A Maisonneuve ankle fracture without convincing evidence of syndesmotic injury on plain radiographs is described. Stress views and computerised tomography (CT) were also negative. A high index of suspicion led to ankle arthroscopy, which revealed a diastasis, and also an osteochondral fragment. This was treated with two percutaneous diastasis screws and removal of the osteochondral fragment. This case suggests that ankle arthroscopy should be considered as part of the management of syndesmotic injury where conventional imaging techniques fail to show syndesmotic disruption.