Equine Models of Articular Cartilage Repair

Articular cartilage injuries of the knee and ankle are common, and a number of different methods have been developed in an attempt to improve their repair. Clinically, there are 2 distinct aims of cartilage repair: 1) restoration of joint function and 2) prevention or at least delay of the onset of osteoarthritis. These goals can potentially be achieved through replacement of damaged or lost articular cartilage with tissue capable of functioning under normal physiological environments for an extended period, but limitations of the final repair product have long been recognized and still exist today. Screening of potential procedures for human clinical use is done by preclinical studies using animal models. This article reviews equine chondral defect models that have been recently recognized to have specific advantages for translation into human articular cartilage regeneration. Defect models in the femoropatellar, femorotibial, and tibiotalar joints have been developed. The horse provides the closest approximation to humans in terms of articular cartilage and subchondral bone thickness, and it is possible to selectively leave the entire calcified cartilage layer or completely remove it. The defect on the equine medial femoral condyle emulates medial femoral condylar lesions in humans. Other advantages of the equine model include an ability to use an arthroscope to create lesions and perform second-look arthroscopies, the large lesion size allowing for more tissue for evaluation, and the ability to have controlled exercise and test the ability of the repair to cope with athletic exercise as well as institute rehabilitation regimens.