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Bone mineral density assessment is essential for spinal fusion surgical planning, but gold standard dual energy X-ray absorptiometry (DEXA) is affected by degeneration often resulting in falsely elevated scores. The opportunistic measurement of Hounsfield units on computed tomography (CTHU) is gaining in popularity given the access to preoperative CTs obtained for instrumentation guidance systems and the ability to evaluate the region of interest while avoiding adjacent degenerative structures. Emerging studies suggest that lower CTHUs predict interbody cage subsidence, yet cutoff values vary, and lack standardization. To determine if the value CTHU<135 is associated with interbody cage subsidence in the lumbar spine and to compare the predictive performance of subsidence between CTHU and DEXA. Single-center, multisurgeon, retrospective cohort study. Circumferential lumbar fusions ≤ 5 interbody levels with perioperative DEXA, CTs, and X-rays. CTHU at L1, lowest DEXA T-score, and postoperative change in disc space height (cage migration) on X-ray. Circumferential lumbar fusions were retrospectively enrolled if DEXA, CT, and x-rays were available, and minimum follow up was one year. Interbody fusions were analyzed for subsidence ≥ 2mm by validated motion detection software. Lowest DEXA any and DEXA spine T-scores were recorded and categorized (normal ≥ -1.0, -1.0 > osteopenia > -2.5, osteoporosis ≤ -2.5) and L1 CTHUs were measured. Statistical analysis determined the association between CTHU<135 and subsidence. Univariate and multivariate binary logistic regression compared the predictive performance of subsidence between CTHU and DEXA. The 127-patient cohort had 96.9% degenerative pathologies, 54.3% were females, median age was 60 (IQR 51-69) years, 2.4% had osteoporosis, 44.1% had CTHU<135, median length of follow-up was 17 (IQR 12-24) months, and 13.4% developed subsidence on or before the last follow up. CTHU<135 (p=0.004) and age (p=0.016) were significantly associated with subsidence; DEXA lowest T-score (p=0.550) was not. The odds of subsidence were significant if CTHU<135 on crude and adjusted (OR=4.0, 95% CI 1.2-13.9, p=0.029) comparisons. The odds of subsidence were not significant if lowest T-score < -1.0 for DEXA any and DEXA spine (OR=1.8, 95% CI 0.6-4.9, p=0.284 and OR=1.1, 95% CI 0.3-4.1, p=0.920, respectively). CTHU<135 was associated with subsidence while DEXA lowest T-score was not in patients with degenerative pathologies. The odds of subsidence were 4.0 times higher for CTHU<135 after controlling for known risks, supporting this cutoff value. This study suggests that CTHU is a more reliable predictor of subsidence than DEXA when assessing degenerative spinal pathologies and is a useful tool for assessing bone quality when planning lumbar surgery. This abstract does not discuss or include any applicable devices or drugs. [ABSTRACT FROM AUTHOR]

Background: Traditional surgical treatment for symptomatic cervical degenerative disc disease is anterior cervical discectomy and fusion (ACDF), yet the increased risk of adjacent segment degeneration (ASD) requiring additional surgery exists and may result in limiting long-term surgical success when it occurs. Disc arthroplasty can preserve or restore physiologic range of motion (ROM), decreasing adjacent level stress and subsequent surgery. For patients with multilevel pathology requiring at least a 1-level fusion, interest is growing in anterior cervical hybrid (ACH) surgery as a partial motion-preserving procedure to decrease the adjacent level burden. This radiographic study compares postoperative superior adjacent segment motion between ACH and ACDF. Secondarily, total global motion, construct motion, inferior adjacent segment motion, and sagittal alignment parameters were compared., Methods: This is a single-center, multi-surgeon, retrospective cohort study of 2- and 3-level ACH and ACDF cases between 2013 and 2021. Degrees of motion were analyzed on flexion/extension views using Cobb angles to measure global (C2-C7) construct and adjacent segment lordosis. Neutral lateral X-rays were analyzed for alignment parameters, including global lordosis, cervical sagittal vertical axis (cSVA), and T1 slope (T1S). Differences were determined by independent t-test and Fisher's exact test., Results: Of 100 patients, 38% were 2-level cases (47% ACH, 53% ACDF) and 62% were 3-level cases: (52% ACH, 48% ACDF). Postoperatively, superior adjacent segment motion increased with ACDF and decreased with ACH (-1.3°±5.3° ACH, 1.6°±4.6° ACDF, P=0.005). Postoperatively, the ACH group had greater ROM across the construct (16.3°±8.7° ACH, 4.7°±3.3° ACDF, P<0.001) and total global ROM (38.0°±12.8° ACH, 28.0°±11.1° ACDF, P<0.001). ACH resulted in a significant reduction of motion loss across the construct (-10.0°±11.7° ACH, -18.1°±10.8° ACDF, P<0.001). Postoperative alignment restoration was similar between both cohorts (-2.61°±8.36° ACH, 0.04°±12.24° ACDF, P=0.21)., Conclusions: Compared to ACDF, hybrid constructs partially preserved motion across operative levels and had greater postoperative global ROM without increasing superior adjacent segment mobility or sacrificing alignment restoration. This supports the consideration of ACH in patients with multilevel degenerative cervical pathology requiring at least a 1-level fusion and suggests a propensity for long-term success by reducing the superior adjacent segment burden., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-23-135/coif). L.D.O. and R.T.R. received institutional research support from Medtronic and Innovasis. C.R.G. serves on an advisory board for Stryker/K2M, Medtronic, and Augmedics. C.R.G. reports royalties and consulting fees from Stryker/K2M and Medtronic; institutional educational research support from Medtronic; owns stock in Audmedics and NSite. E.J. reports consulting fees from Stryker, Medtronic, and Innovasis. C.M.H. reports personal fees from Medtronic, Globus Medical, Spineart, and Innovasis. The other authors have no conflicts of interest to declare., (2024 Journal of Spine Surgery. All rights reserved.)