High severity

Thoroughpin (Tarsal sheath effusion)

Thoroughpin is effusion of the tarsal sheath (deep digital flexor tendon sheath) — a soft swell above and in front of the point of the hock that can be pushed through (through-and-through) — not bog spavin (tarsocrural joint effusion on the front/inside of the hock), not a capped hock (calcaneal bursa at the point), and not curb (plantar tarsal ligament below the point). A photograph cannot diagnose thoroughpin. A still cannot tell thoroughpin from bog spavin, a capped hock, curb, or an infected sheath. Diagnosis is a vet exam. The conformation scan is a first look at the tarsal-sheath swell, not a verdict that your horse has thoroughpin, and there is no thoroughpin scanner.

Symptoms to watch for

A soft, fluid swell above and in front of the point of the hock (the tarsal sheath) that can be pushed through to the other side, not a soft swell on the front/inside of the hock and not a swell right on the point

Heat, filling, or pain over the tarsal sheath (an active, inflamed sheath), or a cool, soft swell that has been there a while

A shorter stride, especially after work or on circles

Reluctance to flex that hock, land, or work on that limb

Hock-region swelling that can look like bog spavin, a capped hock, curb, or an infected sheath

Some horses stay even at walk; the first sign is a new soft swell above and in front of the point of the hock — a reason to book a vet, not a photo verdict

Common causes

Effusion of the tarsal sheath (deep digital flexor tendon sheath) — a soft through-and-through swell above and in front of the point of the hock can follow
Strain, trauma, or hard or fast work of the hock — the history is a clue, not a diagnosis
Not bog spavin (tarsocrural joint effusion on the front/inside of the hock), not a capped hock (calcaneal bursa at the point), and not curb (plantar tarsal ligament below the point)
Not an infected (septic) tarsal sheath, not a sprain, and not a fracture — a still cannot tell thoroughpin from those, and those need a vet

Prevention

Warm up before hard work and build hock-heavy work gradually
Match the work to the footing — avoid sudden heavy or fast work on hard ground
Watch the web of the hock for a new soft swell above and in front of the point, heat, or a shorter hock stride and rest rather than working through it
Do not treat a photo, a tarsal-sheath swell, or a scan result as a diagnosis
Conformation photos can help you and the vet look at the tarsal-sheath swell — they do not confirm or rule out thoroughpin, and they cannot tell thoroughpin from bog spavin, a capped hock, curb, or an infected sheath

What to do

1
Book a vet visit if you find a soft swell above and in front of the point of the hock, heat, or a shorter hock stride. Diagnosis is a vet exam — not a photograph.
2
Stop work. Rest the horse and do not ride through a hot, painful tarsal-sheath swell hoping it will settle.
3
Photograph the tarsal-sheath swell in good light and keep it 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 tarsal-sheath swell to share, not as a thoroughpin test. There is no thoroughpin scanner.
5
If thoroughpin (tarsal sheath effusion) is confirmed, follow the plan your vet prescribes — that may include rest, controlled exercise, or further imaging. 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 you find a soft swell above and in front of the point of the hock, if the swell is hot or painful, if the horse is short on that limb, or if filling appears after work. Call sooner if the horse will not bear weight, the limb is suddenly very swollen, or the horse is dull or off feed. A photograph cannot diagnose thoroughpin. A still cannot tell thoroughpin from bog spavin, a capped hock, curb, or an infected sheath. Diagnosis is a vet exam. The conformation scan is a first look at the tarsal-sheath swell, not a verdict, and there is no thoroughpin scanner.

Get a first look at the tarsal-sheath swell

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.