Sweeney is a neurological condition of horses that is usually the result of a trauma-induced injury to the horse's shoulder that causes damage to the suprascapular nerve. The suprascapular nerve runs along the front of the horse's shoulder blade and attaches to the top of the humerus bone and the shoulder joint. It supplies blood and oxygen to the infraspinatus and supraspinatus muscles, which provide lateral support to the horse's shoulder.

Situations that have been associated with the development of sweeney in affected horses include:

• The horse running into a solid object, such as a stable door frame, tree, side of the barn, and gate posts.
• The horse colliding with another horse while turned out in pastures, during a horse show or other event, or during a group lesson with other riders.
• The horse slipping and falling on ice, while turned out in the pasture or during exercise.
• The horse was asked to pull a heavy load while wearing the traditional card horse equipment such as the heavy collar.

When the suprascapular nerve is crushed, compressed, or stretched it impacts the nerve supply to important muscles in the shoulder, causing them to atrophy. This often causes the shoulder joint to slip sideways, resulting in subluxation.

Clinical signs of sweeney
Clinical signs of sweeney in horses may include a distinctive gait abnormality and stance, in which the horse's shoulder "pops" sideways when the horse puts weight on the associated leg. Most horses also present with varying degrees of muscle atrophy to the shoulder region. There may also be some swelling along the shoulder region, due to the initial trauma.