Analyzing the L4-5 Segmental Alignment Change of Two Minimally Invasive Prone-Based Interbody Fusions.

Study design: Retrospective Cohort Study.

Objective: Restoration of lumbar lordosis (LL) is a principal objective during spinal fusion procedures, traditionally focusing on achieving an LL within 10° of the pelvic incidence (PI). Recent studies have demonstrated a relatively constant L4-S1 alignment of 35-40° at L4-S1 and at least 15° at L4-5, regardless of PI. Based on these results, this study was created to examine the success rate of achieving a minimum of 15° at L4-5 through two differing prone-based techniques: Prone Lateral (pLLIF) and Trans Foraminal Interbody Fusion (TLIF).

Methods: One hundred patients with a primary single-level L4-5 interbody fusion (50 pLLIF and 50 TLIF) were retrospectively analyzed. Pre and post-operative radiographs were measured to examine the segmental change at each level in the lumbar spine and calculate the success rate for achieving a minimum L4-5 segmental lordosis of 15° at the final follow-up.

Results: The overall success rate of achieving an L4-5 segmental alignment >15° at the final follow-up was 70%. Prone LLIF was significantly more likely than TLIF to achieve this goal, achieving L4-5 > 15° 84% of the time vs TLIFs 56% (P = 0.002). Prone LLIF demonstrated an average L4-5 increase of 5.6 ± 5.9° which was larger than the mean increase for TLIF 0.4 ± 3.8° (P < 0.001). In both techniques, there was an inverse correlation between pre-operative L4-5 angle and L4-5 angle change.

Conclusion: Prone lateral lumbar interbody fusion demonstrates a high success rate for achieving a post-operative L4-5 angle >15° and achieves this at a higher rate than TLIF.