Faculty Bibliography

OBJECTIVE Sagittal malalignment requires higher energy expenditure to maintain an erect posture. Because the clinical impact of sagittal alignment is affected by both the severity of the deformity and recruitment of compensatory mechanisms, it is important to investigate new parameters that reflect both disability level and compensatory mechanisms for all patients. This study investigated the clinical relevance of the global sagittal axis (GSA), a novel measure to evaluate the standing axis of the human body. METHODS This is a retrospective review of patients who underwent full-body radiographs and completed health-related quality of life (HRQOL) questionnaires: Oswestry Disability Index (ODI), Scoliosis Research Society-22, EuroQol-5D (EQ-5D), and the visual analog scale for back and leg pain. The GSA was defined as the angle formed by a line from the midpoint of the femoral condyles to the center of C-7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S-1 sacral endplate. After evaluating the correlation of GSA/HRQOL with sagittal parameters, linear regression models were generated to investigate how ODI and GSA related to radiographic parameters (T-1 pelvic angle, pelvic retroversion, knee flexion, and pelvic posterior translation). RESULTS One hundred forty-three patients (mean age 44 years) were included. The GSA correlated significantly with all HRQOL (up to r = 0.6 with EQ-5D) and radiographic parameters (up to r = 0.962 with sagittal vertical axis). Regression between ODI and sagittal radiographic parameters identified the GSA as an independent predictor (r = 0.517, r2 = 0.267; p < 0.001). Analysis of standardized coefficients revealed that when controlling for deformity, the GSA increased with a concurrent decrease in pelvic retroversion (-0.837) and increases in knee flexion (+0.287) and pelvic posterior translation (+0.193). CONCLUSIONS The GSA is a simple, novel measure to assess the standing axis of the human body in the sagittal plane. The GSA correlated highly with spinopelvic and lower-extremities sagittal parameters and exhibited remarkable correlations with HRQOL, which exceeded other commonly used parameters.

BACKGROUND CONTEXT: Degenerative lumbar stenosis (DLS) patients have been reported to lean forward in an attempt to provide neural decompression. Spinal alignment in patients with DLS may resemble that of adult spinal deformity (ASD). No previous studies have compared and contrasted the compensatory mechanisms of DLS and ASD patients. PURPOSE: To determine the differences in compensatory mechanisms between DLS and ASD patients with increasing severity of sagittal spino-pelvic malalignment. Contrasting these compensatory mechanisms may help determine at what severity sagittal malalignment represents a clinical sagittal deformity rather than a compensation for neural compression. STUDY DESIGN/SETTING: Retrospective clinical and radiological review PATIENT SAMPLE:: Baseline x-rays in patients without spinal instrumentation, with the clinical radiological and diagnoses 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: The two diagnosis cohorts were propensity matched for pelvic incidence and age. Each group contained 125 patients. Each group was stratified according to the SRS-Schwab classification. Regional spino-pelvic, lower limb and global alignment parameters were assessed in each group to identify differences in compensatory mechanisms between the two groups with differing degrees of deformity. No funding was provided by any third party in relation to carrying out this study or preparation of the manuscript. RESULTS: With mild to moderate malalignment (SRS-Schwab groups '0', or '+' for pelvic tilt, pelvic incidence-lumbar lordosis mismatch or sagittal vertical axis), DLS patients permit anterior truncal inclination and recruit posterior pelvic shift instead of pelvic tilt to maintain balance, while providing relief of neurological symptoms. ASD patients with mild- moderate deformity recruit pelvic tilt earlier than DLS patients. With moderate- severe malalignment, no significant difference was found in compensatory mechanisms between DLS and ASD patients. CONCLUSIONS: Patients with degenerative lumbar stenosis permit mild-moderate deformity without recruiting compensatory mechanisms of pelvic tilt, reducing truncal inclination and thoracic hypokyphosis in order to achieve neural decompression. However with moderate to severe deformity, their desire for upright posture overrides the desire for neural decompression, evident by the adaptation of compensatory mechanisms similar to that of the adult spinal deformity patients.

DESIGN:Retrospective review. OBJECTIVE:To evaluate gender-related differences in compensatory recruitment to progressive sagittal malalignment. SUMMARY OF BACKGROUND DATA:Recent research has elucidated compensatory mechanisms recruited in response to sagittal malalignment, but gender-specific differences in compensatory recruitment patterns is unknown. METHODS:Single-center study of patients with full body x-rays. A female group was propensity matched by age, body mass index (BMI), and pelvic incidence (PI) to a male group. Patients were then stratified into five groups of progressive PI-lumbar lordosis (LL) mismatch (<0°, 0°-10°, 10°-20°, 20°-30°, >30°). Differences between PI-LL groups were assessed with analysis of variance, and between genders by unpaired t test. Knee flexion to pelvic tilt (PT) ratio was computed and compared between genders. Multivariate regression to develop predictive models for PT was performed for each gender, first with spinopelvic parameters and subsequently with inclusion of lower limb parameters. RESULTS:A total of 942 patient visits were included: 471 females (mean age 54 years, BMI 27, PI 51°) and 471 males (mean age 52 years, BMI 27, PI 51°). At the lowest level of malalignment, females had greater PT and less knee flexion. With progressive malalignment, females continued to exhibit a pattern of greater pelvic retroversion and less knee flexion compared to males. Hip extension was higher in females with progressive PI-LL mismatch groups. Both genders progressively recruited knee flexion and pelvic retroversion with increased PI-LL mismatch, except that at the higher PI-LL mismatch groups, only males continued to recruit knee flexion (all p < .05). Inclusion of lower limbs in the regression for PT markedly improved correlation coefficients for females but not for males. CONCLUSIONS:With progressive sagittal malalignment, men recruit more knee flexion and women recruit more pelvic tilt and hip extension. Knee flexion is a possible mechanism to gain pelvic tilt for females whereas for males, knee flexion is an independent compensatory mechanism.

