Experiment design indicating analytical time points and methods for each experimental group. Forty 16-week-old male Wistar rats were given three papain intra-articular injections (P.I.) and forced to run 15 km on a motorized treadmill. Animals were divided into two different groups: an untreated osteoarthritis (OA) group (n = 20) and a group treated with intra-articular triamcinolone acetonide (TA) injections (n = 20). TA-treated animals were treated with weekly intra-articular TA injections (100 μg/injection), indicated with asterisks in the scheme. During the experiment, three longitudinal micro–computed tomographic (microCT) scans were made to measure subchondral bone changes. At 6 and 12 weeks, a full-analysis sequence was done in ten animals per group, consisting of in vivo determination of activated macrophages using single-photon emission computed tomography/computed tomography and ex vivo cartilage analysis with equilibrium partitioning of an ionic contrast agent using micro-CT and histology.