Post traumatic myositisossificans is a benign condition of heterotropic ossification of unknown aetiology which typically is related to trauma from a single blow or repeated episodes of microtrauma. We describe an unusual case of myositis ossificans which developed as a complication at the donor site for hamstring autologous graft used in open anterior and posterior cruciate repair and posterolateral corner reconstruction in a 15 year old girl.

Case report: A 15 year old girl sustained a closed traumatic dislocation of her left knee when she fell from a trampoline. She underwent emergency manipulation under anaesthetic and closed reduction followed by MRI scan which showed a complete disruption of the lateral collateral ligament complex, posterolateral corner injury, complete tears of the anterior and posterior cruciate ligaments and a partial tear of the medial collateral ligament.

13 days later she had an open reconstruction of her anterior and posterior cruciate ligaments with allograft and a repair of popliteus and lateral structures with Larson reinforcement with controlateral hamstring autologous graft.

Eight months following open reconstruction the patient represented to her primary care practitioner with a painful lump in the postero-medial controlateral right thigh. MRI study showed that there was a lobulated hypervascular appearance with a thin enhancing rim of low signal on all sequences indicating calcification. An xray revealed a calcified mass consistent with the diagnosis of myositis ossificans.

Discussion and conclusion: To date we have found no reported cases of myositis ossificans occurring as a result of surgery to harvest hamstring autograft in the setting of ligament reconstruction about the knee. We believe that this is an unusual complication of the donor site which needs awareness amongst clinicians involved in primary and revision cruciate ligament reconstruction. We suggest that a management strategy of surveillance for this lesion is appropriate and excision biopsy should be reserved for specific indications such as malignant features on imaging or mass effect.