Fibrotic myopathy is a mechanical lameness in horses, caused by restriction of the action of the horse's muscles. It occurs when horses injure their semitendinosus and semimembranosus muscles and can present in acute or chronic form. It is frequently caused by performing abrupt turns and sliding stops. It can also be caused by IM injections, trauma, and due to a congenital form. The majority of horses with fibrotic myopathy had a previous history of trauma in the affected leg.

The associated gait abnormality is most obvious when the horse is walking or at a slow trot. The horse's leg appears to jerk suddenly to the ground rather than continue its forward motion.