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.

Causes

Myositis ossificans is often caused by a single traumatic injury.

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 inactive 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.

Symptoms

Unlike other typical muscle strains or injuries, people with myositis ossificans may notice that their pain worsens with time instead of getting better.

Someone with this condition may also notice changes in the affected muscle, including:

  • warmth
  • swelling
  • a lump or bump
  • decreased range of motion

Diagnosis

An MRI may help diagnose myositis ossificans.

Before diagnosing myositis ossificans, a doctor will ask about what happened, how long ago it happened, the symptoms, and what steps a person has taken to manage the pain or injury.

If it has been at least 2–3 weeks since the pain or other symptoms started, the doctor may order some imaging tests to look for evidence of bone growth in the soft tissue.

The types of tests that the doctor may use include:

  • X-ray: It can be difficult to diagnose myositis ossificans in the early stages with just an X-ray. Most X-rays will not show up any abnormalities in the first 2–3 weeks following the injury but will show changes after 3–4 weeks.
  • Ultrasound: Ultrasounds use sound waves to look at the soft tissues. They are one early diagnostic test that can be used to look for the changes associated with myositis ossificans. Ultrasonography depends on the ability of the person reading the scans, so many doctors do not often recommend it as the first test.
  • Computed tomography (CT) scan: Doctors can usually see the early development of bone tissue in soft tissues. However, it is not 100 percent reliable, and if a doctor suspects that someone has myositis ossificans, they may carry out additional testing to make the diagnosis.
  • Magnetic resonance imaging (MRI): An MRI is a preferred method of looking at soft tissue growths. A doctor may still order additional tests to compare and confirm a diagnosis.

A biopsy of the growth may also be taken and evaluated in a lab.

Sometimes, early diagnostic testing can confuse myositis ossificans with certain types of soft tissue cancers. As a result, the doctor may order additional testing to confirm the diagnosis.

Treatment

Myositis ossificans usually resolves on its own. Taking pain relievers, such as naproxen or ibuprofen, can help relieve discomfort.

Other things that a person can do at home include:

  • resting the area
  • icing the injury
  • elevating the affected area
  • gentle stretching
  • wrapping the affected muscle with an elastic bandage to reduce swelling

After the first 48 to 72 hours, a person can start physical therapy to build up strength in the muscle.

Therapy should start with an assisted range of motion exercises — this involves moving the joints slowly and gently in all directions to see how far they will go — and gradually progressing into full dynamic exercise as the muscle regains strength.

If pain relievers, physical therapy, and other home care measures are not effective in treating myositis ossificans, surgical removal of the growth may be needed.

Surgery is usually only used in cases with:

  • severe pain
  • growths that interfere with nearby nerves, joints, or blood vessels
  • poor range of motion that makes it difficult to perform daily activities

The doctor or surgeon may recommend delaying surgery for a period to reduce the risk that myositis ossificans will reoccur.

Prevention

Every injury should be treated using the R.I.C.E method, which includes holding ice on the injury.

While it can be difficult to predict who will get myositis ossificans, it is important to treat every injury promptly using the R.I.C.E. method. This is:

  • Rest
  • Ice
  • Compression
  • Elevation

An athlete who sustains an injury may need to leave the game or event, especially if there is significant swelling or bruising.

Gentle stretching and range of motion exercises are also essential after an injury; myositis ossificans is more likely to affect a muscle that is not being used.

If the symptoms do not resolve on their own or with proper home care, it is important to see a doctor.

Outlook

The outlook for someone with myositis ossificans is good. The condition usually resolves with home care, though some people will have stiffness or discomfort for up to a year after the initial injury.

It is important to rest after an injury and follow a treatment plan recommended by a doctor or physical therapist.

Someone with myositis ossificans should make sure they follow all instructions about activity, stretching, and other exercises to ensure they do not injure the limb further.