Faculty Bibliography

STUDY DESIGN: Retrospective analysis of relevant in-hospital patient records from the New York State Inpatient Database. OBJECTIVE: We aimed to assess reoperation risk in adolescent idiopathic scoliosis (AIS) by surgeon and hospital operative volume. SUMMARY OF BACKGROUND DATA: The need for early reoperation can be devastating for patient and family, is a burden to the physician and adds significant cost. Previous studies have shown improved outcomes associated with higher volume surgeons and hospitals, but reoperation events have not yet been explored. METHODS: The 2008-2011 New York State Inpatient Database was queried using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes for adolescent idiopathic scoliosis patients aged 10-21 undergoing spine arthrodesis. Patient identifiers and revisit linkage variables were used to identify reoperation events. Annual surgeon and hospital volumes were stratified into tertiles (low, medium, high) via identifier codes. The relative risk of reoperation after spine arthrodesis was computed based on relevant patient inpatient stays. RESULTS: Over 2008 to 2011, a total of 3,928 primary fusion operations for AIS were identified. The overall rate of reoperation after spine fusion for idiopathic scoliosis was 7.1%. Low volume surgeons performed less than 6 AIS fusions per year, medium volume surgeons performed less than 43, and high volume surgeons performed from 43 to 228. Reoperation after a primary fusion for adolescent idiopathic scoliosis showed reduced frequency among higher volume surgeons (14.1% for low vs. 5.1% for high, p<0.001, see Table for Hospitals). CONCLUSIONS: Early reoperation after spine fusion for idiopathic scoliosis is seen more frequently in lower volume institutions and surgeons. Appreciating the resources and limitations at a clinician's institution is important to developing practices to prevent these devastating events. This work also has implications for strategies that aim to direct limited healthcare resources to centers with low complication rates.

BACKGROUND: Multilevel spinal fusions have typically been associated with significant blood loss. Previous studies have shown a reduction in blood loss with antifibrinolytics in both adolescent and adult spinal deformity patients. While this has been mirrored in other subspecialties as well, the dosing of TXA remains highly variable. To date, there remains a paucity of data guiding dosing for TXA in spine surgery and orthopedic surgery as a whole. METHODS/DESIGN: One hundred and fifty patients from 3 institutions (50 each site) will be consecutively enrolled and randomized to either a high dose of TXA (50mg/kg loading followed by 20mg/kg hourly) or a lose dose (10mg/kg, then 1mg/kg hourly). Both surgeons and patients will be blinded to the treatment group. Primary outcomes will be perioperative blood loss, drain output, and transfusion rate. Secondary outcomes will be length of stay, complications, and overall cost. DISCUSSION: The primary goal of this study is to provide level-1 comparative data for two TXA dosing regimens in adult spinal deformity surgery. Management of blood loss remains a critical factor in reducing complications during spinal deformity surgery. The null hypothesis is that there is no difference between high- and low-dose TXA with respect to any of the primary or secondary outcomes.

BACKGROUND CONTEXT: In adult spinal deformity (ASD) surgical planning, deformity magnitude is determined from preoperative radiographs. Sagittal alignment measures show variability in repeat X-ray studies from clinical visits. Past studies have reported intraobserver and interobserver reproducibility of cervico-thoracolumbar (CTL) and pelvic sagittal parameters. However, the preoperative time-dependent variability of radiographic (XR) measures hasn't been determined. PURPOSE: The purpose of this study was to evaluate preoperative timedependent changes in radiographic sagittal parameters. STUDY DESIGN/SETTING: Retrospective review. PATIENT SAMPLE: 140 subjects. OUTCOME MEASURES: Statistical analysis was performed using paired student t-test and simple linear regression (Significance, P < 0.05). METHODS: We analyzed 140 patients with minimum of two preoperative full body spine X-ray images. CTL and pelvic sagittal alignment parameters were analyzed using a validated software program. Patients were grouped by time intervals (weeks) between successive radiographs: Group A: <8 weeks, group B: 10-20 weeks and group C: >21 weeks. For each group, consistency of the following sagittal parameters was assessed between two