneration of the disc. However, there are only a small number of studies available in the literature that used an MRI to assess ASD after ACDF with a follow-up of at least 5 yr.4,15,18 To our knowledge, the present study is the first using an MRI to assess the grade of degeneration of both adjacent and adjoining segment after ACDF with a mean follow-up of 27 yr’ follow-up. Further, it is the first comparing the adjacent to the adjoining segments. The data of the present study demonstrate that the adjacent segments have a higher SDI and lower disc height than the adjoining segment. This shows that the physiological process of degeneration does not overcome the accelerated degeneration of the adjacent segment, not even after more than 18 to 45 yr. Further, ACDF seems to increase the stress on the cranial adjacent segment more than on the caudal adjacent segment. Similar findings concerning the progression of decrease of signal intensity and progression of posterior disc protrusion at the adjacent segment have been reported by Matsumoto et al.15 Recently, it has been reported that the addition of a cervical plate tends to increase adjacent segmental motion and decrease adjacent segmental disc height.19 Further, it has been reported that the plate to adjacent segment disc space distance has influence on the adjacent segment ossification.20,21 At last, it has been reported that the risk of developing degenerative changes at the adjacent segment is 3 times higher in case of a falsely punctured cervical disc.22 Therefore, the authors want to state that the grade of degeneration of 5 cranial adjacent segments and of 2 caudal adjacent segments might have been influenced due to adding of a Caspar plate at repeat procedure. Further, the authors want to state that the grade of degeneration of 4 cranial and 1 caudal adjacent segments might have been influenced by faulty puncture via a needle during identification of the affected segment. Interestingly, ACDF also had an effect on the degeneration of both adjacent and adjoining segments in patients who underwent repeat procedure at the cervical spine. The SDI and the disc height of cranial adjacent segments were significantly higher in patients who underwent repeat procedure compared to patients without repeat procedure. A possible explanation for this finding is that genetic predisposition and environmental factors are believed to influence the degeneration of intervertebral disc.23 As a consequence of this theory, the adjoining segments should also show signs of progressive degeneration. In the present study, the cranial and caudal adjoining segments had higher SDI but the difference was not significant. Therefore, the authors believe that findings of the present study only prove this theory concerning the adjacent segments but fail to prove this theory concerning the adjoining segments, entirely. There is no doubt that degeneration will progress over time. In a 10-yr follow-up study of Matsumoto et al,15 a higher rate of degenerative progression of posterior disc protrusion, a decrease in signal intensity of the intervertebral discs, disc space narrowing, and foraminal stenosis were observed in patients following ACDF compared to asymptomatic volunteers. Significant differences were reported for posterior disc protrusion and decrease of signal intensity.15 Additionally, by comparing the degenerative findings of our patients to degenerative findings of asymptomatic patients who did not had ACDF,13 many interesting aspects of different frequency of degeneration can be observed. In the present study, 98% of adjacent segments showed a decrease of signal intensity, 98% of adjacent segments showed posterior disc protrusion, 73% of cranial and 46% of caudal adjacent segments showed an anterior disc protrusion, 42% of cranial and 28% of caudal adjacent segment showed signs of disc space narrowing, and 88% of cranial and 75% of caudal adjacent segments showed signs of foraminal stenosis (see Table 4). By comparing the aforementioned frequencies to the findings of Matsumoto et al,13,15 the rate of decreased signal intensity is almost identical, the rate of posterior disc protrusion is about 4 times higher, the rate of anterior disc protrusion is about 2.5 to 4 times higher, the rate of disc space narrowing is about 1.5 to 2.3 times higher, and the rate of foraminal stenosis is about 4 to 6 times higher in the present study. This strongly demonstrates that patients who undergo ACDF will have advanced progression of degeneration. Recently, Sasso et al24 reported results of the first 10-yr follow-up study that compared ADR to ACDF. The reoperation rate was in favor of the group treated with ADR (ie, 9% vs 32%) but not statistically significant.24 Other studies with a shorter follow-up have reported similar results regarding the reoperation rate in favor of ADR.25-28 The presumed benefit of ADR over ACDF is maintaining motion in the operated segment and therefore reducing the stress and strain on the adjacent segment. According to the reoperation rate, ADR seems to be superior to ACDF but unfortunately no information about the functionality of the ADR was reported by Sasso et al.24 The authors are curious about a radiographic and MRI assessment of ADR regarding functionality and the development of adjacent and adjoining segment degeneration with a more than 20-yr follow-up. Limitations The limitation of this study is its retrospective design. At the time of initial ACDF in the present cohort, MRI scan was not frequently used, and its technology was poor. Furthermore, in Germany, by law, imaging data have to be filed for maximum 10 yr. To really prove the effect of ACDF on the progression of ASD and the development of sASD, a randomized, controlled, prospective, long-term follow-up study of patients with symptomatic degenerative disc disease, dividing them in an ACDF group and a conservative observational control group, would be necessary. The study design, ethical concerns, and the fact of a long-term follow-up limit the feasibility of this study. The fact that degeneration is more progressive in patients who underwent repeat procedure should be further investigated by spinal researchers. CONCLUSION The findings of the present study prove that ACDF has a major influence on the acceleration of ASD. Adjoining segments do not have the same degree of degeneration. Patients who underwent repeat procedures have an even higher degree of degeneration. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Burkhardt BW, Brielmaier M, Schwerdtfeger K, Sharif S, Oertel JM. Smith-Robinson procedure with an autologous iliac crest graft and caspar plating: report of 65 patients with an average follow-up of 22 years. World Neurosurg . 2016; 90: 244- 250. Google Scholar CrossRef Search ADS PubMed  2. Burkhardt BW, Brielmaier M, Schwerdtfeger K, Sharif S, Oertel JM. Smith-Robinson procedure with an autologus iliac crest for degenerative cervical disc disease: a 28-year follow-up of 95 patients. World Neurosurg . 2016; 92: 371- 377. Google Scholar CrossRef Search ADS PubMed  3. Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am . 1999; 81( 4): 519- 528. Google Scholar CrossRef Search ADS PubMed  4. Ishihara H, Kanamori M, Kawaguchi Y, Nakamura H, Kimura T. Adjacent segment disease after anterior cervical interbody fusion. Spine J . 2004; 4( 6): 624- 628. Google Scholar CrossRef Search ADS PubMed  5. Goffin J, Geusens E, Vantomme N et al.   Long-term follow-up after interbody fusion of the cervical spine. J Spinal Disord Tech . 2004; 17( 2): 79- 85. Google Scholar CrossRef Search ADS PubMed  6. Baba H, Furusawa N, Imura S, Kawahara N, Tsuchiya H, Tomita K. Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine . 1993; 18( 15): 2167- 2173. Google Scholar CrossRef Search ADS PubMed  7. Fuller DA, Kirkpatrick JS, Emery SE, Wilber RG, Davy DT. A kinematic study of the cervical spine before and after segmental arthrodesis. Spine . 1998; 23( 15): 1649- 1656. Google Scholar CrossRef Search ADS PubMed  8. Eck JC, Humphreys SC, Lim TH et al.   Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine . 2002; 27( 22): 2431- 2434. Google Scholar CrossRef Search ADS PubMed  9. Kawakami M, Tamaki T, Yoshida M, Hayashi N, Ando M, Yamada H. Axial symptoms and cervical alignments after cervical anterior spinal fusion for patients with cervical myelopathy. J Spinal Disord . 1999; 12( 1): 50- 56. Google Scholar CrossRef Search ADS PubMed  10. Gore DR, Sepic SB. Anterior discectomy and fusion for painful cervical disc disease. A report of 50 patients with an average follow-up of 21 years. Spine . 1998; 23( 19): 2047- 2051. Google Scholar CrossRef Search ADS PubMed  11. Larsson EM, Holtas S, Cronqvist S, Brandt L. Comparison of myelography, CT myelography and magnetic resonance imaging in cervical spondylosis and disk herniation. Pre- and postoperative findings. Acta Radiol . 1989; 30( 3): 233- 239. Google Scholar CrossRef Search ADS PubMed  12. Tertti M, Paajanen H, Laato M, Aho H, Komu M, Kormano M. Disc degeneration in magnetic resonance imaging. A comparative biochemical, histologic, and radiologic study in cadaver spines. Spine . 1991; 16( 6): 629- 634. Google Scholar CrossRef Search ADS PubMed  13. Matsumoto M, Fujimura Y, Suzuki N et al.   MRI of cervical intervertebral discs in asymptomatic subjects. J Bone Joint Surg . 1998; 80( 1): 19- 24. Google Scholar CrossRef Search ADS   14. Boden SD, Davis DO, Dina TS, Patronas NJ, Wiesel SW. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg . 1990; 72( 3): 403- 408. Google Scholar CrossRef Search ADS PubMed  15. Matsumoto M, Okada E, Ichihara D et al.   Anterior cervical decompression and fusion accelerates adjacent segment degeneration: comparison with asymptomatic volunteers in a ten-year magnetic resonance imaging follow-up study. Spine . 2010; 35( 1): 36- 43. Google Scholar CrossRef Search ADS PubMed  16. Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J . 2004; 4( 6 suppl): 190S- 194S. Google Scholar CrossRef Search ADS PubMed  17. Gore DR, Sepic SB. Anterior cervical fusion for degenerated or protruded discs. A review of one hundred forty-six patients. Spine . 1984; 9( 7): 667- 671. Google Scholar CrossRef Search ADS PubMed  18. Komura S, Miyamoto K, Hosoe H, Iinuma N, Shimizu K. Lower incidence of adjacent segment degeneration after anterior cervical fusion found with those fusing C5-6 and C6-7 than those leaving C5-6 or C6-7 as an adjacent level. J Spinal Disord Tech . 2012; 25( 1): 23- 29. Google Scholar CrossRef Search ADS PubMed  19. Ahn SS, Paik HK, Chin DK, Kim SH, Kim DW, Ku MG. The fate of adjacent segments after anterior cervical discectomy and fusion: the influence of an anterior plate system. World Neurosurg . 2016; 89: 42- 50. Google Scholar CrossRef Search ADS PubMed  20. Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg . 2005; 87( 3): 558- 563. Google Scholar CrossRef Search ADS PubMed  21. Yang H, Lu X, He H et al.   Longer plate-to-disc distance prevents adjacent-level ossification development but does not influence adjacent-segment degeneration. Spine . 2015; 40( 7): E388- E393. Google Scholar CrossRef Search ADS PubMed  22. Nassr A, Lee JY, Bashir RS et al.   Does incorrect level needle localization during anterior cervical discectomy and fusion lead to accelerated disc degeneration? Spine . 2009; 34( 2): 189- 192. Google Scholar CrossRef Search ADS PubMed  23. Mio F, Chiba K, Hirose Y et al.   A functional polymorphism in COL11A1, which encodes the alpha 1 chain of type XI collagen, is associated with susceptibility to lumbar disc herniation. Am J Hum Genet . 2007; 81( 6): 1271- 1277. Google Scholar CrossRef Search ADS PubMed  24. Sasso WR, Smucker JD, Sasso MP, Sasso RC. Long-term clinical outcomes of cervical disc arthroplasty: a prospective, randomized, controlled trial. Spine . 2017; 42( 4): 209- 216. Google Scholar CrossRef Search ADS PubMed  25. Hisey MS, Zigler JE, Jackson R et al.   Prospective, randomized comparison of one-level Mobi-C cervical total disc replacement vs. anterior cervical discectomy and fusion: results at 5-year follow-up. Int J Spine Surg . 2016; 10: 10. Google Scholar CrossRef Search ADS PubMed  26. Phillips FM, Geisler FH, Gilder KM, Reah C, Howell KM, McAfee PC. Long-term outcomes of the US FDA IDE prospective, randomized controlled clinical trial comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. Spine . 2015; 40( 10): 674- 683. Google Scholar CrossRef Search ADS PubMed  27. Burkus JK, Traynelis VC, Haid RW Jr, Mummaneni PV. Clinical and radiographic analysis of an artificial cervical disc: 7-year follow-up from the prestige prospective randomized controlled clinical trial: clinical article. J Neurosurg Spine . 2014; 21( 4): 516- 528. Google Scholar CrossRef Search ADS PubMed  28. Janssen ME, Zigler JE, Spivak JM, Delamarter RB, Darden BV 2nd, Kopjar B. ProDisc-C total disc replacement versus anterior cervical discectomy and fusion for single-level symptomatic cervical disc disease: seven-year follow-up of the prospective randomized U.S. Food and Drug Administration Investigational device exemption study. J Bone Joint Surg Am . 