What is heterotopic ossification?

Heterotopic ossification is a condition where bone forms in soft tissues where bone is not normally found. The word “heterotopic” means “in an abnormal place,” and “ossification” refers to the process of forming bone. In this condition, the body mistakenly creates bone tissue in areas such as muscles, tendons, ligaments, or skin, usually in response to injury or inflammation.

The bone formed in heterotopic ossification is real bone—it contains the same components as normal bone, including osteoid, calcium, and bone-forming cells called osteoblasts. However, because it forms in the wrong location, it can sometimes cause symptoms such as pain, stiffness, or reduced movement.

What causes heterotopic ossification?

Heterotopic ossification can occur after a variety of injuries or procedures.

Common causes include:

• Trauma (such as fractures or blunt injury to muscles).

• Orthopedic surgery, especially hip or knee replacements.

• Spinal cord injury or traumatic brain injury.

• Burns.

• Prolonged immobilization or tissue pressure.

• Certain neurologic or genetic conditions, such as fibrodysplasia ossificans progressiva (FOP), which is a very rare inherited disorder.

The exact mechanism is not fully understood, but it is believed that inflammation, tissue damage, and certain chemical signals trigger immature cells in the tissue to turn into bone-forming cells, leading to bone formation in the wrong place.

What are the symptoms of heterotopic ossification?

Many people with heterotopic ossification have no symptoms and the condition is found incidentally on X-rays or during surgery.

When symptoms do occur, they may include:

• Pain or tenderness in the affected area.

• Swelling or warmth near the site of bone formation.

• Stiffness or limited range of motion, especially around joints.

• A feeling of a hard lump in the muscle or soft tissue.

Symptoms often begin weeks after the injury or surgery, typically as the bone begins to form.

How is heterotopic ossification diagnosed?

Heterotopic ossification is usually diagnosed using imaging studies:

• X-rays can show mature bone forming in soft tissue.

• CT scans or MRI may be used for more detailed evaluation, especially in early stages or before surgery.

• Bone scans can detect early activity before the bone is visible on X-ray.

In some cases, a biopsy is performed to confirm the diagnosis, especially if there is concern for other conditions such as a tumour. Under the microscope, pathologists see osteoid and mature bone forming in soft tissue, often surrounded by inflammatory cells.

How is heterotopic ossification treated?

Treatment depends on the location, severity, and whether the condition is causing symptoms. Many cases do not require treatment and are monitored over time.

Treatment options may include:

• Anti-inflammatory medications (such as NSAIDs) to reduce inflammation and discomfort.

• Physical therapy to maintain joint movement and flexibility.

• Surgical removal of the abnormal bone if it causes significant pain or restricts movement.

• In some cases, radiation therapy is used after surgery to prevent the bone from coming back.

Early detection and treatment may help limit the impact of heterotopic ossification, especially in patients recovering from joint replacement or spinal injury.

Is heterotopic ossification cancer?

No. Heterotopic ossification is not cancer. It is a benign (non-cancerous) process where normal bone forms in an abnormal location. It does not spread to other parts of the body and is not life-threatening, although it can affect mobility and quality of life if it becomes extensive.

Questions to ask your doctor

• What caused the heterotopic ossification in my case?

• Is it likely to grow or cause symptoms?

• Do I need treatment or monitoring?

• Could this affect my recovery after surgery or injury?

• Is there a risk it could come back if removed?