Juvenile osteochondritis dissecans (JOCD)

Juvenile osteochondritis dissecans (JOCD) is a common condition in horses, and is due to abnormalies in the bone formation process. Foals can be affected at a very young age. 

JOCD includes :

• Osteochondral lesions (OCD) are caracterized by :
  • Irregularities or even fragmentation of  the bone surface
  • Formation of subchondral (part of the bone in contact with the joint) bone cysts (focal disturbance in endochondral ossification)
• Bone fragmentation due to ligament traction

These abnormalities result in biomechanical pressure on the foal’s immature skeleton, leading to disturbances in the blood flow to the site of ossification. This biomechanical factor expalins thet lesions often occur in the same place on a joint.

The economic impact of these juvenile disorders for the horse sector can be significant, as they can decrease the foal’s value, and compromise its future performances. Nevertheless, clinical signs are variable and depend on :

• The severity of the lesions (eg : size of the bone fragment)
• The affected joint : Osteochondral affections in tibial-tarsal joints ( between the tibia, and the hock) can be subclinical, whereas lesions located on the stifle more often than not present clinical signs
• The location of the lesion in the joint.
• The use of the horse (leisure vs competition, level of competition, discipline)

Osteochondral lesions are most frequently subclinical. There is often a nonpainful distention of an affected joint, particularly when there is presence of a bone fragment. The distension can also lead to synovial inflammation (inflamation of the synovial membrane around the joint), which in turn leads to joint pain and lameness.
JOCDs are also the cause of poor performances in sport horses. Moreover, JOCDs can lead to development of osteoarthritis or OA (progressive degradation and destruction of articular cartilage: the tissue lining the ends of the bones, and bone proliferation under the cartilage).

These disorders are usually detected on a preventative basis (before a sale, or when starting work) or when there is a clinical suspicion (swelling of a joint, lameness, poor performance).

A clinical examination can orient diagnosis. During a static examination, joints are palpated, and flexion tests carried out, in order to show any signs of pain, or reduced amplitude of movement. This static examination can be supported by a dynamic examination, which will enable to fine-tune the diagnosis, in addition, local anaesthetics may be administered, so as to determine the precise location of pain.

The lesions can only be confirmed by X-ray images which can be supported by Ultrasonographic examination.

A study (ESOAP : Elevage, Statut Ostéo-Articulaire et Performances ;Breeding : osteo- articular status and performances) carried out in 2000 by Professor Jean-Marie Denoix, established an osteo-articular assessment of  Thoroughbreds, Trotteur, and Selle-Français foals in Normandy, through the study of radiographic images of JOCDs between the ages of 6 to 18 months. This study showed that JOCDs evolve greatly during the foal’s first year, and up to 18 months. Indeed, of the population studied in Normandy, only 32.3 % of abnormal X-ray images identified at the age of 6 months had not evolved at 18 months old, whereas 46.6 % had disappeared, and 38.7 % of abnormal Xray-images were new developments.

In the case of JOCDs, healing phenomena take place in the young horse’s joints. Therefore, a radiographic detection examination, at around the age of 12 months, appears to be a good compromise between the necessity of early detection, and the stability of any abnormality observed at an earlier age. This takes into consideration that an assessment at the age of 6 months does not give a genuine idea of the future osteo-articular status of the animal. However, in the case of a physical abnormality detected in the younger foal (joint distension for example) it is recommended to carry out a radiographic examination.

Figure 1 : Complete recovery from an osteochondral lesion on the lateral Trochlear ridge of the distal femora (stifle joint).  © CIRALE-ENVA

Figure 2 : Rear peri-articular osteochondral fragmentation of the first phalanx on a hind fetlock, not identified at the age of 6 months © CIRALE-ENVA

Osteochondritis has a multifactorial etiology, meaning that it results from several different factors :

• Environmental factors :

  • Broodmares and the growing foals diets, plus mineral, vitamin and trace element supplements=> At the age of 6 months , foals from mares having been fed cereal, are more likely to present osteochondral lesions than foals from mares fed exclusively on grass and hay.

  • Exercise and biomechanical pressure on the joints=> Both stabling a foal in a box during its first year, even when turned out in a paddock, and giving access to wide hilly expanses can give rise to JOCDs. Acute joint trauma could also induce JOCDs, or worsen existing lesions.

• Individual factors :
  • Growth=> Several studies have identified that JOCDs in the stifle are more likely to be seen in foals who have a high average daily weight gain during the first few months of their lives.
  • Conformation=> Studies have shown that the foal’s height at the withers (aged 1 month) has an influence on the presence of lesionsduring the following months. Equally, height at the withers of the adult horse is related to prevalence of lesions of osteochondritis of hocks and fetlocks in the sport horse.
  • Breed=> The ESOAP study for example has shown that JOCDs are more frequently observed in Selle-Français horses than in Thoroughbreds, but that the proportion of severe lesions is higher in the latter.

•  Genetic factors : JOCDs are also hereditary, and are influenced by several genes.

Management of JOCDs depends on the severity of the lesions, the joint concerned, and the horse’s use. A conservative approach (rest, anti-inflammatories) mais be sufficient in some cases. However there is always a risk of the horse developing ostearthritis.
It is therefore often advisable to consider arthroscopic surgery. This technique consists in making small incisions, to introduce an arthroscope (a camera) and surgical instuments, so as to treat a cyst, or remove a bone fragment.