Elder, Benjamin D.

OBJECTIVE Proximal junctional kyphosis (PJK) affects 5%–61% of patients following thoracolumbar fusion. Many patients are asymptomatic, but a plurality require surgical revision at a cost of $75,000 per case. This analysis sought to analyze the degree to which bone quality and paraspinal muscle sarcopenia influence PJK failure mode. METHODS Patients undergoing thoracolumbar instrumented fusion with an upper instrumented vertebra (UIV) at the thoracolumbar junction (T10–L2) were identified and data were gathered on surgery, bone quality, pre- and postoperative sagittal alignment, and paraspinal muscle cross-sectional area (CSA). PJK was defined as a ≥ 10° increase in proximal junctional angle from the first postoperative radiograph. PJK was classified as discoligamentous failure (type 1), bone failure (type 2), or screw-bone interface failure (type 3) according to the Yagi-Boachie system. Bone quality was assessed by Hounsfield units (HUs) and the vertebral bone quality (VBQ) score at the UIV. RESULTS One hundred fifty patients were identified (median age 67 years, 53.3% female), 46 of whom experienced PJK (22 type 1, 13 type 2, 11 type 3). The median time to onset was most rapid for type 2 events (2.6 months). There were no differences between patients experiencing PJK versus controls regarding bone quality (HUs or VBQ score) or paraspinal muscle CSA on univariate comparison. However, subdivision by PJK type showed patients experiencing bone failure (type 2) PJK had significantly lower HUs at the UIV and UIV+1 relative to those experiencing type 1 PJK or no PJK (all p < 0.05). The VBQ score trended toward being significant, with a higher VBQ score (worse bone quality) in those suffering type 2 PJK, but did not reach statistical significance (p = 0.07). Patients experiencing discoligamentous failure PJK (type 1) had small multifidus CSA (390 mm 2 ) relative to patients experiencing type 2 (516 mm 2 ) or type 3 (440 mm 2 ) PJK and patients who did not experience PJK (481 mm 2 ), although the difference did not reach statistical significance. On time-to-event analysis, low HUs of the UIV/UIV+1 predicted type 2 (hazard ratio [HR] 0.81, 95% CI 0.70–0.93; p = 0.002) and type 2/3 PJK (HR 0.87, 95% CI 0.78–0.96; p = 0.006) but not type 1 PJK. Low UIV multifidus CSA trended toward being a significant predictor of type 1 PJK (HR 0.85, 95% CI 0.69–1.05; p < 0.10). CONCLUSIONS The combination of underlying bone quality and paraspinal musculature CSA at the UIV appeared to influence failure mode among patients who underwent lumbosacral instrumented fusion terminating at the thoracolumbar junction.

OBJECTIVE The present investigation aimed to 1) develop a new CT-based assessment of endplate bone density (endplate Hounsfield unit [EP-HU]) and 2) analyze if EP-HU was a better predictor than vertebral Hounsfield unit (HU) for subsidence after anterior cervical discectomy and fusion (ACDF). METHODS All adult patients who underwent one- to three-level ACDF with a titanium interbody for radiculopathy and/or myelopathy at an academic center between 2018 and 2020 were retrospectively identified. Based on preoperative sagittal CT scans (left, right, and middle cuts), 2-mm superior and inferior endplate regions were circumscribed with the free draw tool to account for endplate surface undulations. The average of the superior and inferior EP-HUs on all CT cuts was used to calculate EP-HU. Cervical vertebral HUs were determined from the average of axial CT cranial, middle, and caudal cuts circumscribing only trabecular bone. The interbody subsidence of the cranial and caudal endplates of each ACDF level was directly measured on the endplate-facing surface of both coronal and sagittal cuts of postoperative CT scans (at 1 year) to determine the maximum subsidence (subsidence defined as ≥ 2 mm). Univariate and stepwise logistic regression analyses were used to compare subsidence based on CT bone metrics. Receiver operating characteristic (ROC) curve analyses were used to determine the probability of subsidence based on EP-HUs and vertebral HUs. RESULTS A total of 35 patients were included. Subsidence occurred at 32 of 67 unique fusion levels. Subsidence was associated with older age (p = 0.008), diabetes diagnosis (p = 0.015), and decreased interbody length (p = 0.019). EP-HUs exhibited moderate correlation with cervical vertebral HUs (Pearson’s ρ = 0.63). Subsidence was significantly associated with decreased total EP-HUs (subsidence: 475 HU, no subsidence: 543 HU; p = 0.019) and decreased lumbar vertebral HUs (subsidence: 296 HU, no subsidence: 341 HU; p = 0.011). ROC curve analysis identified an optimal EP-HU cutoff of 512.30 (area under the curve [AUC] = 0.701) to predict subsidence. The AUC of the vertebral HUs with respect to subsidence was 0.662. EP-HUs < 512.30 predicted subsidence (OR 6.67, p = 0.001) independent of significant demographic and surgical factors. CONCLUSIONS CT cervical EP-HUs rather than vertebral cervical trabecular HUs may be more efficacious in predicting subsidence after ACDF.

