Heterotopic Ossification

What is heterotopic ossification?

Heterotopic ossification (HO) means bone grows in tissues where it typically wouldn’t. These bone fragments are extraskeletal bone. They often form after an injury. But they may occur for no known reason.

For most people, extraskeletal bone fragments are small and don’t cause many symptoms. Large bone pieces may restrict your movement and cause severe problems.

What are the types of heterotopic ossification?

Heterotopic ossification can be:

• Nongenetic: These can affect people of all ages. Sometimes they occur with no known cause. More often, they’re a response to some sort of trauma. That trauma can be an injury or it may be the trauma of surgery.
• Genetic: These types are far less common. Genetic types are more likely to cause malformations in your spine, hands or feet. Genetic heterotopic ossification can be severe.

Who might get heterotopic ossification?

Anyone can get nongenetic heterotopic ossification. You're most likely to develop it if you have a history of injuries or surgeries.

Up to 3 in 4 people who have HO can point to trauma that led to the condition. It commonly affects people who have:

• Spinal cord injuries: About 2 to 3 in 10 people.
• Head trauma: One or 2 in 10 people with closed-head injury.
• Total hip replacement: Heterotrophic ossification following total hip replacement surgery is usually minor when it occurs, but occasionally limits motion and causes stiffness.
• Amputation after traumatic injury: More than 9 in 10 people.

About half of all people with non-genetic HO are adults in their 20s and 30s. Men are slightly more likely than women to get HO.

The genetic types are rare. Experts estimate that fewer than 5,000 people worldwide have the genetic diseases that cause HO.

How does heterotopic ossification affect my body?

HO can affect any part of your body. But you are most likely to get it in areas that are most likely to get injured, such as your:

• Elbow.
• Fingers.
• Neck or head.
• Pelvis.
• Shoulder.
• Thigh.

What causes heterotopic ossification?

Often, you develop heterotopic ossification after an injury. It may also occur after surgery. People who have a total hip replacement can occasionally develop HO, but it rarely causes symptoms.

You have a higher risk of developing HO if you have had a:

• Bone fracture.
• Burn.
• Spine injury.
• Total joint replacement.
• Traumatic brain injury (TBI).

Rarely, some genetic diseases cause HO, including:

• Fibrodysplasia ossificans progressiva (FOP), which used to be widely known as myositis ossificans progressiva.
• Progressive osseous heteroplasia (POH).

What are the symptoms of nongenetic heterotopic ossification?

Heterotopic ossification symptoms can vary. They depend on how far the disease has progressed and how severe it is. In its early stages, heterotopic ossification often causes:

• Pain.
• Swelling.
• Tenderness.

As heterotopic ossification advances, you may notice a bump under your skin. The bump may grow quickly into a large lump that you can’t easily move with your fingers. It may be tender to the touch.

In later stages, the lump may harden. If it’s near a joint, such as your hip or shoulder, it may restrict your range of motion.

What are the symptoms of genetic heterotopic ossification?

If you have FOP that leads to heterotopic ossification, you may have:

• Misshapen big toe.
• Spinal malformations.
• Structural problems in your fingers.

As FOP progresses, most people have severe symptoms, including difficulty walking or even breathing. This rare cause of HO can shorten your lifespan.

POH is associated with symptoms that affect your skin. In this form, bones form in subcutaneous tissue, the layer of fat between your skin and muscle. As the disease progresses, bones may form in your deeper connective tissues.

How is heterotopic ossification diagnosed?

To diagnose heterotopic ossification, your provider may use imaging tests such as a:

• CT scan.
• MRI.
• Positron emission tomography (PET) scan.
• Ultrasound.
• X-ray.

If your provider suspects you have a genetic form of heterotopic ossification, they may avoid a biopsy. In certain types of genetic HO, any surgery can increase your risk of bone growths spreading to other parts of your body.

How do doctors diagnose heterotopic ossification after total hip arthroplasty?

If you develop HO after total hip arthroplasty (hip replacement), your provider may use grading scales to assess how much HO has progressed.

One of the most widely used grading systems is the Brooker classification. This scale rates heterotopic ossification as:

• Grade 1: Small pieces of bone in the tissue surrounding your hip.
• Grade 2: Irregular bone growths (bone spurs) around your pelvis or thigh bone (femur), spaced at least 1 centimeter apart.
• Grade 3: Bone spurs around your pelvis or femur spaced less than 1 centimeter apart.
• Grade 4: Rigidity or bone fusion (ankylosis) in your hip joint.

Other grading scales look for similar signs of HO. The most significant factor in HO severity is whether you have bone spurs and how far apart the spurs are.

How is heterotopic ossification treated?

Heterotopic ossification treatment varies depending on symptoms, type of HO and the condition’s progression. In general, your healthcare provider may recommend:

• Medications such as corticosteroids to treat HO flare-ups in people with genetic heterotopic ossification.
• Physical therapy to increase range of motion and decrease pain.
• Surgery to remove heterotopic ossification that causes severe pain or restrictions in your daily function. These surgeries are often a last resort, as there is a chance that the HO can form again. Often, if surgery is indicated, medical treatment and radiation therapy will be done afterward to help prevent regrowth of the bone.

How can I prevent heterotopic ossification?

If you’re scheduled for orthopedic surgery, your provider may prescribe treatments to lower your risk of HO. You have a higher risk of HO after hip replacement surgery if you also have:

• Ankylosing spondylitis.
• Osteoarthritis.
• History of HO.

Your provider may use a preventive treatment to improve your chance of an excellent total hip arthroplasty outcome. Some studies have shown that taking nonsteroidal anti-inflammatory drugs (NSAIDs) before or immediately after surgery can decrease your risk of postsurgical HO.

There’s no guaranteed way to prevent heterotopic ossification. But you may lower your risk by treating injuries right away with rest, ice, compression and elevation (RICE). You may also prevent injuries with strength training, stretching and rest.

Does heterotopic ossification go away?

Sometimes. People with nongenetic HO often have a full recovery. Often, HO that develops after an injury goes away with nonsurgical treatment such as rest, ice and light stretching.

There’s no cure for genetic types of HO. You may manage symptoms with treatment, but the disease continues to progress.

What else should I ask my doctor?

You may also want to ask your healthcare provider:

• What type of HO do I have?
• What is the most likely cause of HO?
• What are the treatments for heterotopic ossification?
• Are there lifestyle changes I can make to prevent HO?
• What are the chances that I’ll pass genetic HO to my children?

Is heterotopic ossification painful?

Yes. Pain near the affected area is one of the most common symptoms of heterotopic ossification. Often, pain worsens as the bony growths get bigger.

But there is good news if you develop heterotopic ossification after an injury or surgery. Most people with nongenetic HO fully recover with treatment.

Does osteoporosis affect my risk of postoperative HO?

No. Some conditions can increase your risk of developing HO after surgery. But there’s no proven link between osteoporosis and HO.

A note from Cleveland Clinic

Heterotopic ossification occurs when bone tissue develops in your soft tissues. Some people develop HO after an injury or surgery. Others have genetic types of HO. Genetic HO is rare and causes severe symptoms. People with nongenetic HO can often treat it with nonsurgical methods. You may take NSAIDs or work with a physical therapist to treat nongenetic HO.