Faculty Bibliography

BACKGROUND CONTEXT: Evaluation of sagittal alignment is essential in the operative treatment of spine pathology, particularly adult spinal deformity (ASD). However, software applications for detailed spino-pelvic analysis are usually complex and not applicable to routine clinical use. PURPOSE: This study aimed to validate new clinician-friendly software (Surgimap) in the setting of ASD. STUDY DESIGN/SETTING: Accuracy and inter- and intra-rater reliability of spine measurement software were tested. Five users (two experienced spine surgeons, three novice spine research fellows) independently performed each part of the study in two rounds with 1 week between measurements. PATIENT SAMPLE: Fifty ASD patients drawn from a prospective database were used as the study sample. OUTCOME MEASURES: Spinal, pelvic, and cervical measurement parameters (including pelvic tilt [PT], pelvic incidence [PI], lumbar-pelvic mismatch [PI-LL], lumbar lordosis [LL], thoracic kyphosis [TK], T1 spino-pelvic inclination [T1SPI], sagittal vertical axis [SVA], and cervical lordosis [CL]) were the outcome measures. METHODS: For the accuracy evaluation, 30 ASD patient radiographs were pre-marked for anatomic landmarks. Each radiograph was measured twice with the new software (Surgimap); measurements were compared to those from previously validated software. For the reliability and reproducibility evaluation, users measured 50 unmarked ASD radiographs in two rounds. Intra-class correlation (ICC) and International Organization for Standardization (ISO) reproducibility values were calculated. Measurement time was recorded. RESULTS: Surgimap demonstrated excellent accuracy as assessed by the mean absolute difference from validated measurements: PT: 0.12 degrees , PI: 0.35 degrees , LL: 0.58 degrees , PI-LL: 0.46 degrees , TK: 5.25 degrees , T1SPI: 0.53 degrees , and SVA: 2.04 mm. The inter- and intra-observer reliability analysis revealed good to excellent agreement for all parameters. The mean difference between rounds was <0.4 degrees for PT, PI, LL, PI-LL, and T1SPI, and <0.3 mm for SVA. For PT, PI, LL, PI-LL, TK, T1SPI, and SVA, the intra-observer ICC values were all >0.93 and the inter-observer ICC values were all >0.87. Parameters based on point landmarks rather than end plate orientation had a better reliability (ICC>/=0.95 vs. ICC>/=0.84). The average time needed to perform a full spino-pelvic analysis with Surgimap was 75 seconds (+25). CONCLUSIONS: Using this new software tool, a simple method for full spine analysis can be performed quickly, accurately, and reliably. The proposed list of parameters offers quantitative values of the spine and pelvis, setting the stage for proper preoperative planning. The new software tool provides an important bridge between clinical and research needs.

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

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: Accurate radiographic measurement of sagittal alignment is essential for evaluating adult spinal deformity (ASD) and preoperative planning. However, the limited capabilities of traditional picture archiving and communication systems (PACS) often necessitate rudimentary techniques and estimations of anatomic landmarks and angles. PURPOSE: To assess the reliability and variation between dedicated surgical measurement software (SMS) and PACS measurements. STUDY DESIGN/SETTING: Comparison of radiograph measurement reliability between PACS and SMS. PATIENT SAMPLE: Eleven observers completed measurements of 20 ASD patient radiographs. OUTCOME MEASURES: User-generated radiographic measurements for pelvic incidence (PI), pelvic tilt (PT), lumbar lordosis (LL), PI-LL, thoracic kyphosis (TK), and sagittal vertical axis (SVA); intra-class correlation coefficient (ICC); coefficient of variation (CV). METHODS: Eleven independent observers (7 surgeons, 4 researchers) with varying levels of experience digitally measured 20 primary and revision ASD patient radiographs for PI, PT, PI-LL, LL, TK, and SVA in 2 rounds. Round 1 used the basic line and angle tools in traditional PACS; Round 2 used the sagittal alignment tool in a previously validated software dedicated to spine measurement and operative planning. The SMS automatically calculates spino-pelvic parameters from 6 user-identified anatomic landmarks, including the outline of the femoral heads and vertebral endplates. Results were analyzed for means, CV and ICC. RESULTS: There were significant differences between SMS and PACS in mean values for PI, PT, PI-LL (all P<0.0001), and TK (P=0.019). For each parameter, the PACS measurement was larger than the SMS measurement. The standard deviations were also significantly larger for the PACS measurements in all parameters (P<0.012 for all) except TK. Excluding TK, the variation in measurement was significantly greater for PACS (CV=14-34%) versus SMS (CV=11-23%). The ICC values for all parameters were greater than 0.64, and when PI was excluded, all were greater than 0.92. Inter-rater reliability was greater in SMS compared to PACS for nearly all measurements: PI, PT, PI-LL, LL and SVA. For both SMS and PACS, the lowest ICC was observed in PI, and the highest ICC was seen in SVA. The parameters with the greatest differences in inter-rater reliability between PACS and SMS were PI (PACS ICC: 0.647 vs SMS ICC: 0.810) and PI-LL (PACS ICC: 0.921 vs SMS ICC: 0.970). TK had the most similar ICC values between PACS (0.955) and SMS (0.945), and was the only parameter for which the PACS ICC was greater than the SMS ICC. When only the surgeons' measurements were considered, the differences between PACS and SMS ICC were substantially greater. Among the surgeons, SMS had higher ICC than PACS for all parameters (ex PI-LL: 0.957 vs 0.896). PI still had the lowest inter-rater reliability (PACS ICC: 0.505 vs SMS ICC: 0.752) and SVA had the highest (PACS ICC: 0.985 vs SMS ICC: 0.994). CONCLUSIONS: SMS measurements provide significantly more accurate and reliable measurements with less variation than PACS. The greater reliability of SMS is amplified in surgeon-only analyses, demonstrating the clinical utility of SMS versus traditional PACS. Consistent use of SMS in the clinical evaluation and operative planning of ASD patients would be advantageous given the significant differences in values, standard deviations, variances and reliability between PACS and SMS

