High severity

Curb (Plantar tarsal ligament thickening)

Curb is thickening of the plantar tarsal ligament on the back of the hock — a firm swell a few inches below the point of the hock — not bone spavin (lower-hock osteoarthritis), not bog spavin (soft tarsocrural effusion), not a capped hock, and not a bowed tendon in the cannon. A photograph cannot diagnose curb. A still cannot tell curb from bone spavin, bog spavin, a capped hock, a sprain, or a bowed tendon in the hock region. Diagnosis is a vet exam. The conformation scan is a first look at the back-of-hock swell, not a verdict that your horse has curb, and there is no curb scanner.

Symptoms to watch for

A firm swell on the back of the hock, a few inches below the point of the hock (the plantar tarsal ligament), not a hard bony bump on the inside of the lower hock and not a soft fluid swell higher on the hock

Heat, filling, or pain over the back of the hock (an active strain), or a cold, firm ridge that has been there a while

A shorter stride with less hock flexion; the horse may resent work on that limb, especially after rest or on circles

Reluctance to flex that hock, land, or work on that limb — lameness that may ease with work and return after rest

Back-of-hock swelling that can look like bone spavin, bog spavin, a capped hock, a sprain, or a bowed tendon — or a long-standing firm ridge with little heat

Some horses stay even at walk; the first sign is a firm swell below the point of the hock after work — a reason to book a vet, not a photo verdict

Common causes

Thickening or sprain of the plantar tarsal (long plantar) ligament on the back of the hock — a firm swell a few inches below the point of the hock can follow
Strain, trauma, sickle hocks, or hard or fast work — the work and the shape are clues, not a diagnosis
Not bone spavin (osteoarthritis of the distal intertarsal / tarsometatarsal joints), not bog spavin (tarsocrural effusion), and not a capped hock
Not a bowed tendon (typically the superficial digital flexor in the cannon), not a sprain elsewhere in the hock, and not a fracture — a still cannot tell curb 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, especially in sickle-hocked horses
Watch the back of the hock for a new firm swell, heat, or a shorter hock stride and rest rather than working through it
Do not treat a photo, a back-of-hock swell, or a scan result as a diagnosis
Conformation photos can help you and the vet look at the back-of-hock swell — they do not confirm or rule out curb, and they cannot tell curb from bone spavin, bog spavin, a capped hock, a sprain, or a bowed tendon

What to do

1
Book a vet visit if you find a firm swell a few inches below 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 back-of-hock swell hoping it will settle.
3
Photograph the back-of-hock 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 back-of-hock swell to share, not as a curb test. There is no curb scanner.
5
If curb (plantar tarsal ligament thickening) 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 firm swell a few inches below the point of the hock, if the swell is hot or painful, if the horse is short on that limb, or if the hock stride shortens 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 curb. A still cannot tell curb from bone spavin, bog spavin, a capped hock, a sprain, or a bowed tendon. Diagnosis is a vet exam. The conformation scan is a first look at the back-of-hock swell, not a verdict, and there is no curb scanner.

Get a first look at the back-of-hock swell

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Scan conformation

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Educational content only. Not a substitute for veterinary advice.