Bog spavin

Joints are complicated structures that are prone to a variety of disorders. Bog spavin is one such condition that is most commonly seen in young horses with osteochondrosis, where cartilage and bone around the joint fails to develop normally. Early detection of bog spavin is important, as the condition can have an important impact on the horses future athletic capabilities.

‘Bog spavin’ refers to low-grade inflammation of the membrane (synovitis) of the tarsocrural joint (also known as the tibiotarsal joint); this is the articulation between the tibial tarsal bone and the tibia and fibula bones of the hock joint.
This picture shows a radiograph of a normal, healthy hock:

  1. Tarsocrural joint
  2. Tibial tarsal bone
  3. Tibia
  4. Calcaneum

There are a number of causes, but most commonly bog spavin is caused by osteochondrosis in young horses. Other causes include biomechanical stresses, for example conformational faults such as straight hocks, sickle hocked or cow hocked; lameness in another limb; intense training.
Other causes include osteochondrosis in young horses, blood in the joint cavity, infection and osteoarthritis (arthritis).
Vitamin and mineral deficiencies are also possible causes, namely deficiencies of phosphorus, calcium, vitamin A or vitamin D.
Zinc poisoning has also been found to be a cause.

The most obvious sign of bog spavin is an enlargement of the tarsocrural joint on both sides of the hock. The swellings are lower than those of ‘thoroughpin’ which are seen at the point of the hock.
The swellings may fluctuate and if pressure is put on one side of the swelling the other side will enlarge further.
Horses with bog spavin aren’t always lame, and the extent of any lameness will depend on the cause, however extensive swelling can lead to mechanical lameness. Decreased flexion of the hock may also lead to a slight change in gait due to the inability of the horse to step through and ‘track up’.

If your vet suspects bog spavin they may want to take some x-rays to investigate any possible bony changes in the joint which might be causing the inflammation.
Ultrasonography, computed tomography, magnetic resonance imaging and scintigraphy are other methods of imaging that might also be used to get to the bottom of the problem.
Other methods of investigation include arthroscopy, this is where your vet will use an arthroscope (endoscope) to examine the inside of the joint.

Before treatment is considered, any possible causes should be eliminated.
If diet is found to be the cause, careful analysis of the horse’s diet is necessary to determine what is deficient, and then the diet can be altered to ensure it is balanced and the condition does not recur.
If your horse is young, bog spavin will often resolve itself with rest and compression bandaging. However, surgical drainage of the joint may be necessary followed by anti-inflammatory injections directly into the joint.
Where cartilage and bone fragments within the joint are causing problems, these can be removed arthroscopically.
Following surgical treatment your horse will need to be on restricted turnout for a couple of weeks before they can be returned to their normal paddock and a slow return to work should be undertaken.
Recurrence without lameness is possible, and as a result the swelling remains but just as a cosmetic blemish and should be accepted as the long-term result with complete resolution unlikely.

Ensure your horse receives a balanced diet to avoid nutrition-related bog spavin. Calcium and zinc balance is important in preventing osteochondrosis.
Unfortunately if a horse has poor conformation, prevention is difficult but you can bear this in mind when planning your horse’s exercise regime.
When working your horse you should minimise stress or injury to the hock joints.