Functional and perceived response to intra-articular hyaluronan injection in patients with knee osteoarthritis: persistence of treatment effects over 5 months

Intra-articular injections of hyaluronic acid are currently indicated as a symptom-modifying treatment for knee osteoarthritis to palliate symptoms and improve function. A series of three to five weekly injections are typically delivered once per week and a period of at least 6 months must pass between consecutive injection series. Little is known about why some patients do not respond to this treatment or about its effects on outcome measures recorded during functional activities. In addition to investigating short-term self-report and measured functional changes, the purpose of this study was to evaluate the persistence of treatment effects over the typical time interval between consecutive treatment series. According to the a priori definition for response to treatment, over two-thirds of patients experienced improved knee function during the typical period between series of intra-articular injection of hyaluronic acid while a one-third did not demonstrate a change in self-report scores. Differences in response were similarly seen between groups in functional tests. Many had immediate benefits and although some did not retain their gains, others experienced a delayed response in the following months. Knee flexion range of motion was related to self-report and tested function, and improvements in range of motion were associated with concurrent improvements in other functional measures across the testing period. A short functional test and knee-specific questionnaire may provide an index that provides an indication as to whether or not a particular patient is likely to respond to hyaluronan injections. Such information may provide valuable input when decisions are made regarding which treatment option is recommended to individuals with knee osteoarthritis.