Journal of Hip Preservation Surgery Vol. 5, No. 2, pp. 131–136 doi: 10.1093/jhps/hny004 Advance Access Publication 9 March 2018 Research article Adolescent spine patients have an increased incidence of acetabular overcoverage Ena Nielsen and Rachel Y. Goldstein* Children’s Orthopaedic Center, Children’s Hospital Los Angeles, 4650 Sunset Blvd, MS#69, Los Angeles, CA 90027, USA *Correspondence to: R. Y. Goldstein. E-mail: email@example.com Submitted 1 June 2017; Revised 15 December 2017; revised version accepted 11 February 2018 ABSTRACT Changes in spino-pelvic alignment can lead to changes in acetabular coverage and predispose those with spinal pathologies to hip pathologies. The purpose of this study was to deﬁne the incidence of acetabular overcoverage in pediatric spine patients. Retrospective review of charts and EOS radiographs was conducted for patients21 years old with adolescent idiopathic scoliosis (AIS) or Scheuermann’s Kyphosis (SK) who were treated with posterior spinal fusion (PSF) between 12/01/2015–7/26/2016. Radiographs were measured for lateral center edge angles (LCEA), anterior center edge angle (ACEA), and lumbar lordosis pre- and postoperatively. 32 patients met inclusion criteria. Preoperatively, mean LCEA was 44.1 degrees (range: 32–55, SD: 5.1) on the right and 42.8 degrees (range: 33–52, SD: 4.4) on the left. Mean preoperative ACEA was 56.0 degrees (range: 35–90, SD: 10.4). Mean preoperative lordosis was 56.0 degrees (range: 22–105, SD: 19.1) Preoperative LCEA was not associated with lordosis (right: r¼ 0.002, p¼ 0.78, left: r¼ 0.006, p¼ 0.66). Preoperative ACEA was no associated with lordosis (r¼ 0.02, p¼ 0.49). Overall, the mean percent change in LCEA was 3.4% (range: 19.6–21.9, SD: 10.3) on the right and 3.5% (range: 31.0–27.9, SD: 13.3) on the left. Mean percent change in ACEA was 9.1% (range: 20.6–35.7, SD: 15.1). Mean percent change in lordosis was 12.2% (range: 150–33.3, SD: 33.3. The incidence of acetabular overcoverage may be signiﬁcantly higher in a pediatric spinal population than the general population. Careful monitoring of these patients for signs and symptoms of hip pathology may be warranted. lordosis and decreased acetabular coverage of the femoral INTRODUCTION head . Expanding on this finding, Buckland et al. dem- Spine and hip alignment are inextricably linked by the na- onstrated that changes in acetabular version had a strong ture of the pelvic attachment at the lumbosacral junction. negative relationship with changes in lumbar lordosis; that Sagittal spine balance affects pelvic tilt at this point of at- is, increasing lordosis resulted in increased acetabular retro- tachment and thus pelvic tilt is able to function as a com- version . Similarly, Hu et al. found that changes in ace- pensatory mechanism for sagittal malalignment. Due to the tabular anteversion were significantly positively correlated nature of the pelvic bone, this change in tilt can lead to hip with changes in pelvic tilt after performing lumbar pedicle morbidities co-existing with spinal deformities [1, 2]. In an subtraction for treatment of thoracolumbar kyphosis . adult cadaveric study, changes in pelvic tilt were directly While this phenomenon has been well documented in correlated with changes in measures of acetabular coverage, adults, little is known about the incidence of hip morbid- including lateral center-edge angle (LCEA), percentage of ities associated with spinal deformity in the pediatric popu- acetabular crossover and Tonnis angle . Recent studies lation. One study of healthy adolescents by Pytiak et al. have shown a relationship between increased hip path- showed a correlation between lumbar lordosis and pelvic ology, most notably acetabular anteversion, following de- tilt, but no correlation between pelvic tilt and measures of creases in spinal lordosis [1, 4]. acetabular coverage . Clinically, surgeons at our institu- Correction of these spinal conditions has been shown to tion have observed that patients with adolescent idiopathic improve acetabular coverage in the adult population. scoliosis (AIS) and Scheuermann’s kyphosis (SK) seem to Watanabe et al. showed a correlation between decreased V C The Author(s) 2018. