Different Risk Factors of Rod Fracture between L5-S1 and ≥ L4-5 Levels in Adult Spinal Deformity Surgery.

Background: Given the different biomechanical properties and surgical techniques between L5-S1 and at ≥ L4-5 levels, different factors might contribute to rod fracture (RF) development between the L5-S1 and ≥ L4-5 levels. Recognizing segment-specific risk factors can be helpful when planning surgery. Therefore, this study aims to analyze the risk factors for RF separately for L5-S1 and ≥ L4-5 levels after adult spinal deformity surgery. Methods: This study analyzed consecutive patients who underwent ≥ 5-level fusion including the sacrum or pelvis and were followed up for ≥ 2 years. RF was assessed at the segment level between the L1-2 and L5-S1 levels. Multivariate logistic regression analyses were performed to identify independent risk factors for RF separately for L5-S1 and ≥ L4-5 levels. Results: A total of 318 patients were included in the study (mean age, 69.3 years; female, 88.4%; mean fusion length, 7.3 levels). A total of 1,329 segments were evaluated (247 for L5-S1 and 1,082 for ≥ L4-5 levels). The mean follow-up duration was 47.4 months. Multivariate analysis revealed that increased fusion length (odds ratio [OR], 1.251; Conclusions: This study demonstrated that the risk factors for RF are different between L5-S1 and ≥ L4-5 levels. Increased fusion length and poor postoperative correction of PT were significant risk factors for RF at the L5-S1 level, while non-use of teriparatide, ACR, and PF, performance of PSO, and dual rod construct significantly increased the risk of RF at ≥ L4-5 levels. Understanding the differing risk factors can help establish suitable preventive strategies tailored to each patient.