How changes in segmental lordosis impact L1-pelvic-angle after adult spinal deformity surgery: Which lumbar levels matter most?
PURPOSE Achieving target L1-pelvic-angle (L1PA) is heavily influenced by segmental lordosis changes during adult spinal deformity (ASD) surgery. Understanding the effect of changing each lordotic segmental level on L1PA will aid in preoperative planning and intraoperative alignment assessment in ASD. In patients undergoing ASD surgery, we aimed to evaluate the impact of segmental lordosis changes on postoperative L1PA. METHODS A retrospective cohort study (2009-24) was performed for ASD surgery patients. Inclusion criteria were: ≥5-level fusion and sagittal/coronal deformity. Primary exposure variable was change in segmental lordosis at each lumbar level. Primary outcome was the change in L1PA. Multivariable regression controlling for preoperative and change in segmental lordosis at each level was performed. RESULTS Of 180 patients (mean age:59 ± 19 years, 32% males), mean preoperative/postoperative L1PA were 14 ± 11° and 12 ± 9°, respectively. L1/2: Mean change in lordosis was 7 ± 6°. For a 10° increase in L1/2 lordosis, the L1PA increased by 0.33° (β = -0.03, p = 0.684). L2/3: Mean change in lordosis was 8 ± 8°. For a 10° increase in L2/3 lordosis, the L1PA decreased by 0.01° (β = 0.00, p = 0.991). L3/4: Mean change in lordosis was 9 ± 8°. For a 10° increase in L3/4 lordosis, the L1PA decreased by 1.05° (β = 0.10, p = 0.086). L4/5: Mean change in lordosis was 9 ± 8°. For a 10° increase in L4/5 lordosis, the L1PA decreased by 1.78° (β = 0.18, p = 0.001). L5/S1: Mean change in lordosis was 11 ± 12°. For a 10° increase in L5/S1 lordosis, the L1PA decreased by 1.41° (β = 0.14, p = 0.002). CONCLUSION Changes in segmental lordosis at the L4/5 level were associated with greatest decrease in L1PA following ASD surgery, followed by L5/S1 and L3/4. Changes at L5/S1 influenced the L1PA slightly less than L4/5. These findings suggest that focusing on adding lordosis at the L4/5 and L5/S1 level will result in the greatest improvement in L1PA.