Hyaluronic acid therapy in hip osteoarthritis: differential efficacy in secondary osteoarthritis due to inflammatory rheumatic diseases vs. primary osteoarthritis—a step toward phenotyping osteoarthritis

Objective The hip joint is frequently affected by osteoarthritis (OA) and is a leading cause of disability. This study aims to assess the long-term efficacy of ultrasound-guided intra-articular viscosupplementation for pain relief in patients with hip osteoarthritis secondary to rheumatic diseases compared to primary OA. Methods This single-center, retrospective, observational cohort study included patients with hip OA who received intra-articular injections of hyaluronic acid (HA) (Hylan G-F 20). Fisher's exact test was applied to evaluate baseline variables, with 95% confidence intervals (CI) calculated for differences in mean outcomes. Results A total of 55 patients with primary hip OA (POA) and 16 patients with secondary hip OA (SOA) were included. The mean observation period was 31.3 months (±29.9), with an average of 5 intra-articular injections administered. Both groups showed a positive response to HA injections, with the POA group demonstrating a mean Visual Analog Scale (VAS) pain reduction of 2.97 (95% CI 2.38–3.56), compared to 1.28 (95% CI 0.18–2.37) in the SOA group. At the end of follow-up, pain reduction was less pronounced in the SOA group, which showed higher residual VAS pain scores compared to the POA group ( p = 0.029). Conclusions This study highlights that HA injections significantly reduce pain in both primary and secondary hip osteoarthritis. However, patients with primary OA experienced greater pain relief, as evidenced by a more substantial reduction in VAS scores compared to those with secondary OA.