visits: T1 pelvic angle (TPA), sagittal vertical axis (SVA), pelvic tilt (PT), pelvic incidence (PI), lumbar lordosis (LL), PI minus LL (PI-LL), T1 slope minus cervical lordosis (TS-CL), cervical thoracic pelvic angle (CTPA), cervical SVA (cSVA). Changes in sagittal parameters were correlated to age and deformity magnitude (TPA>20degree). RESULTS: 140 subjects: mean age/BMI 59/27, male 30%, 45 patients with no prior surgery and 95 patients at minimum one year since prior spine surgery. Groups: A 25, group B 38, and group C 72 patients. In group C, changes in PT were significant with mean difference 1.5degree (p< 0.05). Substratification of patients in group C for deformity revealed that both patients with and without deformity demonstrated statistically but not clinically significant changes in PT (mean difference 1.5degree, all p<0.05). The 95 patients presenting at minimum 1-year since prior spinal surgery, in group C with TPA>20degree had significant changes in PT (3.7degree), TPA (2.3degree) and PI-LL (1.8degree), all p<0.05. The changes in PT and TPA sagittal parameters were greater than reported standard error of measurement. CONCLUSIONS: All radiographic measures of ASD showed good time-based consistency when radiograph intervals were <21 weeks. Additionally, changes in PT, PI-LL and TPA when intervals between radiographs were >21 weeks were significant with changes in PT and TPA greater than measurement standard error in subgroup of patients with prior surgery and deformity (TPA>20degree). These findings should be factored into whether new X-ray studies need to be ordered for ASD surgical planning

BACKGROUND CONTEXT: Numerous surgical strategies can be used to achieve alignment goals in adult spinal deformity (ASD) surgery, depending on surgeon training and preference. For similar deformity, the variability in surgical strategy for achievement of comparable surgical goals may result in differences in both radiological and clinical outcomes. PURPOSE: To evaluate variability in surgical strategies, radiological and clinical outcomes and complications among different centers for severe ASD. STUDY DESIGN/SETTING: Retrospective analysis of multicenter prospective cohort. PATIENT SAMPLE: 231 patients undergoing severe ASD surgery. OUTCOME MEASURES: Demographics; comorbidities; estimated blood loss; operative time; length of stay; surgical strategy including approach, staging, number of levels fused, number and type of osteotomy, interbody fusion and use of BMP-2; preoperative and postoperative (6 weeks and 2 years) spinopelvic radiographic parameters including SVA, PI-LL, PT and TPA; preoperative and postoperative ( 6 weeks and 2 years) health related quality of life (HRQL) outcomes including ODI, SF-36, SRS-22; complications. METHODS: Inclusion criteria for severe ASD were age >18 years, T1 pelvic angle >20degree, and one of the following: Cobb angle >20degree, sagittal vertical axis (SVA) >5 cm, thoracic kyphosis >60degree or pelvic tilt (PT) >25degree. Comparison between outcomes among 5 centers was performed using chisquare analysis and ANOVA. RESULTS: 231 patients from 5 centers were included. The only differences for patient demographics were age and Charlson comorbidity score. Mean operative time, estimated blood loss and length of stay were 369 minutes, 1,879 ml and 8.8 days, respectively, with significant variability across centers (p<0.01). There was significant variability in use of IBF and BMP-2 (P< 0.01). The site with the highest usage of BMP-2 simultaneously had the lowest usage of IBF and the fewest patients who reached the goal SVA (<4cm); however, this site had the best 2-year HRQL outcomes. There were also significant differences in the type/level of osteotomy (P<0.01). The site that performed the fewest osteotomies was significantly less likely to achieve correction in sagittal modifiers and the goal PI-LL<10degree. This low-osteotomy site also had the least improvement in 6-week and 2-year HRQLs. While sites were similar in the lengths of fusion (mean number levels fused 51164.5) and the upper termination of instrumentation, there was significant variability in the choice of LIV (P=0.01). The site that most frequently instrumented to the ilium also performed the highest number of 3-column osteotomy and the fewest Smith-Peterson Osteotomies, though it had lowBMP-2 use. However, this site had the greatest correction in sagittal modifiers and the highest number of patients who achieved the PI-LL<10degree goal with intermediate HRQLs. There was a difference in the number of minor but not major complications among centers. CONCLUSIONS: Considerable variability in surgical strategy between different centers may result in varying radiological and clinical outcomes. Further efforts to identify the surgical strategies which maximize patient outcomes are necessary

