Orthopaedic Case of the Month: Ossified Calf Mass in a 32-year-old Woman

Abstract

A 32-year-old woman presented with onset of progressive left leg pain and swelling after minor trauma 8 weeks previously. Approximately 6 weeks after injury, she was evaluated by a physician at an outside hospital and was prescribed crutches. Imaging studies at that time revealed a calf mass. She then was referred to our orthopaedic clinic for further evaluation. The pain was aggravated by walking, prolonged sitting, or standing. On physical examination, her left calf was tender to palpation and asymmetrically enlarged relative to the contralateral side. A calf mass was palpated. The mass extended from the proximal popliteal fossa down to the lower distal third of the tibia, clinically measured approximately 18 cm, was firm throughout its length, not freely movable from the tibia, and appeared to be deep to the subcutaneous tissue. Radiographic and MR evaluations of the patient's left calf were performed. Based on the history, physical examination, and imaging studies, what is the differential diagnosis? A biopsy of the mass initially was performed 2 months after the onset of symptoms. The initial biopsy sections were interpreted as showing heterotopic ossification without evidence of malignant cells.