2015; 97( 21): 1738- 1747. Google Scholar CrossRef Search ADS PubMed  COMMENT In an effort to further define the natural history of adjacent segment degeneration in patients in whom an uninstrumented ACDF was performed, the authors report a radiographic analysis of 59 patients who underwent an ACDF with a mean follow-up of 27 years. The data set contained a minimum follow-up of 18 years and a remarkable follow-up as long as 45 years. The question that the authors wish to answer is whether or not degeneration occurs from physiologic aging of the spine or whether the forces from an arthrodesis prompt degeneration of the adjacent segment. The authors used a complex grading system (segmental degeneration index) in addition to disc height to further elucidate the effects of an ACDF over time. The authors identified that the disc heights of the cranial and caudal segments were lower and the SDI were higher. The authors conclude that physiological aging of the spine does not overcome the natural history of adjacent segment degeneration. It is important to recognize that the patients in this dataset were uninstrumented cervical fusions. This is especially germane given the fact that the current literature demonstrates that there is an impact on the proximity of the plate to the adjacent disc space. Therefore, the data in the current report may actually under report the incidence of adjacent segment degeneration when compared to the techniques used currently with plating.1 Proponents of arthroplasty will take heart in the data presented by the authors. Given the long-term follow-up and the conclusion that the impact of an arthrodesis has greater impact on the adjacent segment than physiological aging, a stronger argument for the potential benefit of arthroplasty could not be made. The authors should be commended for their work, which stands out in the literature for its mean follow-up and radiographic analysis. The current manuscript represents a meaningful contribution to our understanding of adjacent segment degeneration in cervical arthrodesis patients. Luis Manuel Tumialan Phoenix, Arizona 1. Kim HJ, Kelly MP, Ely CG, Dettori JR, Riew KD. The risk of adjacent-level ossification development after surgery in the cervical spine: are there factors that affect the risk? A systematic review. Spine (Phila Pa 1976) . 2012; 37( 22 suppl): S65- 74. Google Scholar CrossRef Search ADS PubMed  Copyright © 2017 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Neurosurgery Oxford University Press

Adjacent Segment Degeneration After Anterior Cervical Discectomy and Fusion With an Autologous Iliac Crest Graft: A Magnetic Resonance Imaging Study of 59 Patients With a Mean Follow-up of 27 Years

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Congress of Neurological Surgeons
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Copyright © 2017 by the Congress of Neurological Surgeons
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0148-396X
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1524-4040
D.O.I.
10.1093/neuros/nyx304
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Abstract

Abstract BACKGROUND Anterior cervical decompression and fusion (ACDF) is a widely accepted surgical technique for the treatment of degenerative disc disease. ACDF is associated with adjacent segment degeneration (ASD). OBJECTIVE To assess whether physiological aging of the spine would overcome ASD by comparing adjacent to adjoining segments more than 18 yr after ACDF. METHODS Magnetic resonance imaging of 59 (36 male, 23 female) patients who underwent ACDF was performed to assess degeneration. The mean follow-up was 27 yr (18-45 yr). Besides measuring the disc height, a 5-step grading system (segmental degeneration index [SDI]) including disc signal intensity, anterior and posterior disc protrusion, narrowing of the disc space, and foraminal stenosis was used to assess the grade of adjacent and adjoining segments. RESULTS The SDI of cranial and caudal adjacent segments was significantly higher compared to adjoining segments (P < .001). The disc height of cranial and caudal adjacent segments was significantly lower compared to adjoining segments (P < .001, P < .01). The SDI of adjacent segments in patients with repeat cervical procedure was significantly higher than in patients without repeat procedure (P = .02, P = .01). The disc height of the cranial adjacent segments in patients with repeat procedure was significantly lower than in patients without repeat procedure (P = .01). CONCLUSION The physiological aging of the cervical spine does not overcome ASD. The disc height and the SDI in adjacent segment are significantly worse compared to adjoining segments. Patients who underwent repeat procedure had even worse findings of disc height and SDI. ACDF, Adjacent segment degeneration, Cervical spine, Long-term follow-up, Magnetic resonance imaging, MRI, Cervical disc height ABBREVIATIONS ABBREVIATIONS ACDF anterior cervical decompression and fusion ASD adjacent segment degeneration MRI magnetic resonance imaging sASD symptomatic adjacent segment degeneration SDI segmental degeneration index Aging of the society has increased during the last decades. As a consequence, degenerative cervical disorders are frequently surgically treated. Anterior cervical decompression and fusion (ACDF) is an accepted procedure for this treatment. Long-term follow-up studies have demonstrated clinical success rates of 84.2% to 86.4% after ACDF.1,2 Although there is no proof that ACDF is superior to discectomy without fusion, surgeons around the world tend to perform ACDF because of a lower postoperative kyphosis rate. Despite the high acceptance of ACDF, it is associated with several disadvantages. One of those is the acceleration of adjacent segment degeneration (ASD). ASD might become a symptomatic condition that requires repeat surgery (sASD). Following this awareness, several studies have reported data on radiographic outcome after anterior cervical fusion. The literature presents 2 different opinions on the development of ASD. One supports the hypothesis that ASD is the result of a physiological process of degeneration.2-4 Other authors believe that fusion increases the stress and strain at the 2 adjacent segments and thereby accelerate segmental degeneration.5-8 The prevalence of ASD using radiographic images has been reported to have a wide range, ie, from 18% to 96%.9,10 However, magnetic resonance imaging (MRI) is a more sensitive technique to evaluate the grade of disc degeneration.11,12 Until today, studies that have assessed ASD via MRI in long-term follow-up are rare and, to the best of the authors’ knowledge, currently there is no study with follow-up of more than 15 yr. It is unknown whether accelerated degeneration of the adjacent segments will stop at a certain time after ACDF. Further, it is unknown whether or not the degeneration of the adjoining segment will reach the level of the adjacent segment over time. The present study is unique and presents 2 important aspects. This is the first study that assessed the grade of degeneration of the 2 segments that are located cranial and caudal to the fused level (adjacent segments) using an MRI with a follow-up of 27 yr. Secondly, this study assessed and compared the grade of degeneration of the first and second segments, which are located cranial to the cranial adjacent segment (cranial adjoining segments) and located caudal to the caudal adjacent segment (caudal adjoining segments). The purpose of this study is to evaluate whether physiological aging of the adjoining segments would overcome the degeneration of the adjacent segments after ACDF in a long-term follow-up. METHODS We retrospectively reviewed all consecutive files of patients who had undergone a de novo 1- or 2-level ACDF for a minimum of 18 yr and a maximum of 45 yr previously at our neurosurgical department. Inclusion criteria were patients who underwent ACDF without adding a cervical plate for degenerative disorders with documentation of preoperative neurological status, a detailed operation report of the initial ACDF and repeat procedures, the