Study Design Retrospective cohort analysis. Objective (1) Develop a novel computed tomography (CT)-based assessment of endplate bone density (EP-HU), (2) Determine if EP-HU was a stronger predictor than trabecular HU for subsidence after transforaminal lumbar interbody fusion (TLIF). Methods All adult patients who underwent single-level TLIF for lumbar degenerative conditions at an academic center between 2017-2022 were retrospectively identified. EP-HU was calculated from a 2 mm superior and inferior endplate region on the preoperative mid sagittal CT scans, accounting for surface undulations. Lumbar vertebral HUs (trabecular region) were determined in a standard fashion on axial CT. EP-HU + vertebral HU served as an aggregate bone quality metric. Interbody subsidence (≥2 mm threshold) was directly measured on the endplate-facing surface of 1 year CT scans. Univariate and multivariate analysis compared subsidence based on CT bone metrics. Results A total of 114 patients met the inclusion/exclusion criteria. There was no significant difference in fusion or reoperation rate based on subsidence occurrence. Both vertebral HU ( P = .012) and EP-HU ( P < .001) were associated with subsidence. In receiver operating curves, EP-HU was more optimal for subsidence prediction than vertebral HU, but the aggregate metric further optimized the specificity and total area under the curve. In a predictive logistic regression model EP-HU + vertebral HU (aggregate HU < 515 odds ratio: 7.82, P < .001) was a strong independent predictor of subsidence. Conclusion Preoperative calculation of EP-HUs in addition to vertebral HUs may enhance prediction of TLIF subsidence where aggregate endplate and vertebral HU < 515 can be used to identify high risk patients.

OBJECTIVE Idiopathic normal pressure hydrocephalus (iNPH) is characterized by gait deterioration, cognitive disturbances, and urinary incontinence. Gait deficits pose safety hazards due to frequent falls, yet objective investigations of gait improvement following ventriculoperitoneal shunt (VPS) placement are limited. Therefore, the aim of this study was to assess objective improvement in gait parameters for patients with iNPH after VPS placement. METHODS All patients treated with a VPS for iNPH by the senior author at a single tertiary care center from December 2017 to January 2023 were retrospectively reviewed. Patients who underwent detailed motion analysis testing before surgery with > 1 follow-up assessment were included. Analyzed parameters included gait velocity, gait cadence, stride length, stride width, gait stability ratio, total support, and single support. Time-dependent linear mixed-effects models and generalized additive mixed-effects models (GAMMs) were used to model short-term and longitudinal gait parameter changes, respectively. RESULTS A total of 212 patients (137 male, median age was 75.2 years) who underwent VPS placement for iNPH were included, with a total of 747 gait analyses performed at a median last-gait analysis follow-up duration of 12.0 months. Statistically significant changes in all gait parameter values were seen between the preoperative time point and first postoperative follow-up (within 3 months) time point (paired Wilcoxon p < 0.001), with a statistically significant majority of patients experiencing improvement (binominal p < 0.0001). Longitudinal analyses using a GAMM showed increased gait velocity, single support, and stride length, with decreased stability ratio, step width, and total support at early time points, while a plateau was achieved around 6 months. CONCLUSIONS A detailed gait analysis demonstrated significant improvements in objective ambulation metrics, particularly in the gait velocity, stride length, and gait stability ratio, following VPS placement in patients with iNPH. Most patients maintained marked improvement from baseline to the last follow-up assessment, although a plateau of the benefit was experienced over longer follow-up.