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by- nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact firstname.lastname@example.org Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/131/4925394 by Ed 'DeepDyve' Gillespie user on 17 June 2018 132 E. Nielsen and R. Goldstein have an unusually high incidence of acetabular overcover- age but actual rates are unknown. Their overcoverage may resolve upon decrease of lordosis with correction of their scoliosis through bracing or surgery [7–14]. This study aims to determine the incidence of acetabu- lar overcoverage among AIS and SK patients, and to assess the improvement of this condition following spinal fusion for the correction of spinal curvature. MATERIALS AND METHODS Institutional review board approval was granted for this study. Patient population Patients21 years old with AIS or SK who were treated with PSF between 1 December 2015 and 26 July 2016 at the participating institution were eligible for this study. CPT and ICD-9 codes were used to identify the patient population. Patients were excluded from the study if they did not receive EOS imaging pre- and postoperatively or if their radiographs were inadequate for anterior and lateral measurements. Radiographs EOS imaging was used to evaluate the LCEA, anterior cen- ter edge angle (ACEA) and degree of lumbar lordosis in all patients preoperatively and immediately postoperatively. Pelvic tilt and rotation was assessed in all radiographs to ensure measurement accuracy. This imaging modality was chosen due to its ability to visualize the vertebral column Fig. 1. Measurement of LCEA, bilateral. Reproduced with per- and hips simultaneously. EOS imaging has been shown to mission from the Children’s Orthopaedic Center, Los Angeles. be comparable to traditional radiography in the assessment of hip parameters used in acetabular overcoverage assess- ment . head and a line drawn from the center of the femoral head to the anterior edge on the acetabulum (Figs 3 and 4). Data collection The primary study endpoint was the incidence of lateral and anterior acetabular overcoverage pre- and postopera- This study was conducted as a retrospective chart review. Patient charts were reviewed for demographic information tively. A secondary endpoint was the association between changes in lordosis and changes in LCEA and ACEA. (age,sex,BMI)and diagnosis. Preoperative and first postop- erative radiographs were analyzed to determine the LCEA of Statistical analysis each hip and the degree of lumbar lordosis. Lateral acetabular overcoverage was defined as a LCEA40 degrees. Anterior Descriptive data were summarized using mean, range and acetabular overcoverage was defined as an ACEA50 standard deviation. Significance of perioperative differences degrees. Normal lumbar lordosis was defined as lordosis in LCEA, ACEA and lumbar lordosis were calculated using between 40 and 60 degrees. a paired t-test. Linear regression was used to determine the LCEA was defined as the angle formed by the intersec- correlation between lumbar lordosis and LCEA or ACEA, tion of a vertical line drawn through the center of the fem- both preoperatively and perioperatively. oral head and a line drawn from the center of the femoral RESULTS head to the lateral edge of the acetabulum (Figs 1 and 2). ACEA was defined as the angle formed by the intersec- A total of 32 patients met inclusion criteria: 34.4% tion of a vertical line drawn through the center of the femoral (n ¼ 11/32) were male and 65.6% (n ¼ 21/32) were Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/131/4925394 by Ed 'DeepDyve' Gillespie user on 17 June 2018 Acetabular overcoverage in idiopathic scoliosis 133 female. Mean patient age was 14.5 years (range: 11–20, SD: 2.2). Mean BMI was 23.6 (range: 15.7–31.8, SD: 4.7). About 81.3% (n ¼ 26/32) of patients were diagnosed with AIS and 18.7% (n ¼ 6/32) were diagnosed with SK (Table I). Preoperatively, mean LCEA was 44.1 degrees (range: 32–55, SD: 5.1) on the right and 42.8 degrees (range: 33–52, SD: 4.4) on the left. Mean preoperative ACEA was 56.0 de- grees (range: 35–90, SD: 10.4). Mean preoperative lordosis was 56.0 degrees (range: 22 to 105, SD: 19.1) (Table II). About 96.9% (n ¼ 31/32) of patients had lateral acetabular overcoverage on at least one hip. About 75.0% (n ¼ 24/32) of patients had anterior acetabular overcoverage. About 28.1% (n ¼ 9/32) of patients were hyperlordotic, 56.2% (n¼ 18/32) had