Differential Effects of Degenerative Spine Disease and Spinal Fusion on the Risk and Progression of Hip Osteoarthritis: A Nationwide Time-Varying Cohort Study.

BACKGROUND: The hip and lumbar spine function as an integrated biomechanical unit, and spinal pathology may influence hip joint loading. However, population-level evidence regarding whether lumbar degeneration or spinal fusion increases the risk of hip osteoarthritis (HOA) remains limited. The purpose of this study was to investigate whether degenerative spine disease and spinal fusion are associated with the incidence and progression of HOA in a nationwide cohort.

METHODS: We conducted a retrospective cohort study using the nationwide population-based database linked to the national health screening database, including individuals aged ≥ 50 years from 2010 to 2022. Spinal pathology was modeled as a time-varying exposure and classified into three groups: control, degenerative spine disease (SPINE_DX), and spinal fusion (SPINE_FUSION). Incident HOA was assessed using time-varying Cox proportional-hazards models. Among individuals who developed HOA, progression to total hip arthroplasty (THA) was evaluated using Kaplan-Meier methods and multivariable Cox models adjusting for demographic, clinical, and lifestyle factors. Inverse probability of treatment weighting (IPTW) was performed as a sensitivity analysis.

RESULTS: Among 1,620,585 individuals, HOA incidence rates were 12.31, 20.91, and 17.44 per 1,000 person-years in the control, SPINE_DX, and SPINE_FUSION groups, respectively. Compared with controls, both SPINE_DX (HR [hazard ratio], 1.66; 95% CI [confidence interval], 1.64 to 1.68) and SPINE_FUSION (HR, 1.22; 95% CI, 1.19 to 1.25) were independently associated with increased risk of incident HOA; these associations remained consistent after IPTW adjustment. Among patients who developed HOA, progression to THA was highest in the SPINE_FUSION group. Both SPINE_FUSION (HR, 2.32; 95% CI, 2.06 to 2.62) and SPINE_DX (HR, 1.51; 95% CI, 1.41 to 1.62) were associated with increased THA risk.

CONCLUSIONS: Spinal pathology was significantly associated with both the development and progression of HOA. Degenerative spine disease was strongly associated with increased HOA incidence, whereas SPINE_FUSION was associated with a higher risk of progression to end-stage disease requiring THA.