Digital sheath
Tenosynovitis (windgall)
The digital sheath is a synovial fluid-filled structure at the back of the fetlock running from the pastern to mid-canon and provides lubrication for the movement of the flexor tendons. Tenosynovitis, inflammation of the tendon sheath, can be idiopathic (of unknown origin, windgalls), be caused by palmer annular ligament syndrome, be cause by direct trauma or be caused by infection.
Signs
All cases will have an obvious enlargement of the sheath seen above the fetlock and in the pastern region. Lameness can vary from a non-weight bearing lameness with infection to no lameness at all with the idiopathic form.
A swelling of the digital sheath.
Diagnosis
Infectious tenosynovitis is usually diagnosed by analyzing a sample of the synovial fluid. Ultrasound scanning and x-rays are often useful in finding the underlying cause. If no cause can be found and the horse remains lame after a period of treatment surgery can be performed to see inside the joint using an athroscope (key-hole surgery). This is often necessary as there are many structures than cannot be seen using normal diagnostic tools. In performing this surgery there is a better a chance of finding a diagnosis and then attempting treatment if possible at the same time.
Treatment
There is no treatment required for the idiopathic form.
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. As explained above key-hole surgery can be performed to flush the joint to dispose of any debris and inflammatory cells that contribute to the damage as well as aiding in finding a diagnosis.
Palmer annular ligament syndrome
The palmer annular ligament wraps round the back part of the fetlock. In some occasions this ligament can put pressure on the structures at the back of the fetlock, e.g. the flexor tendons. This pressure can be caused by damage and subsequent thickening of the ligament itself, inflammation within the digital sheath or inflammation of the flexor tendons (uncommon cause). The affected animal usually has a swelling of the sheath, seen just above the fetlock joint, and a persistent lameness.
Diagnosis
Nerve blocks, blocking the digital sheath and ultrasound scanning are the main tools for the diagnosis of palmer annular ligament syndrome.
Treatment
In mild cases or in the early stages treatment is 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. If cases are unresponsive surgery can be performed to cut the annular ligament and, therefore, reduce the constriction.