BACKGROUND CONTEXT: In transforminal lumbar interbody fusion (TLIF), bilateral pedicle screw/rod fixation has been shown to increase fusion construct stability and decrease posterior instrumentation stress when compared to unilateral instrumentation. However, unilateral instrumentation is beneficial over bilateral instrumentation due to shorter operative time, less blood loss and reduced implant costs. It is important to note though that comparative studies between unilateral and bilateral instrumentation in TLIF have shown similar patient satisfaction outcomes, they are limited in their evaluation of complications due to small sample size of studies. PURPOSE: The purpose of this meta-analysis was to evaluate complications, and fusion rates between unilateral and bilateral instrumentation in TLIF. STUDY DESIGN/SETTING: Meta-analysis of randomized controlled trials. PATIENT SAMPLE: 549 patients undergoing one- and multi-levels TLIF. OUTCOME MEASURES: Outcome data extracted included fusion rates, health related quality of life (HRQoL) scores and complications including cage migration, dural tear, deep vein thrombosis, surgical site infections and screw failures. METHODS: Randomized controlled trials (RCTs) that compared outcomes between unilateral and bilateral pedicle screw instrumentation in single- and multi-level TLIF were identified. Data extraction was performed by two independent reviewers. Meta-analysis was performed using RevMan 5. Weighted standardized mean difference (SMD) and odds ratio (OR) 95% confidence intervals (CI) were calculated. Jadad scoring was used to assess bias of included studies. RESULTS: Eight RCTs were included, having a total of 549 patients (267 unilateral/282 bilateral). Minimum follow-up ranged from 3 to 24 months. Bias-assessment scores varied between 0 and 3 indicating high-moderate bias-risk. Six involved open TLIF procedures and two involved minimally invasive TLIF. There was no difference between postoperative Health Related Quality of Life scores in the unilateral and bilateral instrumented groups (SMD = 0.29; [-0.77, 0.18]; p=0.69). There was no statistical difference in fusion rates (OR = 0.47; 95% CI [0.21, 1.04], p=0.68), with 88.9% and 95.0% achieving fusion in the unilateral and bilateral groups, respectively. The unilateral cohort had a higher incidence of cage migration (5.6%) when compared to the bilateral cohort (2.5%), approaching statically significant (p=0.07). Other complications which included dural tears, deep vein thrombosis, surgical site infections and screw failures were comparable between the groups. CONCLUSIONS: Fusion rates and complications appear comparable in unilateral and bilateral instrumentation in TLIF. Though not statistically significant, there was higher incidence of cage migration in the unilateral cohort

BACKGROUND CONTEXT: Preoperative planning with objective is an important component of adult spinal deformity (ASD) surgery. Recent studies have expanded the SRS-Schwab classification for defining sagittal deformity by including age-adjusted ideals for postoperative alignment, but it is unknown whether surgical plans properly integrate these ideals. PURPOSE: Evaluate the discrepancies between age-adjusted alignment ideals and actual surgical plans. STUDY DESIGN/SETTING: Consecutively enrolled prospective database. PATIENT SAMPLE: 71 ASD patients with severe sagittal deformity. OUTCOME MEASURES: Radiographic measurements, surgeon-created alignment plans on dedicated software. METHODS: ASD patients >18 years of age with severe sagittal alignment (SVA >50mm, PT >20degree, or PI-LL >10degree) undergoing corrective surgery were consecutively enrolled. For each patient, the baseline X-ray images were measured and the operative plan was simulated using dedicated, validated software for spine measurement and surgical planning. Sagittal radiographic parameters were compared between baseline, the plan and the age-adjusted ideal. Thresholds for significant clinical differences between planned and ideal alignments were: SVA620mm, PT610degree, PI-LL610degree. RESULTS: 71 patients (63+/-11 years; 80% revisions) were included. Planned alignments matched age-adjusted ideals in 76% of cases for PT, 65% of PI-LL, and 49% of SVA. Compared to ideal alignment, a total of 30% and 17% of the patients were planned for overcorrection in SVA and PI-LL respectively; 