postoperative process during hospitalization, the postoperative neurological status, and full contact detail. All patients who did not fulfill the inclusion criteria were excluded. Out of 451 patient files, 212 patients fulfilled inclusion criteria and 239 patients were excluded because the initial diagnosis was trauma or tumor, or incomplete clinical documents, or incomplete contact details. We were able to successfully contact 198 patients via the telephone (93.4%). Ninety-five patients participated in the study (48.0%) and 60 patients agreed to visit our department for a personal follow-up examination and an MRI scan of the cervical spine (63.2%). An MRI scan of the cervical spine was performed in 59 participants by the Department of Neuroradiology. In 1 case, an MRI scan could not be performed due to cochlea implant. The study was approved by the local ethical committee, and informed consent from all patients was obtained. Surgical Technique of Initial ACDF In all cases, a transverse skin incision was performed, and a combination of sharp and blunt dissection was used to identify the prevertebral fascia. The presumptive segment was identified using either a needle or a dissector with a blunt tip. A complete discectomy and decompression of both nerve roots were performed. An autologous iliac crest graft was harvest and tapped gently into position in each disc space. Before closure of the wound, the position of the graft was confirmed fluoroscopically. MRI Protocol A 3.0 Tesla MRI was used for all participants (Siemens Magnetom Skyra, Erlangen, Germany). The protocol for each scan consisted of T1 sagittal images (TR 833 ms; TE 12 ms; flip angle 150°), T2 sagittal images (TR 5110 ms; TE 96 ms; flip angle 150°), T1 axial images (TR 530 ms; TE 9 ms; flip angle 150°), T2 axial images (TR 5740 ms; TE 92 ms; flip angle 150°), and sagittal T2-SPACE images (TE 1600 ms; TR 232 ms; flip angle 100°). Evaluation of MRI The MRI imaging was independently reviewed using the Centricity PACS-system (General Electric Healthcare, Chalfont St Giles, United Kingdom) by an experienced neurosurgeon and a neuroradiologist. No information about the patients’ history was given. The reviewers assessed the 2 segments that were located cranial and caudal to the fused level. These 2 segments were defined as cranial and caudal adjacent segment (see Figure 1). FIGURE 1. View largeDownload slide SDI and disc height measurements. A, 1 = second cranial adjoining segment, 2 = first cranial adjoining segment, 3 = cranial adjacent segment, 4 = caudal adjacent segment, 5 = first caudal adjoining segment, 6 = second caudal adjoining segment, a = anterior disc height, b = middle disc height, c = posterior disc height; white ring: disc signal intensity (dark and/or speckled—1 point). B, White arrow = posterior disc protrusion (disc material protruding beyond the posterior margin of the vertebral body without compression—1 point), white arrowhead = anterior disc protrusion (disc material protruding beyond the anterior margin of the vertebral body—1 point). FIGURE 1. View largeDownload slide SDI and disc height measurements. A, 1 = second cranial adjoining segment, 2 = first cranial adjoining segment, 3 = cranial adjacent segment, 4 = caudal adjacent segment, 5 = first caudal adjoining segment, 6 = second caudal adjoining segment, a = anterior disc height, b = middle disc height, c = posterior disc height; white ring: disc signal intensity (dark and/or speckled—1 point). B, White arrow = posterior disc protrusion (disc material protruding beyond the posterior margin of the vertebral body without compression—1 point), white arrowhead = anterior disc protrusion (disc material protruding beyond the anterior margin of the vertebral body—1 point). Further, the reviewers assessed the 2 segments that were located cranial to the cranial adjacent segment and caudal to the caudal adjacent segment. These segments were defined as first and second cranial and caudal adjoining segments (see Figure 1). Depending on the location of the initial fusion, 2 adjacent segments (1 cranial and 1 caudal) and 4 adjoining segments (2 cranial and 2 caudal) were assessed. For MRI assessment of each segment, the authors used a modified 5-step grading system that was designed by Matsumoto et al13 (see Table 1). A T2-weighted sequence was used to determine the segmental degeneration on behalf of 5 categories specific for the segment (see Figures 1 and 2). For each category, points were given depending on the grade of degeneration. FIGURE 2. View largeDownload slide Foraminal stenosis measurements. A, T2-weighted sagittal and axial image of C4-5 with foraminal stenosis (1 point). B, T2-weighted sagittal and axial image of C7-Th1 without foraminal stenosis (0 point). FIGURE 2. View largeDownload slide Foraminal stenosis measurements. A, T2-weighted sagittal and axial image of C4-5 with foraminal stenosis (1 point). B, T2-weighted sagittal and axial image of C7-Th1 without foraminal stenosis (0 point). TABLE 1. Five-Step Grading System for Segmental Degeneration Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  View Large TABLE 1. Five-Step Grading System for Segmental Degeneration Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  Category  Grade of degeneration  Points  Disc signal intensity  Bright as or slightly less bright than cerebrospinal fluid  0    Dark and/or speckled  1    Almost black  2  Posterior disc protrusion  Disc material confined within the posterior margin of the VB  0    Disc material protruding beyond the posterior margin of the VB without compression  1    Beyond the VB with cord compression  2  Anterior disc protrusion  Disc material confined within the anterior margin of the VB  0    Disc material protruding beyond the anterior margin of the VB  1  Narrowing of disc space  0%-25% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  0    25%-50% difference of disc height narrowing between the adjacent segment compared to the median disc height of nonadjacent segment  1    >50% difference of disc height narrowing between the adjacent segment compared to the median disc height of the nonadjacent segment  2  Foraminal stenosis  Axial foraminal diameter > 4.0 mm  0    Axial foraminal diameter < 4.0 mm  1  View Large The total score for each segment ranged from 0 to 8 points. If 1 category could not be evaluated with absolute certainty, the authors did not assess this specific category and the maximum of possible points were downgraded according to the maximum points of this specific category. For better comparison of the degeneration, a segmental degeneration index (SDI) was created for each segment. The SDI was assessed as follows: the total of determined points according to the 5-step grading system divided by the maximum of possible points. The SDI might range from .0 to 1.0. An SDI of .0 describes a segment without signs of degeneration, whereas an SDI of 1.0 describes a segment that shows the most distinct signs of degeneration according to the 5-step grading system. The authors defined an SDI of <.333 as mild, an SDI of .334 to .667 