To examine the effect of MIA, we tested both treatments (0.1 mg MIA and PBS alone) in the same animal, with each knee receiving a different treatment, because we wished to exclude inter-animal variability. This matched analyses enabled to examine the effect of MIA in more strict manner. However, the use of the contralateral knee as a control is potentially problematic. Gait abnormalities could lead to abnormal stresses on the saline-injected contralateral knee which therefore might not be normal.