What you see. The starting point for addressing any equine health related issue is your observation.


Shoulder Popping or Slipping Laterally

Suprascapular nerve injury video- Lateral Movement of Shoulder


Unlike a typical joint that is supported by strong collateral ligaments, the equine shoulder joint is supported almost entirely by tendons of shoulder muscles that traverse the joint.

If these shoulder muscles are damaged, lost, or weakened, the shoulder joint becomes loose and the upper arm bone can literally "pop" into and out of the shoulder joint, usually outwardly (laterally). In most cases, the outward appearance of the shoulder looks strange in horses with instability of the shoulder joint.

"Sweeney" is the common name given to the atrophy of muscles of the shoulder and scapula that usually results from a nerve injury to the large nerve (Supra-scapular nerve) passing over the point of the shoulder. This usually is caused by a collision into a stationary object. In polo horses, collisions with other horses tend to cause this injury. If any muscle loses it's supplying nerve, the muscle wastes away (atrophies).

  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If you feel the problem is severe or has come on suddenly.
  • Code Yellow

    Contact Your Vet at Your Convenience for an Appointment
    • If this seems mild or occasional and the horse seems normal otherwise.

your role


What To Do

If you notice consistent abnormal movement of your horse's shoulder area, contact your vet. Instability of this area, even without obvious lameness, is a serious problem that needs to be addressed. Try to capture some of this abnormal movement with a video and send it to your vet.

In severe cases of Sweeney, an observer can actually see the arm move to the outside relative to the shoulder area, a disturbing sight.

What Not To Do

Do not ride the horse if you notice any change in function or movement of the shoulder area. A horse with a problem here could collapse resulting in further injury, and may also injure a rider.

your vet's role

Through careful examination, neurologic evaluation and comparison to the normal side, your vet should be able to make a diagnosis. Once that is done, treatment and prognosis can be discussed.
Questions Your Vet Might Ask:
  • When did you first notice this problem?
  • Do you recall an accident or injury in the horse's history?
  • Can you see loss of the muscle relative to the normal side?
  • Does the horse show any signs of lameness or resistance to move?
  • How frequently is this happening?
  • What are the results of the Whole Horse Exam (WHE)?

Treatments Your Vet May Recommend

A way to resolve the condition or diagnosis. Resolving the underlying cause or treating the signs of disease (symptomatic treatment)

Very Common
more treatments

further reading & resources

Author: Doug Thal DVM Dipl. ABVP