as moderate and an SDI of >.667 as severe. If there was a disagreement between the raters concerning the grade of segmental degeneration, consensus was reached by evaluating the grade together again. The intervertebral disc height of each segment was defined as the mean of anterior, middle, and posterior disc height (see Figure 1). The mean value was assigned in cases of disagreement between the radiographic data. The SDI and the disc height of adjacent and adjoining segments were compared to each other. For comparison, the SDI of each segment was subtracted from one another. The frequency of positive and negative actual difference was compared to each other. Data Analysis SPSS software version 23 was used for statistical analysis (IBM, Armonk, New York). A P-value <.05 was considered to be statistically significant. A t-test, Wilcoxon test, and Mann–Whitney U-test were used to compare the index and the mean disc height of adjacent to the adjoining segments. RESULTS Patient Demographics Fifty-nine patients participated in this evaluation. The patients’ mean age at time of ACDF was 42 yr (range: 26-56 yr). At mean follow-up of 27 yr (range: 18-45 yr), the mean age was 70 yr (range: 51-79 yr). The basic surgical technique was identical in every case. A standard Smith-Robinson approach was performed with autologous iliac crest graft without adding of a cervical plate. A compilation of patient characteristics at follow-up is shown in Table 2. The result of the personal examination of these 59 patients was previously reported by Burkhardt et al.2 TABLE 2. Patient Characteristics at Follow-up Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  aOne case with ADR C4-5 and ACDF C6-7. View Large TABLE 2. Patient Characteristics at Follow-up Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  Follow-up        Mean  27 yr    Range  18-45 yr  Gender        male  36 (61.0%)    female  23 (39.0%)  Age at follow-up        50-59 yr  5 (8.5%)    60-69 yr  16 (27.1%)    70-79 yr  36 (61.0%)    ≥80 yr  2 (3.4%)  Diagnosis        Soft disc herniation  48 (81.4%)    Cervical spondylotic myelopathy  7 (11.9%)    Cervical spondylosis  4 (6.8%)  Fused levels prior to follow-up MRI       1 level  C4-5  2    C5-6  13    C6-7  18    C7-Th1  1   2 level  C4-5 and C6-7  2a    C4-6  1    C5-7  16    C6-Th1  1   3 level  C3-4 and C5-7  1    C3-6  1    C4-7  1    C5-Th1  1   4 level  C4-Th1  1  aOne case with ADR C4-5 and ACDF C6-7. View Large Patients With Repeat Procedure Twelve patients underwent repeat surgery for degenerative changes. The period from initial ACDF to repeat procedure varied from 1 to 27 yr. In all cases, repeat procedure was performed via an anterior approach. One patient had a third procedure 3 yr after repeat procedure and 11 yr after initial ACDF. Ten among those 12 repeat procedures were caused by sASD. In 4 of those 10 procedures, an ACDF was performed, and in 6 of those 10 repeat procedures, an ACDF with an autologous iliac crest with adding of a Caspar plate (ACDF+PS) was performed. In 2 cases, an ACDF+PS was performed at the cranial adjacent segment (1-level procedure), in 2 cases an ACDF+PS was performed at the cranial adjacent and the first cranial adjoining segment (2-level procedure), and in 2 cases an ACDF+PS was performed at the caudal adjacent segment (1-level repeat procedure). In 1 case each, an ACDF+PS (1-level repeat procedure) and an ADR was performed at the first cranial adjoining segment. A detailed compilation of all operated segments at initial ACDF and repeat procedures is shown in Table 3. TABLE 3. Initial ACDF and Repeat Procedures Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  View Large TABLE 3. Initial ACDF and Repeat Procedures Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  Number segments at initial ACDF  Level  Number of initial procedures  Number of repeat procedure  Surgical technique at repeat procedure (n)  1  C4-5  2  0  NA    C5-6  17  4  C3-5 ACDF+PS (1)          C6-7 ACDF+PS (1)          C6-7 ACDF (2)    C6-7  22  4  C4-5 ADR (1)          C5-6 ACDF (1)          C5-7 ACDF+PS (1)          C7-Th1 ACDF+PS (1)    C7-Th1  1  0  NA  2  C4-5 and C6-7  1  0  NA    C4-6  1  0  NA    C5-7  14  3  C3-4 ACDF+PS (1)          C4-5 ACDF+PS (1)          C7-Th1 ACDF (1)    C6-Th1  1  1  C4-6 ACDF+PS (1)  View Large Identification of the Affected Segment The following data are based on the operative reports, which were reviewed thoroughly. In 33 cases, the affected segment was identified using lateral fluoroscopy and a dissector or retractor with a blunt tip, the disc was not punctured via the dissector or retractor. In 26 cases, the presumptive segments were identified using lateral fluoroscopy and a needle. The correct disc was punctured in 21 cases, and the wrong disc was punctured in 5 cases (ie, in 4 cases, the cranial adjacent disc, in 1 case, the caudal adjacent disc). None of the patients in whom the wrong segment was punctured via a needle had to undergo a repeat procedure at the falsely punctured segment. In all repeat procedures, the affected adjacent or adjoining segment was located using the lateral fluoroscopy and a retractor. In none of these repeat procedures, a needle was used for identification. SDI and Disc Height Measurement The frequencies of positive findings of the 5-step grading system are shown in Table 4. TABLE 4. Compilation of Positive Findings According to the 5-Step Grading System Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  View Large TABLE 4. Compilation of Positive Findings According to the 5-Step Grading System Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  Category  Points  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  Disc signal intensity  0/2 points  2.0%  .0%  1.8%  1.8%  .0%  .0%    1/2 points  96.0%  98.2%  94.7%  94.7%  100.0%  100.0%    2/2 points  2.0%  1.8%  3.5%  3.5%  .0%  .0%  Posterior disc protrusion  0/2 points  2.0%  .0%  1.9%  1.9%  .0%  .0%    1/2 points  82.3%  64.3%  42.6%  78.8%  92.5%  100.0%    2/2 points  15.7%  35.7%  55.5%  19.2%  7.5%  .0%  Narrowing of the disc space  0/2 points  96.0%  88.9%  58.2%  71.4%  92.5%  93.8%    1/2 points  .0%  9.2%  29.1%  25.0%  7.5%  6.3%    2/2 points  4.0%  1.9%  12.7%  3.6%  .0%  .0%  Foraminal stenosis  0/2 points  32.1%  10.9%  12.3%  25.5%  53.7%  50.0%    1/2 points  67.9%  89.1%  87.7%  74.5%  46.3%  50.0%  Anterior disc protrusion  0/2 points  80.0%  54.4%  27.1%  54.2%  42.9%  70.9%    1/2 points  20.0%  45.6%  72.9%  45.8%  57.1%  29.1%  View Large A compilation of frequency of all SDI according to location of the segment is shown in Table 5. The disc height measures are shown in Figure 3. FIGURE 3. View largeDownload slide Disc height. FIGURE 3. View largeDownload slide Disc height. TABLE 5. Compilation of Frequency of Mild, Moderate, and Severe SDI SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  View Large TABLE 5. Compilation of Frequency of Mild, Moderate, and Severe SDI SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  SDI  2. cranial adjoining segment  1. cranial adjoining segment  Cranial adjacent segment  Caudal adjacent segment  1. caudal adjoining segment  2. caudal adjoining segment  .000-.333 (mild degeneration)  45.1%  8.9%  6.6%  24.6%  31.6%  55.6%  .334-.666 (moderate degeneration)  52.9%  80.4%  60.7%  62.3%  66.7%  29.6%  .667-1.000 (severe degeneration)  2.0%  10.7%  32.8%  13.1%  1.8%  14.8%  View Large Comparison of SDI and Disc Height The SDI and disc height of cranial and caudal adjacent segments, first and second cranial and caudal adjoining segments were compared to each. A compilation of comparison for SDI is shown in Table 6, and a compilation of comparison for disc height is shown in Table 7. TABLE 6. Comparison of Adjacent and Adjoining SDI 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  View Large TABLE 6. Comparison of Adjacent and Adjoining SDI 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent SDI  Caudal adjacent SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Cranial adjacent SDI  Cranial 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.001  Caudal adjacent SDI  Caudal 1. