They are usually due to the sheaths surrounding the tendons becoming distended with synovia.
"Common Diseases of Farm Animals"
R. A. Craig, D. V. M.
This, however, must be performed with care, especially if a flow of synovia is absent.
"Diseases of the Horse's Foot"
Harry Caulton Reeks
Healthy granulation may be profuse in one spot, while in another it may be checked either by a flow of synovia from the still open bursa, or by fragments of bone or of tendon still acting as foreign bodies in the wound.
"Diseases of the Horse's Foot"
Harry Caulton Reeks