STUDY DESIGN: Retrospective. OBJECTIVE: This study assessed the feasibility of combining Oswestry and Neck Disability Index (ODI and NDI) into 1 shorter "Total Disability Index" (TDI) from which reconstructed scores could be computed. SUMMARY OF BACKGROUND DATA: ODI and NDI are not pure assessments of disability related to back and neck, respectively. Because of similarities/redundancies of questions, ODI scores may be elevated in neck-pain patients and the converse is true for NDI in back-pain patients. METHODS: Spine patients completed ODI and NDI, and complaints were recorded as back pain (BP), neck pain (NP), or both (BNP). Questionnaire scores were compared across cohorts via descriptives and Spearman (rho) correlations. In exploring the feasibility of merging ODI/NDI, TDI was constructed from 9 ODI and 5 NDI items. Extracting questions from TDI, reconstructed 9-item rODI and 10-item rNDI indices were formed and compared with true ODI/NDI. RESULTS: There were a total of 1207 patients: 741 BP, 134 NP, and 268 BNP. Mean ODI was 37 +/- 21 and mean NDI was 32 +/- 21. Patients with concurrent BP and NP had significantly more disability. Seventy-eight patients of 134 (58%) patients with NP only had at least "moderate disability" by ODI and 297 of 741 (40%) patients with back pain only, had at least "moderate disability" by NDI. ODI versus NDI correlation was rho = 0.755; ODI versus reconstructed rODI correlated at rho = 0.985, and NDI versus reconstructed rNDI correlated at rho = 0.967 (P < 0.01). CONCLUSION: Elevated ODI/NDI scores in patients with isolated complaints show that disability in 1 region affects scores on both surveys. This study constructed a 14-item TDI that represents every domain of ODI/NDI with exception of ODI "Sex Life." From this TDI, reconstructed scores correlated near perfectly with true scores. TDI provides a more global assessment of spinal disability and is a questionnaire that reduces the time burden to patients. The TDI allows for simultaneous assessment of back, neck, and global spinal disability. LEVEL OF EVIDENCE: 2.

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: 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: 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: Adjacent segment degeneration (ASD) has been described after anterior cervical fusion surgeries though ASD is not always clinically relevant. Hilibrand et al described a grading system for ASD after anterior cervical fusion. We expand the ASD definition with an analysis of radiographic adjacent segment pathology (RASP) by also assessing the progression of kyphotic alignment, and spondylolisthesis at adjacent segments in patients following cervical laminoplasty (LP) and posterior cervical decompression and fusion (CDF). PURPOSE: To assess radiographic adjacent segment pathology by analyzing adjacent segment degeneration, and the progression of kyphotic alignment and spondylolisthesis at segments adjacent to operated levels for LP and CDF surgery. STUDY DESIGN/SETTING: Retrospective analysis of cervical radiographs in patients undergoing prior LP and CDF surgery. PATIENT SAMPLE: 64 patients undergoing prior LP and CDF surgery. OUTCOME MEASURES: NDI and mJOA. METHODS: Preoperative and postoperative radiographs were analyzed for ASD, progression of adjacent level kyphosis and spondylolisthesis at proximal, distal or any other segments. The RASP was determined by combining proximal and distal ASD, and the adjacent level kyphosis and spondylolisthesis into one spectrum of disease. The presence and rate of development of adjacent segment pathology was compared for LP and CDF. HRQOLs included NDI and mJOA. RESULTS: 64 patients were included (24 LP and 40 CDF) with mean age 59.9 years (46.9% female) and 30.2 months mean follow-up. Spondylolisthesis at the adjacent segment was more prevalent in CDF (29.2% vs 4.5%). Both LP and CDF demonstrated a similar rate of RASP (LP 40.9%, CDF 44%). NDI correlated with proximal adjacent level degeneration (r = 0.34, p = 0.024) and kyphosis (r = 0.36 p = 0.017). CONCLUSIONS: Both cervical laminoplasty and posterior cervical decompression and fusion are associated with adjacent level degeneration. However, there is a higher rate of adjacent segment spondylolisthesis after CDF. Motion preservation procedures may have less of a role in preventing adjacent level degeneration than previously thought. Adjacent segment degeneration correlated with NDI disability in these patients