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.
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.
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 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.
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
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.