Impact of lateral plate and screw fixation on long-term radiographic subsidence in lateral lumbar interbody fusion.

Abstract

Lateral lumbar interbody fusion (LLIF) can be performed as a stand-alone procedure, with lateral plate and screw fixation, or with supplemental posterior instrumented fusion. In vitro biomechanical data suggest that lateral plate fixation limits segmental motion. The aim of this study was to evaluate the impact of lateral screw and plate fixation on the rate and grade of long-term radiographic implant subsidence after LLIF. A review of patients who underwent LLIF for degenerative lumbar spondylosis from 2014 to 2022 at two quaternary referral centers was conducted. All patients underwent CT evaluation a minimum of 1 year after surgery. Patients with posterior instrumented fusion were excluded. Age, sex, BMI, smoking status, cage material, and the bone density of the operative level (in Hounsfield units) were collected. Postoperative implant subsidence at the long-term follow-up was graded according to Marchi criteria by two separate spine surgeons. A stepwise multivariate logistic regression analysis was performed. Overall, 146 patients (219 surgical levels; 85 female, mean age 67.9 years) met inclusion criteria. Sixty-five patients (45%) underwent LLIF with lateral plate and screw fixation, and 81 patients (55%) underwent stand-alone LLIF. No intraoperative subsidence was observed. In the univariate analysis, age, sex, smoking status, bone density at the operative level, and BMI were not significantly associated with radiographic subsidence on a per-level basis. Multivariable logistic regression analysis showed that a 3D-printed porous titanium cage was moderately associated with reduced subsidence (OR 0.401, 95% CI 0.202-1.069; p = 0.071). Lateral plate fixation was significantly associated with reduced subsidence (OR 0.484, 95% CI 0.099-0.652; p = 0.006). All 4 patients (4.9%) with grade II (severe) subsidence underwent stand-alone LLIF. One patient with lateral plating experienced delayed vertebral body fracture. All patients with lateral plates received 18-mm-wide interbody implants, while all but 2 patients who underwent stand-alone LLIF received 22-mm-wide implants. LLIF with lateral plate and screw fixation was significantly associated with a lower rate of radiographic subsidence at the long-term follow-up compared with stand-alone LLIF. There was no significant difference in the reoperation rate between the two procedure groups. No cases of reoperation were identified in patients who received 3D-printed porous titanium cages, and there was a trend toward the superiority of 3D-printed porous titanium over PEEK cage material. The results of this study suggest that LLIF with lateral plate and screw fixation has potential to protect against severe (grade II or worse) radiographic subsidence.