Heterotopic ossification arising from an anterolateral thigh free flap donor site: a previously unreported phenomenon

Heterotopic ossification is defined as abnormal bone deposition within non-skeletal tissues. Although it is rare, it has been associated with a history of trauma and surgical interventions. Herein, we present the case of a 74-year-old male patient, who was referred to our specialist center with a high-grade myxofibrosarcoma affecting his left knee. After a multidisciplinary discussion, wide resection and reconstruction with a contralateral free anterolateral thigh (ALT) free flap were performed. A 25 × 12 cm flap was harvested and its donor site repaired using a split-thickness skin graft, followed by adjuvant radiotherapy. Over the course of 9 months following radiotherapy, the patient slowly developed a painless swelling on his right thigh. On examination, he presented a hard, raised mass measuring 12 × 5 cm under the healed split-thickness skin graft on the ALT donor site (Fig. 1). The mass did not affect his mobility. Plain X-ray films (Fig. 2A) and a computed tomography scan (Fig. 2B) were obtained and evaluated by senior radiologists with experience in sarcoma surgery, who agreed that the findings were consistent with heterotopic ossification and that histological confirmation was not required. The patient was reassured, and no further surgical intervention was sought