Pelvic Fixation and Spinopelvic Realignment Accelerate Hip Osteoarthritis Following Long-Segment Fusion: A Five-Year Retrospective Study.

Abstract

Spinopelvic fixation is commonly used to reduce the risk of distal adjacent segment disease in adult spinal deformity surgery. However, it may impose increased stress on the hip joint, potentially leading to hip osteoarthritis (OA). The concept of adjacent joint disease has been proposed to describe hip joint degeneration due to compensatory overload following rigid spinopelvic fixation, but longitudinal data supporting this are lacking. To investigate the prevalence and risk factors for the progression of hip OA after spinal fusion surgery, and to evaluate adjacent joint disease as a distinct pathological entity. Retrospective single-center cohort study with 5-year follow-up. A total of 290 patients (580 hips) who underwent spinal fusion surgery between 2011 and 2018, and met inclusion/exclusion criteria. Radiographic hip OA progression was defined by an increase in Kellgren-Lawrence (KL) grade at 5 years postoperatively. Spinopelvic parameters and hip morphology were also assessed. Radiographs were evaluated preoperatively, and at 1 month and 5 years postoperatively. Patients were divided based on the presence or absence of OA progression. Logistic regression was used to identify independent risk factors. A post hoc exploratory subgroup analysis was performed in patients with long fusion (≥6 levels) and baseline KL grade 0-1. In the full cohort, OA progression was observed in 13.8%, and new-onset OA in 10.8%. Risk factors for progression in the overall cohort included female sex (OR 3.95, p=0.0048), pelvic incidence (PI) (OR 1.04, p=0.0012), sacral slope (SS) correction (OR 1.04, p=0.018), pelvic fixation (OR 5.04, p=0.0016), and baseline KL grade (OR 2.49, p=0.00001). In the long fusion subgroup (n=122; 244 hips), new-onset OA was observed in 21.7%. Within this subgroup, pelvic fixation (OR: 8.48, p=0.0069), larger SS correction (OR: 1.04, p=0.027), and higher PI (OR: 1.05, p=0.0017) remained significant predictors of hip OA. Spinopelvic fixation was associated with an increased risk of hip OA progression, especially in female patients and those with high PI or large SS correction. These findings support adjacent joint disease as a clinically relevant entity and suggest the need for surgical caution and postoperative strategies to protect the hip joint in vulnerable individuals.