What Is Heterotopic Ossification?

Medically Reviewed by Jabeen Begum, MD on October 11, 2022
5 min read

Heterotopic ossification happens when bone grows outside of its normal location and into the surrounding soft tissues of your body. When this happens, the pieces of bone that develop are called extraskeletal bone growth or fragments. These bone fragments can grow up to three times as fast as normal bone, causing stiffness and pain in your joints.

Heterotopic ossification affects each person differently depending on where and how much extraskeletal bone grows. Most cases of heterotopic ossification happen in the hips, but it can also affect your knees, shoulders, or elbows. 

Continue reading to learn more about heterotopic ossification types, causes, symptoms, treatment options, and more. 

There are two types of heterotopic ossification — genetic and non-genetic.

Genetic heterotopic ossification is very rare. It happens when certain genetic diseases cause extraskeletal bone growth.

Non-genetic heterotopic ossification can happen to anyone, usually after a traumatic injury or hip replacement surgery. Most commonly, heterotopic ossification will happen within 3-12 weeks. In some cases, the abnormal bone fragments can grow in as little as a few days after injury or even several months afterward.

One of the most common heterotopic ossification causes is total hip or joint replacement surgery. Around 90% of people who have a hip replaced will have some form of extraskeletal bone growth, often around the metal hardware used during the surgery.

Other common non-genetic heterotopic ossification causes are:

Most people who have heterotopic ossification have had some type of bone trauma or injury, but there are several other health problems that could cause the condition. These health conditions include:

In very rare cases, people who have certain genetic diseases might develop heterotopic ossification. Fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH) are two diseases that cause abnormal and extraskeletal bone growth.

Genetic heterotopic ossification is very rare, with less than 5,000 people worldwide estimated to have the condition. 

Non-genetic heterotopic ossification can affect anyone but is more likely to develop if you have had a traumatic injury or surgery.

People between the ages of 20-40 are the most likely to develop heterotopic ossification. Men are slightly more likely to have extraskeletal bone growth than women. 

Heterotopic ossification affects each person differently depending on where and how much extraskeletal bone grows. Common early symptoms are tenderness or pain and swelling around the bone fragments. Sometimes people with heterotopic ossification might develop a fever. The fever is usually higher at nighttime than during the day.

As the condition progresses, you will be able to feel the abnormal bone growth as a lump or bump under your skin. If you push it, you won't be able to easily move it. The bone that grows is usually jagged or sharp, so it will probably feel sore to the touch. If the bone fragment grows near a joint, it will eventually become painful and difficult to move or bend as it should. 

If you have genetic heterotopic ossification caused by FOP or POH your symptoms will be a little different.

People with FOP that causes extraskeletal bone growth might have abnormally shaped fingers, toes, and spines. If the bone growth continues, it can affect your ability to walk or even breathe normally. Your doctor will take severe symptoms very seriously as they can affect both the quality and span of your life. 

If you have heterotopic ossification from POH, the bone growth will normally happen in the subcutaneous fat between your skin and muscles. Eventually, the bone growth can also spread to deeper layers of your soft and connective tissues.

Early heterotopic ossification symptoms such as fever, swelling, and joint pain can often be mistaken for other conditions. 

To help rule out other possibilities, your doctor might order blood tests and various imaging tests to look for bone fragments. The imaging tests might include:

If you develop heterotopic ossification after an injury or total hip replacement, your doctor will likely rate the bone fragments on a scale between 1 and 4. The most commonly used grading scale is called the Brooker classification. 

Grade 1 is the earliest stage of heterotopic ossification. In grade 1, you might have small bone fragments growing in the tissue around your hip. 

Grade 2 heterotopic ossification happens when the bone fragments spread to other parts of your pelvis and femur (thigh bone). The bone growths will be at least 1 centimeter apart from each other. 

Grade 3 happens when the growths increase and are less than 1 centimeter apart. 

Grade 4 is the final stage of heterotopic ossification and happens when the bone growth fuses and prevents your joint from moving as it should.

If your doctor gives you a heterotopic ossification diagnosis, there are a few different treatment options available. Your treatment will depend on how much the disease has progressed and how severe your symptoms are. 

Your doctor might prescribe pain relievers or suggest you take certain medications like corticosteroids to help prevent further abnormal bone growth.

Physical therapy is often helpful for many people with heterotopic ossification. The exercises your care provider suggests will help you to maintain or increase your range of motion in your joints. Physical therapy can also help to manage any pain you feel from abnormal bone growth. 

If your heterotopic ossification has become very severe, your doctor might recommend surgery to remove the extraskeletal bone. Surgery is often the last resort for people whose daily lives are significantly affected by the disease. Since the extraskeletal bone growth can come back after surgery, doctors often recommend radiation therapy to keep the bone from regrowing. 

The exact cause of heterotopic ossification is hard to pinpoint, making prevention difficult. Some medications may help to prevent or slow bone growth and therefore decrease your chances of developing heterotopic ossification. 

Coumadin (Warfarin) is a type of blood thinner that might help prevent heterotopic ossification. Vitamin K is necessary for bone development, and Coumadin decreases its efficiency in your body. 

Non-steroidal anti-inflammatory drugs (NSAIDS) might also be effective at preventing bone growth by blocking bone cells from being made.

Make sure to ask your health care provider before taking any medication. It is important to talk to your doctor so you can work together to create a health care plan that is right for you.