Development and Validation of a Novel Adult Spinal Deformity Surgical Invasiveness Score: Analysis of 464 Patients

Development and Validation of a Novel Adult Spinal Deformity Surgical Invasiveness Score:... Abstract BACKGROUND A surgical invasiveness index (SII) has been validated in general spine procedures but not adult spinal deformity (ASD). OBJECTIVE To assess the ability of the SII to determine the invasiveness of ASD surgery and to create and validate a novel ASD index incorporating deformity-specific factors, which could serve as a standardized metric to compare outcomes and risk stratification of different ASD procedures for a given deformity. METHODS Four hundred sixty-four patients who underwent ASD surgery between 2009 and 2012 were identified in 2 multicenter prospective registries. Multivariable models of estimated blood loss (EBL) and operative time were created using deformity-specific factors. Beta coefficients derived from these models were used to attribute points to each component. Scoring was iteratively refined to determine the R2 value of multivariate models of EBL and operative time using adult spinal deformity-surgical (ASD-S) as an independent variable. Similarly, we determined weighting of postoperative changes in radiographical parameters, which were incorporated into another index (adult spinal deformity-surgical and radiographical [ASD-SR]). The ability of these models to predict surgical invasiveness was assessed in a validation cohort. RESULTS Each index was a significant, independent predictor of EBL and operative time (P < .001). On multivariate analysis, ASD-S and ASD-SR explained more variability in EBL and operative time than did the SII (P < .001). The ASD-SR explained 21% of the variation in EBL and 10% of the variation in operative time, whereas the SII explained 17% and 3.2%, respectively. CONCLUSION The ASD-SR, which incorporates deformity-specific components, more accurately predicts the magnitude of ASD surgery than does the SII. Adult spinal deformity, Risk stratification, Estimated blood loss, Operative time, Surgical complexity, Surgical invasiveness index ABBREVIATIONS ABBREVIATIONS ASD adult spinal deformity ASD-S adult spinal deformity-surgical ASD-SR adult spinal deformity-surgical and radiographical EBL estimated blood loss SII surgical invasiveness index In appropriately selected patients, surgery for adult spinal deformity (ASD) can lead to improvements in pain, disability, and health-related quality of life.1-4 Surgery often involves complex reconstruction with multiple soft-tissue releases, osteotomies, segmental instrumentation through several levels, placement of interbody grafts, and major maneuvers to restore spinal alignment.5,6 As such, it is associated with substantial risk of complications.4,7-11 Quantifying the invasiveness of a complex spine procedure reliably and reproducibly is challenging but may be useful in point-of-care decision making, patient counseling, and evaluation of treatment success. Various surgical options exist for the treatment of ASD. The magnitude of ASD surgery depends not only on the extent of the deformity but also on factors such as patient age, symptoms, bone quality, function, and risk of complications. Data comparing ASD procedures for a given deformity on the basis of outcomes and risk of complications are sparse. An index that can quantify the magnitude (ie, invasiveness) of ASD surgical procedures would be useful to help estimate the risks associated with procedures for a particular deformity. This would allow counseling of patients with a particular set of risk factors about the greater risks associated with more invasive procedures. The surgical invasiveness index (SII) proposed by Mirza et al12 quantifies the invasiveness of general spine procedures for all indications. The SII assigns numerical scores to the components of a typical spine operation, which are then summed for all operative levels. Each surgical component (decompression, instrumentation, and fusion from an anterior or posterior approach) is assigned 1 point (Table 1). The total SII score is the sum of the 6 component scores for all operative levels. The authors validated this approach for general spine procedures by showing that their index has a strong association with the invasiveness of the surgery as determined by the extent of estimated blood loss (EBL) and operative time.12 Studies have shown a positive correlation of surgical invasiveness with blood loss and operative time, which makes these parameters reliable indicators of surgical invasiveness.13-16 TABLE 1. Surgical Components Used to Calculatea the SII12 Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. SII, surgical invasiveness index. aThe total SII score is the sum of the scores for each vertebral level. View Large TABLE 1. Surgical Components Used to Calculatea the SII12 Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. SII, surgical invasiveness index. aThe total SII score is the sum of the scores for each vertebral level. View Large The utility of the SII in more complex deformity procedures has not been shown. Deformity-specific factors such as osteotomies, revision surgery, pelvic fixation, and correction of alignment are not accounted for by the SII. Therefore, we assessed the accuracy of the SII in determining the invasiveness of deformity surgeries in ASD patients and created a new scoring system that includes deformity-specific factors with the goal of creating a tool to more accurately predict the invasiveness of ASD surgical procedures. This too can assist with risk stratification and outcome assessment for surgeries of various magnitudes for a given deformity. A standard ASD invasiveness index would allow comparison of the invasiveness of different procedures for a given deformity and assessment of whether the risks of the more invasive procedure would outweigh the benefits compared with a less invasive procedure. Our null hypothesis was that the deformity-specific invasiveness index (adult spinal deformity-surgical and radiographical [ASD-SR]) would be similarly accurate in explaining variation in EBL and operative time compared with the SII in ASD surgeries. METHODS Patient Population To develop the initial cohort used to derive the ASD invasiveness index, we queried a multicenter prospective registry of patients with ASD from 11 centers. Each participating institution obtained approval from its institutional review board. ASD was defined as a coronal major curve of 20° or more, sagittal vertical axis of 5 cm or more, pelvic tilt of 25° or more, and/or thoracic kyphosis of 60° or more. Patients younger than 18 yr, those with spinal deformity secondary to a neuromuscular cause, and those with active infection or malignancy were excluded. Informed consent was obtained for each patient included in the study. We identified 564 patients who had undergone operative treatment for ASD from 2008 through 2012. Of these, 253 patients (herein, the development cohort) had complete radiographical and clinical follow-up at 2 yr and were used for the development phase of the ASD invasiveness index. To identify the cohort for validation, we queried a different multicenter prospective registry consisting of 309 surgically treated patients with ASD. The inclusion and exclusion criteria for the validation cohort were the same as for the development cohort. Of these, 211 patients (herein, the validation cohort) had complete radiographical and clinical follow-up at 2 yr and were used for the validation phase of the ASD invasiveness index. Index Construction The SII score, developed by Mirza et al,12 was calculated for all patients. Using the development cohort, we created multivariate linear regression models of operative time and log-linear transformed EBL (transformed to approximate