Tenosynovitis of the carpal sheath
The carpal sheath is a synovial fluid-filled structure down the back of the knee. Tenosynovitis, inflammation of the tendon sheath, can be caused by fracture of the accessory carpal bone, direct trauma (often bleeding into the sheath), tendon strain (tendonitis) or be caused by infection.
Signs
All cases will have an obvious enlargement of the sheath seen above and below the knee. Lameness can vary from a non-weight bearing lameness with infection to no lameness at all with the idiopathic form.
Diagnosis
Infectious tenosynovitis is usually diagnosed by analyzing a sample of the synovial fluid. Ultrasound scanning is often useful in finding the underlying cause.
Treatment
Sheath infection is best treated by flushing the sheath surgically, usually via arthroscopy (key hole surgery), combined with antibiotic therapy. The affected limb should be bandaged tightly and the horse placed on box rest. Traumatic tenosynovitis is initially treated with rest and anti-inflammatory drugs such as phenylbutazone (‘bute’). Agents are often injected directly into the sheath such as corticosteroids and hyaluronic acid to reduce the inflammation.