Myositis ossificans (MO) occurs when bone or bone-like tissue grows where it’s not supposed to. It most commonly happens in your muscle after an injury — like when you get hit hard in the thigh during a soccer game or maybe after a car or bicycle accident.

About of the time, these bony growths develop in the muscles of your thigh or upper arm.

MO is typically caused by direct trauma to the muscle, like a knee to the thigh in rugby or landing hard on the ground in a bike accident. If you develop a large contusion (bruise) and a pool of blood forms a lump over the injury (hematoma), bone may grow at the injury site. This is responsible for of MO cases.

Repeated minor trauma — sometimes seen on the inside thighs of horseback riders — can also result in MO. Fractures and surgery, especially hip replacement, are other possible causes.

Although larger muscles of the upper arm and thigh are most commonly affected, MO can also occur in fat or connective tissue like tendons, ligaments, and fascia.

Sports injuries or accidents usually initiate MO. Adolescents and young adults in their 20s are to develop MO. It’s rare for to get the condition. People who have paraplegia are to MO, but usually with no evidence of trauma.

Most contusions, strains, and hematomas will start to feel better after a few days or weeks with RICE therapy: rest, ice, compression, and elevation.

But with MO, your pain will increase and your range of motion in the affected leg or arm will get worse within after your initial injury.

The injury site will swell and feel warm or hot to the touch. You may feel a lump in the muscle. Pain and tenderness can be severe, but will be limited to the injured muscle. Your movement in that limb will be limited. It’s unlikely you’ll have a fever.

If your injury doesn’t start to feel better after 10 to 14 days of RICE therapy, your doctor may suspect MO.

To make a diagnosis, your doctor will examine the affected area and ask you questions about:

  • how you injured it
  • how long ago the injury happened
  • how you’ve taken care of it

Within two to four weeks after the initial injury, any new bone growth can be seen on an X-ray. This will help your doctor make the final diagnosis.

Your doctor may also order other imaging tests. These may include a diagnostic ultrasound, MRI, CT, or bone scan. However, an X-ray is usually enough to see the bone growth.

Other diseases characterized by bony tissue growing where it doesn’t belong include fibrodysplasia (myositis) ossificans progressiva and extraskeletal osteosarcoma.

Fibrodysplasia ossificans progressiva is a that’s seen in children under the age of 10. Extraskeletal osteosarcoma is a that’s seldom seen in people younger than 40.

You may be able to prevent MO by properly taking care of your injury in the first two weeks. You can reduce inflammation by immobilizing the affected muscle with slight compression, icing, and elevation.

Contusions and strains are vulnerable to additional trauma during the first couple of weeks. Avoid heavy activity, massage, and forceful stretching.

If MO has already been diagnosed, your treatment will be similar to what you did right after the injury first occurred. Physical therapy is generally conservative, as symptoms and the size of the bony mass will shrink over time.

Home remedies

Some things you can do at home include:

  • Rest: You don’t have to just lie there, but don’t stress the muscle too much.
  • Ice: Apply for 15 to 20 minutes at a time.
  • Compression: Wrap an elastic bandage firmly around your injury to minimize swelling and keep the area stable.
  • Elevation: Raise your injured limb above the level of your heart to help drain excess fluid from the area.
  • Non-painful stretching and strengthening: Gently stretch the affected muscle and start doing strengthening exercises when your doctor says it’s OK. Don’t perform any movements to the point of pain.

Medications and orthotics

You can take nonsteroidal anti-inflammatory drugs like ibuprofen (Advil) or naproxen (Aleve) to reduce pain and swelling. Topical treatments like Biofreeze or Tiger Balm can also help ease pain.

When your pain and movement allow you to get back to sports, wear some padding or other protection on the injured muscle to prevent additional damage.

Physical therapy and surgery

A physical therapist may use these methods to decrease your pain, increase your mobility, and get you on the playing field again:

  • Passive range of motion and mobilization: This is when a person or machine moves your body parts for you.
  • Active range of motion and mobilization: This is when you use your own strength to move your body parts.
  • Ultrasound therapy: Sound waves can provide deep heating to speed healing.
  • Extracorporeal shock wave therapy (ESWT): High-energy sound waves (shock waves) to the injured muscle, helping it heal more quickly.

If conservative treatments don’t relieve your pain and restore your range of motion, you and your doctor may consider surgery. Surgery happens after the bony mass has stopped developing. The removal of the bone mass will cure MO.

With nonsurgical treatment, stiffness and tenderness about one year.

It’s important to follow your physical therapist or doctor’s instructions for increasing your:

  • activity level
  • range-of-motion exercises
  • stretching
  • strengthening

Doing too much too soon can worsen MO. But not working to recover your range of motion when the doctor says it’s safe may make your pain and stiffness last longer.

Small ossifications (bony masses) may resolve without any long-term effects. Larger masses may end up needing surgery. But once removed, the bone mass is unlikely to return unless you injure that muscle again.