Too much of a good thing? Association between high preoperative L4-S1 lordosis and outcomes after adult spinal deformity surgery.

Abstract

The authors sought to determine the impact of preoperative and postoperative L4-S1 lordosis on 1) mechanical complications, 2) reoperations, and 3) patient-reported outcomes (PROs) using PRO metrics in patients undergoing adult spinal deformity (ASD) surgery. A retrospective cohort study (2011-2021) was performed for patients undergoing ASD surgery with ≥ 5-level fusion, instrumentation to the ilium, and ≥ 2-year follow-up. Primary exposures were preoperative/postoperative L4-S1 lordosis trichotomized into < 35°, 35°-45°, and > 45°. Primary outcomes were mechanical complications and reoperations. Secondary outcomes included PROs. Multivariable analysis controlled for age, BMI, T-score, pelvic incidence, and postoperative alignment. In 153 patients (mean age 69.0 ± 11.3 years; 75.8% female) undergoing ASD surgery, the mean L4-S1 lordosis was similar in the preoperative and postoperative states (28.1° ± 15.2° vs 28.1° ± 12.5°, p = 0.993). L4-S1 lordosis distribution changed significantly from preoperatively to postoperatively: hypolordosis < 35°, from 66.0% to 69.9%; normal lordosis 35°-45°, from 19.0% to 22.2%, and hyperlordosis > 45°, from 15.0% to 7.8%. In patients with preoperative L4-S1 hyperlordosis, 3 (13.0%) had further increase in lordosis while 20 (87.0%) had a decrease. Overall mechanical complications were similar between the groups based on preoperative (61.4% vs 51.7% vs 82.6%, p = 0.065) and postoperative (65.4% vs 50.0% vs 75.0%, p = 0.177) L4-S1 lordosis; however, when controlling for confounders, preoperative hyperlordosis independently increased the risk of mechanical complications (OR 5.34, 95% CI 1.02-27.89; p = 0.047) compared with preoperative hypolordosis. A higher preoperative L4-S1 lordosis (> 45°) was associated with spinopelvic complications (32.7% vs 20.7% vs 56.5%, p = 0.023), spinopelvic complications requiring reoperation (21.8% vs 10.3% vs 39.1%, p = 0.045), and rod fractures (23.8% vs 13.8% vs 52.2%, p = 0.005). There was no significant association between postoperative L4-S1 lordosis and individual mechanical complications (p > 0.05). No significant difference was found between preoperative or postoperative L4-S1 and PROs (p > 0.05). In the current single-center study over 10 years, most patients undergoing ASD surgery presented with L4-S1 lordosis < 35°, with no significant change from the preoperative to postoperative condition. Interestingly, high preoperative L4-S1 lordosis (> 45°) was independently associated with increased mechanical complications, rod fracture/pseudarthrosis, and spinopelvic complications. Moreover, half of the patients with L4-S1 hyperlordosis lost lordosis and were downgraded to the normal lordosis group (35°-45°). Complications were lowest in the preoperative group with L4-S1 lordosis of 35°-45°. Special attention should be given to patients presenting with a high L4-S1 lordosis, as they are likely compensating for upper lumbar and thoracic kyphosis and are more likely to lose L4-S1 lordosis during surgery, which could place them at a higher risk for certain mechanical complications.