normal distribution), including the components of the SII index and the deformity surgical factors. These factors were posterior decompression, posterior instrumentation, posterior fusion, transforaminal/posterior lumbar interbody fusion, anterior lumbar interbody fusion, Smith-Petersen osteotomies, 3-column osteotomies, iliac fixation, and revision surgery. Beta coefficients derived from these models were used to assign points to surgical components to create a new ASD score, the ASD-S (with “S” referring to surgical parameters; Table 2). The same method was then used to determine appropriate weighting for postoperative change in spinopelvic radiographical parameters, including sagittal vertical axis, pelvic incidence–lumbar lordosis mismatch, pelvic tilt, and thoracic kyphosis. The scores for these factors were added to the SII score and the deformity-specific factor score, creating a second index, the ASD-SR (with “SR” referring to surgical and radiographical parameters). TABLE 2. Surgical Components Used to Calculate the ASD-S Invasiveness Score Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 ASD-S, adult spinal deformity-surgical. View Large TABLE 2. Surgical Components Used to Calculate the ASD-S Invasiveness Score Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 ASD-S, adult spinal deformity-surgical. View Large Estimates of the effect of specific surgical factors on operative time and EBL were derived from separate linear regression models of each of these variables. Beta coefficients from these models were used to attribute scores to each deformity-specific surgical factor included in ASD-S (the final index scoring system is presented in Table 2). In the construction of ASD-SR, changes in radiographical parameters from pre- to postoperative imaging were incorporated and weighted on the basis of their multivariate association with operative time and EBL. The final scores for these parameters were refined to maximize the ASD-SR model's predictive power and are shown in Table 3. TABLE 3. Additional Parametersa Included in the ASD-SR Invasiveness Index Score Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ ASD-SR, adult spinal deformity-surgical and radiographical aThese points are added to those of the ASD-S developed in the current study. bFrom preoperatively to postoperatively. cExpressed as points per 1-mm change. View Large TABLE 3. Additional Parametersa Included in the ASD-SR Invasiveness Index Score Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ ASD-SR, adult spinal deformity-surgical and radiographical aThese points are added to those of the ASD-S developed in the current study. bFrom preoperatively to postoperatively. cExpressed as points per 1-mm change. View Large Index Validation Both indices, the ASD-S and ASD-SR, were applied to the validation cohort. We created univariate linear regression models of operative time and log-transformed EBL with ASD-S or ASD-SR as the independent variable. Scoring of surgical factors was then iteratively refined to optimize the amount of variability explained (R2) by each model. Finally, multivariate linear regression models of operative time and log-transformed EBL were created for the SII, ASD-S, and ASD-SR and adjusted for patient age, sex, Charlson Comorbidity Index, and body mass index. Thus, the 3 indices were compared with respect to their predictive ability. The level of significance was set at P < .05. SAS, version 9.2, software (SAS Institute Inc, Cary, North Carolina) was used to analyze the data. RESULTS In the validation cohort, the mean EBL was 3024 mL (range 400-15 000 mL), and the mean operative time was 562 min (range 211-1175 min). The mean SII, ASD-S, and ASD-SR index scores were 33.6 (range 21-55), 52.9 (range 21-114), and 106 (range 44.9-221), respectively, in the validation cohort (Table 4). Patient demographic characteristics, preoperative radiographic parameters, and surgical details for the validation cohort are in Table 4. TABLE 4. Parameters Describing 211 Patients in the Validation Cohort Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 ALIF, anterior lumbar interbody fusion; ASD, adult spinal deformity; ASD-S, adult spinal deformity-surgical; ASD-SR, adult spinal deformity-surgical and radiographical; BMI, body mass index; EBL, estimated blood loss; LL, lumbar lordosis; PI, pelvic incidence; SD, standard deviation; SII, surgical invasiveness index; SVA, sagittal vertical axis aOther than ALIF. View Large TABLE 4. Parameters Describing 211 Patients in the Validation Cohort Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 ALIF, anterior lumbar interbody fusion; ASD, adult spinal deformity; ASD-S, adult spinal deformity-surgical; ASD-SR, adult spinal deformity-surgical and radiographical; BMI, body mass index; EBL, estimated blood loss; LL, lumbar lordosis; PI, pelvic incidence; SD, standard deviation; SII, surgical invasiveness index; SVA, sagittal vertical axis aOther than ALIF. View Large All 3 indices were significant, independent predictors of EBL and operative time (P < .001). For EBL, the ASD-SR had the strongest correlation (Pearson r = .34), followed by the ASD-S (r = .28) and SII (r = .22; P < .001; Figure 1). Similarly, the adjusted multivariate model with ASD-SR predicted more variability (R2 = .21) in EBL than ASD-S or SII (R2 = .17 for both; Table 5). For operative time, the ASD-SR had the highest correlation (r = .34), followed by the ASD-S (r = .26) and SII (r = .18; P < .001; Figure 2). The adjusted model of operative time with ASD-SR as the main predictor explained the most variability (R2 = .10). Models with ASD-S and SII were less robust (R2 = .065 and R2 = .032, respectively). The addition of postoperative changes in radiographical parameters to the scoring system, ASD-SR, explained 21% of the variation in EBL and 10% of the variation in operative time, whereas SII explained only 17% and 3.2%, respectively. FIGURE 1. View largeDownload slide Regression plot showing that the ASD-SR index has a stronger correlation with EBL than the ASD-S and SII. FIGURE 1. View largeDownload slide Regression plot showing that the ASD-SR index has a stronger correlation with EBL than the ASD-S and SII. FIGURE 2. View largeDownload slide Regression plot showing that the ASD-SR invasiveness index has a stronger correlation with operative time than the ASD-S and SII. FIGURE 2. View largeDownload slide Regression plot showing that the ASD-SR invasiveness index has a stronger correlation with operative time than the ASD-S and SII. TABLE 5. Correlations of Surgical Invasiveness Indices with Estimated Blood Loss and Operative Timea Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ ASD, adult spinal deformity; ASD-S, adult spinal deformity, with “S” referring to surgical parameters; ASD-SR, adult spinal deformity, with “SR” referring to surgical and radiographical parameters; SII, surgical invasiveness index. aPercentage of variability explained by multivariate models of estimated blood loss and operative time using each index separately as the main predictor. bModels adjusted for patient age, sex, Charlson Comorbidity Index, and body mass index. cDeveloped by Mirza et al.12 View Large TABLE 5. Correlations of Surgical Invasiveness Indices with Estimated Blood Loss and Operative Timea Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ ASD, adult spinal deformity; ASD-S, adult spinal deformity, with “S” referring to surgical parameters; ASD-SR, adult spinal deformity, with “SR” referring to surgical and radiographical parameters; SII, surgical invasiveness index. aPercentage of variability explained by multivariate models of estimated blood loss and operative time using each index separately as the main predictor. bModels adjusted for patient age, sex, Charlson Comorbidity Index, and body mass index. cDeveloped by Mirza