Myositis ossificans traumatica of the piriformis muscle: a rare mature case in an adult African male

Myositis ossificans traumatica (MOT) is a common form of heterotopic ossification associated to trauma. Rare mature manifestations and topographically atypical presentations of MOT are often misdiagnosed as osteosarcoma. This case study discusses a rare, mature case of MOT of the piriformis muscle, potentially clinically associated with piriformis syndrome. The ossification was observed on a dry sacral bone of an adult skeleton belonging to a South African male during routine inventory of the Raymond A. Dart Collection of Human Skeletons, the University of the Witwatersrand, Johannesburg. The MOT was located on the anterior aspect of the sacrum at a site corresponding to the upper portion of the origin of the muscle and extended laterally towards the greater trochanter, beyond the greater sciatic notch. It was cylindrical in shape and measured approximately 52.70 mm in length and 12.10 mm in diameter. Micro-focus CT revealed an extensive and mature bony development of the piriformis muscle with distinct outer cortical and inner trabecular bone. In addition, the skeleton showed widespread healed skeletal trauma, suggesting a history of trauma. The MOT was completely fused to the sacral bone excluding the possibility of congenital anomalies. Information on the MOT of the piriformis muscle is vital to clinicians and radiographers to aid in successful diagnosis and management of the piriformis syndrome and sciatica in the gluteal region. This case also provides a rare example to biological anthropologists, paleoanthropologists and bioarchaeologists of the representation of pathologies like these on a dry bone sample.