Does adding an interbody cage in L4–L5 posterolateral fusion for degenerative spondylolisthesis and stenosis improve clinical outcome?

Introduction: As the population ages, L4-L5 degenerative spondylolisthesis is increasingly common. Posterolateral fusion was long standard; interbody cages are widely used for perceived higher fusion rates. Research question: Does adding an interbody cage to posterolateral fusion improve outcomes or reduce complications in elderly patients with grade I spondylolisthesis and severe stenosis? Materials and methods: We retrospectively studied 319 adults aged 60-85 who underwent single-level L4-L5 fusion (2011-2018) after failed conservative care. Patients received posterior lumbar fusion (PLIF, n = 155) or posterolateral lumbar fusion (PLF, n = 164). Primary outcomes were Oswestry Disability Index (ODI) change and complications over a median five-year follow-up; secondary outcomes were operative time, hospital stay, and transfusions. Multivariable analyses adjusted for age, sex, BMI, year of surgery, and sagittal alignment. Results: Functional improvement was similar (median ODI reduction ≈22 points; p = 0.97), and implant-related revision and revision-free survival did not differ. Cage use increased overall complications (24.5 % vs 7.9 %), prolonged surgery (125 vs 95 min) and hospital stay (4 vs 3 days), and raised transfusions (9.7 % vs 1.8 %), dural tears (11.6 % vs 2.4 %), and radicular deficits (6.5 % vs 1.2 %). The association between cage use and complications persisted after adjustment. Conclusion: In this elderly, low-grade L4-L5 degenerative spondylolisthesis cohort, adding a posterior interbody cage to instrumented posterolateral fusion did not improve 5-year disability but was associated with higher peri-operative morbidity and greater resource use.