Description

Suprascapular neuropathy often referred to as sweeny, is a condition that occurs when the shoulder muscles of the horse degenerate or atrophy damaging the nerves in the shoulder. The wasting away of the muscles  on both sides of the scapula causes a characteristic prominence of a ridge like spine of the shoulders. 

In the past, sweeny was common in draft horses when yokes were used to pull plows. Because there can be a number of causes, it is important to realize that the term sweeny is a description of the condition of the muscles and not a diagnosis in itself.

Symptoms

• Front leg swings to the side because of outward motion of shoulder 
• Lateral slippage of the horse's shoulder sometime accompanied by a popping sound
• Severe and localized wasting (atrophy) of the shoulder muscles, usually on one side
• Lameness and instability of the shoulder joint
• A prominent scapular spine

Causes

Injury to the suprascapular nerve is the most common cause of suprascapular neuropathy. This typically happens when there is trauma, usually caused by a collision to the front of the shoulder where the nerve is less protected.

Other causes include disuse atrophy, which is milder wasting that is more generalized from a lack of use of the involved muscles. Disease or damage to the nerves of the lower neck can also cause the condition.

Prevention

Since suprascapular neuropathy can arise from a number of causes, prevention should be aimed toward reducing as many of those causes as possible, such as having appropriate-sized enclosures and gates and aisles that allow for a horse to pass through with adequate room on either side. Owners should exercise care when turning-out new animals into a herd, as the new animal may suffer injury due to collision resulting from the commotion of the herd when a new horse is introduced.

Treatment

Treatment will be related to the cause of the atrophy, and designed to support muscle and nerve recovery. Treatment options may range from conservative management such as rest and confinement to physiotherapy or surgery.

Therapy is aimed at maintaining muscle health during the period of nerve recovery. Horses should be restricted to stable rest or a very small paddock. Complete immobilization may negatively impact the nerve and muscles, but activity probably hastens joint degeneration. This tradeoff should be discussed with your veterinarian.

A surgical procedure for removing part of the scapula over which the nerve courses has been described, aiming to provide optimal conditions for nerve recovery. This should be considered, but its usefulness has not been proven.

Muscle stimulation, under the guidance of a trained physiotherapist, will help to limit muscle fibrosis and may encourage nerve regeneration. Clinical observations show that the vast majority of cases will recover function with time.

However, this process can take many months and frequently some loss of muscle bulk will remain. The prognosis seems most affected by duration of injury before diagnosis, degree of atrophy at diagnosis, and willingness of the owner to perform time-consuming physical treatments for many months.

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Merck Veterinary Manual: Suprascapular neuropathy

Nonsurgical treatment of suprascapular nerve injury in horses: 8 cases (1988-1998)