Heterotopic ossification refers to the growth of bone material in the soft tissues of the body, including muscles, tendons, and fascia. The severity of the conditions varies; some patients only have small nodules of excess bone which are noted on x-rays, while others suffer severe and debilitating pain. The cause of heterotopic ossification is not fully understood, and the most effective treatment for the condition is aggressive surgery, although some doctors have had success with radiation.

”Heterotopic” essentially means “wrong place,” while “ossification” refers to bone formation. Originally, heterotopic ossification was grouped under the heading “myositis ossificans,” along with an assortment of similar conditions. This term is no longer widely used in reference to heterotopic ossification, since the problem is not confined to the muscles. A related condition, ossifying fibromyopathy, usually confines itself to the fibrous tissue of the body, while periarticular ossification can be found in the region around the joints.

Study on heterotopic ossification has suggested that it may be linked to injuries to the spinal cord, along with neurological conditions. It appears that mixed signals in the body stimulate normally dormant osteoprogenitor cells, causing them to start growing bone. When these cells are in the soft tissues of the body, it results in heterotopic ossification. The condition often appears in the form of periarticular ossification, especially around the site of hip injuries.

When heterotopic ossification is caused by trauma or an injury, it is known as heterotopic ossification traumatica, while a case with no known cause is termed “atraumatica.” Heterotopic bone formation has also been known to strike amputees, especially those who have experienced violent or traumatic amputations such as victims of mines. In amputees, the condition can cause serious problems, as surgeons may have to amputate part of the residual limb to treat the condition, thus making the amputation even more severe.

While not inherently painful by nature, heterotopic ossification can become painful. Severe cases may restrict the patient's movement, or cause internal bruising and injury. Typically, anti-inflammatories and pain medication will be prescribed to bring the rate of soft tissue swelling down and ease the pain associated with the condition. If it becomes clear that the heterotopic ossification is spreading, the patient will have to have surgery to remove the offending bone material, in the hopes of removing the rogue osteoprogenitor cells. In some cases, surgeons may have to replace an entire joint, if the new bone formation has surrounded or damaged the joint too extensively.