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Caudal adjacent SDI  Caudal 2. adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  All adjacent SDI  All adjoining SDI  SDI of 1 is higher than SDI of 2  <.01  Cranial adjacent SDI in patients with repeat procedure  Cranial adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .02  Caudal adjacent SDI in patients with repeat procedure  Caudal adjacent SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .01  Cranial 1. adjoining SDI in patients with repeat procedure  Cranial 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .70  Cranial 2. adjoining SDI in patients with repeat procedure  Cranial 2. adjoining SDI in patients without repeat procedure  No difference  1.0  Caudal 1. adjoining SDI in patients with repeat procedure  Caudal 1. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .21  Caudal 2. adjoining SDI in patients with repeat procedure  Caudal 2. adjoining SDI in patients without repeat procedure  SDI of 1 is higher than SDI of 2  .43  View Large TABLE 7. Comparison of Adjacent and Adjoining Segment Disc Height 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  DH, disc height View Large TABLE 7. Comparison of Adjacent and Adjoining Segment Disc Height 1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  1  2  Comparison of 1 vs 2  P-value  Cranial adjacent segment disc height  Caudal adjacent segment disc height  DH of 1 is lower than DH of 2  .04  Cranial adjacent segment disc height  Cranial 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height  Cranial 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 1. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Caudal adjacent segment disc height  Caudal 2. adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  All adjacent segment disc height  All adjoining segment disc height  DH of 1 is lower than DH of 2  <.001  Cranial adjacent segment disc height of patients with repeat procedure  Cranial adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .01  Caudal adjacent segment disc height of patients with repeat procedure  Caudal adjacent segment disc height of patients without repeat procedure  DH of 1 is lower than DH of 2  .19  Cranial 1. adjoining segment disc height of patients with repeat procedure  Cranial 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .20  Cranial 2. adjoining segment disc height of patients with repeat procedure  Cranial 2. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .66  Caudal 1. adjoining segment disc height of patients with repeat procedure  Caudal 1. adjoining segment disc height of patients with repeat procedure  DH of 1 is lower than DH of 2  .89  DH, disc height View Large DISCUSSION The development of degenerative changes at the cervical spine is a physiological process. Boden et al14 evaluated the MRI scans of 63 asymptomatic volunteer and reported that volunteers over 40 yr of age had significantly more degenerative findings compared to volunteers under the age of 40. Also, Matsumoto et al15 reported that the frequency of degenerative findings on MRI of asymptomatic volunteers will increase with aging and that over 85% of asymptomatic volunteers over 60 yr of age had loss of signal intensity (grade 1 and grade 2) and about 25% of volunteers over 60 yr of age had posterior disc protrusion. The SDI is based on the 5-step grading system of Matsumoto et al,13,15 which has good interobserver agreement. However, the authors want to state that the SDI as an outcome measurement is not validated yet. The acceleration of ASD was first noticed after lumbar spinal fusion procedures.16 Since then, many studies have analyzed the clinical and radiographic outcome after ACDF. Gore et al17 evaluated the pre- and postoperative radiographs of 121 patients who underwent ACDF with a mean follow-up of 5 ± 3 yr. They reported a prevalence of 25.6% for ASD. In a 21-yr follow-up series, Gore et al10 reported a postoperative prevalence of 32.0% for ASD. Goffin et al,5 however, reported a 92.0% rate of ASD at the superior and/or inferior adjacent disc levels in a considerably shorter follow-up of over 5 yr. In these earlier studies, lateral radiographs were taken to assess the degeneration. It has to be noted that radiographs are limited in their ability to assess the degeneration of the disc itself. Since the late 1990s, MRI is frequently used in diagnostics, and it is the most sensitive technique in order to evaluate degeneration of the disc. However, there are only a small number of studies available in the literature that used an MRI to assess ASD after ACDF with a follow-up of at least 5 yr.4,15,18 To our knowledge, the present study is the first using an MRI to assess the grade of degeneration of both adjacent and adjoining segment after ACDF with a mean follow-up of 27 yr’ follow-up. Further, it is the first comparing the adjacent to the adjoining segments. The data of the present study demonstrate that the adjacent segments have a higher SDI and lower disc height than the adjoining segment. This shows that the physiological process of degeneration does not overcome the accelerated degeneration of the adjacent segment, not even after more than 18 to 45 yr. Further, ACDF seems to increase the stress on the cranial adjacent segment more than on the caudal adjacent segment. Similar findings concerning the progression of decrease of signal intensity and progression of posterior disc protrusion at the adjacent segment have been reported by Matsumoto et al.15 Recently, it has been reported that the addition of a cervical plate tends to increase adjacent segmental motion and decrease adjacent segmental disc height.19 Further, it has been reported that the plate to adjacent segment disc space distance has influence on the adjacent segment ossification.20,21 At last, it has been reported that the risk of developing degenerative changes at the adjacent segment is 3 times higher in case of a falsely punctured cervical disc.22 Therefore, the authors want to state that the grade of degeneration of 5 cranial adjacent segments