Predictors of clinical response to intraarticular Hylan injections -- a prospective study using synovial fluid measures, clinical outcomes, and magnetic resonance imaging.

OBJECTIVE

To evaluate synovial fluid (SF) and clinical and imaging predictors of clinical response in patients receiving intraarticular Hylan GF-20 injections.

METHODS

Thirty-two patients with mild to moderate osteoarthritis (OA) of the knee [OsteoArthritis Research Society International (OARSI) grades I-II] were followed over 6 months. SF and clinical and radiographic measures were assessed. Patella and tibial cartilage volume and cartilage defect scores were measured at baseline and 6 months using magnetic resonance imaging (MRI). The primary outcome measure was the relationship between SF measures and clinical response as defined by the OARSI-Outcome Measures in Rheumatology Clinical Trials responder criteria for OA ("High improvement" >or= 50% improvement in pain or function; absolute change >or= 20 NU on Western Ontario and McMaster University Osteoarthritis Index questionnaire). Secondary outcomes included MRI outcomes (change in cartilage volume and cartilage defect scores).

RESULTS

Fifteen patients achieved "High improvement." High baseline SF hyaluronic acid (HA) concentration was a statistically significant predictor of clinical response with odds ratio (OR) 6.04 (p < 0.02). HA concentration was divided into tertiles and fitted to a univariate regression model against clinical response. A baseline HA concentration value of > 2 mg/ml provided the greatest tradeoff between sensitivity and specificity with values of 60% and 77%, respectively, a likelihood ratio of 2.55, and OR of 4.88. Baseline clinical and radiological measures did not predict clinical response in this cohort with mild to moderate OA. Nineteen subjects had MRI at both timepoints. No change was noted in cartilage volumes or cartilage defect scores over 6 months. There was no association between baseline HA concentration and baseline cartilage volume.

CONCLUSION

Baseline SF HA concentration predicts clinical response in patients receiving intraarticular Hylan. This has implications for the selection of patients who are likely to respond to this therapy.