et al.12 View Large DISCUSSION By using components of the general SII developed by Mirza et al12 and adding deformity-specific surgical and radiographic factors, we have developed a novel ASD SII (ASD-SR). Our new scoring system is a better predictor of surgical invasiveness (defined as EBL and operative time) than the previously established SII. Studies have shown that more extensive spinal surgeries are associated with greater EBL and longer operative time.13-16 This suggests that these factors are reasonable surrogates for the invasiveness of a surgical procedure. The SII for general spine procedures was created by Mirza et al.12 In studies that evaluate general spine procedures, the SII has been shown to be strongly associated with EBL and operative time and to explain approximately 50% of variation in these 2 variables.12,17 Previous studies have not applied the SII to deformity procedures. These operations are inherently complex with higher and more variable EBL and operative time compared with general spine procedures. Indeed, in the present study, when we applied the SII to deformity procedures, its correlations with EBL and operative time were less robust compared with those of previous reports of general spine procedures. For the SII, the Pearson correlation coefficients were only .22 for EBL and .18 for operative time. This discrepancy may result, at least in part, from greater complexity of ASD procedures compared with those in previous studies. We hypothesized that the addition of deformity-specific factors in a new invasiveness index could better account for the aforementioned differences between general and deformity spine operations. Specifically, in the ASD-S, we incorporated revision vs primary surgery, osteotomies, iliac fixation, and interbody fusion (anterior and posterior). Revision surgery18 and 3-column osteotomies19 are associated with higher rates of intraoperative blood transfusion. The addition of these factors yielded an index with higher correlations to EBL and operative time than the SII. The ASD-S also explained more of the variability in EBL and operative time when incorporated in an adjusted model of these variables. Larger deformity correction, measured by changes in standard radiographical parameters, is associated with more blood loss19 and ostensibly represents a higher degree of invasiveness. We therefore created a second index, the ASD-SR, which incorporates changes in sagittal vertical axis, pelvic incidence–lumbar lordosis mismatch, pelvic tilt, and thoracic kyphosis. This index performed better than the SII or ASD-S in predicting EBL and operative time. Unlike the SII and ASD-S, however, the ASD-SR cannot be calculated on the basis of preoperative information alone. To use the more accurate ASD-SR index, it may be possible to use planned magnitude of correction (manually or from surgical planning software) for each of the 4 radiographical parameters to calculate the score preoperatively. The feasibility and accuracy of such a strategy would require further study. The prospective collection of our multicenter data is a strength of this study. This allowed us to capture a wide range of methods to treat complex spine disorders and allows each component of deformity surgery to be well represented in our study. An invasiveness index could be useful for preoperative risk stratification and is a key component for predictive modeling for ASD surgery. The current ASD-SR index uses variables that cannot be obtained before surgery; however, the scoring system could be used preoperatively by using the planned surgical procedure and planned magnitude of correction as the radiographic component. If this goal is met, the maximum invasiveness of the surgery could be determined. By planning the various surgical techniques and determining the magnitude of curve correction, a quantitative measurement of surgical invasiveness could be calculated. Having a method to measure invasiveness will allow surgeons to assess the magnitude of different surgical procedures for a given deformity preoperatively and to estimate an individual patient's risks for each surgical option. Multiple studies have validated the use of EBL and operative time to determine the invasiveness of a procedure.12-17 By using this methodology, our study shows that the ASD-SR index is a better predictor of ASD surgical invasiveness than the SII. The development of the ASD-SR invasiveness index is the first step in determining the effects that the magnitude of a surgery has on the perioperative risk of complications. With the use of the ASD-SR invasiveness index, further research can be conducted to assess the association of the invasiveness of the procedure with outcomes and complications. Furthermore, studies should examine the combined use of the ASD-SR and a patient frailty index to help in risk stratification of various surgical options for a given deformity. Limitations This study has several limitations. Although the database is maintained prospectively, this was a retrospective review and is thus subject to selection and information bias. Comparison of our results with those of Mirza et al12 is limited by differences in patient populations that may not have been completely accounted for in our analysis. Also, although EBL and operative time are parameters that can define invasiveness, other factors besides the magnitude of the surgery can influence these parameters. Therefore, it is not surprising that the invasiveness of the surgery explains only a portion of the variability in EBL and operative time. In assessing the magnitude of the surgery to explain the variability of EBL and operative time, the ASD-SR is a better predictor of “invasiveness” than the SII in ASD surgeries. CONCLUSION The inclusion of deformity surgical factors in a novel ASD SII resulted in a tool that more accurately predicts surgical invasiveness than the SII in ASD patients. The inclusion of radiographical parameters that quantify the magnitude of correction in regional and global alignment yields an incrementally superior index. For quantifying the invasiveness of a deformity correction procedure, the ASD-S and ASD-SR offer improved predictive ability compared with the SII. The development of the ASD-SR invasiveness index is the first step in risk-stratifying ASD patients on the basis of the magnitude of their surgeries. Disclosures The International Spine Study Group received funding from DePuy Synthes, Innovasis, Biomet, K2M, NuVasive, Medtronic, and Stryker. Dr Klineberg is a consultant for DePuy Synthes and Stryker and received honoraria from K2M, and honoraria and a fellowship grant from AOSpine. Dr Sciubba is a consultant for Medtronic, DePuy Synthes, Globus, and Orthofix. Dr Burton is a consultant for and receives research support and royalties from DePuy Spine. The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Bridwell KH , Glassman S , Horton W et al. Does treatment (nonoperative and operative) improve the two-year quality of life in patients with adult symptomatic lumbar scoliosis: a prospective multicenter evidence-based medicine study . Spine . 2009 ; 34 ( 20 ): 2171 - 2178 . Google Scholar CrossRef Search ADS PubMed 2. Smith JS , Shaffrey CI , Berven S et al. 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Neurosurg Focus . 2010 ; 28 ( 3 ): E1 - E10 . Google Scholar CrossRef Search ADS PubMed 7. Bridwell KH , Lewis SJ , Lenke LG , Baldus C , Blanke K . Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance . J Bone Joint Surg Am . 2003 ; 85 ( 3 ): 454 - 463 . Google Scholar CrossRef Search ADS PubMed 8. Hassanzadeh H , Jain A , El Dafrawy MH et al. Three-column osteotomies in the treatment of spinal deformity in adult patients 60 years old and older: outcome and complications . Spine (Phila Pa 1976) . 