Hip osteoarthritis (OA) leads to approximately 200，000 annual total hip replacements in the United States. As magnetic resonance imaging (MRI) is sensitive to early, subtle tissue abnormalities, this study used MRI to assess the response of hip OA to hyaluronic acid (HA) injections, using the hip MRI inflammatory scoring system (HIMRISS)．

Subjects were 60 adults with symptomatic hip OA, with an inadequate response to NSAIDs or oral analgesics, each of whom had undergone a pelvic MRI before a HA hip injection. Pain, stiffness, and function were assessed with the Western Ontario and McMaster (WOMAC) questionnaire with global health assessed using a Visual Analogic Scale (VAS) at baseline and at three months post-HA injection. Inflammation was assessed with the Hip MRI Inflammatory Scoring System (HIMRISS), before and after the injection. A positive response to the injections was defined as an improvement of WOMAC pain and/or WOMAC function scores by more than 50% (WOMAC50%)．

At baseline, WOMAC function scores were found to be significantly related to HIMRISS synovitis scores (P＝ 0.03). At three months, 45.5% of the patients achieved a WOMAC50%. No baseline WOMAC values or clinical parameters were associated with a WOMAC 50% response at three months. A multivariate analysis revealed that patients who had low HIMRISS-bone marrow lesion femoral scores and low HIMRISS total scores were more likely to achieve a WOMAC50% response to HA (P＝0.02 and P＝0.016, respectively)．

This study suggests that inflammation, as measured by magnetic resonance imaging, may be useful in predicting the response to hyaluronic acid injection in patients with symptomatic hip osteoarthritis.