and of 2 caudal adjacent segments might have been influenced due to adding of a Caspar plate at repeat procedure. Further, the authors want to state that the grade of degeneration of 4 cranial and 1 caudal adjacent segments might have been influenced by faulty puncture via a needle during identification of the affected segment. Interestingly, ACDF also had an effect on the degeneration of both adjacent and adjoining segments in patients who underwent repeat procedure at the cervical spine. The SDI and the disc height of cranial adjacent segments were significantly higher in patients who underwent repeat procedure compared to patients without repeat procedure. A possible explanation for this finding is that genetic predisposition and environmental factors are believed to influence the degeneration of intervertebral disc.23 As a consequence of this theory, the adjoining segments should also show signs of progressive degeneration. In the present study, the cranial and caudal adjoining segments had higher SDI but the difference was not significant. Therefore, the authors believe that findings of the present study only prove this theory concerning the adjacent segments but fail to prove this theory concerning the adjoining segments, entirely. There is no doubt that degeneration will progress over time. In a 10-yr follow-up study of Matsumoto et al,15 a higher rate of degenerative progression of posterior disc protrusion, a decrease in signal intensity of the intervertebral discs, disc space narrowing, and foraminal stenosis were observed in patients following ACDF compared to asymptomatic volunteers. Significant differences were reported for posterior disc protrusion and decrease of signal intensity.15 Additionally, by comparing the degenerative findings of our patients to degenerative findings of asymptomatic patients who did not had ACDF,13 many interesting aspects of different frequency of degeneration can be observed. In the present study, 98% of adjacent segments showed a decrease of signal intensity, 98% of adjacent segments showed posterior disc protrusion, 73% of cranial and 46% of caudal adjacent segments showed an anterior disc protrusion, 42% of cranial and 28% of caudal adjacent segment showed signs of disc space narrowing, and 88% of cranial and 75% of caudal adjacent segments showed signs of foraminal stenosis (see Table 4). By comparing the aforementioned frequencies to the findings of Matsumoto et al,13,15 the rate of decreased signal intensity is almost identical, the rate of posterior disc protrusion is about 4 times higher, the rate of anterior disc protrusion is about 2.5 to 4 times higher, the rate of disc space narrowing is about 1.5 to 2.3 times higher, and the rate of foraminal stenosis is about 4 to 6 times higher in the present study. This strongly demonstrates that patients who undergo ACDF will have advanced progression of degeneration. Recently, Sasso et al24 reported results of the first 10-yr follow-up study that compared ADR to ACDF. The reoperation rate was in favor of the group treated with ADR (ie, 9% vs 32%) but not statistically significant.24 Other studies with a shorter follow-up have reported similar results regarding the reoperation rate in favor of ADR.25-28 The presumed benefit of ADR over ACDF is maintaining motion in the operated segment and therefore reducing the stress and strain on the adjacent segment. According to the reoperation rate, ADR seems to be superior to ACDF but unfortunately no information about the functionality of the ADR was reported by Sasso et al.24 The authors are curious about a radiographic and MRI assessment of ADR regarding functionality and the development of adjacent and adjoining segment degeneration with a more than 20-yr follow-up. Limitations The limitation of this study is its retrospective design. At the time of initial ACDF in the present cohort, MRI scan was not frequently used, and its technology was poor. Furthermore, in Germany, by law, imaging data have to be filed for maximum 10 yr. To really prove the effect of ACDF on the progression of ASD and the development of sASD, a randomized, controlled, prospective, long-term follow-up study of patients with symptomatic degenerative disc disease, dividing them in an ACDF group and a conservative observational control group, would be necessary. The study design, ethical concerns, and the fact of a long-term follow-up limit the feasibility of this study. The fact that degeneration is more progressive in patients who underwent repeat procedure should be further investigated by spinal researchers. CONCLUSION The findings of the present study prove that ACDF has a major influence on the acceleration of ASD. Adjoining segments do not have the same degree of degeneration. Patients who underwent repeat procedures have an even higher degree of degeneration. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Burkhardt BW, Brielmaier M, Schwerdtfeger K, Sharif S, Oertel JM. Smith-Robinson procedure with an autologous iliac crest graft and caspar plating: report of 65 patients with an average follow-up of 22 years. World Neurosurg . 2016; 90: 244- 250. Google Scholar CrossRef Search ADS PubMed  2. Burkhardt BW, Brielmaier M, Schwerdtfeger K, Sharif S, Oertel JM. Smith-Robinson procedure with an autologus iliac crest for degenerative cervical disc disease: a 28-year follow-up of 95 patients. World Neurosurg . 2016; 92: 371- 377. Google Scholar CrossRef Search ADS PubMed  3. Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am . 1999; 81( 4): 519- 528. Google Scholar CrossRef Search ADS PubMed  4. Ishihara H, Kanamori M, Kawaguchi Y, Nakamura H, Kimura T. Adjacent segment disease after anterior cervical interbody fusion. Spine J . 2004; 4( 6): 624- 628. Google Scholar CrossRef Search ADS PubMed  5. Goffin J, Geusens E, Vantomme N et al.   Long-term follow-up after interbody fusion of the cervical spine. J Spinal Disord Tech . 2004; 17( 2): 79- 85. Google Scholar CrossRef Search ADS PubMed  6. Baba H, Furusawa N, Imura S, Kawahara N, Tsuchiya H, Tomita K. Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine . 1993; 18( 15): 2167- 2173. Google Scholar CrossRef Search ADS PubMed  7. Fuller DA, Kirkpatrick JS, Emery SE, Wilber RG, Davy DT. A kinematic study of the cervical spine before and after segmental arthrodesis. Spine . 1998; 23( 15): 1649- 1656. Google Scholar CrossRef Search ADS PubMed  8. Eck JC, Humphreys SC, Lim TH et al.   Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine . 2002; 27( 22): 2431- 2434. Google Scholar CrossRef Search ADS PubMed  9. Kawakami M, Tamaki T, Yoshida M, Hayashi N, Ando M, Yamada H. Axial symptoms and cervical alignments after cervical anterior spinal fusion for patients with cervical myelopathy. J Spinal Disord . 1999; 12( 1): 50- 56. Google Scholar CrossRef Search ADS PubMed  10. Gore DR, Sepic SB. Anterior discectomy and fusion for painful cervical disc disease. A report of 50 patients with an average follow-up of 21 years. Spine . 