Disorders of the shoulder and elbow include arthritis of the shoulder joint, bicipital bursitis, fractures, and sweeney.
Arthritis of the Shoulder Joint
Inflammation of the structures of the shoulder joint is uncommon. Causes include changes in the joint membrane or, more often, in the joint surfaces of the humerus or scapula, such as might be caused by osteochondritis dissecans (see Bone, Joint, and Muscle Disorders in Horses: Osteochondritis Dissecans). Fractures affecting the joint surfaces or trauma to the shoulder 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, 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.
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.
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 usually causes the inflammation.
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.
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 (Shoulder Atrophy)
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 difficult. As weakness progresses, there is loss of muscle from each side of the spine of the scapula, resulting in prominence of the spine. Weakness of the muscles leads to a looseness in the shoulder joint. The shoulder pulls away from the body 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 disuse of the muscles is to blame, wasted muscles can be restored by correcting the original problem. When nerve tissue is damaged, massaging with stimulating liniments or an electrical vibrator can be of major benefit. 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.
When muscles atrophy due to disuse, the outlook for recovery depends on removing the cause of the disuse and allowing the muscle to rebuild. When nerve damage is involved, the outlook for recovery is guarded. 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.