Just A Blemish?

Horse & Hound|May 14, 2020

Just A Blemish?
If a puffy lump appears on a hock joint, how worried should we be? Matt Smith MRCVS discusses the significance of swellings
Matt Smith

Fluid-filled swellings around the hock are not uncommon. Some may be innocuous, but others represent a potentially significant injury that requires investigation and treatment.

It can be difficult for even the trained eye to discern whether a particular lump is worth worrying about, but it may be useful to ask yourself the following:

is it a new swelling?

has lameness developed alongside its appearance?

is it warm, or painful to touch?

is it large or tense?

If the answer to any point is yes, it would be prudent to consult your vet. Conversely, if it has been there as long as you can remember and doesn’t appear to be causing a problem, it may be sufficient to monitor the swelling but otherwise leave it alone unless changes occur.

A COMPLEX STRUCTURE

WHY do swellings arise?

The hock is complex, comprising at least six different bones, four major joints, various supporting ligaments and a number of tendons. As the muscles above the hock contract, they pull on the tendons and cause the leg to flex and extend.

To ensure a smooth, gliding action, the tendons are bathed in synovial fluid – a thick, lubricating substance found in capsules called tendon sheaths and bursae. The difference between these is purely anatomical: sheaths encircle one or more tendons, whereas bursae are interposed between two surfaces, such as tendon and bone or cartilage.

The swelling of a joint, tendon sheath or bursa occurs as a response to inflammation – spaces open up in the synovial membrane (the tissue lining the capsule), allowing more cells, protein and fluid to enter and causing visible swelling. This inflammation of the synovial membrane (known as synovitis) is a sign of an underlying problem, rather than being the problem itself.

Common causes of joint swelling include chip fractures, arthritis and the developmental condition osteochondritis dissecans (OCD), which results in loose fragments of bone or flaps of cartilage within the joint. Tendon injuries usually cause swellings in tendon sheaths and bursae. At the milder end of the spectrum, synovitis with no underlying structural injury can occur following periods of hard work.

There is no known link with poor conformation – nor are these injuries more frequent in a particular discipline or type of horse. While most causes must be a result of over-stressing a tendon or the affected structure, their occurrence is sporadic. It’s a bit like twisting your ankle – there’s little you can do to reduce risk.

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May 14, 2020