Thoroughpin—Should I Worry?

Last Updated on February 26, 2022 by Allison Price

Horse owners wonder what the hock condition is and whether there are any remedies.

Q My 10-year-old part Arabian gelding seems to have a large thoroughpin within the web of his hip. It causes no discomfort for him and doesn’t feel warm to his skin. Is this due to a conformation defect or injury? Is there anything we can do to fix it?

A Threshold is a cosmetic problem of the hip that involves the distention of the tarsal layer of the deep digital tendon above the hock. It is characterized by fluid that runs up and down the leg towards the tarsal sheath. The fluid can also be visible from the outside of your hock. Thoroughpin can be distinguished from bog Spavin, which is a fluid that fills the hock joint.

Thoroughpin typically affects one leg and can vary in size. It is usually of unknown origin. It is not usually associated with heat or pain and doesn’t cause lameness. However, it can lead to chronic conditions that are considered blemishes.

Officially, the swelling is called “tenosynovitis (unknown) origin”. However, trauma can cause damage to the deep digital tendon or hock bones near the tendon. This could be from a blow or penetrating injuries. Poor conformation in the hock area could increase your horse’s risk of developing thoroughpin. Horses who do heavy work could also be at risk because of the additional stress placed on their legs.

Arrange for a lameness examination and imaging of your leg to rule out any other conditions (such bog spavin, capped hock) which could cause a swelling in the hock. Radiographs may reveal changes in the joints and bones around the tendon sheath at the deep digital flexor tendon. Ultrasound can show changes in soft tissues like tendons or ligaments.

Routine cases of thoroughpin do not require treatment. However, treatment can include withdrawing the fluid and injecting hyaluronate or a long-acting Corticosteroid. These procedures may need repeated until the swelling stops. The fluid may be reduced by pressure bandaging the hock after injections. This will help prevent future complications.

Horses with thoroughpin can have a variety of prognoses depending on the underlying cause. The prognosis for horses with idiopathic thoroughpin (again unknown origin) is excellent, except for the cosmetic blemish. Horses that have only minor damage to the tendon sheath or the bone surrounding it can still do well provided there is no damage to the deep digital tendon.

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