Equine Osteochondrosis Terminology Revamped

If you’ve ever been confused by the differences between osteochondrosis and osteochondritis dissecans, or wondered whether these are the same as developmental orthopedic disease (DOD) or just examples of it, you’re not alone. For decades, diseases of the bones, joints, and cartilage in young horses have sparked many word-slinging debates among researchers.

But as science leads to better understanding of what the various lesions in growing horse skeletons are, and how they get there, researchers are finally coming up with clearer terminology for them. French equine orthopedics researcher Jean-Marie Denoix, DVM, PhD, professor and director of the Centre d'Imagerie et de Recherche sur les Affections Locomotrices Equines in Normandy, has created a new naming path in an effort to clarify bone diseases in young horses.

Deniox said the new terminology will not only lead to better communication among the people working with these horses, but also help researchers and clinicians collaborate as they strive to better understand the disease, its prevention, and its treatment.

Juvenile osteochondral condition (JOCC) is the new term that now regroups “those developmental disorders that are related to the immature joints or growth plates,” Deniox stated. “JOCC does not replace DOD or osteochondritis dissecans,” however. All three terms are useful and now have clearer, more distinct definitions, he noted.

JOCC encompasses osteochondrosis, cuboidal bone disease, and “various forms of failure of the immature skeleton such as osteochondral collapse or avulsion (tear) fracture at insertion sites,” he stated. Physitis can be a result of the same mechanisms that cause osteochondral collapse, so it is also been included in the broad category of JOCC.

JOCC results from biomechanical influences (various kinds of forces) on the growing musculoskeletal system, Denoix said. JOCC is not osteochondrosis, but osteochondrosis is the most common form of JOCC. Osteochondrosis can, but does not always, lead to bone fragmentation. When the bone does fragment, the lesion is referred to as “osteochondritis.” Within the category of osteochondritis, there are:

  • Osteochondritis dissecans, meaning the fragment is loose;
  • Osteochondritis manifesta, meaning the fragment is not loose but is visible on routine radiograph (X ray); and
  • Osteochondritis latens (formerly known as dyschondroplasia), meaning the fragment is in the very early stages of development and is not yet visible on routine radiograph.

What JOCC does not include are disorders that appear more visible to the naked eye, such as flexural limb deformities, angular limb deformities, or Wobbler syndrome, even though these disorders might be related to JOCC lesions or result from them, he said; however, these disorders would still be considered to be within the scope of DOD.

Within the broad definition of JOCC are several subcategories of lesions, Denoix stated. Some of the new names for these subcategories include:

  • Osteochondral fragmentation of the articular surface (AS-OCF), meaning actual fragments of bone are coming off angled or round parts of joints.
  • Periarticular osteochondral fragmentation (PA-OCF), meaning actual fragments of bone are coming off the side corners of bones at the edge of joints.
  • Juvenile subchondral bone cystlike lesions (JSBC), meaning lesions that look like cysts (but aren’t filled with fluid like true cysts) are located under the cartilage, often diagnosed in yearlings and 2-year-old Thoroughbred racehorses when they start training.
  • Osteochondral fragmentation resulting from ligament avulsion (LA-OCF), meaning bone fragments are created by pressure from the pull of a ligament on developing bone (epiphyseal or metaphyseal bone) where the ligament is inserted.

“Juvenile” was used in the name JOCC instead of “developmental,” as these conditions are specifically related to youth and not development per se— they can be acquired conditions in an immature skeleton—although the difference might seem slight, he said. JOCC would only refer to disorders appearing before two years of age.

Details of the terminology are available in Denoix’s publication, “A Review of Terminology for Equine Juvenile Osteochondral Conditions (JOCC) Based on Anatomical and Functional Considerations,” which appeared in July in The Veterinary Journal.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.