Myositis ossificans (also known as heterotopic ossification) is a condition marked by muscle tissue being replaced by bone. The condition is also referred to as heterotopic ossification.

The condition is considered to be a non-tumor or false tumor (pseudotumor) condition referred to as a stress-reactive lesion occurring mostly in the extremities. The condition is usually found in the quadriceps muscle, and is caused by a direct blow or a tearing injury to the muscle. Myositis ossificans (also known as heterotopic ossification) most often occurs after an injury. However, there may or may not be a history of injury.

The condition may not develop for several months after an injury, or it may not be associated with an injury. Stress fractures may be a symptom, and there may be stiffness in the neck and back, progressing to rigidity of the spine, trunk and limbs.

Tests include x-rays which show mature peripheral ossification patterns. X-rays are done to rule out sarcoma. Other tests include: complete blood count (CBC) which shows phagocytosis and an elevated erythrocyte sedimentation rate (ESR). Electromyography and a muscle biopsy with histological studies are other tests included in the diagnosis.

Treatment may include the administration of bisphosphonates to prevent the abnormal deposition of bone. Surgery is the only effective treatment once the diagnosis of myositis ossificans (also known as heterotopic ossification) has been established.

Residuals may include extreme weakness of muscles requiring the person to be wheelchair-bound or bedridden. There may be an inability to lift the head off the pillow and contractures may be present. The person may be on maintenance dosages of corticosteroids indefinitely.

• The rating schedule for musculoskeletal was updated on February 7, 2021. Protection still does apply and should be considered with existing evaluations (38 CFR 3.951(a)).

• If Diagnostic Code 5023 applies, rate on limitation of motion of affected parts as arthritis degenerative. 38 CFR 4.71a [Schedule of ratings-musculoskeletal system]

• The provisions for 10 and 20 percent evaluations for arthritis with multiple joint involvement without limitation of motion do not apply to these conditions as is reflected in Note (2) under DC 5003.

• Evaluate the diseases under diagnostic codes 5013 through 5024 as degenerative arthritis, based on limitation of motion of affected parts.