Investigating sagittal spinal alignment, low back pain, and clinical outcomes after total hip arthroplasty for lumbar hyperlordosis: a retrospective study

Introduction: Hip-spine syndrome, wherein flexion deformity of the hip might exaggerate normal lumbar lordosis (LL), was first described in 1983. It could result in subluxation of the posterior facets and cause low back pain (LBP). However, the clinical outcomes of total hip arthroplasty (THA) and spinal alignment changes in patients with lumbar hyperlordosis (hyper LL) remain unknown. We aimed to clarify the proportion of patients with hyper LL before THA and compare pre- and post-operative sagittal spinal alignment, LBP, and clinical outcomes between patients with hyper LL and those with normal LL.

Materials and methods: We investigated 278 patients who underwent primary THA between December 2015 and December 2019. Spine radiographs in the standing position were examined preoperatively and 1 year postoperatively. Patients with hyper LL were defined as having a pelvic incidence (PI) minus LL of < - 9° preoperatively. The control group included age- and sex-matched patients with normal LL, defined by a PI minus LL of - 9° to 9°. Clinical outcomes were evaluated using the visual analogue scale (VAS) for LBP, Harris hip score (HHS), Oxford hip score (OHS), and University of California, Los Angeles (UCLA) activity score.

Results: Thirty-eight patients (13.7%) had hyper LL, and they exhibited a lower pelvic tilt, lower sagittal vertical axis, and greater sigmoid curvature than did the controls. Evaluation of changes in the spinal alignment after surgery showed that the pelvis tilted more posteriorly, and LL decreased more in the hyper LL group than in the control group. Pre- and post-operative VAS for LBP, HHS, OHS, and UCLA activity scores were not significantly different between the two groups.

Conclusion: Hyper LL in patients with hip osteoarthritis had no adverse effects on LBP and the clinical outcomes of THA. Hyper LL may partially result from a flexible and adaptable lumbo-pelvic structure.