Procedure rates for knee and hip replacement in people aged 40-64 in Massachusetts and comparison states, 2004-10. Because of seasonal trends in procedure use, we obtained seasonally adjusted procedure rate for each quarter, defined as moving average of four quarters. We compared time trend in procedure rate before reform between Massachusetts and comparison states with log linear time series regression model. Results indicated that rates in Massachusetts after reform rose faster among black and Hispanic people (P<0.001) and residents of low income areas (P<0.01) but at similar rates among white people and residents of high income areas