Post-traumatic heterotopic ossification of distal tibiofibular syndesmosis mimicking a surface osteosarcoma

AimTo present the imaging features of post-traumatic heterotopic ossification (HO) of the distal tibiofibular syndesmosis initially suspected to be a surface osteosarcoma.Materials and methodsA retrospective review was conducted of the presenting complaint and imaging features of patients with a final diagnosis of HO referred over an 8 year period to a specialist orthopaedic oncology centre.ResultsFive patients with HO were identified. All were adult males with an age range of 19–41 years. There was a history of prior ankle trauma in all cases but the significance was not recognized at the time of referral to the specialist centre. There was radiographic evidence of HO arising from the inner aspects of the distal tibia and fibula approximately 3 cm proximal to the ankle joint. The HO was “kissing” in two cases and partially fused (synostosis) in two. The HO in the fifth case was arising on the inner fibular cortex alone. Magnetic resonance imaging (MRI), available in four cases, showed predominantly low signal intensity due to the dense bone formation.ConclusionThe history of prior ankle trauma with ossification arising from the inner aspects of both the distal tibia and fibula is typical of post-traumatic HO and distinguish this benign condition from the rare surface osteosarcoma at this site.