Osteochondrosis (OCD) is a failure of normal cartilage and bone development at the joint surfaces of long bones. This leads to bone fragmentation or subchondral bone cysts which are common causes of lameness in the horse. Young horses are most frequently affected and the condition can have an important impact on the horses future athletic capabilities.
The role of joints is to act as hinges to enable movement of the skeleton. The ends of long bones are covered with hyaline cartilage, which in its normal state, has a glass-like appearance. Synovial fluid is produced by the joint capsule which lubricates the connection between the two bone ends. Along with the smooth cartilage, the synovial fluid permit frictionless movement of the bone ends during locomotion.
During growth, the cartilage at the ends of long bones (at the growth plate) ossifies (mineralises) to form mature bone. Abnormalities in this ossification process during growth leads to the formation of defects in the articular cartilage and/or subchondral bone.
Osteochondrosis occurs as a result of a number of factors:
- Fast growth rate.
- Dietary imbalance.
- Genetic predisposition.
Subchondral bone cysts
Osseous cyst-like lesions in the bone directly beneath the cartilage surface of a joint. These cysts can communicate with the joint surface leading to a defect in the overlying cartilage. Areas of abnormal, exposed subchondral bone results in a loss of frictionless joint movement and can cause pain and subsequent lameness.
The formation of osteochondral fragments which, under normal weightbearing forces can dislodge from the articlular surface and become mobile within the joint causing clinical signs.
Some horses with osteochondrosis lesions show no clinical signs and can perform as normal.
Clinical signs are usually related to the degree of cartilage disruption and subchondral bone involvement. Often, horses will remain clinically silent until a fragment dislodges within the joint.
With cyst-like lesions the occurrence of lameness can be extremely variable and can change from day to day which can make diagnosis challenging. Joint effusion (swelling) and lameness in young horses are the predominant clinical findings.
As with any cause of lameness in the horse, a thorough clinical investigation will be required by your vet. Nerve blocks and joint blocks with local anaesthetic will be used to localise the source of pain. Radiographs (x-rays) of the affected joint are often sufficient to diagnose the lesion. In some cases, there may be no bone changes visible on radiography and surgical investigation (arthroscopy) of the joint may be required to make a diagnosis.
Surgical arthroscopy is usually indicated in the treatment of osteochondrosis and can be a useful tool in determining the extent of the lesion and likely prognosis. Arthroscopy involves inserting a camera into the joint under general anaesthesia to enable direct visualisation of the lesion. Loose osteochondral fragments can be removed and areas of abnormal cartilage and subchondral bone damage removed to reduce inflammation and to a limited extent encourage healing.
Surgical treatment is always performed in association with a controlled exercise regime. Non-steroidal anti inflammatory medication such as bute may be recommended by your vet. Other treatment methods include the use of corticosteroids (potent anti-inflammatories), injected either into the joint or directly into the subchondral bone cyst under general anaesthesia.
Feed supplements containing glycosaminoglycans have been advocated in the management of joint disease. Their use is unlikely to cause any harm but at present, there are limited clinical studies supporting their efficacy.
As osteochondrosis has a heritable component, it is not advisable to breed from horses that have been previously diagnosed with the condition.
Providing a good quality, balanced diet to young horses is important in the prevention of the disease.
Restricting the growth rate of young horses by feeding a low plane of nutrition (reduced concentrates, good quality forage) should be encouraged.