Failure to correct the fractional curve in adult spinal deformity surgery is associated with rod fractures

Introduction

Coronal malalignment (CM) remains an understudied and challenging problem in adult spinal deformity (ASD) surgery, and the impact of the lumbosacral fractional curve (LSF) correction on postoperative outcomes remains poorly understood. In patients undergoing ASD surgery with preoperative CM, we sought to determine the impact of LSF correction on: 1) radiographic variables, 2) mechanical complications, and 3) patient-reported outcome measures (PROMs).

Methods

A retrospective cohort study (2011–21) included patients undergoing ASD surgery with preoperative CM (coronal vertical axis, CVA>3 cm), ≥ 5-level fusion, instrumented to ilium, and ≥ 2-year follow-up. Primary exposure variables were preoperative/postoperative LSF. LSF correction was defined as an improvement of ≥ 5°. Postoperative outcomes included mechanical complications, reoperations, and PROMs. Bivariate and multivariable analyses controlling for age, sex, osteoporosis, preoperative maximum Cobb angle and lumbar interbody fusion were performed.

Results

Of 52 patients undergoing ASD surgery with preoperative CM, instrumented to pelvis (68.2 ± 11.1 years, 23.1 % males), mean instrumented levels were 11.8 ± 3.6. Mean LSF preoperatively was 11.1 ± 8.4º vs. 6.9 ± 6.4º postoperatively (p < 0.001), with a mean correction of 4.2 ± 6.2º. Moreover, only 24 (46.2 %) patients had an improved LSF. Similar postoperative CVA or maximum Cobb angle were seen between the groups. Patients with an improved LSF had reduced rate of rod fractures (12.5 % vs. 39.3 %,p = 0.030), with no difference in other mechanical complications, reoperations, or PROMs. The association between LSF correction and reduced rod fractures was confirmed on multivariable logistic regression analysis (OR=0.18, 95 %CI:0.04–0.86,p = 0.031).

Conclusion

In patients undergoing ASD surgery with CM, 54 % patients failed to show a ≥ 5° improvement in LSF. Failure to correct LSF resulted in higher rates of rod fracture, with no impact on other mechanical complications or PROMs. Though the current pilot, preliminary study represents a small sample size in a single institution, meticulous attention to correcting the LSF may mitigate the risk of rod fracture and the potential need for reoperation.