Resident Physician Barrow Neurological Institute Phoenix, Arizona, United States
Introduction: Patients with lumbar degenerative disease adopt compensatory mechanisms such as proximal lumbar hyperlordosis and pelvic retroversion to counteract loss of lordosis and maintain sagittal balance. Anterior lumbar interbody fusion (ALIF) at the L5-S1 disc space has been shown to significantly improve local segmental lordosis, overall lumbar lordosis, and sagittal balance. We investigated the reciprocal changes in lumbar lordosis and spinopelvic alignment following L5-S1 ALIF.
Methods: We retrospectively identified patients without prior thoracolumbar fusion who underwent L5-S1 ALIF. Pre-operative, immediate post-operative, and delayed post-operative x-rays were evaluated for: 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. On immediate post-operative x-rays, patients were found to have 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 at L5-S1 and decreased significantly at L2-3, L3-4, and L4-5. LDI increased from 72.6 to 81.4 (p < 0.001). These findings persisted on delayed x-rays. PTK, DTK, and CL did not change significantly.
Conclusion : L5-S1 ALIF results in a significant increase in segmental lordosis at L5-S1. This is accompanied by anteversion of the pelvis and reciprocal decreases in segmental lordosis at the proximal lumbar levels, leading to a redistribution of lordosis to the distal lumbar spine. These changes likely represent a reversal of compensatory mechanisms that offset loss of distal lumbar lordosis and suggest an overall “relaxation” of the spinopelvic alignment following L5-S1 ALIF.
