By Lara Hummel
Moving away from our geriatrics with osteoarthritis in last month’s article, this month we take a look at another bone condition, osteochondrosis, which affects younger, fast growing horses.
Osteochondrosis is one of the Developmental orthopaedic diseases. Other such diseases include:
- Angular limb deformities
- Flexural deformities
- Cervical vertebral Malformations-wobblers
Osteochondrosis is particularly seen in thoroughbreds, Warmbloods and Standardbreds and most other breeds of horses( 10-25% horses affected) but it is very rare in ponies and feral horses. It is a very important disease as it can cause significant welfare issues and loss of performance, not to forget the expensive veterinary bills!
Bones grow in length by a process called ‘endochondral ossification’, which is basically the formation of bone tissue within the cartilage. This process occurs at the growth plates, which are situated at the ends of the bones, beneath the joint surface. This is how bones and joints effectively grow in length. However, like most things, there is scope for things to go wrong. . Ostechondrosis arises from a failure in the process of endochondral ossification. The cartilage becomes variable in thickness and weaker than in normal joints. The primary lesions (dyschondroplasia) are microscopic and do not cause clinical disease. These can either heal or progress to clinical Osteochondrosis dissicans(OCD). The flaps of bone and cartilage can either remain attached to the associated bone or they can become detached and float around in the joint space (joint mice). Subchondral bone cysts are another manifestation of osteochondrosis and are holes in the cartilage. These holes in the cartilage become engulfed by bone rather than repair. These loose flaps and areas of abnormal cartilage and bone cause inflammation in the joint and over time may lead to the development of arthritis.
The clinical signs include:
- Joint distension
- Lameness (inconsistent and of varying severity)
- Postural abnormalities
- Reduced activity
- Difficulty and reluctance to get up
The history is important in the diagnosis as OCD lesions develop before animals are 9 months old. The clinical presentation may not be obvious until the horse enters a training programme and can vary significantly in severity. Approximately 50% of horses are affected bilaterally. There may only be a joint distension, with or without lameness. The hock, stifle
and fetlock joints are most commonly affected but it can occur in all joints. Occasionally lameness can precede joint distension and in this case local analgesic techniques can be used to locate the problem joint. In most cases there is a swollen joint and radiography is the most useful in identifying the OCD changes in a joint. There are certain OCD predilection sites in the different joints. This will help the vet find the sometimes subtle changes found on an x ray. Unfortunately on x rays we can only see the bony changes, so cartilage disruptions often are not seen. The signs the vet will look for on an x ray are the loss of a smooth contour to the bone, mineralised fragments of bone and changes in the density of the bone (radiolucencies).
If there is a suspicion of OCD, arthroscopy provides the most useful information when examining the integrity of the cartilage.
There are a large number of trigger factors that have been implicated in the progression of the primary lesions to that of OCD. These include:
- Dietary imbalances-a high carbohydrate diet
- A rapid growth rate – the exact mechanism is unknown but is thought to be related to the bone growth outstripping the blood supply
- A copper deficiency
- Biomechanical trauma
- Endocrinological- high insulin levels
- Genetics- this is important when considering breeding from a mare
Rational treatments depend on the age at diagnosis, the degree of lameness and radiological changes.
Conservative management involves rest initially, followed by a controlled exercise programme. Feeding a good quality balanced diet is important in the role of prevention and overfeeding should be avoided. There is some evidence to support the possibility that pre or post natal diet may influence the development of OCD. The use of some intrarticular medications such as corticosteriods and hyaluronic acid may be useful in the management of bone cysts.
However, if young horses are still showing lameness despite exercise restriction, surgery is indicated. This is performed by arthoscopy, which involves placing a small camera into the joint of the horse under general anaesthetic and removing any cartilage flaps and debriding any defective subchondral bone.
Prognosis for athletic function is good to excellent for most OCDs that are treated surgically. Some OCD locations, such as the shoulder, may have a reduced prognosis. In general, if the OCD lesion is not removed the prognosis for future soundness will be decreased. Also if there is evidence of osteoarthritis the prognosis will be poorer.
If you have any questions about any aspects of your horse’s health, or indeed your pet, farm or smallholding animals, please do not hesitate to contact us on 01892 835456. Putlands Veterinary Surgery is based in Paddock Wood in Kent, and offers a friendly, professional and personal service for all species of animal. We have four dedicated large animal vets with a wealth of equine experience between us, and are always happy to help.