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

Hypothesis: Cervical kyphosis may be a physiologic alignment necessary for the maintenance of horizontal gaze depending on underlying thoracolumbar (TL) alignment. Design: Retrospective review. Introduction: Cervical curvature (CC) is affected by thoracic and global alignment. Recent studies suggest large variability in normative CC ranging from lordotic to kyphotic alignment. This study investigates the effect of thoracic and global alignment on CC in maintenance of horizontal gaze. Methods: For formula development, full body xrays of 744 patients (pts) without presenting cervical complaints or existing fusions higher than T3 were studied. Only pts who maintained their horizontal gaze (CBVA -5degree and 17degree or McGregor's slope between -6degree and 14degree) were included. Pts were stratified based on thoracic kyphosis (TK) into (>50, 40-50, 30-40 and<30). Pts were sub-stratified by SRSSchwab sagittal vertical axis (SVA) modifier into (posterior alignment SVA <0, aligned 0-50 and malaligned >50 mm). C2-C7 cervical curvature was assessed among SVA grade in every TK group. Stepwise linear regression analysis was applied. A simplified formula was validated on random selection of 1905 patient visits from same database. Results: In each TK group (n = 265, 172, 163, 144), CC was significantly more lordotic by increased Schwab SVA grade. In SVA<0, CC was neutral for TK 40-50degree, and kyphotic for TK<40degree. All pts with SVA<50 mm, and TK<30degree were kyphotic. Regression analysis revealed LL minus TK (LL-TK) as an independent predictor (r = 0.653, r² = 0.426) with formula: CC = 10 - (LL-TK)/2. Validation of the formula revealed error of 1.2degree between predicted CC and real CC (r = 617, r² = 381). Conclusions: Kyphotic cervical alignment is necessary in the maintenance of horizontal gaze in some well aligned and some sagittal backward pts depending on thoracic curvature. CC can be predicted from underlying TK and lumbar lordosis, which can be clinically relevant in thoracolumbar deformity correction

Hypothesis: Global sagittal angle is clinically relevant. Design: Single center retrospective review. Introduction: 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 GSA. Methods: Retrospective review of patients who underwent full body X-rays and completed ODI and SRS-22. GSA was defined as the angle subtended by a line from the midpoint of the femoral condyles to the center of >7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S1 sacral endplate. 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 44y) were identified. GSA correlated significantly with ODI, PT, SVA, TPA and lower limb alignment. 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. GSA is a significant and clinically relevant metric that quantifies both spinal deformity and disability even among those with alternative compensation mechanisms

Hypothesis: Mechanisms of relaxation after sagittal correction may differ from the compensation mechanisms of sagittal deformity development. Design: Retrospective cohort. Introduction: Adult spinal deformity patients recruit compensatory mechanisms to maintain alignment with increasing deformity. While attention has been paid to pre-operative compensatory adaptations, little is known regarding the sequence of relaxation of these parameters based upon the amount of residual PI-LL mismatch. This study details the progression of compensatory mechanism relaxation as PILL mismatch improves. Methods: Single site review of post-operative full-body x-rays of patients, at least 9 months after surgery. Radiographic measurements were obtained with dedicated spine software and included PT, knee flexion (KA), ankle dorsiflexion (AD), pelvic shift (PShift), T1 spinopelvic inclination (T1SPi), SVA and T1 pelvic angle (TPA). Patients were stratified by their remaining need for lordosis based on ageadjusted normative published values. Group comparisons were carried out via ANOVA analysis. Results: 262 patients were included, mean age 61.5, mean BMI 28, and males 31 %. PI-LL groups were significantly (p<0.05) different in terms of PT, KA, PShift, TPA, SVA and AD (Fig). Analysis of the sequence of correction revealed that the majority of age-adjusted offset in terms of SVA and PT was corrected (59 %, 57 %) during the first stage of correction ([>30degree] to [20degree-30degree] of remaining need for lordosis). This stage was associated with significant changes in PShift and T1SPi (p<0.05). Additional stages of corrections were associated with gradual decreases in SVA, while no additional decreases in PT were observed until the post-operative lordosis was near ideal. Conclusions: When improving from severe to moderate age-adjusted PI-LL mismatch, there is a correction in age-adjusted SVA to normal range. Nevertheless, these patients still exhibit high degree of compensation with respect to the pelvis and lower limbs to maintain alignment. PT and SVA can be corrected to an age-adjusted ideal when PI-LL is also corrected