2013 ; 38 ( 9 ): 726 - 731 . Google Scholar CrossRef Search ADS PubMed 9. Lafage V , Smith JS , Bess S et al. Sagittal spino-pelvic alignment failures following three column thoracic osteotomy for adult spinal deformity . Eur Spine J . 2012 ; 21 ( 4 ): 698 - 704 . Google Scholar CrossRef Search ADS PubMed 10. Smith JS , Sansur CA , Donaldson WF III et al. Short-term morbidity and mortality associated with correction of thoracolumbar fixed sagittal plane deformity: a report from the Scoliosis Research Society Morbidity and Mortality Committee . Spine . 2011 ; 36 ( 12 ): 958 - 964 . Google Scholar CrossRef Search ADS PubMed 11. Smith JS , Shaffrey CI , Ames CP et al. Assessment of symptomatic rod fracture after posterior instrumented fusion for adult spinal deformity . Neurosurgery . 2012 ; 71 ( 4 ): 862 - 867 . Google Scholar CrossRef Search ADS PubMed 12. Mirza SK , Deyo RA , Heagerty PJ et al. Development of an index to characterize the "invasiveness" of spine surgery: validation by comparison to blood loss and operative time . Spine . 2008 ; 33 ( 24 ): 2651 - 2661 ; discussion 2662 . Google Scholar CrossRef Search ADS PubMed 13. Cha CW , Deible C , Muzzonigro T , Lopez-Plaza I , Vogt M , Kang JD . Allogeneic transfusion requirements after autologous donations in posterior lumbar surgeries . Spine . 2002 ; 27 ( 1 ): 99 - 104 . Google Scholar CrossRef Search ADS PubMed 14. Cho KJ , Suk SI , Park SR et al. Complications in posterior fusion and instrumentation for degenerative lumbar scoliosis . Spine . 2007 ; 32 ( 20 ): 2232 - 2237 . Google Scholar CrossRef Search ADS PubMed 15. Nuttall GA , Horlocker TT , Santrach PJ , Oliver WC Jr , Dekutoski MB , Bryant S . Predictors of blood transfusions in spinal instrumentation and fusion surgery . Spine . 2000 ; 25 ( 5 ): 596 - 601 . Google Scholar CrossRef Search ADS PubMed 16. Zheng F , Cammisa FP Jr , Sandhu HS , Girardi FP , Khan SN . Factors predicting hospital stay, operative time, blood loss, and transfusion in patients undergoing revision posterior lumbar spine decompression, fusion, and segmental instrumentation . Spine . 2002 ; 27 ( 8 ): 818 - 824 . Google Scholar CrossRef Search ADS PubMed 17. Mirza SK , Deyo RA , Heagerty PJ , Turner JA , Lee LA , Goodkin R . Towards standardized measurement of adverse events in spine surgery: conceptual model and pilot evaluation . BMC Musculoskelet Disord . 2006 ; 7 ( 53 ): 1 - 16 . Google Scholar PubMed 18. Yoshihara H , Yoneoka D . Predictors of allogeneic blood transfusion in spinal fusion for pediatric patients with idiopathic scoliosis in the United States, 2004-2009 . Spine . 2014 ; 39 ( 22 ): 1860 - 1867 . Google Scholar CrossRef Search ADS PubMed 19. Yu X , Xiao H , Wang R , Huang Y . Prediction of massive blood loss in scoliosis surgery from preoperative variables . Spine . 2013 ; 38 ( 4 ): 350 - 355 . Google Scholar CrossRef Search ADS PubMed COMMENTS The goal of this publication has been to develop a score that would provide insight into the surgical invasiveness of adult deformity procedures and thus potentially stratify the risk associated with these procedures. I applaud the authors in providing a well-written paper with a large cohort of patients with long-term follow-up. It would be interesting to see if the authors' scoring system could go beyond predicting operative time and estimated blood loss alone to predicting complications or clinical outcomes such as postoperative patient function, recovery, or satisfaction scores. Laura A. Snyder Phoenix, Arizona The authors seek to build on the Surgical Invasiveness Index (SII), initially published by Mirza et al in 20081 (reference 12 from index paper) to incorporate features common to spinal deformity surgery. They used registry data from 464 patients to associate various pre- and intraoperative variables with operative time and blood loss, used here and elsewhere as proxies for surgical invasiveness. To the SII, they added surgical parameters specific to deformity surgery (eg Smith-Peterson vs 3 Column Osteotomies) to create the ASD-S Index. Then, they added radiographic parameters to create the ASD-SR Index. They found that all 3 indices were predictive of blood loss and operative time, but the addition of surgical (ASD-S) and radiographic (ADS-SR) parameters strengthened the correlation. The goals of this work lie in better predicting of risks and improved patient counselling ahead of major deformity reconstruction surgery. This form of risk adjustment may also prove valuable in clinical quality and research efforts. This work is iterative toward those goals. First, the additional time required to calculate these scores must be shown to practically impact the decision for surgery and the type of surgery offered for spine surgeons to utilize them clinically. In the future, advanced electronic medical records systems could calculate these scores automatically. Second, as interesting as this measure of invasiveness might be, true patient outcomes and risk measures, such as complication rates, need to be incorporated in these efforts to broaden their utility. Beyond direct patient counselling, broader utilization of these scores systems to risk-adjust patient outcome data will both improve the scores’ predictive power and our ability to benchmark the quality of care delivered in this diverse array of morbid surgeries. Eeric Truumees Austin, Texas 1. Mirza SK , Deyo RA , Heagerty PJ , et al. Development of an index to characterize the 259 "invasiveness" of spine surgery: validation by comparison to blood loss and operative 260 time . Spine . 2008 ; 33 ( 24 ): 2651 - 2661 ; discussion 2662 . Google Scholar CrossRef Search ADS PubMed The objective of this study was to use postoperative surgical and radiographic data to validate new surgical invasiveness scores for the operative treatment of adult spinal deformity. This investigation was a well-designed study with a large, multi-center cohort of patients with long-term follow-up. It will be both interesting and important for the authors to test their invasiveness score with preoperative data to analyze the tool's viability for use in preoperative planning. Kern Singh Chicago, Illinois 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

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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
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10.1093/neuros/nyx303
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Abstract

Abstract BACKGROUND A surgical invasiveness index (SII) has been validated in general spine procedures but not adult spinal deformity (ASD). OBJECTIVE To assess the ability of the SII to determine the invasiveness of ASD surgery and to create and validate a novel ASD index incorporating deformity-specific factors, which could serve as a standardized metric to compare outcomes and risk stratification of different ASD procedures for a given deformity. METHODS Four hundred sixty-four patients who underwent ASD surgery between 2009 and 2012 were identified in 2 multicenter prospective registries. Multivariable models of estimated blood loss (EBL) and operative time were created using deformity-specific factors. Beta coefficients derived from these models were used to attribute points to each component. Scoring was iteratively refined to determine the R2 value of multivariate models of EBL and operative time using adult spinal deformity-surgical (ASD-S) as an independent variable. Similarly, we determined weighting of postoperative changes in radiographical parameters, which were incorporated into another index (adult spinal deformity-surgical and radiographical [ASD-SR]). The ability of these models to predict surgical invasiveness was assessed in a validation cohort. RESULTS Each index was a significant, independent predictor of EBL and operative time (P < .001). On