Resident Physician Barrow Neurological Institute Phoenix, Arizona, United States
Introduction: Anterior lumbar interbody fusion (ALIF) at the L5-S1 disc space is a technique which has been shown to significantly improve local segmental lordosis, lumbar lordosis, and sagittal balance. We investigated whether L5-S1 ALIF results in reciprocal changes in sagittal alignment in the remainder of the spine.
Methods: We retrospectively identified patients with no prior thoracolumbar fusion who underwent L5-S1 ALIF. Pre-operative, immediate post-operative, and delayed post-operative x-rays were analyzed to evaluate for changes in: pelvic tilt (PT), sacral slope (SS), proximal (L1-L4) lumbar lordosis (PLL), distal (L4-S1) lumbar lordosis (DLL), overall lumbar lordosis (LL), segmental lordosis at each level of the lumbar spine, pelvic incidence-lumbar lordosis mismatch (PI-LL), proximal (T2-5) thoracic kyphosis (PTK), distal (T5-12) thoracic kyphosis (DTK), cervical lordosis (CL), and sagittal vertical axis (SVA).
Results: 48 patients were identified for inclusion. Immediate post-operative x-rays were obtained an average of 17 days (SD: 20) after surgery; delayed x-rays were obtained an average of 184 days (SD: 82) after surgery. Following surgery, patients were found to have significantly decreased PT (17.5 vs. 15.6, p = 0.003), increased SS (39.5 vs. 36.3, p < 0.001), increased LL (55.4 vs. 51.6, p = 0.001), increased DLL (43.2 vs. 35.8, p < 0.001), and decreased PLL (11.9 vs. 16.0, p < 0.001). Segmental lordosis increased significantly at L5-S1 and decreased significantly at L2-3, L3-4, and L4-5. The overall distribution of lordosis shifted to the distal lumbar spine, with the LDI increasing to 81.4 from 72.6 (p < 0.001). PTK, DTK, and CL did not change significantly. These findings persisted on delayed x-rays. Mixed effects testing did not reveal any effect of high vs. low PI, pre-operative PI-LL mismatch, or posterior fixation.
Conclusion : L5-S1 ALIF results in a significant increase in segmental lordosis at L5-S1. This change is accompanied by anteversion of the pelvis and a reciprocal loss of segmental lordosis in the proximal lumbar spine, leading to a redistribution of lordosis to the distal lumbar spine. These changes likely represent a reversal of compensatory mechanisms that patients adopt to offset loss of distal lumbar lordosis and suggest an overall “relaxation” of the spine following L5-S1 ALIF.
