Disorders of the Shoulder and Elbow in Horses
Disorders of the shoulder and elbow are less common than one might expect. Horses with shoulder disorders often have a characteristically abnormal gait, whereas those with elbow disorders do not. However, shoulder and elbow disorders cannot be diagnosed based only on the observation of a horse’s gait. Veterinarians often need to perform a full lameness examination, which may include observation for loss of muscle tone in the upper limb, regional analgesia, evaluation of joint fluid (arthrocentesis), x-rays, and ultrasonography. Disorders of the shoulder and elbow include developmental diseases, arthritis, bicipital bursitis, fractures, collateral ligament injury in the elbow, and sweeney.
Osteoarthritis (arthritis) is inflammation of the cartilage and underlying structures of a joint. It causes progressive cartilage loss and deterioration of the joint. Degenerative joint disease affecting the shoulder or elbow joints pose the same problems as it does elsewhere in the body. Causes include changes in the joint membrane or, more often, in the joint surfaces (such as the humerus or scapula in the shoulder). For example, damage to the cartilage or bone of the humerus caused by osteochondritis dissecans can lead to osteoarthritis of the shoulder. Fractures affecting the joint surfaces or trauma to the shoulder or elbow may also produce inflammation. Septic (infectious) arthritis (for example, from a puncture wound to the joint) may also occur.
In severe cases, lameness may be present in both the swinging (non-weight-bearing) and supporting (weight-bearing) legs. Milder cases may produce lameness only in the swinging leg. Typically, in horses with shoulder arthritis, the forward movement is shortened, with the horse moving the leg in a circular motion to avoid bending the joint. The toe shows signs of wear. Forcing the leg to extend, which pulls the shoulder forward, often causes pain. X-rays of the shoulder joint, preferably taken with the horse lying down under general anesthesia, may show changes that are typical of arthritis. Some horses with evidence of an elbow disorder do not show evidence of arthritis on x-rays.
Although signs may improve with treatment, the condition cannot be cured. When arthritis is severe, treatment often is ineffective. Injections of a corticosteroid into the joint may be of some benefit. Whole-body steroids or other anti-inflammatory drugs may relieve signs of pain. Hyaluronic acid, which lubricates joints and seems to benefit cases of degenerative disease in other joints, may also provide some relief. Your veterinarian may also recommend other treatments (such as polysulfated intra-articular glycosaminoglycans, pentosan polysulfate, and autologous conditioned serum) to reduce inflammation and protect the remaining joint cartilage.
A bursa is a small, fluid-filled sac between a tendon and bone that reduces friction around the joint. In bicipital bursitis, the bursa between the tendon of the biceps and the bicipital groove of the humerus becomes inflamed. Direct trauma to the point of the shoulder, underlying bone cysts, or an injury to the biceps tendon usually causes the inflammation. Occasionally, the inflammation arises from a bacterial or fungal infection (called septic bursitis) or from an unknown cause (called idiopathic primary bursitis).
A physical examination, x-rays, and ultrasonography are typically used to identify the underlying cause. Repeat examinations may be necessary because it may take time for the cause to become apparent. Scintigraphy (a test involving the injection of a radioactive substance that is detected by a specialized camera) may also be necessary in cases in which the underlying cause cannot be determined.
Bicipital bursitis tends to produce lameness that shortens the forward phase of movement in the swinging leg. The horse may fail to lift the toe sufficiently to clear the ground, causing it to stumble. In severe cases, the horse rests the supporting leg in a semi-flexed position. Forced extension of the leg usually causes pain, as can firm pressure over the bursa and the tendon of the biceps. Ultrasonography can show the excess fluid and associated physical changes of the biceps tendon. In longterm cases, x-rays may show calcification of the bursa, a common consequence.
The treatment for bicipital bursitis depends on the cause. Horses afflicted with bicipital bursitis require prolonged rest, often for more than 6 months. Injection of hyaluronic acid or corticosteroids within the bursa may help. Anti-inflammatory drugs and oral steroids may also be helpful. The outlook for recovery is guarded.
Fractures of the bones of the elbow occur most often as a result of a kick or fall. The most frequent is fracture of the ulna. The onset of lameness is sudden, with pain and swelling of the elbow. The fractures typically affect the joint, causing the elbow to drop and be incapable of extension. The carpus and fetlock are bent, with the toe resting on the ground. The diagnosis is confirmed using x-rays.
Treatment may be nonsurgical or surgical. In fractures that are not displaced or that do not involve the joint, full-leg splinting and stall rest are sufficient. Otherwise, surgery is recommended. With proper treatment, the outlook for recovery is favorable.
Fractures of the scapula and humerus are the most common shoulder fractures. They usually result from falls or kicks. Lameness is severe and sudden in onset. The local soft tissues swell, often with the formation of a large blood clot. Diagnosis of the fracture is confirmed using x-rays. Conservative treatment, including prolonged stall rest, often produces improvement. Surgery may be advised in certain cases. The outlook for recovery is poor if joint surfaces are involved.
Sweeney is wasting of the muscles of the shoulder caused by damage to the muscles’ nerve supply. Muscles may also waste away due to disuse following damage to the limb or foot that leads to prolonged, reduced use of the limb. The condition occasionally affects polo ponies following collisions during competition.
If the horse has not been obviously injured, it may feel no pain, and lameness may be difficult to detect until the muscles have weakened. Injury usually makes extension of the shoulder (to advance the leg forward) difficult. As weakness progresses, there is loss of muscle on each side of the spine of the scapula, resulting in the spine becoming prominent. Weakness of the muscles leads to a looseness in the shoulder joint. The shoulder typically "pops out" away from the body when bearing weight and, in severe cases, is sometimes incorrectly diagnosed as a dislocation. When the horse is at rest, the lower part of the limb (in addition to the shoulder) also pulls away from the body.
When nerve tissue is damaged, the outlook for recovery is guarded. Passive exercise techniques, such as the application of an alternating electric current to stimulate nerve and muscle function, may help maintain muscle bulk until the nerve regenerates. Surgery to free the nerve from scar tissue has also been recommended. For best results, the surgery should be performed before looseness and slipping of the shoulder joint are advanced. Mild cases should recover in 6 to 8 weeks. In cases of severe nerve damage, spontaneous recovery may take many months, if it occurs at all. Such cases are candidates for surgery. If the nerve has been severed, recovery is unlikely.
When disuse of the muscles is to blame, wasted muscles can be restored by correcting the original problem. The outlook for recovery depends on removing the cause of the disuse and allowing the muscle to rebuild.