The most likely problem for this patient is a condition known as myositis ossificans, a problem involving localized calcium deposits in soft tissue. This condition can develop following significant blunt force trauma to soft tissue. It also can result following penetrating trauma as well as surgically related tissue injury. There are actually two forms of myositis, one being trauma related, the other, the progressive form, actually involves an autosomal dominant genetic abnormality. The case presented above obviously was specifically trauma related.
The diagnosis of this condition involves obtaining a detailed history that may reveal precedent trauma as in this case. On exam, pain and tenderness as well as a finding of a palpable soft tissue mass may be helpful. However, the problem may be lodged deep within the muscle mass, and in that case no mass may be palpable. At times this condition may be totally asymptomatic, and may only be uncovered as an incidental finding years following the trauma on x-rays taken for other indications. The majority of myositis ossificans cases involve the thigh or the upper extremity, but this problem can be seen in other large muscles such as the gluteal or pectoral muscles.
On plain x-ray, myositis ossificans will appear as a circumscribed often circular area of calcification, which is frequently adherent to the periosteum. Because the differential diagnosis includes osteosarcoma, review of these films in conjunction with a radiologist is prudent.
Treatment involves immobilization of the injured part for seven to 10 days followed by increasing exercise. Surgical intervention is occasionally needed when ossifications mechanically interfere with joints or nerves, but surgery usually should be delayed for 12–24 months until the lesion has matured and the extent of associated injury is clear.