Patients Undergoing L4-S1 Decompression and Fusion Surgery: Are We Giving Them Enough Lordosis or Setting Them up for Future Surgery?

Introduction: Adequate L4-S1 lordosis is critical to maintain a harmonious spinal shape. In a pilot study of patients undergoing primary, degenerative L4-S1 decompression/fusion, we sought to: 1) describe changes in L4-S1 and L1-S1 lordosis, 2) report the change in lordosis apex with respect to Roussouly type, and 3) determine the impact of lordosis and apex changes on reoperation.

Methods: A single-institution, retrospective cohort study was conducted of patients undergoing primary, degenerative L4-S1 decompression/fusion from 2016-21. Exposure variables included preoperative L4-S1 and L1-S1 lordosis, lordosis apex, and Roussouly type. A “False Type 2” was defined as a pelvic incidence (PI)>50° with a pelvic tilt (PT) >50% of the PI. A change in lordosis of 5º was deemed significant to be improved/worsened. The primary outcomes were postoperative L4-S1 and L1-S1 lordosis. Secondary outcomes were reoperation and postoperative lordosis apex. Bivariate statistics were performed (α≤0.05).

Results: 149 patients were included with a mean follow-up of 8.4±3.6 years. Mean age was 59.7±13.3 and 71 (47.7%) were males. L4-S1: Mean preoperative/postoperative L4-S1 lordosis was 30.6±12.4º vs. 28.9±10.7º (p=0.081) with 34.2% showing increased lordosis, 52.1% decreased and 13.7% unchanged ( < 5° change from preoperative). L1-S1: Mean preoperative/ postoperative L1-S1 lordosis was 51.5±15.2º vs. 49.9±13.9º (p=0.174) with 25.6% showing increased lordosis, 41.0% decreased and 33.3% unchanged. The number of False Type II patients increased from 24.2% to 32.2% (p=0.050). Reoperation: 26 (17.4%) patients underwent reoperation after a mean of 21.9±28.5 months. Patients with worsened L1-S1 lordosis had a non-significant higher reoperation rate (20.8% vs. 14.7%,p=0.390). In patients with a misplaced apex postoperatively, 8/48 (14.3%) underwent reoperation compared to 15/68 (18.1%) (p=0.556).

Conclusion : In elective L4-S1 decompression/fusion, 66% experienced worsening or showed no improvement in L4-S1 and 74% in L1-S1 lordosis. The number of False Type II patients significantly increased postoperatively (24% to 32%). A higher but non-significant rate of reoperation was seen in patients with worsened L1-S1 lordosis. The results of this pilot study suggest that little attention is paid to lordosis maintenance/correction in primary, degenerative L4-S1 decompression/fusion surgery.