The ipsilateral epiphyseal and central endplate Hounsfield Units accurately predicts intraoperative endplate violation and delayed cage subsidence with Oblique Lateral Interbody Fusion

Abstract

Purpose: There are favorable results with oblique lateral interbody fusion (OLIF) to achieve indirect decompression. Some of the most dreaded complications include intraoperative endplate violations and delayed cage subsidence. The endplate plays an important role in distributing compressive load across a functional spinal unit. The Hounsfield units (HUs) can provide detailed information regarding bone quality across endplates at surgical levels. We aimed to investigate the risk factors for intraoperative endplate violations and delayed cage subsidence after OLIF surgery. Methods: A total of 61 consecutive patients (mean age, 65.1±9.5 years; 107 segments) who underwent OLIF with or without posterior instrumentation from May 2015 to April 2019 were studied. Intraoperative endplate violation was defined as more than 2 mm collapse of the cage into the endplate of the adjacent vertebral body on sagittal reconstructed computed tomography images immediate postoperatively. Delayed cage subsidence was evaluated using lateral radiographs and defined as more than 2 mm migration of the cage into the adjacent vertebral endplate at 1-month follow-up or later. As potential contributors, bone mineral density, number of surgical levels, preoperative and postoperative disc height and Hounsfield units (HUs) at different regions of the endplate were obtained along with other demographic factors. Results: Total postoperative cage subsidence was identified in 45 surgical levels (42.0%) in 26 patients (42.6%) up till postoperative 1-year follow-up. These consisted of 25 intraoperative endplate violation segments (23.4%) and 20 levels (18.7%) with delayed cage subsidence. Low HU value at the ipsilateral epiphyseal ring was an independent risk factor for intraoperative endplate violation (p=0.01) with a cut-off value of 326.21 HUs (sensitivity 79.0%, specificity 77.3%). Low HU values at the central endplate had a significant correlation with delayed cage subsidence in stand-alone cases (p=0.01) with a cut-off value of 296.42 HUs (sensitivity 76.9%, specificity 76.6%). Conclusions: HUs of the endplate are good predictors for intraoperative endplate violation and cage subsidence since they can represent the regional bone quality of the ndplate in contact with the implant. These are important parameters for consideration preoperatively to plan for cage sizes and posterior instrumentation.