Early Compensatory Segmental Angle Changes at L3-4 and L4-5 Following a L5-S1 Interbody Fusion for a Grade 1 Spondylolisthesis.

STUDY DESIGN:Retrospective study included patients who underwent a L5-S1 ALIF or TLIF with posterior pedicle screw instrumentation for grade 1 spondylolisthesis 2018-2022. OBJECTIVE:To compare early reciprocal changes at the L3-4 and L4-5 adjacent levels six months after anterior (ALIF) or transforaminal (TLIF) lumbar interbody fusion at L5-S1. BACKGROUND:Degenerative and chronic isthmic spondylolistheses often result in decreased segmental lordosis at L5-S1. This can lead to lordotic overcompensation at adjacent levels to maintain spinopelvic balance. However, the fate of adjacent angles following interbody fusion is not well understood. METHODS:Preoperative and 6-month postoperative measurements of segmental lordosis (L3-4, L4-5, and L5-S1), lumbar lordosis, and pelvic incidence were obtained from sagittal standing radiographs. Preliminary t-tests were performed for descriptive purposes, and multiple regression was used for hypothesis testing. RESULTS:Ninety-eight patients met the inclusion criteria (50 ALIF and 48 TLIF). A greater amount of lordosis achieved at L5-S1 was significantly associated with a greater reduction of segmental lordosis at L4-5 (r=-0.65, P<.001) or L3-4 (r=-0.46, P<.001) (Fig. 3A). A greater preoperative PI was associated with a greater reduction of segmental lordosis at L4-L5 (r=-0.42, P<.001) and at L3-L4 (r=-0.44, P<.001). CONCLUSION:At six months following a lumbar interbody fusion at L5-S1, greater compensatory changes with lordosis reduction are observed at the supra-adjacent L4-5 and L3-4 levels in patients achieving greater L5-S1 segmental lordosis. Additionally, preoperative pelvic incidence (PI) played a role in influencing lordotic correction.