Myositis ossificans is a condition where bone tissue forms inside muscle or other soft tissue after an injury. It tends to develop in young adults and athletes who are more likely to experience traumatic injuries. Most of the time, myositis ossificans occurs in the large muscles of the arms or the legs.
Myositis ossificans usually occurs where a person has experienced a single traumatic injury, such as sustaining a hit while playing football or soccer that causes a deep muscle bruise.
It can also happen when there is a repetitive injury to the same area, such as in the thighs of horseback riders. Very rarely, myositis ossificans can occur after a severe muscle strain.
Regardless of the cause, myositis ossificans happens when the body makes an error in the healing process. Muscle cells, also known as fibroblasts, are accidentally replaced by immature bone cells at the site of the injury.
Eventually, this can cause a hard lump or bump to develop within the muscle. This is a gradual process and begins within a few weeks after the initial injury.
It can be hard to predict who will get myositis ossificans, but the condition is more prevalent in active young adults and athletes.
Myositis ossificans occurs in people who participate in sport at all levels, from those who are playing just for fun through to highly competitive or professional athletes.
Also, people who are paralyzed from the waist down are more likely to develop myositis ossificans, even if they do not have a specific injury.