Risk factors for equine osteochondrosis

A combination of growth, nutrition and inheritance likely come into play.
Aug 01, 2012

Osteochondrosis is a manifestation of developmental orthopedic disease widely recognized in young horses across many breeds. This condition is of particular interest because of its potential to cause joint effusion and lameness in horses preparing for yearling sales or entering training.

Osteochondrosis affects many horses, with prevalence estimates greater than 60 percent in some radiographic surveys.1 Although surgical treatment is often curative, severe or untreated lesions can lead to long-term debilitative consequences.

Despite its great impact on the horse industry, the risk factors contributing to osteochondrosis development have been imperfectly understood. But as new findings from researchers emerge, previous theories are being revised, and, we hope, a more definitive picture of its etiology, genetics, metabolic profile and treatment are on the horizon.

Other conditions fall within the developmental orthopedic disease constellation, including angular limb deformities ("crooked-legged foals"), physitis, subchondral bone cysts, cuboidal bone malformation (collapsed or crushed carpal and tarsal bones), cervical vertebral malformation (wobbler syndrome) and flexural limb deformity.2 However, these conditions are quite disparate, and while some risk factors may be shared among them, their pathophysiologies are distinct from that of osteochondrosis.

About osteochondrosis

Osteochondrosis is characterized by a failure of normal endochondral ossification, the process by which a cartilage template becomes bone in the limbs of a growing animal. It is characterized by abnormal cartilage within a joint that may be thickened, soft or collapsed, or it may be separated entirely from the underlying bone. In the latter case, the condition is commonly referred to as osteochondritis dissecans (OCD).3 Osteochondrosis and OCD thus represent the same pathologic process but are at different points along the spectrum of disease. The terms often are used interchangeably.

Figure 1: A typical osteochondritis dissecans lesion of the distal intermediate ridge of the tibia in a young horse. The arrow points to the osteochondral fragment.
The disease is most commonly diagnosed in survey radiographs of yearling horses, often before clinical signs have become apparent. It is characterized by irregularities or roughening of the joint surface or by the presence of an osteochondral fragment partially or completely separated from the parent bone (Figures 1 & 2).4

Figure 2: An osteochondritis dissecans lesion of the lateral trochlear ridge of the femur. The arrow indicates multiple osteochondral fragments at this location. This lesion is extensive and would be considered severe.
While osteochondrosis can occur in nearly any joint, certain areas of predilection include the stifle (lateral trochlear ridge of the femur), tarsus (distal intermediate ridge of the tibia, lateral or medial trochlear ridges of the talus, medial malleolus) and fetlock (distal dorsal midsagittal ridge of the third metacarpus/metatarsus).4