Reduction of passive extension and radiographic evidence of degenerative knee joint diseases in cage-raised and free-ranging aged rhesus monkeys (Macaca mulatta).

The knee joints of aged (greater than or equal to 15 years) rhesus macaques raised and maintained in individual cages were compared with those of formerly free-ranging monkeys using radiographs and measures of passive joint flexion and extension. Free-ranging monkeys had a significantly higher prevalence (p less than 0.01) and severity (p less than 0.0003) of degenerative joint diseases (osteoarthritis and/or pseudogout) based on radiographic findings and significantly (p less than 0.02) more restricted passive knee joint extension than caged animals of the same age.