multivariate analysis, ASD-S and ASD-SR explained more variability in EBL and operative time than did the SII (P < .001). The ASD-SR explained 21% of the variation in EBL and 10% of the variation in operative time, whereas the SII explained 17% and 3.2%, respectively. CONCLUSION The ASD-SR, which incorporates deformity-specific components, more accurately predicts the magnitude of ASD surgery than does the SII. Adult spinal deformity, Risk stratification, Estimated blood loss, Operative time, Surgical complexity, Surgical invasiveness index ABBREVIATIONS ABBREVIATIONS ASD adult spinal deformity ASD-S adult spinal deformity-surgical ASD-SR adult spinal deformity-surgical and radiographical EBL estimated blood loss SII surgical invasiveness index In appropriately selected patients, surgery for adult spinal deformity (ASD) can lead to improvements in pain, disability, and health-related quality of life.1-4 Surgery often involves complex reconstruction with multiple soft-tissue releases, osteotomies, segmental instrumentation through several levels, placement of interbody grafts, and major maneuvers to restore spinal alignment.5,6 As such, it is associated with substantial risk of complications.4,7-11 Quantifying the invasiveness of a complex spine procedure reliably and reproducibly is challenging but may be useful in point-of-care decision making, patient counseling, and evaluation of treatment success. Various surgical options exist for the treatment of ASD. The magnitude of ASD surgery depends not only on the extent of the deformity but also on factors such as patient age, symptoms, bone quality, function, and risk of complications. Data comparing ASD procedures for a given deformity on the basis of outcomes and risk of complications are sparse. An index that can quantify the magnitude (ie, invasiveness) of ASD surgical procedures would be useful to help estimate the risks associated with procedures for a particular deformity. This would allow counseling of patients with a particular set of risk factors about the greater risks associated with more invasive procedures. The surgical invasiveness index (SII) proposed by Mirza et al12 quantifies the invasiveness of general spine procedures for all indications. The SII assigns numerical scores to the components of a typical spine operation, which are then summed for all operative levels. Each surgical component (decompression, instrumentation, and fusion from an anterior or posterior approach) is assigned 1 point (Table 1). The total SII score is the sum of the 6 component scores for all operative levels. The authors validated this approach for general spine procedures by showing that their index has a strong association with the invasiveness of the surgery as determined by the extent of estimated blood loss (EBL) and operative time.12 Studies have shown a positive correlation of surgical invasiveness with blood loss and operative time, which makes these parameters reliable indicators of surgical invasiveness.13-16 TABLE 1. Surgical Components Used to Calculatea the SII12 Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. SII, surgical invasiveness index. aThe total SII score is the sum of the scores for each vertebral level. View Large TABLE 1. Surgical Components Used to Calculatea the SII12 Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. Score component Points Anterior  Decompression 1 per vertebra requiring excision, regardless of the surgical approach, or 1 for the caudal disc excised from an anterior approach.  Fusion 1 per vertebra that has graft material attached to or replacing it.  Instrumentation 1 per vertebra that has screws, plate, or cages attached to or replacing it. Posterior  Decompression 1 per vertebra requiring laminectomy or foraminotomy from a posterior approach.  Fusion 1 per vertebra that has graft material on the lamina, facet, or transverse process.  Instrumentation 1 per vertebra that has screws, hooks, or wires attached. SII, surgical invasiveness index. aThe total SII score is the sum of the scores for each vertebral level. View Large The utility of the SII in more complex deformity procedures has not been shown. Deformity-specific factors such as osteotomies, revision surgery, pelvic fixation, and correction of alignment are not accounted for by the SII. Therefore, we assessed the accuracy of the SII in determining the invasiveness of deformity surgeries in ASD patients and created a new scoring system that includes deformity-specific factors with the goal of creating a tool to more accurately predict the invasiveness of ASD surgical procedures. This too can assist with risk stratification and outcome assessment for surgeries of various magnitudes for a given deformity. A standard ASD invasiveness index would allow comparison of the invasiveness of different procedures for a given deformity and assessment of whether the risks of the more invasive procedure would outweigh the benefits compared with a less invasive procedure. Our null hypothesis was that the deformity-specific invasiveness index (adult spinal deformity-surgical and radiographical [ASD-SR]) would be similarly accurate in explaining variation in EBL and operative time compared with the SII in ASD surgeries. METHODS Patient Population To develop the initial cohort used to derive the ASD invasiveness index, we queried a multicenter prospective registry of patients with ASD from 11 centers. Each participating institution obtained approval from its institutional review board. ASD was defined as a coronal major curve of 20° or more, sagittal vertical axis of 5 cm or more, pelvic tilt of 25° or more, and/or thoracic kyphosis of 60° or more. Patients younger than 18 yr, those with spinal deformity secondary to a neuromuscular cause, and those with active infection or malignancy were excluded. Informed consent was obtained for each patient included in the study. We identified 564 patients who had undergone operative treatment for ASD from 2008 through 2012. Of these, 253 patients (herein, the development cohort) had complete radiographical and clinical follow-up at 2 yr and were used for the development phase of the ASD invasiveness index. To identify the cohort for validation, we queried a different multicenter prospective registry consisting of 309 surgically treated patients with ASD. The inclusion and exclusion criteria for the validation cohort were the same as for the development cohort. Of these, 211 patients (herein, the validation cohort) had complete radiographical and clinical follow-up at 2 yr and were used for the validation phase of the ASD invasiveness index. Index Construction The SII score, developed by Mirza et al,12 was calculated for all patients. Using the development cohort, we created multivariate linear regression models of operative time and log-linear transformed EBL (transformed to approximate normal distribution), including the components of the SII index and the deformity surgical factors. These factors were posterior decompression, posterior instrumentation, posterior fusion, transforaminal/posterior lumbar interbody fusion, anterior lumbar interbody fusion, Smith-Petersen osteotomies, 3-column osteotomies, iliac fixation, and revision surgery. Beta coefficients derived from these models were used to assign points to surgical components to create a new ASD score, the ASD-S (with “S” referring to surgical parameters; Table 2). The same method was then used to determine appropriate weighting for postoperative change in spinopelvic radiographical parameters, including sagittal vertical axis, pelvic incidence–lumbar lordosis mismatch, pelvic tilt, and thoracic kyphosis. The scores for these factors were added to the SII score and the deformity-specific factor score, creating a second index, the ASD-SR (with “SR” referring to surgical and radiographical