In Reply Dr Luijsterburg and colleagues question whether factors such as persistence of inflammation or severity of pain might have modified the effect on cartilage of the repeated intra-articular corticosteroid injections. The presence of synovitis based on ultrasonographic criteria was required for eligibility in our study so, presumably, all participants had this to some degree. Nevertheless, these characteristics could vary over time and we did perform ultrasonography at each visit. However, these data have not yet been analyzed. The influence of these disease characteristics on the study outcome as time-varying covariates certainly merit a future exploratory analysis.