Etiology, Diagnosis, and Treatment of OC(D)

Osteochondrosis (OC) can be defined as a disturbance of the process of endochondral ossification of the articular-epiphyseal complex. The ensuing irregularities of the ossification front lead to thick cartilage plugs, the deeper parts of which may become necrotic because nutrition by diffusion becomes insufficient. In the final stage osteochondral fragments may detach and become loose or semiloose intraarticular bodies or joint mice. In this stage, the term osteochondritis dissecans is used. Osteochondrosis has a high incidence (on average 25%) in most Warmblood breeds and in the racing breeds. Performance is not always affected, but losses to the equine industry are huge, both directly and indirectly through loss of breeding potential and depreciation of market value of affected animals. Osteochondrosis is a multifactorial disease in which genetic influences (accounting for about 25% of the phenotype), nutritional factors, biomechanical influences, and conformation play a role. The disease is very dynamic during the first months of life when lesions may appear and regress spontaneously, indicating that OC has a dualistic character in which the final clinical outcome is determined by the etiologic factors mentioned above and a repair process incited by the lesions. With increasing age, the remodeling rate of the extracellular matrix of the cartilage decreases and after a certain age no substantial change in the radiographic appearance of lesions is seen anymore. In general, no major change can be expected after 1 year of age. For this reason it is advised not to apply the treatment of choice, which is arthroscopic surgery, before this age. Diagnosis of OC has always been based on clinical and radiographic findings, but more advanced imaging techniques, such as magnetic resonance imaging, and the use of biomarkers may play a more important role in the future. Biomarkers may also be used for prevention to identify animals that are at risk for the development of OC. For these animals, environmental conditions may then be manipulated to maximally reduce the risk of OC. Genetic markers may become a tool too, but the complex character of OC and the relatively big influence of environmental factors make a real breakthrough in this area improbable.