High severity

Sweeney (Suprascapular nerve atrophy)

Sweeney is atrophy of the supraspinatus and infraspinatus after injury to the suprascapular nerve — a hollowed shoulder, not a locked stifle, not kissing spine, and not ordinary shoulder soreness. A photograph cannot diagnose sweeney. A still cannot tell sweeney from disuse atrophy, a shoulder injury, or poor muscling. Diagnosis is a vet exam. The conformation scan is a first look at the shoulder outline to share with a vet, not a sweeney test, and there is no sweeney scanner.

Symptoms to watch for

A hollowed or wasted look over the shoulder, so the spine of the scapula stands out — the outline is a clue, not a still-photo verdict

Less muscle over the supraspinatus and infraspinatus than on the other shoulder

A shoulder that looks sunken after trauma, a collar or stall injury, or a blow to the point of the shoulder

Stumbling, shoulder instability, or reluctance to take that front limb forward — or a horse that looks even at rest

A hollowed shoulder that can look like disuse atrophy, a shoulder injury, or poor muscling — a still cannot tell them apart

Some horses show only a flatter shoulder; the first sign is a new hollow after injury — a reason to book a vet, not a photo verdict

Common causes

Injury to the suprascapular nerve — the nerve that supplies the supraspinatus and infraspinatus — so those shoulder muscles waste
Trauma where the nerve crosses the front of the scapula — a blow, a fall, a collar or harness injury, or stall trauma — the history is a clue, not a diagnosis
Not a locked stifle (a hind-limb patella lock), not kissing spine (back/spinous processes), and not ordinary shoulder soreness without nerve atrophy
Not disuse atrophy from another lameness, not a shoulder-joint injury, and not poor muscling — a still cannot tell sweeney from those, and those need a vet

Prevention

Protect the point of the shoulder in work and in the stall — trauma there is extra load on the suprascapular nerve
Fit collars, harness, and blankets so they do not rub or bruise the front of the scapula
Watch both shoulders for a new hollow, a standing-out scapular spine, or a sudden drop in that front limb and rest rather than working through it
Do not treat a photo, a hollowed shoulder, or a scan result as a diagnosis
Conformation photos can help you and the vet look at the shoulder outline — they do not confirm or rule out sweeney, and they cannot tell sweeney from disuse atrophy, a shoulder injury, or poor muscling

What to do

1
Book a vet visit if one shoulder looks hollowed, if the spine of the scapula stands out, or if that front limb stumbles or will not step through. Diagnosis is a vet exam — not a photograph.
2
Stop riding through a hollowed or unstable shoulder. Rest the horse and do not add collection, jumping, or extra work hoping the muscle will fill in.
3
Photograph both shoulders in good light, from the front and the side, and keep the photos on the horse's record so you and the vet can see change over time — a first look to share, not a diagnosis.
4
Use a conformation scan only as a first look at the shoulder outline to share, not as a sweeney test. There is no sweeney scanner.
5
If sweeney (suprascapular nerve atrophy) is confirmed, follow the plan your vet prescribes — that may include rest, time for the nerve, physiotherapy, or further exam. Do not start a treatment protocol from a photo.
6
Keep the vet on the same page. Share what you see; do not treat a photo as a verdict.

When to call the vet

Pick up the phone if…

Schedule a vet visit if one shoulder looks hollowed, if the spine of the scapula stands out, if that front limb stumbles or will not step through, or if the hollow appeared after trauma. Call sooner if the horse will not bear weight, the shoulder is suddenly very swollen, or the horse is in obvious pain. A photograph cannot diagnose sweeney. A still cannot tell sweeney from disuse atrophy, a shoulder injury, or poor muscling. Diagnosis is a vet exam. The conformation scan is a first look at the shoulder outline, not a sweeney test, and there is no sweeney scanner.

Get a first look at the shoulder outline

Scan conformation in HorseCare. 5 free scans this month, then Pro.

Scan conformation

5 free scans this month, then Pro. Scans run in the HorseCare app.

Educational content only. Not a substitute for veterinary advice.