Static vs Expandable Cages in Single-Level Prone Transpsoas Lateral Lumbar Interbody Fusion: A Retrospective Radiographic Cohort Study

Background Prone transpsoas lateral lumbar interbody fusion (PTP-LLIF) enables simultaneous lateral interbody access and posterior instrumentation from a single prone position. While expandable interbody cages have demonstrated improved radiographic restoration in other lumbar fusion approaches, their outcomes in PTP-LLIF remain poorly defined. This study compares radiographic and perioperative outcomes between static and expandable cages in single-level PTP-LLIF. Methods A retrospective cohort study was conducted at a single academic center evaluating patients who underwent single-level PTP-LLIF with posterior instrumentation. Patients were stratified by cage type (static vs expandable). Standing full-length radiographs were analyzed preoperatively, early postoperatively, and at latest follow-up. Outcomes included disc height, foraminal height, disc angle, segmental lordosis, lumbar lordosis, spinopelvic alignment, and perioperative variables. An additional 1:1 matched cohort analysis was performed based on age, body mass index, American Society of Anesthesiologists classification, operative level, preoperative foraminal height, and preoperative segmental lordosis. Results A total of 45 patients met inclusion criteria, including 38 (84%) with static cages and 7 (16%) with expandable cages. Expandable cages demonstrated significantly greater early postoperative anterior disc height (7.1 ± 1.8 vs 5.0 ± 2.2 mm, P = 0.026) and posterior disc height (4.3 ± 1.8 vs 2.6 ± 2.0 mm, P = 0.05). Posterior disc height remained significantly greater at late follow-up (P = 0.032). Expandable cages were also associated with greater increases in lumbar lordosis (11.4° ± 4.9° vs 4.0° ± 4.8°, P = 0.006 early; 11.6° ± 4.2° vs 3.0° ± 4.8°, P < 0.001 late) and segmental lordosis (7.9° ± 3.8° vs 3.8° ± 3.4°, P = 0.028 late). Postoperative pelvic incidence–lumbar lordosis mismatch trended lower in the expandable cohort (P = 0.092 early, 0.068 late). Perioperative outcomes, including estimated blood loss, operative time, and length of stay, were comparable between groups. Similar findings were observed in the matched cohort analysis. Conclusions Expandable cages in PTP-LLIF were associated with greater improvements in disc height and sagittal alignment parameters compared with static cages. Findings were consistent with literature on other lumbar fusion approaches. Given the small sample size and potential for confounding by indication, these findings should be interpreted cautiously. Clinical Relevance Expandable cage technology may enhance sagittal alignment correction in PTP-LLIF, though further study is required to determine independent contribution and clinical impact. Level of Evidence 3.