Radiological scoring of osteoarthritis progression in STR/ORT mice

The progressive changes observed in the knee and ankle joints of male STR/ORT mice, which spontaneously develop osteoarthritis (OA), were quantified by a radiological scoring system. The knee scores for males increased with age whereas those for females plateaued from 5 months. Comparison of scores for the knee and ankle joints showed that the male knee scores increased directly with age but were not significantly different from female scores until 7 months whereas the male ankle scores increased dramatically at 5-6 months and plateaued thereafter. In addition, correlations between patellar and calcaneal displacement showed that they rarely occurred together in the same limb, suggesting that knee and ankle OA are almost independent events. Although an association between high knee scores and patellar displacement was noted, even at 11 months of age not all mice with OA had displaced patellae, demonstrating that patellar displacement cannot be a primary event. Remarkably, summing the scores of all calcified structures in the ankle and knee joints revealed that the scores became significantly greater for males than for females by 3 months of age. It is considered that calcification is an earlier event than cartilage erosion and that OA in male STR mice may result from calcification placing abnormal stresses on joints.