Expandable Cages Demonstrate Greater Improvement in Radiographic Outcomes Post-Operatively in Patients Undergoing Open Transforaminal Lumbar Interbody Fusions

Introduction: The restoration of sufficient lumbar lordosis holds great significance in achieving optimal sagittal balance, decreasing overall back pain, and enhancing functional levels for patients. This imperative applies not only to scoliosis correction surgery but also to routine single- or two-level lumbar fusion procedures. The new expandable lumbar interbody cages with preferentially anterior expansion hold a great promise for effectively improving radiographic parameters, including lumbar lordosis, without resorting to the highly morbid and unstable three column lumbar osteotomy procedures.

Methods: We identified an institutional retrospective cohort of patients who underwent 1 or 2 level open TLIF with either expandable cage or static cages. Demographic and radiographic features, including pre-operative, post-operative, and last follow-up, were extracted from each patient. We examined the radiographic parameter changes and assessed for progression over time.

Results: 149 patients met the inclusion criteria, who were followed for an average of 15 months after surgery. Patients with static cages placed (n=99) and expandable cages (n=50) were similar with respect to baseline demographics, number of levels instrumented, pre-operative radiographic features, and length of follow-up. Static cages demonstrated significant differences in only Cobb Angle from pre-operation (12.7 ± 8.6) to post-operation (10.3 ± 6.6) and most-recent follow-up (MRFU) (10.6 ± 7.9) (p < 0.0001). Expandable cages were associated with significant improvements post-operatively in pelvic tilt (PT) (23.5 ± 10 to 18.0 ± 9.1) (p < 0.0001), Pelvic Incidence-Lumbar Lordosis mismatch (PI-LL) (30.9 ± 13 to 25.8 ± 12.6) (p=0.007), and sacral slope (SS) (33.2 ± 7.8 to 35.2 ± 8.3) (p=0.046), with durable improvement to PT (p = 0.007) and SS (p = 0.05) at MRFU. When compared to static cages, expandable cages with associ ated with significantly improved LL post-operatively (p < 0.001), as well as PT (p = 0.005), and PI-LL (p=0.025).

Conclusion : The use of expandable cages in open TLIF surgery is associated with improved radiographic outcomes post-operatively. Furthermore, when directly compared with static cages, expandable cages show greater benefit in correcting radiographic parameters post-operatively.