normal lordosis, and 15.6% (n ¼ 5/32) were hypolordotic. Preoperative LCEA was not associated with lordosis (right: r ¼ 0.002, P ¼ 0.78, left: r ¼ 0.006, Fig. 2. Measurement of LCEA, detailed. Reproduced with per- mission from the Children’s Orthopaedic Center, Los Angeles. P ¼ 0.66). Preoperative ACEA was not associated with lordosis (r ¼ 0.02, P ¼ 0.49) (Table III). Postoperatively, mean LCEA was 42.4 degrees (range: 35–59, SD: 5.3) on the right and 41.1 degrees (range: 29–55, SD: 5.7) on the left. Mean postoperative ACEA was 59.1 de- grees (range: 40–78, SD: 7.6). Mean postoperative lordosis was 52.2 degrees (range: 11–102, SD: 16.7). Overall, the mean percent change in LCEA was 3.4% (range: 19.6 to 21.9, SD: 10.3) on the right and 3.5% (range: 31.0 to 27.9, SD: 13.3) on the left. Mean percent change in ACEA was 9.1% (range: 20.6 to 35.7, SD: 15.1). Mean percent change in lordosis was 12.2% (range: 150 to 33.3, SD: 33.3) (Table II). The change in LCEA after PSF was significant on the right, but not on the left (right: P ¼ 0.04, left: P ¼ 0.09). ACEA signifi- cantly decreased after PSF was (P ¼ 0.03). The change in lordosis after PSF was not significant (P ¼ 0.11). There was no association between the change in lordosis and the change in LCEA (right: P ¼ 0.52; left: P ¼ 0.24) or ACEA (P ¼ 0.65) (Table III). DISCUSSION Hip and spine pathology can be linked as a consequence of pelvic attachment at the lumbosacral junction. Previous studies have demonstrated that changes in spino-pelvic alignment can lead to changes in acetabular coverage and, as a consequence, predispose those with spinal pathologies to hip pathologies such as FAI or dysplasia. The purpose of this study was to define the incidence of acetabular over- coverage in pediatric AIS and SK patients. Secondarily, we hoped to determine if a correction of the spinal deformity through PSF would also affect hip morphology. Fig. 3. Measurement of ACEA, bilateral. Reproduced with per- In a meta-analysis of 2114 asymptomatic hips across 26 mission from the Children’s Orthopaedic Center, Los Angeles. studies, the incidence of pincer-type FAI (characterized by Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/131/4925394 by Ed 'DeepDyve' Gillespie user on 17 June 2018 134 E. Nielsen and R. Goldstein questionably correlated with an increase in osteoarthritis [17, 18]. If indeed pediatric spine patients have high rates of acetabular overcoverage, they may be at risk for worsen- ing hip pathology later in life. While radiographic findings alone are not enough for a diagnosis of FAI, it may be worthwhile to monitor AIS and SK patients for develop- ment of characteristic symptomatology. This can include the gradual onset of hip pain, clicking or popping on the af- fected side, pain with flexion and internal rotation and a positive impingement test [18–20]. About 34.7% (n ¼ 17/49) of patients were hyperlor- dotic. Of the 24 patients that fell into the normal range for lordosis (40–60 degrees), 41.7% (n ¼ 10/24) were in the upper quartile of normal (55–60 degrees). Thus, the over- Fig. 4. Measurement of ACEA, detailed. Reproduced with per- all rate of high-normal lordosis and hyperlordotic curves mission from the Children’s Orthopaedic Center, Los Angeles. was 55.1% (n ¼ 27/49), which is consistent with previous studies demonstrating increased lordosis in AIS and SK pa- tients [9–11, 13, 14, 21, 22]. Previous studies have postu- Table I. Patient demographics lated a correlation between lumbar lordosis and acetabular Mean (range, SD) coverage [1, 4, 6], but our study failed to find any signifi- Age (years) 14.5 (11–20, 2.2) cant relationship between these measures (right: r ¼ 0.01, P ¼ 0.52, left: r ¼ 0.02, P ¼ 0.45). BMI 23.6 (15.7–31.8, 4.7) Despite a significant 9.2% decrease in lordosis (P ¼ 0.04), we found no significant change in LCEA after PSF (right: %(N) P ¼ 0.49, left: P ¼ 0.08). Several adult studies of hip-spine Sex pathologies have found significant changes in measures of hip morphology after treatment of spinal conditions [1, 4, 5]; Male 34.4% (11/32) however, two of these studies enrolled only patients whose Female 65.6% (21/32) spinal pathology affected the lumbar region. Treatment of these conditions may have resulted in a greater change in Diagnosis lumbosacral alignment than treatments affecting