Osteoarthritis is for the birds.

The purpose of this study was to assess birds as a potential model for osteoarthritis. Compromised by confounding factors, it has not been possible to clearly delineate causation in humans. Nonhuman mammals manifest osteoarthritis in the natural state too rarely for comparative study. Artificial environments (of captive animals) are associated with higher frequencies, but are still inadequate for comparative study, and surgical and chemical models provide only limited insight. As frequency of pathology (except trauma-related) in birds has not been systematically examined across species lines, several families were selected for examination. Skeletal collections of major museums were examined for presence of osteophytes in hawks and pigeons. Three percent of 2,243 free-ranging hawks and 9.8% of 2,718 pigeons had osteoarthritis, all localized to the ankle. The bird ankle morphologically resembles the human knee. Frequency in pigeons was significantly greater than in hawks (chi (2)=86.48, p<0.00001), but was no difference in frequency between wild caught and captive birds (chi (2)=1.06). While misconceptions have plagued past perspectives, it turns out that the most common form of arthritis in humans (osteoarthritis) is actually for, or at least, is common in the class Aves (birds). The frequency of osteoarthritis and cacophony of bird morphologies and behaviors provides an opportunity to start to understand such causation.