Hygromas are thought to be the body's reaction to repeated trauma to
an area in which bone lines close to the surface of the skin. Usually they
occur on elbows. They are a collection of serum in a thick capsule that
the body builds to cushion the area. Affected dogs are not usually lame.
If these are small, just providing padding over the area can allow them
to either maintain their present size or even shrink. However, since they
can get to be pretty large and will occasionally get infected, it is not
uncommon for veterinarians to recommend surgical drainage, usually with
post-operative bandaging to protect the area. If they get really large
and then infected, it can be necessary to do skin grafting to fix the defect
made in removing the hygroma.