Analysis of a Unilateral Bridging Cage for Lumbar Interbody Fusion: 2-Year Clinical Results and Fusion Rate with a Focus on Subsidence

Abstract

The aim of this study was to evaluate the biomechanical stability and the clinical and radiographic outcomes in patients undergoing transforaminal lumbar interbody fusion (TLIF) using an oblique bridging cage with a particular focus on subsidence. Finite element models were developed to compare the biomechanics of the oblique cage with conventional posterior lumbar interbody fusion and banana-shaped cages with TLIF. Additionally, a retrospective review of a prospective collected database was performed to investigate the clinical and radiologic results with a focus on the subsidence rate using an oblique polyetheretherketone (PEEK) cage with a bicortical load-bearing design. We included 87 patients with degenerative pathologic conditions of the lumbar spine who underwent TLIF. The clinical outcome was assessed using the Oswestry Low Back Pain Disability Questionnaire and the visual analogue scale. Fusion and subsidence rates were assessed radiographically. The finite element models showed no differences in stability on compression or extension/flexion. Theoblique cage differed in terms of the location of the maximal stresses. A total of 105 levels were fused. The level at which fusion was most frequently performed was L4-L5 (59%). The fusion rate was 93.2% after 24 months. Subsidence was found at 4 levels after the last follow-up visit (3.9%). Overall clinical outcome improvement was achieved after 24 months. Regarding fusion, the use of an oblique PEEK cage with a cortical load-bearing design provided highly satisfactory clinical and radiologic results after 2 years. A review of the literature suggests a lower rate of cage subsidence after lumbar interbody fusion using bridging cages rather than single cages.