21% (SVA) and 18% (PI-LL) were planned for undercorrection. Discrepancies between the plan and the ideal were not affected by BMI, comorbidities, gender, revision status or HRQOL. However, as age increased, the plan was more likely to overcorrect versus the ideal (P<0.003 for PT, PI-LL; P<0.001 for SVA). When compared to the ideal alignment formula, planned SVA was overcorrected in 58% of patients >70 years versus 20% in patients<70 (P=0.003), and planned SVA of these >70 years patients matched the age-adjusted alignment ideals of a 62-year-old. Plans for patients with severe deformity and/or higher PI were more likely to be undercorrected compared to ideals (P< 0.001). The discrepancy between planned and ideal alignment correlated significantly with the difference between the postoperative alignment and ideal alignment (P<0.001). PI-LL plans had a significant impact on postop alignment. When PI-LL plans called for ideal correction, the mean postop PI-LL was within 2degree of ideal alignment and matched the plan in 59% of cases. However, when PI-LL plans called for undercorrection, postop PI-LL was 13degree greater than ideal (P<0.001). When the planned alignment was within the ideal threshold, the postop PI-LL matched the ideal in 66% of cases, versus only 18% when the plan was over- or under-corrected. CONCLUSIONS: Preoperative plans for sagittal alignment correction overcorrected in comparison to age-adjusted ideals, especially in elderly patients. More severe deformity led to greater likelihood of having undercorrected plans. Favorable postoperative outcomes occurred when the planned alignment incorporated age-adjusted ideals. This emphasizes the importance of considering patient age and similar characteristics into the surgical strategy, as patient-specific plans, rather than generic approaches, are likely to produce the best outcome

BACKGROUND CONTEXT: Degenerative lumbar stenosis (DLS) patients adopt forward-bending posture as a compensatory mechanism, increasing spinal canal and foraminal volume. Previous data show laminectomy 6 short segment fusion results in improvement of sagittal vertical axis (SVA), pelvic tilt (PT) and PI-LL (pelvic incidence-lumbar lordosis) mismatch by SRS-Schwab classification in <25% of patients. The magnitude of deformity for which a DLS patient should have realignment remains unknown. PURPOSE: To identify differences in compensatory mechanisms between DLS and adult spinal deformity (ASD) patients with increasing, and to identify at what point DLS patients recruit ASD-type compensatory mechanisms. STUDY DESIGN/SETTING: Retrospective clinical and radiological review. PATIENT SAMPLE: Baseline X-ray images of 239 patients without spinal instrumentation, with the clinical radiological and diagnosis of DLS or ASD were assessed for patterns of spino-pelvic compensatory mechanisms. Patients were stratified by sagittal vertical axis (SVA) by the Schwab-SRS classification. OUTCOME MEASURES: Radiographic spino-pelvic parameters were measured in the DLS and ASD groups, including SVA, PI-LL, T1SPi, TPA and PT. METHODS: Patients were identified using a single-institution database with sole diagnosis of DLS, >40 years and if they had any of the following: PT >25degree, SVA >5cm, thoracic kyphosis (TK) >60degree or PI-LL mismatch >10degree. The patient's diagnosis was taken from the patient history chart based on correlation between history, examination and available imaging. Matched cohort with sole diagnosis of ASD was identified. Groups were stratified by SVA using Schwab-SRS classification: 0(<4cm), +(4-9.5cm), ++( >9.5cm). Sagittal spino-pelvic parameters were compared between the 2 groups with unpaired t-test. RESULTS: 239 patients were identified (122 DLS, 117 ASD). There was no difference in age or pelvic incidence between DLS and ASD with SVA stratifications. DLS patients with SVA 0 had less PT (19.8degree vs 29.2degree p<0.0001), less PI-LL mismatch (3.3degree vs 15.8degree, p<0.001), lower TPA (14.6degree vs 21.8degree, p<0.001) but higher T1SPi (-5.17degree vs -7.44degree, p< 0.001) than those with ASD. DLS patients with SVA+ had less PT (22.6degree vs 26.1degree, p=0.019) and higher T1SPi (0.64degree vs -0.70degree, p=0.008) than ASD patients. DLS patients resembled a decompensated deformity with a higher T1SPi relative to TPA when compared to the ASD cohort in groups 0 and +. No significant differences between ASD and DLS for any parameters in the SVA++ group were identified. No difference was found between DLS or ASD in TK for SVA groups 0, + or ++. CONCLUSIONS: The difference in PI-LL observed in ASD/DLS group '0' underlies the pathogenesis of ASD vs DLS. DLS patients increase SVA for neuronal decompression but without a PI-LL mismatch, they need not increase PT. As PI-LL increases in SVA >9.5cm, recruitment of PT ensues as the need for alignment overtakes desire for decompression. Their compensatory mechanism then resembles ASD. Laminectomy 6 fusion may be more appropriate for DLS patients with SVA< 9.5cm. Given <25% of patients improve in classification after fusion, surgeons should consider realignment surgery in DLS with SVA >9.5cm. Further understanding of HRQOL scores in mal-aligned DLS patients is required to best understand the importance of alignment in DLS

