Eur J Orthop Surg Traumatol. 2026 Jul 10;36(1):283. doi: 10.1007/s00590-026-04868-x.
ABSTRACT
OBJECTIVE: To compare the mismatch between the curvature of the spine and the rods between mono-axial and poly-axial screws.
BACKGROUND: In ASD, pre-contoured rods are gaining attraction to help restore sagittal spinal alignment to ultimately improve the patient’s quality of life. However, studies have reported that the curvature of the spine does not correlate with that of the rod. One of the postulated reasons is the usage of poly-axial screws.
METHODS: 75 patients who have undergone ASD surgery between 2012 and 2024 with intra-operatively contoured rods were included. These patients were divided into two groups, based on the axiality of the screws they had being either mono-axial (group M) or poly-axial (group P).
RESULTS: Among all the included patients, there was a minimal difference of 2.5° (p = 0.06) in lordosis at L1S1 and 1.4° (p = 0.291) at L4S1. Looking solely at group M, the difference was 3.7° (p = 0.06) and 0.5° (p = 0.80) at L1S1 and L4S1 lordosis, respectively. In group P, the difference was 1.2° (p = 0.51) and 2.3° (p = 0.24) at L1S1 and L4S1 lordosis, respectively and therefore the curvature of the spinal column and the rod are highly correlated, and their mean mismatch is not statistically significant. Furthermore, there was no difference between group M and group P when comparing the rod-spine mismatch. A linear regression model to predict the mismatch between the spine and rod curvature controlling for the baseline and improvement in spinopelvic parameters revealed that a smaller baseline SS and L4S1, and a smaller L4S1 correction were all predictors of a greater mismatch at L4S1 between the spine and the rod.
CONCLUSION: Following surgery for ASD, mismatch between the spine and rod curvature remains whether mono-axial or poly-axial screws were utilized. Caution should be taken in patients with a hypolordotic lower lumbar lordosis where spine mobilization maneuvers such as osteotomies and interbodies may be necessary, even when pre-contoured rods are employed.
PMID:42429975 | DOI:10.1007/s00590-026-04868-x
