Myocitus refers to a muscle. Ossifying is hardening. The condition is more common in breeds with dense muscles, like Quarter Horses and Mustangs.
Ossifying myopathy is a mechanical lameness caused by improper healing of an old injury to the belly of a muscle (as opposed to the fibrous ends that attach to bone). Scar tissue forms and the muscle loses its ability to stretch. The result is that the leg where the muscle is located loses it’s ability to move through a normal range of motion. There are several muscles in the horse that seem to be predisposed to this complication.
I recently visited a client, a Mustang, that was showing discomfort at the canter going left. Going in the other direction did not seem to be a problem. I worked on her, and much of her body felt great. This mare gets regular body work. Where I did find a lot of tightness and stress was in her left hind above the hock: the gastricnemius and semitendinosus muscle at the back of the thigh. When I watched her walk, the left hock was not flexing as it should. Without X-ray vision, it is impossible for me to determine: Was the tight muscle coming from a bad joint? Or was the hock not flexing because of the tight muscle?
After a good massage session, the mare felt good everywhere except in that left hind. I suggested that my client have the vet come out. He felt that the leg had suffered some recent trauma (maybe a kick or wild pasture play) and confirmed the diagnosis: The muscle healing was being complicated by excessive fibrous connective tissue. The presence of this scar tissue severely restricts the action of the muscle.
In trying to avoid surgery (which has not had great success in other horses), we are all in agreement to try anti-inflammatory treatments, cold laser, DMSO massaged directly into the muscle, heat packs, good nutrition, and light stretching.
I will follow up in a few weeks, and hope to report good progress in returning to an active life for this sweet mare.