Predictive factors for segmental lordosis angle restoration in oblique lumbar interbody fusion at L4/5

STUDY DESIGN: Retrospective study. OBJECTIVES: To identify the factors that determine segmental lordosis angle (SLA) at L4/5 after oblique lumber interbody fusion (OLIF). METHODS: A total of 65 patients who underwent single-level L4/5 OLIF (6°-lordotic cage) with posterior pedicle screw fixation without posterior osteotomy for lumbar degenerative disease were analyzed. The SLA was measured preoperatively (pre), postoperatively (post), and at the last follow-up (last) (at least 12 months) on the midline sagittal CT views. Demographics, surgical, and radiological factors were included. Clinical outcomes (ODI and VAS) were assessed. RESULTS: The mean preoperative SLA at L4/5 increased from 7.1 ± 3.9° preoperatively to 9.8 ± 3.4° postoperatively (P < 0.001) and was maintained as 9.1 ± 3.5° at the last follow-up (P < 0.001). Multiple regression analysis revealed that Pre-SLA, cage position and cage subsidence were predictors of Last-SLA. Small-angle group (Pre-SLA < 6°) showed a stronger capacity in the increase of SLA (Pre-SLA - Post-SLA) and change of SLA (Last-SLA - Pre-SLA) than large-angle group (Pre-SLA ≥ 6°). Anterior cage position is associated with the more increase of SLA than posterior cage position. Cage subsidence led to approximately 3° in decrease of SLA (Last-SLA - Post-SLA). No significant correlation was observed between Last-SLA and clinical outcomes. CONCLUSION: The Last-SLA is strongly associated with the Pre-SLA condition and OLIF has a higher capability to restore SLA in patients with a smaller preoperative SLA. To achieve a greater SLA, surgeons should try to insert cage in the anterior disc space and reduce the occurrence of cage subsidence.