Review Question - QID 215803

XR and MRI of this patient show an ossified mass within the quadriceps muscle. This in conjunction with his age and history of playing football make myositis ossificans the most likely diagnosis.

Myositis Ossificans is a reactive soft tissue bone-forming process that commonly occurs following a traumatic event to soft tissues. Patients typically present with a painful swollen mass that upon imaging is found to be within a muscle belly (Figure B). Treatment typically consists of rest, icing and activity modifications. Physical therapy is often recommended, however, passive range of motion is contraindicated as it typically worsens this conditions. Surgery is offered as a last resort if symptoms are present for >6 months and the lesion has matured.

Beiner et al. reviewed muscle contusion injuries and myositis ossificans. Three different types of MO exist: (1) stalk type (thin stalk of bone connecting ossified muscle to underlying bone), (2) periosteal type (broad-based ossification in contact with underlying bone, (3) non-connected type (derived entirely from muscle, not connected to underlying bone. They conclude that surgical removal should be delayed until the bone has matured (up to 1 year) and no longer shows increased uptake on a bone scan.

Tyler et al review the imaging of myositis ossificans. They report that myositis ossificans (MO) is characterized by abnormal heterotopic bone formation involving striated muscle, tendons, ligaments, fasciae, and aponeuroses. Further, the myocardium, the diaphragm, tongue, larynx, smooth muscle, and sphincters are all spared with this condition. They conclude that there are several types including posttraumatic myositis ossificans (PTMO), nontraumatic/pseudomalignant myositis ossificans, and myositis ossificans progressiva (MOP).

Figure A demonstrates a lateral radiograph of the femur with an ossified structured visualized anterior to the femur. Figure B is the axial MRI of the same patient showing ossification within the quadriceps muscle.

Incorrect Answers:
Answer 1: Mutation of the COMP gene is associated with pseudochondroplasia and MED Type 1.
Answer 2: Abnormal Type X collagen is seen in Schmid subtype of metaphyseal chondrodysplasia, not myositis ossificans.
Answer 3: Translocation of 9:22 is linked to myxoid chondrosarcoma.
Answer 5: Mutation of p53 is associated with numerous cancers, including osteosarcoma, but there is no association with myositis ossificans.