OBJECTIVE The purpose of this study was to identify risk factors for mechanical complications following complex spinal reconstruction for spondylectomy of primary spinal column tumors. METHODS A retrospective chart review identified patients treated with spondylectomy for primary spinal column tumors in the thoracic or lumbar spine followed by posterior instrumentation and anterior column reconstruction. Variables collected included basic demographics, smoking status, chronic steroid use, frailty (Charlson Comorbidity Index), extent of resection, Weinstein-Boriani-Biagini classification, tumor volume, Spine Instability Neoplastic Score, anterior column reconstruction and fixation techniques, rod characteristics, Hounsfield units (HUs), and neoadjuvant/adjuvant chemoradiation. RESULTS Twenty-five patients were included (14 men, 11 women) with an average (± SD) age of 45 ± 18 years, BMI of 28 ± 5.7, and follow-up of 6.0 ± 6.2 years. Primary spinal column tumor pathology included chordoma (40%), chondrosarcoma (16%), giant cell tumor (16%), osteosarcoma (16%), osteoblastoma (8%), and aneurysmal bone cyst (4%). Six patients (24%) experienced mechanical complications, including rod fractures (n = 5) and distal junctional failure (n = 1). Of the 6 patients with mechanical complications, 4 (67%) underwent reoperation. The length of follow-up was the only statistically significant risk factor for patients with mechanical complications (average 11 years) compared to those without complications (average 4.4 years, p = 0.047). Average HUs were 144 for mechanical complication patients versus 180 for those without (p = 0.08). Anterior column reconstruction materials included a titanium cage (13 patients, 3 failures), structural allograft (6 patients, 2 failures), vascularized fibular strut autograft (6 patients, no failures), nonvascularized structural autograft (5 patients, 1 failure), vascularized rib autograft (5 patients, 2 failures), and a polyetheretherketone cage (2 patients, no failures). The vascularized fibular strut autograft had a 0% mechanical failure rate, but this did not reach statistical significance (p = 0.28). Twelve patients (48%) had anterior fixation placed, with a 17% rate of mechanical complications (p = 0.65). Five patients (20%) had > 2-rod constructs, with a 20% mechanical complication rate (p = 0.99). CONCLUSIONS Reconstruction following primary spinal column tumor resection is a significant challenge, as evident by a high rate of mechanical complications and instrumentation failure. Future studies are needed with larger sample sizes to identify techniques that may mitigate the risk of failure.

OBJECTIVE The purpose of this study was to evaluate the risks and benefits of removing painful pelvic/iliac screws in spine fusion surgery patients. METHODS A retrospective review identified patients who had traditional iliac and S2-alar-iliac (S2AI) screws removed for pain. The minimum follow-up was 24 months. RESULTS Fifty-two patients (75% women) were included with a mean age of 63 years, BMI of 28, and follow-up of 65 months. Most of the removed screws were S2AI (83%) compared with traditional iliac screws (17%). Forty-three patients (83%) had improvement in their pelvic screw related–pain following removal. Eight patients (15%) experienced lumbosacral mechanical complications following pelvic screw removal including sacral fracture (n = 3, 6%) and/or L4–5 or L5–S1 rod fracture (n = 7, 13%). On multivariable analysis, risk factors for mechanical complications following pelvic screw removal included a longer fusion construct (OR 1.34, p = 0.035), greater postoperative L4–S1 lordosis (OR 1.14, p = 0.04, ideal cutoff > 40°), and lack of bone morphogenetic protein (BMP; OR 0.03, p = 0.02). Ten patients (19%) underwent subsequent SI joint fusion following pelvic screw removal, and higher standing pelvic incidence (OR 1.10, p = 0.03) was the only independent predictor of SI fusion. CONCLUSIONS Removal of painful pelvic screws resulted in a high rate of postoperative pain relief, albeit with a risk of lumbosacral mechanical complications and subsequent SI joint fusion. Patients at risk for lumbosacral mechanical complications following pelvic screw removal included those with longer fusion constructs, more lordosis from L4 to S1 (> 40°), and lack of BMP. Patients at risk for receiving an instrumented SI joint fusion following pelvic screw removal included those with a higher pelvic incidence.

OBJECTIVE While traditional literature in adult spinal deformity (ASD) examining mechanical complications has focused on proximal junctional kyphosis and failure, distal junctional failure (DJF) of constructs ending at the sacrum with or without spinopelvic fixation remains less explored. The current study sought to 1) propose a new DJF classification with a panel of experienced deformity surgeons, and 2) analyze intra- and interreliability of the novel classification. METHODS A prior review study was completed that identified all types of distal complications for lumbosacral fusions. A panel of 25 experienced spinal deformity surgeons used a modified Delphi approach with three rounds of review to create a classification system. Ten deformity surgeons then reviewed a representative series of 14 de-identified cases to assess the interrater reliability of the classification system using the intraclass correlation coefficient (ICC). A second round of review was conducted by each investigator to determine intrarater reliability using Cohen’s kappa coefficient. RESULTS Complications were classified as acute (< 90 days from the date of surgery) or chronic (≥ 3 months from the date of surgery). Acute failures included mechanical failure of the screws or screw-rod interface, such as pelvic set plug dissociation, tulip head dissociation, and fracture of the pelvic screw at any point along its trajectory. Fractures of the rod (proximal vs distal to S1) and distal bony anatomy (sacrum vs pelvis) were included, as was failure of the offset connector. Chronic failures also consisted of pseudarthrosis at distal levels, sacroiliac joint (SIJ) pain, screw halo formation, and painful screw prominence. The intrarater and interrater reliability were both high with Cohen’s kappa of 0.91 and an ICC of 0.98, respectively. CONCLUSIONS These data provide a comprehensive and systematic classification scheme of distal complications following long-segment ASD fusion to the sacrum. This new paradigm will allow for more detailed and consistent reporting of distal junctional complications following spinopelvic fusion, with or without supplemental pelvic fixation and/or concomitant SIJ fusion. This classification scheme resulted in high intra- and interrater reliability.

