Fibrotic or ossifying myopathy is a mechanical lameness caused by improper healing of an old injury to a muscle belly. Scar tissue forms and the muscle loses its ability to stretch. The result is the appendage loses its ability to move through the normal range of motion. There are several muscles in the horse that seem to be predisposed to this complication. Either term fibrotic myopathy or fibrotic myositis are correct and whether it is fibrotic or ossified depends on the age and extent of the injury. This article discusses the clinical signs, treatment, and most importantly prevention following injury.

In most cases fibrotic and ossifying myopathy is a complication of external trauma to affected muscles, subsequent inflammation, and fibrosis. Occasionally it is associated with work and is seen in QH that are required to perform abrupt turns and sliding stops. Horses caught in ropes or fences may struggle violently enough to induce sufficient trauma and FM. In one report five of 18 horses developed this condition secondary to intramuscular injections of the hind legs.

A congenital form of fibrotic myopathy has also been described. Affected animals are usually less than 12 months old when clinical signs are first evident. Horses affected with this form of the disorder frequently have no palpable thickening of affected muscles or tendons and no history or evidence of trauma.