A hook situated on the inside and bottom end of the thigh bone, on its hind leg, cups the patella and the medial patella ligament, so preventing the leg from bending. Concussion is a contributory cause. They can be caused by poor conformation or striking the leg with the other foot. Protective boots can help prevent splints. Both of these conditions are more common in younger horses and if suspected veterinary advice sought.
Synovia is the name of the oily fluid that lubricates joints and tendons.
It's secreted by a membrane that covers the joint or forms a protective sheath over a tendon. Synovia is also present over prominent bony points such as the elbows and hocks. If a bursa becomes infected, abscesses may form and permanent damage caused if urgent veterinary treatment is not given. It occurs on the front and towards the side of the hock. Faulty conformation, mineral imbalance and injury to the hock joints are all possible causes of bog spavin.