A hygroma, or a false bursa

Bursa (anatomy)

A bursa is a small fluid-filled sac lined by synovial membrane with an inner capillary layer of slimy fluid . It provides a cushion between bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement...

, is a discrete, fluid-filled sac that can form on the joints of dogs in response to repeated pressure, such as that from sitting on a hard surface. It is treated by draining the fluid and may be prevented by providing padded bedding.

Treatment

An untreated hygroma can develop into in a large enough swelling that stress the surrounding skin and becomes an open wound with the possibility of infection that is much more difficult to treat. In most cases a hygroma is a once in a lifetime occurrence for an animal, bu other individuals will have repeated problems with hygromas.

Surgery or Aspiration

It is common for veterinarians to treat hygromas by aspiration (using a syringe and drawing the fluid out) or surgically placing a drain

Drain (surgery)

A surgical drain is a tube used to remove pus, blood or other fluids from a wound. Drains inserted after surgery do not result in faster wound healing or prevent infection but are sometimes necessary to drain body fluid which may accumulate and in itself become a focus of infection...

. This can address the symptom, but does not treat the cause of the hygroma. In addition any incision at a joint can be difficult to close and may result in an open sore.

Additional Bedding

Providing bedding or other padding in the areas the animal lays down can be helpful. In addition, trauma to the joint may occur during play or other physical activities.