The hock joint is comprised of 12 bones, fitting together like a jigsaw puzzle. The multiple joints of the hock flex and move to absorb shock. The two lower joints are the distal intertarsal and tarsometatarsal joints. When fusing occurs, it tends to happens in these two joints.
How Does Fusing Begin?
Fusing begins when the protective cartilage in the joint wears away and synovial fluid production decreases. Bones begin rubbing against each other irritating the bone, promoting bony growth resulting in degenerative joint disease (DJD), or osteoarthritis. Eventually, the bony growth will fuse the bones together.
These radiographs show a hock in the advanced stages of the fusing process. The space between the bones is no longer apparent. A healthy hock joint will have a dark black line, indicating open space, between the bones. Here, we see bright white interrupting what should be a black line. This is bone fusing the hocks together.
Managing Pain Associated with Fusing Hocks
The fusing process is painful. Thankfully, pain can be managed with intraarticular injections (joint injections) of the distal hock joints with a combination of corticosteroids and hyaluronic acid.
3 Types of Fusing Hock Processes
Because hock fusion is a precursor to DJD, it is not reversible. With that in mind, there are three types of hock fusing (arthrodesis) and treatment options:
- Natural Fusion: The horse can be worked with pain management while the joint fuses naturally. This can be a slow, painful process and there is no telling how long it will take. It is estimated less than 25% of hocks will fuse naturally.
- Surgical Arthrodesis: A surgeon will drill away the cartilage lining between the joint‚Äôs bones leaving the subchondral bone exposed and free to grow together. This procedure is performed under general anesthesia. Fusion is estimated to take a year to complete. Your surgeon will recommend pain management options during that process.
- Chemical Arthrodesis: An alcohol solution is injected into the hock destroying the cartilage lining. The subchondral bone is exposed and free to grow together. This is a standing procedure done under local anesthesia. Fusion is expected to take place within a year.
Surgical and chemical arthrodesis is recommended by surgeons when pain from fusing can no longer be managed through injections. If your horse is suffering from hock arthritis, contact your veterinarian.
When Hocks Have Completely Fused
Fusing hocks are not necessarily a bad thing and can almost be looked at as a cure. Once the hocks are completely fused the joint is no longer painful and will no longer require joint injections to manage the pain. In addition, the two lower joints account for very little of the hock’s movement. In most instances, a fused lower hock does not affect the movement or gait of the horse.