What is the fate of the adjacent segmental angles 6 months after single-level L3-4 or L4-5 lateral lumbar interbody fusion?

BACKGROUND CONTEXT:Lateral lumbar interbody fusion (LLIF) is an effective technique for fusion and sagittal alignment correction/maintenance. Studies have investigated the impact on the segmental angle and lumbar lordosis (and pelvic incidence-lumbar lordosis mismatch), however not much is documented regarding the immediate compensation of the adjacent angles. PURPOSE:To evaluate acute adjacent and segmental angle as well as lumbar lordosis changes in patients undergoing a L3-4 or L4-5 LLIF for degenerative pathology. STUDY DESIGN/SETTING:Retrospective cohort study. PATIENT SAMPLE:Patients included in this study were analyzed pre- and post-LLIF performed by one of three fellowship-trained spine surgeons, 6 months following surgery. OUTCOME MEASURES:Patient demographics (including body mass index, diabetes diagnosis, age, and sex) as well as VAS and ODI scores were measured. Lateral lumbar radiograph parameters: lumbar lordosis (LL), segmental lordosis (SL), infra and supra-adjacent segmental angle, and pelvic incidence (PI). METHODS:Multiple regressions were applied for the main hypothesis tests. We examined any interactive effects at each operative level and used the 95% confidence intervals to determine significance: a confidence interval excluding zero indicates a significant effect. RESULTS:We identified 84 patients who underwent a single level LLIF (61 at L4-5, 23 at L3-4). For both the overall sample and at each operative level, the operative segmental angle was significantly more lordotic postop compared to preop (all ps≤.01). Adjacent segmental angles were significantly less lordotic postop compared to pre-op overall (p=.001). For the overall sample, greater lordotic change at the operative segment led to more compensatory reduction of lordosis at the supra-adjacent segment. At L4-5, more lordotic change at the operative segment led to more compensatory lordosis reduction at the infra-adjacent segment. CONCLUSION:The present study demonstrated that LLIF resulted in significant increase in operative level lordosis and a compensatory decrease in supra- and infra-adjacent level lordosis, and subsequently no significant impact on spinopelvic mismatch.