BACKGROUND CONTEXT: TPA (T1 pelvic angle) is a valuable perioperative planning tool that accounts for both pelvic tilt (PT) and trunk inclination. While this parameter correlates with patient reported outcomes, it is limited as a standalone parameter because it does not distinguish patients' ability to compensate with pelvic retroversion. PURPOSE: Investigate the TPA and its close relation with pelvic tilt in order to assess patients HRQOL (health-related quality of life) with a given TPA and a varying PT. STUDY DESIGN/SETTING: Retrospective cohort. PATIENT SAMPLE: Single-center study of 230 patients (58.7+/-15.5 years old, 60% females) with full body radiographs, HRQOL forms and TPA>10degree. OUTCOME MEASURES: Sagittal spino-pelvic parameters including SVA, PT, PI-LL, and TPA, and the following health related quality of life questionnaires: ODI and EQ-5D. METHODS: Proportions of PT to TPA (PTp5PT/TPA) and T1SPi to TPA (T1SPip5T1SPi/TPA) were calculated and investigated against increased values of TPA. Then, two sub-groups of similar TPA were created (HighPT and LowPT) based on mean (PTp)60.5 standard deviation. HighPT and LowPT were compared across the entire cohort using an unpaired T-test. RESULTS: Mean sagittal parameters included: PI-LL 12.3+/-16.3degree, SVA 41+/-49mm, TPA 21.9+/-10.1degree and PT 24.4+/-8.6degree. The analysis of PTp distribution revealed a decrease in PT recruitment as TPA increases (137+/-39% for patients with TPA<15degree, 87+/-15% for patients with TPA >40degree). Comparing LowPT (n=57) with HighPT (n=69) revealed that for a similar TPA (24.1 vs 22.1degree, p=0.308), patients with LowPT (and therefore little compensatory PT) had significantly worse HRQOL scores in terms of ODI (45 vs 32 in HighPT; p=0.002) and EQ-5D (9.7 vs 8.5 in HighPT, p=0.003). CONCLUSIONS: While TPA captures the severity of deformity, disability is a product of deformity severity and the inability to recruit compensatory mechanisms. TPA measures the severity of the thoracolumbar deformity separate from pelvic compensation. Therefore, to develop a complete picture of standing sagittal alignment, TPA should be considered in conjunction with PT to convey the full radiological and clinical picture. Failing to do so potentially results in inadequate assessment of a patient's disability

BACKGROUND CONTEXT: Complications in ASD are frequent and surgeons are constantly attempting to decrease these and improve their outcomes. Centers have developed systems using 2 attending surgeons in attempts to improve efficiency in the operating room (OR). PURPOSE: The purpose of our study is to assess operative, clinical and radiographic outcomes of ASD surgery based on performance by 1 vs 2 attending surgeons from a multicenter (ISSG) database. STUDY DESIGN/SETTING: Retrospective review of prospectively collected multicenter data. PATIENT SAMPLE: 188 patients had ASD surgery performed by 1 surgeon (1S) and 77 were performed by 2 attendings (2S). OUTCOME MEASURES: Perioperative variables included EBL, length of stay (LOS) and operative time. Complications were recorded and X-ray parameters include: sagittal vertical axis (SVA), pelvic tilt and pelvic incidence - lumbar lordosis (PI-LL). Patients were classified by SRS-Schwab modifier grades. HRQOL questionnaires (Oswestry Disability Index [ODI], SRS-22r and Short Form SF-12) were analyzed. METHODS: Patients with surgical ASD with >5 levels posterior fusion with >2-year follow up were included. Number of attending surgeons performing each procedure was obtained from each individual institution. Outcomes were compared between 1-surgeon and 2-surgeon centers. After initial analysis, a separate cohort matched for demographic and severity of deformity was also analyzed. RESULTS: Patients in the 2S group were older (61.5 vs 54.2; p<0.01). Preoperative radiographs demonstrated that the 2S group had worsened deformity. X-ray parameters PI-LL (12.1 vs 21.7), SVA C7-S1 (54.2 