To induce inflammatory injury, rats were anesthetized with 2% to 5% isoflurane mixed with 95% O2/5% CO2 and placed in the left lateral recumbent position. With the right foot in neutral position, the junction of the tibia and fibula just superior to the talus was identified. At this location, a 0.5-inch, 27-gauge needle was advanced in a posterior medial direction through the skin and subcutaneous tissue and into the joint capsule. If resistance was encountered, the ankle was dorsiflexed while the needle was advanced into the joint space. After the needle entered the joint space, 0.05 mL of 0.75%, 1.5%, or 3% carrageenan (non-gelling, mixture of κ and λ carrageenans, catalog #C1867, Sigma Aldrich) in 0.9% saline (pH 7.4) or saline alone was injected. In one of the experiments, to create a bilateral injury, the procedure was repeated for the left foot. To standardize intra-articular injections, each investigator was trained to find the articular capsule and perform the injection in less than 30 seconds. The injection site was monitored for bleeding and regurgitation of injection fluid. Intra-articular injections were performed between 6 am and 8 am.