1998; 23( 19): 2047- 2051. Google Scholar CrossRef Search ADS PubMed  11. Larsson EM, Holtas S, Cronqvist S, Brandt L. Comparison of myelography, CT myelography and magnetic resonance imaging in cervical spondylosis and disk herniation. Pre- and postoperative findings. Acta Radiol . 1989; 30( 3): 233- 239. Google Scholar CrossRef Search ADS PubMed  12. Tertti M, Paajanen H, Laato M, Aho H, Komu M, Kormano M. Disc degeneration in magnetic resonance imaging. A comparative biochemical, histologic, and radiologic study in cadaver spines. Spine . 1991; 16( 6): 629- 634. Google Scholar CrossRef Search ADS PubMed  13. Matsumoto M, Fujimura Y, Suzuki N et al.   MRI of cervical intervertebral discs in asymptomatic subjects. J Bone Joint Surg . 1998; 80( 1): 19- 24. Google Scholar CrossRef Search ADS   14. Boden SD, Davis DO, Dina TS, Patronas NJ, Wiesel SW. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg . 1990; 72( 3): 403- 408. Google Scholar CrossRef Search ADS PubMed  15. Matsumoto M, Okada E, Ichihara D et al.   Anterior cervical decompression and fusion accelerates adjacent segment degeneration: comparison with asymptomatic volunteers in a ten-year magnetic resonance imaging follow-up study. Spine . 2010; 35( 1): 36- 43. Google Scholar CrossRef Search ADS PubMed  16. Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J . 2004; 4( 6 suppl): 190S- 194S. Google Scholar CrossRef Search ADS PubMed  17. Gore DR, Sepic SB. Anterior cervical fusion for degenerated or protruded discs. A review of one hundred forty-six patients. Spine . 1984; 9( 7): 667- 671. Google Scholar CrossRef Search ADS PubMed  18. Komura S, Miyamoto K, Hosoe H, Iinuma N, Shimizu K. Lower incidence of adjacent segment degeneration after anterior cervical fusion found with those fusing C5-6 and C6-7 than those leaving C5-6 or C6-7 as an adjacent level. J Spinal Disord Tech . 2012; 25( 1): 23- 29. Google Scholar CrossRef Search ADS PubMed  19. Ahn SS, Paik HK, Chin DK, Kim SH, Kim DW, Ku MG. The fate of adjacent segments after anterior cervical discectomy and fusion: the influence of an anterior plate system. World Neurosurg . 2016; 89: 42- 50. Google Scholar CrossRef Search ADS PubMed  20. Park JB, Cho YS, Riew KD. Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg . 2005; 87( 3): 558- 563. Google Scholar CrossRef Search ADS PubMed  21. Yang H, Lu X, He H et al.   Longer plate-to-disc distance prevents adjacent-level ossification development but does not influence adjacent-segment degeneration. Spine . 2015; 40( 7): E388- E393. Google Scholar CrossRef Search ADS PubMed  22. Nassr A, Lee JY, Bashir RS et al.   Does incorrect level needle localization during anterior cervical discectomy and fusion lead to accelerated disc degeneration? Spine . 2009; 34( 2): 189- 192. Google Scholar CrossRef Search ADS PubMed  23. Mio F, Chiba K, Hirose Y et al.   A functional polymorphism in COL11A1, which encodes the alpha 1 chain of type XI collagen, is associated with susceptibility to lumbar disc herniation. Am J Hum Genet . 2007; 81( 6): 1271- 1277. Google Scholar CrossRef Search ADS PubMed  24. Sasso WR, Smucker JD, Sasso MP, Sasso RC. Long-term clinical outcomes of cervical disc arthroplasty: a prospective, randomized, controlled trial. Spine . 2017; 42( 4): 209- 216. Google Scholar CrossRef Search ADS PubMed  25. Hisey MS, Zigler JE, Jackson R et al.   Prospective, randomized comparison of one-level Mobi-C cervical total disc replacement vs. anterior cervical discectomy and fusion: results at 5-year follow-up. Int J Spine Surg . 2016; 10: 10. Google Scholar CrossRef Search ADS PubMed  26. Phillips FM, Geisler FH, Gilder KM, Reah C, Howell KM, McAfee PC. Long-term outcomes of the US FDA IDE prospective, randomized controlled clinical trial comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. Spine . 2015; 40( 10): 674- 683. Google Scholar CrossRef Search ADS PubMed  27. Burkus JK, Traynelis VC, Haid RW Jr, Mummaneni PV. Clinical and radiographic analysis of an artificial cervical disc: 7-year follow-up from the prestige prospective randomized controlled clinical trial: clinical article. J Neurosurg Spine . 2014; 21( 4): 516- 528. Google Scholar CrossRef Search ADS PubMed  28. Janssen ME, Zigler JE, Spivak JM, Delamarter RB, Darden BV 2nd, Kopjar B. ProDisc-C total disc replacement versus anterior cervical discectomy and fusion for single-level symptomatic cervical disc disease: seven-year follow-up of the prospective randomized U.S. Food and Drug Administration Investigational device exemption study. J Bone Joint Surg Am . 2015; 97( 21): 1738- 1747. Google Scholar CrossRef Search ADS PubMed  COMMENT In an effort to further define the natural history of adjacent segment degeneration in patients in whom an uninstrumented ACDF was performed, the authors report a radiographic analysis of 59 patients who underwent an ACDF with a mean follow-up of 27 years. The data set contained a minimum follow-up of 18 years and a remarkable follow-up as long as 45 years. The question that the authors wish to answer is whether or not degeneration occurs from physiologic aging of the spine or whether the forces from an arthrodesis prompt degeneration of the adjacent segment. The authors used a complex grading system (segmental degeneration index) in addition to disc height to further elucidate the effects of an ACDF over time. The authors identified that the disc heights of the cranial and caudal segments were lower and the SDI were higher. The authors conclude that physiological aging of the spine does not overcome the natural history of adjacent segment degeneration. It is important to recognize that the patients in this dataset were uninstrumented cervical fusions. This is especially germane given the fact that the current literature demonstrates that there is an impact on the proximity of the plate to the adjacent disc space. Therefore, the data in the current report may actually under report the incidence of adjacent segment degeneration when compared to the techniques used currently with plating.1 Proponents of arthroplasty will take heart in the data presented by the authors. Given the long-term follow-up and the conclusion that the impact of an arthrodesis has greater impact on the adjacent segment than physiological aging, a stronger argument for the potential benefit of arthroplasty could not be made. The authors should be commended for their work, which stands out in the literature for its mean follow-up and radiographic analysis. The current manuscript represents a meaningful contribution to our understanding of adjacent segment degeneration in cervical arthrodesis patients. Luis Manuel Tumialan Phoenix, Arizona 1. Kim HJ, Kelly MP, Ely CG, Dettori JR, Riew KD. The risk of adjacent-level ossification development after surgery in the cervical spine: are there factors that affect the risk? A systematic review. Spine (Phila Pa 1976) . 2012; 37( 22 suppl): S65- 74. Google Scholar CrossRef Search ADS PubMed  Copyright © 2017 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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NeurosurgeryOxford University Press

Published: May 30, 2017

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