Study Design Retrospective Cohort Study. Objectives To determine if 3D printed porous titanium (Ti) cages compared to non-porous polyetheretherketone (PEEK) cages predicted improved fusion rate or clinical outcomes after transforaminal lumbar interbody fusion (TLIF). Methods All adult patients who underwent one- and two-level TLIF for degenerative conditions by a single surgeon at an academic center between 2017-2021 were retrospectively identified. Patients were dichotomized into porous Ti and non-porous PEEK interbody cage groups. Fusion status was assessed by at 6-months and 1-year postoperatively by CT Bridwell scale and flexion/extension X-Rays. Postoperative complications (CT-based subsidence, adjacent segment disease, reoperation rates) and interval changes in lumbar radiographic alignment at short- and long-term follow-up were determined. Univariate and multivariate analysis compared patient and surgical factors, fusion rates, alignment, and complications across interbody groups. Results A total of 136 patients with 169 unique fusion levels (125 Ti cages, 44 PEEK cages) met the inclusion/exclusion criteria. Ti relative to PEEK interbodies had significantly decreased surface area and increased height and lordosis. Ti cage use was associated with greater subsidence ( P < 0.001) but did not independently predict maximum subsidence on regression ( P = 0.109). In the overall cohort, there were no significant differences in fusion rates or lumbopelvic alignment between interbody groups. Reoperation (Ti: 10.9% vs PEEK: 28.6%, P = 0.026) and reoperation for pseudoarthrosis (Ti: 2.0% vs PEEK: 11.4%, P = 0.038) was significantly more likely in the PEEK relative to the Ti group. Conclusions Use of 3D printed porous Ti cages relative to non-porous PEEK cages may mitigate pseudoarthrosis related reoperation after TLIF.

OBJECTIVE Pelvic incidence (PI) is a key parameter of sagittal alignment. While conventionally held to be fixed, increasing evidence suggests PI may be variable. This study aimed to identify predictors of change in PI with patient position and to assess the association of preoperative radiographic characteristics and intraoperative maneuvers with postoperative PI. METHODS Patients who underwent thoracolumbosacral fusion were identified, and data were gathered on preoperative spinopelvic parameters, patient demographic characteristics, and operative details. Preoperative spinopelvic parameters were measured on upright, supine, and prone radiographs. Univariable comparisons of PI between the different patient positions were performed. Multivariable analysis was performed to identify variables independently correlated with PI on 6-week postoperative radiographs. Change in PI was defined as ≥ 5° change between positions. RESULTS In total, 138 patients were identified (mean ± SD age 66.0 ± 8.7 years; 38.4% male). Statistically significant differences in PI were noted between preoperative standing and supine (mean −3.2° ± 4.2°, p < 0.001), preoperative supine and prone (3.5° ± 4.7°, p < 0.001), preoperative and 6-week postoperative standing (1.5° ± 6.2°, p = 0.01), and immediate and 6-week upright (1.1° ± 3.9°, p = 0.007) radiographs. Univariable comparisons showed PI decrease from standing to supine was predicted only by weight (87.0 ± 15.0 vs 81.1 ± 19.3 kg, p = 0.04); there were no significant predictors of increase in PI from standing to prone. Increase in PI from preoperative to 6-week standing radiographs was predicted by lower preoperative PI class (p < 0.001), L5/S1 interbody placement (74.4% vs 52.0%, p = 0.02), and change in PI from preoperative standing to supine (12.8% vs 39.8%, p = 0.002) and from standing to prone (51.3% vs 13.3%, p < 0.001). Multivariable analysis showed that 6-week postoperative PI was associated with only preoperative supine PI (B = 0.293, 95% CI 0.10–0.48, p = 0.003) and prone PI (B = 0.647, 95% CI 0.44–0.85, p < 0.001). CONCLUSIONS There are position-dependent changes in PI among patients without prior pelvic fixation. Statistically significant changes in PI are seen even after pelvic fixation with a single S2-alar-iliac screw bilaterally. Postoperative PI was best predicted by preoperative PI on supine and prone radiographs rather than upright radiographs, suggesting that preoperative prone and supine radiographs may provide surgeons with the best information for achieving PI–lumbar lordosis mismatch < 10°.