parameters). TABLE 2. Surgical Components Used to Calculate the ASD-S Invasiveness Score Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 ASD-S, adult spinal deformity-surgical. View Large TABLE 2. Surgical Components Used to Calculate the ASD-S Invasiveness Score Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 Surgical component Points Posterior  Decompression 1 per vertebra  Fusion 2 per vertebra  Instrumentation 1 per vertebra Osteotomies  3-column 14 per osteotomy  Smith-Petersen 1 per osteotomy Interbody fusion  Anterior lumbar 8 per interbody fusion  Transforaminal/posterior lumbar 2 per interbody fusion Iliac fixation 2 Revision surgery 3 ASD-S, adult spinal deformity-surgical. View Large Estimates of the effect of specific surgical factors on operative time and EBL were derived from separate linear regression models of each of these variables. Beta coefficients from these models were used to attribute scores to each deformity-specific surgical factor included in ASD-S (the final index scoring system is presented in Table 2). In the construction of ASD-SR, changes in radiographical parameters from pre- to postoperative imaging were incorporated and weighted on the basis of their multivariate association with operative time and EBL. The final scores for these parameters were refined to maximize the ASD-SR model's predictive power and are shown in Table 3. TABLE 3. Additional Parametersa Included in the ASD-SR Invasiveness Index Score Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ ASD-SR, adult spinal deformity-surgical and radiographical aThese points are added to those of the ASD-S developed in the current study. bFrom preoperatively to postoperatively. cExpressed as points per 1-mm change. View Large TABLE 3. Additional Parametersa Included in the ASD-SR Invasiveness Index Score Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ Radiographical parameter Points per 1° changeb Pelvic incidence − lumbar lordosis .5$$^{\phantom{c}}$$ Pelvic tilt $$\phantom{.}$$2$$^{\phantom{c}}$$ Sagittal vertical axis .2c Thoracic kyphosis .5$$^{\phantom{c}}$$ ASD-SR, adult spinal deformity-surgical and radiographical aThese points are added to those of the ASD-S developed in the current study. bFrom preoperatively to postoperatively. cExpressed as points per 1-mm change. View Large Index Validation Both indices, the ASD-S and ASD-SR, were applied to the validation cohort. We created univariate linear regression models of operative time and log-transformed EBL with ASD-S or ASD-SR as the independent variable. Scoring of surgical factors was then iteratively refined to optimize the amount of variability explained (R2) by each model. Finally, multivariate linear regression models of operative time and log-transformed EBL were created for the SII, ASD-S, and ASD-SR and adjusted for patient age, sex, Charlson Comorbidity Index, and body mass index. Thus, the 3 indices were compared with respect to their predictive ability. The level of significance was set at P < .05. SAS, version 9.2, software (SAS Institute Inc, Cary, North Carolina) was used to analyze the data. RESULTS In the validation cohort, the mean EBL was 3024 mL (range 400-15 000 mL), and the mean operative time was 562 min (range 211-1175 min). The mean SII, ASD-S, and ASD-SR index scores were 33.6 (range 21-55), 52.9 (range 21-114), and 106 (range 44.9-221), respectively, in the validation cohort (Table 4). Patient demographic characteristics, preoperative radiographic parameters, and surgical details for the validation cohort are in Table 4. TABLE 4. Parameters Describing 211 Patients in the Validation Cohort Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 ALIF, anterior lumbar interbody fusion; ASD, adult spinal deformity; ASD-S, adult spinal deformity-surgical; ASD-SR, adult spinal deformity-surgical and radiographical; BMI, body mass index; EBL, estimated blood loss; LL, lumbar lordosis; PI, pelvic incidence; SD, standard deviation; SII, surgical invasiveness index; SVA, sagittal vertical axis aOther than ALIF. View Large TABLE 4. Parameters Describing 211 Patients in the Validation Cohort Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 Parameter Mean (SD) Range No. (%) of patients Patient  Age, years 60 (13) 21 to 83  Charlson Comorbidity Index 2 (2) 0 to 8  Body mass index, kg/m2 28 (5.7) 18 to 48 Radiographic (preoperative)  Maximum coronal major curve, degree 36 (25) 15 to 122  C7 to S1 SVA, mm 86 (79) –126 to 304  LL major curve, degree 37 (17) 10 to 93  Pelvic tilt, degree 27 (10) –.5 to 53  PI–LL 23 (22) –38 to 70 Surgical  No. of levels fused 12 (3) 7 to 26  Operative time, min 561 (421) 202 to 982  EBL, mL 3024 (2142) 250 to 15 000 Procedure  Interbody fusiona 147 (70)  Smith-Petersen osteotomy 129 (61)  Revision surgery 98 (46)  3-column osteotomy 60 (28)  ALIF 53 (25) Invasiveness index  SII score12 34 (8.6) 19 to 60  ASD-S score 53 (18) 18 to 114  ASD-SR score 105 (37) 35 to 221 ALIF, anterior lumbar interbody fusion; ASD, adult spinal deformity; ASD-S, adult spinal deformity-surgical; ASD-SR, adult spinal deformity-surgical and radiographical; BMI, body mass index; EBL, estimated blood loss; LL, lumbar lordosis; PI, pelvic incidence; SD, standard deviation; SII, surgical invasiveness index; SVA, sagittal vertical axis aOther than ALIF. View Large All 3 indices were significant, independent predictors of EBL and operative time (P < .001). For EBL, the ASD-SR had the strongest correlation (Pearson r = .34), followed by the ASD-S (r = .28) and SII (r = .22; P < .001; Figure 1). Similarly, the adjusted multivariate model with ASD-SR predicted more variability (R2 = .21) in EBL than ASD-S or SII (R2 = .17 for both; Table 5). For operative time, the ASD-SR had the highest correlation (r = .34), followed by the ASD-S (r = .26) and SII (r = .18; P < .001; Figure 2). The adjusted model of operative time with ASD-SR as the main predictor explained the most variability (R2 = .10). Models with ASD-S and SII were less robust (R2 = .065 and R2 = .032, respectively). The addition of postoperative changes in radiographical parameters to the scoring system, ASD-SR, explained 21% of the variation in EBL and 10% of the variation in operative time, whereas SII explained only 17% and 3.2%, respectively. FIGURE 1. View largeDownload slide Regression plot showing that the ASD-SR index has a stronger correlation with EBL than the ASD-S and SII. FIGURE 1. View largeDownload slide Regression plot showing that the ASD-SR index has a stronger correlation with EBL than the ASD-S and SII. FIGURE 2. View largeDownload slide Regression plot showing that the ASD-SR invasiveness index has a stronger correlation with operative time than the ASD-S and SII. FIGURE 2. View largeDownload slide Regression plot showing that the ASD-SR invasiveness index has a stronger correlation with operative time than the ASD-S and SII. TABLE 5. Correlations of Surgical Invasiveness Indices with Estimated Blood Loss and Operative Timea Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ ASD, adult spinal deformity; ASD-S, adult spinal deformity, with “S” referring to surgical parameters; ASD-SR, adult spinal deformity, with “SR” referring to surgical and radiographical parameters; SII, surgical invasiveness index. aPercentage of variability explained by multivariate models of estimated blood loss and operative time using each index separately as the main predictor. bModels adjusted for patient age, sex, Charlson Comorbidity Index, and body mass index. cDeveloped by Mirza et al.12 View Large TABLE 5. Correlations of Surgical Invasiveness Indices with Estimated Blood Loss and Operative Timea Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ Estimated blood loss Operative time Index Pearson correlation coefficient (r) % of Variability explainedb (R2) Pearson correlation coefficient (r) % of Variability explainedb (R2) SIIc .22 .17 .18 .032 ASD-S .28 .17 .26 .065 ASD-SR .34 .21 .34 .10$$\phantom{2}$$ ASD, adult spinal deformity; ASD-S, adult spinal deformity, with “S” referring to surgical parameters; ASD-SR, adult spinal deformity, with “SR” referring to surgical and radiographical parameters; SII, surgical invasiveness index. aPercentage of variability explained by multivariate models of estimated blood loss and operative time using each index separately as the main predictor. bModels adjusted for patient age, sex, Charlson Comorbidity Index, and body mass index. cDeveloped by Mirza et al.12 View Large DISCUSSION By using components of the general SII developed by Mirza et al12 and adding deformity-specific surgical and radiographic factors, we have developed a novel ASD SII (ASD-SR). Our new scoring system is a better predictor of surgical invasiveness (defined as EBL and operative time) than the previously established SII. Studies have shown that more extensive spinal surgeries are associated with greater EBL and longer operative time.13-16 This suggests that these factors are reasonable surrogates for the invasiveness of a surgical procedure. The SII for general spine procedures was created by Mirza et al.12 In studies that evaluate general spine procedures, the SII has been shown to be strongly associated with EBL and operative time and to explain approximately 50% of variation in these 2 variables.12,17 Previous studies have not applied the SII to deformity procedures. These operations are inherently complex with higher and more variable EBL and operative time compared with general spine procedures. Indeed, in the present study, when we applied the SII to deformity procedures, its correlations with EBL and operative time were less robust compared with those of previous reports of general spine procedures. For the SII, the Pearson correlation coefficients were only .22 for EBL and .18 for operative time. This discrepancy may result, at least in part, from greater complexity of ASD procedures compared with those in previous studies. We hypothesized that the addition of deformity-specific factors in a new invasiveness index could better account for the aforementioned differences between general and deformity spine operations. Specifically, in the ASD-S, we incorporated revision vs primary surgery, osteotomies, iliac fixation, and interbody fusion (anterior and posterior). Revision surgery18 and 3-column osteotomies19 are associated with higher rates of intraoperative blood transfusion. The addition of these factors yielded an index with higher correlations to EBL and operative time than the SII. The ASD-S also explained more of the variability in EBL and operative time when incorporated in an adjusted model of these variables. Larger deformity correction, measured by changes in standard radiographical parameters, is associated with more blood loss19 and ostensibly represents a higher degree of invasiveness. We therefore created a second index, the ASD-SR, which incorporates changes in sagittal vertical axis, pelvic incidence–lumbar lordosis mismatch, pelvic tilt, and thoracic kyphosis. This index performed better than the SII or ASD-S in predicting EBL and operative time. Unlike the SII and ASD-S, however, the ASD-SR cannot be calculated on the basis of preoperative information alone. To use the more accurate ASD-SR index, it may be possible to use planned magnitude of correction (manually or from surgical planning software) for each of the 4 radiographical parameters to calculate the score preoperatively. The feasibility and accuracy of such a strategy would require further study. The prospective collection of our multicenter data is a strength of this study. This allowed us to capture a wide range of methods to treat complex spine disorders and allows each component of deformity surgery to be well represented in our study. An invasiveness index could be useful for preoperative risk stratification and is a key component for predictive modeling for ASD surgery. The current ASD-SR index uses variables that cannot be obtained before surgery; however, the scoring system could be used preoperatively by using the planned surgical procedure and planned magnitude of correction as the radiographic component. If this goal is met, the maximum invasiveness of the surgery could be determined. By planning the various surgical techniques and determining the magnitude of curve correction, a quantitative measurement of surgical invasiveness could be calculated. Having a method to measure invasiveness will allow surgeons to assess the magnitude of different surgical procedures for a given deformity preoperatively and to estimate an individual patient's risks for each surgical option. Multiple studies have validated the use of EBL and operative time to determine the invasiveness of a procedure.12-17 By using this methodology, our study shows that the ASD-SR index is a better predictor of ASD surgical invasiveness than the SII. The development of the ASD-SR invasiveness index is the first step in determining the effects that the magnitude of a surgery has on the perioperative risk of complications. With the use of the ASD-SR invasiveness index, further research can be conducted to assess the association of the invasiveness of the procedure with outcomes and complications. Furthermore, studies should examine the combined use of the ASD-SR and a patient frailty index to help in risk stratification of various surgical options for a given deformity. Limitations This study has several limitations. Although the database is maintained prospectively, this was a retrospective review and is thus subject to selection and information bias. Comparison of our results with those of Mirza et al12 is limited by differences in patient populations that may not have been completely accounted for in our analysis. Also, although EBL and operative time are parameters that can define invasiveness, other factors besides the magnitude of the surgery can influence these parameters. Therefore, it is not surprising that the invasiveness of the surgery explains only a portion of the variability in EBL and operative time. In assessing the magnitude of the surgery to explain the variability of EBL and operative time, the ASD-SR is a better predictor of “invasiveness” than the SII in ASD surgeries. CONCLUSION The inclusion of deformity surgical factors in a novel ASD SII resulted in a tool that more accurately predicts surgical invasiveness than the SII in ASD patients. The inclusion of radiographical parameters that quantify the magnitude of correction in regional and global alignment yields an incrementally superior index. For quantifying the invasiveness of a deformity correction procedure, the ASD-S and ASD-SR offer improved predictive ability compared with the SII. The development of the ASD-SR invasiveness index is the first step in risk-stratifying ASD patients on the basis of the magnitude of their surgeries. Disclosures The International Spine Study Group received funding from DePuy Synthes, Innovasis, Biomet, K2M, NuVasive, Medtronic, and Stryker. Dr Klineberg is a consultant for DePuy Synthes and Stryker and received honoraria from K2M, and honoraria and a fellowship grant from AOSpine. Dr Sciubba is a consultant for Medtronic, DePuy Synthes, Globus, and Orthofix. Dr Burton is a consultant for and receives research support and royalties from DePuy Spine. The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Bridwell KH , Glassman S , Horton W et al. Does treatment (nonoperative and operative) improve the two-year quality of life in patients with adult symptomatic lumbar scoliosis: a prospective multicenter evidence-based medicine study . Spine . 