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Capped Hock

A capped hock represents a swelling over the point of the horse’s hock (tarsus). If you look at your horse from the side, the point of the hock is located on the back of the hock where the tendons turn the corner and then head down the lower leg.

The anatomy of the hock is complicated because of the number of vital structures in this area. The digital flexor tendons run over the back of the hock and one of their functions is to extend the hock.

A bursa is a small pillow filled with synovial fluid that cushions tendons as they run over or around a bony prominence. At the point of the hock, there are up to three bursae interposed between the local tendons. These three bursae do not communicate in all horses, but they can. This consideration is very important if infection is involved.

A capped hock usually involves the most superficial bursa, which is located just under the skin. This seems logical as capped hocks are usually the result of external trauma and the most superficial bursa is most likely to be injured.

If one of the deeper bursae is involved, this is sometimes referred to as a deep capped hock. This deeper swelling often appears as two distinct prominences on either side of the superficial digital flexor tendon above the point of the hock. A deep capped hock can cause lameness due to local pressure and inflammation, but usually improves with rest.

Capped hocks almost always merely represent a cosmetic blemish, but if a wound is involved, the bursa can become infected which represents a much more serious condition.

A capped hock results from external trauma to the point of the hock. It can often be self-inflicted by kicking the walls of the box or a trailer. This results in inflammation of the bursa, which causes increased production of synovial fluid within the bursa. This leads to the characteristic appearance of a soft, fluid-filled swelling over the point of the hock. If your horse has a capped hock, the swelling will not usually be painful and your horse won’t be lame. If your horse is lame, infection could be present so you should call your vet immediately.

Much less commonly, the bursa becomes infected during the original injury. These cases are much more serious because the infection can extend into the deeper bursae. In these cases, there is usually a skin wound present and the horse is lame. The severity of lameness varies between cases, from mild to severe; and the degree of lameness often relates to whether or not the infection is draining through a skin defect. If there is no drainage and pressure builds up in the bursa, the lameness becomes more severe.

If your vet examines your horse for a swelling around the hock, an ultrasound examination may be recommended to visualise the soft tissue structures for accumulation of fluid and signs of inflammation. Less commonly, radiographs (x-rays) will be obtained if there is concern over the involvement of underlying bones.

Usually, no treatment is required for capped hock, particularly if your horse is not lame and if there is no wound. In cases where treatment is advised for cosmetic reasons, there is no uniformly successful treatment and many cases are not responsive to any form of treatment. If treatment is advised, your vet may drain the excess fluid under sterile conditions and inject a steroid as an anti-inflammatory drug, followed by bandaging the hock to prevent recurrence of fluid accumulation. Unfortunately, fluid distention of the bursa often returns as soon as this bandage is removed.

The hock is also a difficult area to bandage without creating bandage pressure rubs/sores, but some of the elasticated pressure bandages with a side zip can be useful as they uniformly distribute pressure and make these complications less likely.

With any therapeutic or diagnostic injection into a joint or bursa, infection is a real risk and benefits of draining a cosmetic swelling must be weighted against the potential risk of infection.

Surgery is also usually avoided as incisions in this area heal poorly and frequently break down due to high local skin tension.