only the AIS 81.3% (26/32) thoracic or cervical vertebrae. The majority of spinal fusions in the current study occurred in the thoracic and high lumbar SK 18.7% (6/32) region, which may explain why we saw minimal change in pelvic parameters after treatment. acetabular overcoverage) was 67%; however, the average This study has several limitations. First, due to the con- LCEA was only 31.2 degrees, below the threshold for overco- straints of radiographs available for retrospective review, verage used in the current study. This discrepancy may be this study used plain radiographs for measurements, which due to varying parameters used to diagnose and define pincer can be affected by pelvic tilt, rotation and patient distance deformity across studies, and actual incidence in the general from the beam source . In addition, we used only population may be lower . A separate study of 99 asymp- standing radiographs, which have been shown to give tomatic adolescents found a 14% incidence of abnormal decreased measures of LCEA relative to standard supine LCEA . Despite this discrepancy, the incidence of acetabu- films [15, 24]. It is possible these limitations introduced lar overcoverage in the AIS and SK populations in the current random error into the measurements and true values may study was still higher than in the general population. be even higher than those presented in the study. Preoperatively, 93.9% (n ¼ 46/49) of patients met criteria Finally, our center began using EOS imaging in late for acetabular overcoverage on at least one hip. To our know- 2015 and as a result there are relatively few patients ledge this is the first study demonstrating this high incidence included in this study. This may have contributed to the of acetabular overcoverage associated with AIS and SK. lack of significant associations between LCEA and lordosis. Acetabular overcoverage predisposes to femoro-acetab- Our results suggest that the incidence of acetabular ular impingement (FAI), a hip pathology which is overcoverage may be significantly higher in a pediatric Downloaded from https://academic.oup.com/jhps/article-abstract/5/2/131/4925394 by Ed 'DeepDyve' Gillespie user on 17 June 2018 Acetabular overcoverage in idiopathic scoliosis 135 Table II. Radiographic measurements and percent change Measure Mean Range SD Pre-op LCEA, right 44.1 degrees 32–55 5.1 Pre-op LCEA, left 42.8 degrees 33–52 4.4 Pre-op ACEA 56.0 degrees 36–90 10.4 Pre-op lordosis 56.0 degrees 22 to 105 19.1 Post-op LCEA, right 42.4 degrees 35–59 5.3 Post-op LCEA, left 41.1 degrees 29–55 5.7 Post-op ACEA 59.1 degrees 40–78 7.6 Post-op lordosis 52.2 degrees 11–102 16.7 % Change LCEA, right 3.4% 19.6 to 21.9 10.3 % Change LCEA, left 3.5% 31.0 to 27.9 13.3 % Change ACEA 9.1% 20.6 to 35.7 15.1 % Change lordosis 12.2% 150 to 33.3 33.3 Table III. Signiﬁcant of association between radiographic measurements Measure P-value: P-value: P-value: pre-op association with lordosis change pre-op to post-op association with change in lordosis LCEA, right 0.78 0.04* 0.52 LCEA, left 0.66 0.09 0.24 ACEA 0.49 0.03* 0.65 Lordosis — 0.11 — *Statistically signiﬁcant. FUNDING spinal population than in the general population. Further None declared. longitudinal studies examining the incidence of hip mor- bidity in AIS and SK patients should be done to evaluate REFERENCES the clinical significance of this finding. Careful monitoring of these patients for signs and symptoms of hip pathology 1. Buckland AJ,VigdorchikJ,SchwabFJ et al. Acetabular antever- sion changes due to spinal deformity correction: bridging the may be warranted, especially in patients with additional gap between hip and spine surgeons. J Bone Joint Surg Am 2015; risk factors for FAI. 97: 1913–20. 2. Lafage V, Bharucha NJ, Schwab F et al. Multicenter validation of ACKNOWLEDGEMENTS a formula predicting postoperative spinopelvic alignment. J Neurosurg Spine 2012; 16: 15–21. The authors would like to thank the research staff who lent ad- 3. Henebry A, Gaskill T. The effect of pelvic tilt on radiographic ministrative support and proofreading for this study. We also markers of acetabular coverage. 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Journal of Hip Preservation Surgery – Oxford University Press
Published: Mar 9, 2018
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