Figure 1

When contemplating on the use of animal models of articular cartilage defects, the important difference between focal, non-OA cartilage defects and OA lesions needs to be kept in mind. Focal defects are usually surrounded by a normal cartilaginous tissue (left side, shown is a lesion caused by osteochondritis dissecans of the human knee). The often ill-defined OA lesions are often larger in size and may affect the entire joint (right side, shown is a case of tricompartimental osteoarthritis of the human knee).