Allen, Tyler

Study Design: Retrospective cohort analysis. Objective: To determine the effect of long-segment posterior cervical decompression and fusion (PCDF) on perioperative changes in vertebral Hounsfield Units (HUs) and the impact of these changes on radiographic outcomes and fusion status. Summary of Background Data: Low preoperative CT HUs have been associated with adverse outcomes after spinal fusion, including hardware complications and reoperation. No existing studies have investigated the preoperative to postoperative change in HUs after cervical spinal fusion. Stress shielding may decrease bone quality within the fusion construct. Whereas, altered junctional loading and increased segmental mobility may precipitate bony hypertrophy in the terminal and adjacent levels. Methods: All adult patients who underwent C2-T2 PCDF for myelopathy/ myeloradiculopathy at an academic center between 2013 and 2020 were retrospectively identified. Preoperative and postoperative HUs were assessed on axial CT images in the cranial, middle, and caudal C2, C6, T2, and T3 vertebral bodies, outside of the region of instrumentation and artifact by 2 independent reviewers. Paired t test compared preoperative to postoperative changes in HUs. Preoperative and long-term postoperative cervical alignment, fusion, and revision rates were assessed. Univariate and regression analysis compared patient factors and outcomes between groups with perioperative increase versus decrease in vertebral HUs. Results: One hundred patients were included. The average preoperative to postoperative change in HUs in the C2, C6, T2, and T3 vertebral bodies were −19.80 (P=0.008), −52.63 (P<0.001), 15.15 (P=0.014), and 9.41 (P=0.346), respectively. Perioperative increase in C2 HUs was predictive of increased postoperative distal junctional angle (β=3.41, P=0.048) and increased T1–T4 kyphosis (β=6.50, P=0.003). Perioperative increase in C6 HU predicted pseudoarthrosis (fusion odds ratio: 0.19, P=0.007). Conclusions: Significant perioperative decreases in C6 HUs within a long-fused construct may demonstrate stress shielding. The significant association between greater distal kyphosis and an increase in C2 HUs may be attributed to a stress riser effect. Level of Evidence: Level III.

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.

Background: Increased posterior tibial slope (PTS) leads to a relative anterior translation of the tibia on the femur. This is thought to decrease the stress on posterior cruciate ligament (PCL) reconstruction (PCLR) grafts. Purpose/Hypothesis: The purpose of this study was to analyze the effect of PTS on knee laxity, graft failure, and patient-reported outcome (PRO) scores after PCLR without concomitant anterior cruciate ligament reconstruction (ACLR). It was hypothesized that patients with higher PTS would have less knee laxity, fewer graft failures, and better PROs compared with patients with lower PTS. Study Design: Case-control study; Level of evidence, 3. Methods: All patients who underwent PCLR between 2001 and 2020 at a single institution were identified. Patients were excluded if they underwent concomitant or prior ACLR or proximal tibial osteotomy, were younger than 18 years, had <2 years of in-person clinical follow-up, and did not have documented PRO scores (Lysholm score and International Knee Documentation Committee [IKDC] score). Data were collected retrospectively from a prospectively gathered database. PTS measurements were recorded from perioperative lateral knee radiographs. A linear regression model was created to analyze PTS in relation to PRO scores. Patients with a grade 1 (1-5 mm) or higher posterior drawer were compared with those who had a negative posterior drawer. Results: A total of 37 knees met inclusion criterion; the mean age was 30.7 years at the time of surgery. The mean clinical follow-up was 5.8 years. No significant correlation was found between either the Lysholm score or the IKDC score and the PTS. Twelve knees (32.4%) had a positive posterior drawer at final follow-up. The mean PTS in knees with a positive posterior drawer was 6.2°, whereas that for knees with a negative posterior drawer was 8.3° ( P = .08). No significant differences in PRO scores were identified for knees with versus knees without a positive posterior drawer. No documented graft failures or revisions were found. Conclusion: No significant differences were found in PROs or graft failure rates based on PTS at a mean of 5.8 years after PCLR. Increased tibial slope trended toward being protective against a positive posterior drawer, although this did not reach statistical significance.