vs 61.5), T1-PA (20.2 vs 25.1) and SRS-Schwab classification system were significantly different (p<0.05). There was no difference in the number of levels fused (11.2 vs 11.5 p=0.57). There was no significant difference in LOS (8.7 vs 8.9 days), OR time (445.9 vs 453.2 min) or EBL (2008 vs 1898 cc); (p>0.05). Patients in 2S group were more likely to obtain a 3 column osteotomy (3CO) 21.7% vs 59.6% (p=<0.001) and used less BMP 79.9% vs 15.6% (p<0.001). The 2S group had fewer intraoperative complications (1.3% vs 11.1%; p=0.006). But postoperative (6 weeks - 2 year) complications (4.8 vs 15.6%), implant related (4.2 vs 15.6%) and those requiring reoperation (5.3 vs 18.2%) were more frequent (p<0.002).After matching for PI-LL, SVA and 3CO, there was no difference in preoperative demographics. There was no difference in LOS (9.1 vs 10.1 days), OR time (467.8 vs 508.4 min) or EBL (3,045 vs 2,247 cc) p>0.05. 2SM group used less BMP (20.6% vs 84.8%; p=<0.001) and less intra operative complications (p=0.015). Postoperative (>6wks to 2 year) complications due to instrumentation failures/pseudoarthrosis were more frequent in 2SM group (p <0.01). CONCLUSIONS: Patients with ASD surgery performed by 2 surgeons were older with worse deformity. Both groups improved X-ray parameters and HRQOL but no difference was found in LOS, OR time or EBL even when matching cohorts for amount of deformity. 2S group had more 3COs, less BMP and had fewer intraoperative complications but more postoperative (>6 weeks to 2 years) complications that could be tied to low BMP use and/or fusion techniques. Overall it appears that for high complexity surgery, teams of multiple surgeons can reduce operative risk significantly

BACKGROUND CONTEXT: According to Dubousset's "conus of economy" theory, deterioration of sagittal alignment requires higher energy expenditure to maintain erect posture. Since the clinical impact of sagittal alignment is affected both by the severity of the deformity and a patient's inability to recruit compensatory mechanisms, it is important to investigate new parameters that reflect both disability level and compensatory mechanisms for all patients. This study investigates the clinical relevance of the global sagittal angle (GSA). PURPOSE: Provide a substantive measure of sagittal deformity which offers clinically significant information about disability for all patients in one easy to calculate metric. STUDY DESIGN/SETTING: Single center retrospective review. PATIENT SAMPLE: 143 Spinal deformity patients with full body sagittal X-ray imaging. OUTCOME MEASURES: Full body sagittal radiographic measures and health related quality of life measure (Oswestry Disability Index [ODI], Scoliosis Research Society 22r [SRS]). METHODS: Retrospective review of patients who underwent full body radiography and completed ODI and SRS-22r. GSA was defined as the angle subtended by a line from the midpoint of the femoral condyles to the center of C7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S1 sacral endplate (knee-C7 vs knee- S1). After evaluating the correlation of GSA/ODI with classic sagittal parameters, linear regression models were generated to investigate how ODI related to radiographic parameters (TPA, PT). TPA and PT's relation to GSA was then investigated. RESULTS: 143 patients (mean 44 years) were identified. GSA correlated significantly (ie, all with p<0.05) with ODI (r=0.517), SRS-22r (r= -0.543), PT(r=0.622), SVA(r=0.962), TPA (r=0.844) and lower limb alignment, knee flexion (r=0.793), ankle dorsiflexion (r=0.561) and pelvic posterior shift (0.870). Regression between ODI and classic parameters only retained GSA as independent predictor (r=0.517, r2=0.267, p<0.001). Analysis of standardized coefficients revealed that GSA increases when TPA increases (beta: 1.991) with concurrent decrease in PT (-1.323). These findings echoed those of ODI, which increased with increased TPA (beta: 1.038) and decreased PT (-0.696). CONCLUSIONS: GSA goes further than classic parameters and quantifies the clinical impact of all patients' compensation mechanisms in addition to their malalignment. Analyzing the relationship between GSA and PT revealed that compensation is the body's defense against malalignment, and patients who lack compensation have both higher GSA and higher ODI scores. However, this subset of patients possibly recruit knee flexion which further increases their global sagittal angle and disability. GSA is a significant and clinically relevant metric that quantifies both spinal deformity and disability even among those with alternative compensatory mechanisms