Myositis ossificans

Background

Myositis ossificans (MO), also known as heterotopic calcification, is a condition of benign bone deposition within soft tissues, most often skeletal muscle. The condition can arise secondary to one larger traumatic event or repeated small trauma and will be localized to a single muscle or group of muscles involved in the trauma. Alternatively, the condition can be generalized, widespread, progressive and unrelated to trauma. The latter of which is generally considered to be hereditary and has a separate pathophysiology and treatment approach than what is discussed here.

Pathophysiology

The pathophysiology of myositis ossificans is not completely understood but likely involves inappropriate differentiation of mesenchymal stem cells into chondrocytes and osteoblasts in the setting of inflammation.

Clinical Features

Patients often present with reports of pain lasting longer than expected following a trauma to the hip or thigh muscles with associated decreased range of motion. Often there is a palpable painful mass within 2 weeks of the initial trauma.

Typical scenario involves blunt soft tissue injury to the thigh such as with football players who then present with protracted pain and stiffness with a palpable mass in the thigh. Alternatively, those who experience repeated minor trauma such as horseback riders or shooters (rifleman or marksman) may develop pain decreased range of motion in their thighs or deltoid respectively.

Plain radiograph taken two months after injury demonstrates irregular calcification located along muscle on medial aspect of right thigh. Diagnosis was myositis ossificans

Differential Diagnosis

Extremity trauma

• Compartment syndrome
• Contusion
• Crush syndrome
• Degloving injury
  • Morel-Lavallée lesion
  • Ring avulsion injury
• Fracture
  • Open fracture
• Laceration
• Myositis ossificans
• Open joint injury
• Peripheral nerve injury
• Rhabdomyolysis
• Tendon injury
• Vascular injury

Evaluation

The diagnosis of myositis ossificans can be relatively straightforward with a good patient history of an inciting event and a plain radiograph showing peripheral calcifications consistent with the diagnosis. However, early radiographs may be non-specific showing an indeterminate lesion wherein an MRI and biopsy may be necessary. It is important to note that it can be difficult to distinguish MO from malignancy such as a soft-tissue sarcoma without a biopsy. Additional conditions to consider include soft-tissue abscess and calcifying peritendinitis or bursitis.

Management

Thigh Contusion

As soon as possible following injury the patient should have their knee painlessly held in 120 degrees of flexion with a brace or wrap and maintain this flexion for 24 hours. This can help minimize hematoma formation and subsequent MO. Following that, active painless range of motion exercises should begin. NSAIDs can be used for the first 48 to 72 hours only; beyond this NSAIDs can negatively affect healing.

Myositis Ossificans

Surgical management is rarely necessary as MO is often self-limiting and self-resolving. Management is focused on minimizing symptoms and maintaining function of the involved muscle group. Range of motion and strengthening exercises can be used to improve range of motion and function. MO may take as long as 1 year to mature and resolve.

Disposition

Patients benefit from referral to sports medicine specialist or orthopedist for core treatment.

See Also

• Extremity trauma