2009 ; 34 ( 20 ): 2171 - 2178 . Google Scholar CrossRef Search ADS PubMed 2. Smith JS , Shaffrey CI , Berven S et al. Improvement of back pain with operative and nonoperative treatment in adults with scoliosis . Neurosurgery . 2009 ; 65 ( 1 ): 86 - 93 ; discussion 93-84 . Google Scholar CrossRef Search ADS PubMed 3. Smith JS , Shaffrey CI , Berven S et al. Operative versus nonoperative treatment of leg pain in adults with scoliosis: a retrospective review of a prospective multicenter database with two-year follow-up . Spine . 2009 ; 34 ( 16 ): 1693 - 1698 . Google Scholar CrossRef Search ADS PubMed 4. Smith JS , Shaffrey CI , Glassman SD et al. Risk-benefit assessment of surgery for adult scoliosis: an analysis based on patient age . Spine . 2011 ; 36 ( 10 ): 817 - 824 . Google Scholar CrossRef Search ADS PubMed 5. Ailon T , Smith JS , Shaffrey CI et al. Degenerative spinal deformity . Neurosurgery . 2015 ; 77 ( suppl 4 ): S75 - S91 . Google Scholar CrossRef Search ADS PubMed 6. Silva FE , Lenke LG . Adult degenerative scoliosis: evaluation and management . Neurosurg Focus . 2010 ; 28 ( 3 ): E1 - E10 . Google Scholar CrossRef Search ADS PubMed 7. Bridwell KH , Lewis SJ , Lenke LG , Baldus C , Blanke K . Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance . J Bone Joint Surg Am . 2003 ; 85 ( 3 ): 454 - 463 . Google Scholar CrossRef Search ADS PubMed 8. Hassanzadeh H , Jain A , El Dafrawy MH et al. Three-column osteotomies in the treatment of spinal deformity in adult patients 60 years old and older: outcome and complications . Spine (Phila Pa 1976) . 2013 ; 38 ( 9 ): 726 - 731 . Google Scholar CrossRef Search ADS PubMed 9. Lafage V , Smith JS , Bess S et al. Sagittal spino-pelvic alignment failures following three column thoracic osteotomy for adult spinal deformity . Eur Spine J . 2012 ; 21 ( 4 ): 698 - 704 . Google Scholar CrossRef Search ADS PubMed 10. Smith JS , Sansur CA , Donaldson WF III et al. Short-term morbidity and mortality associated with correction of thoracolumbar fixed sagittal plane deformity: a report from the Scoliosis Research Society Morbidity and Mortality Committee . Spine . 2011 ; 36 ( 12 ): 958 - 964 . Google Scholar CrossRef Search ADS PubMed 11. Smith JS , Shaffrey CI , Ames CP et al. Assessment of symptomatic rod fracture after posterior instrumented fusion for adult spinal deformity . Neurosurgery . 2012 ; 71 ( 4 ): 862 - 867 . Google Scholar CrossRef Search ADS PubMed 12. Mirza SK , Deyo RA , Heagerty PJ et al. Development of an index to characterize the "invasiveness" of spine surgery: validation by comparison to blood loss and operative time . Spine . 2008 ; 33 ( 24 ): 2651 - 2661 ; discussion 2662 . Google Scholar CrossRef Search ADS PubMed 13. Cha CW , Deible C , Muzzonigro T , Lopez-Plaza I , Vogt M , Kang JD . Allogeneic transfusion requirements after autologous donations in posterior lumbar surgeries . Spine . 2002 ; 27 ( 1 ): 99 - 104 . Google Scholar CrossRef Search ADS PubMed 14. Cho KJ , Suk SI , Park SR et al. Complications in posterior fusion and instrumentation for degenerative lumbar scoliosis . Spine . 2007 ; 32 ( 20 ): 2232 - 2237 . Google Scholar CrossRef Search ADS PubMed 15. Nuttall GA , Horlocker TT , Santrach PJ , Oliver WC Jr , Dekutoski MB , Bryant S . Predictors of blood transfusions in spinal instrumentation and fusion surgery . Spine . 2000 ; 25 ( 5 ): 596 - 601 . Google Scholar CrossRef Search ADS PubMed 16. Zheng F , Cammisa FP Jr , Sandhu HS , Girardi FP , Khan SN . Factors predicting hospital stay, operative time, blood loss, and transfusion in patients undergoing revision posterior lumbar spine decompression, fusion, and segmental instrumentation . Spine . 2002 ; 27 ( 8 ): 818 - 824 . Google Scholar CrossRef Search ADS PubMed 17. Mirza SK , Deyo RA , Heagerty PJ , Turner JA , Lee LA , Goodkin R . Towards standardized measurement of adverse events in spine surgery: conceptual model and pilot evaluation . BMC Musculoskelet Disord . 2006 ; 7 ( 53 ): 1 - 16 . Google Scholar PubMed 18. Yoshihara H , Yoneoka D . Predictors of allogeneic blood transfusion in spinal fusion for pediatric patients with idiopathic scoliosis in the United States, 2004-2009 . Spine . 2014 ; 39 ( 22 ): 1860 - 1867 . Google Scholar CrossRef Search ADS PubMed 19. Yu X , Xiao H , Wang R , Huang Y . Prediction of massive blood loss in scoliosis surgery from preoperative variables . Spine . 2013 ; 38 ( 4 ): 350 - 355 . Google Scholar CrossRef Search ADS PubMed COMMENTS The goal of this publication has been to develop a score that would provide insight into the surgical invasiveness of adult deformity procedures and thus potentially stratify the risk associated with these procedures. I applaud the authors in providing a well-written paper with a large cohort of patients with long-term follow-up. It would be interesting to see if the authors' scoring system could go beyond predicting operative time and estimated blood loss alone to predicting complications or clinical outcomes such as postoperative patient function, recovery, or satisfaction scores. Laura A. Snyder Phoenix, Arizona The authors seek to build on the Surgical Invasiveness Index (SII), initially published by Mirza et al in 20081 (reference 12 from index paper) to incorporate features common to spinal deformity surgery. They used registry data from 464 patients to associate various pre- and intraoperative variables with operative time and blood loss, used here and elsewhere as proxies for surgical invasiveness. To the SII, they added surgical parameters specific to deformity surgery (eg Smith-Peterson vs 3 Column Osteotomies) to create the ASD-S Index. Then, they added radiographic parameters to create the ASD-SR Index. They found that all 3 indices were predictive of blood loss and operative time, but the addition of surgical (ASD-S) and radiographic (ADS-SR) parameters strengthened the correlation. The goals of this work lie in better predicting of risks and improved patient counselling ahead of major deformity reconstruction surgery. This form of risk adjustment may also prove valuable in clinical quality and research efforts. This work is iterative toward those goals. First, the additional time required to calculate these scores must be shown to practically impact the decision for surgery and the type of surgery offered for spine surgeons to utilize them clinically. In the future, advanced electronic medical records systems could calculate these scores automatically. Second, as interesting as this measure of invasiveness might be, true patient outcomes and risk measures, such as complication rates, need to be incorporated in these efforts to broaden their utility. Beyond direct patient counselling, broader utilization of these scores systems to risk-adjust patient outcome data will both improve the scores’ predictive power and our ability to benchmark the quality of care delivered in this diverse array of morbid surgeries. Eeric Truumees Austin, Texas 1. Mirza SK , Deyo RA , Heagerty PJ , et al. Development of an index to characterize the 259 "invasiveness" of spine surgery: validation by comparison to blood loss and operative 260 time . Spine . 2008 ; 33 ( 24 ): 2651 - 2661 ; discussion 2662 . Google Scholar CrossRef Search ADS PubMed The objective of this study was to use postoperative surgical and radiographic data to validate new surgical invasiveness scores for the operative treatment of adult spinal deformity. This investigation was a well-designed study with a large, multi-center cohort of patients with long-term follow-up. It will be both interesting and important for the authors to test their invasiveness score with preoperative data to analyze the tool's viability for use in preoperative planning. Kern Singh Chicago, Illinois 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)

Journal

NeurosurgeryOxford University Press

Published: Jun 6, 2017

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