Extensive Myositis Ossificans with Extra-articular Ankylosis of the Hip Joint

Myositis ossificans, also known as heterotrophic ossification, is characterised pathologically by the presence of lamellar bone at sites where bone normally does not exist. Its aetiology is unknown but is known to occur following damage to the muscle. The resultant proliferative connective tissue later differentiates into the mature bone mass. Extensive myositis ossificans leading to a complete extra- articular bony ankylosis is rare. We report a case of post-traumatic myositis ossificans in a 27-year-old female following a head injury. The iliopsoas was involved in this case, and lead to extra-articular bony ankylosis of the hip causing severe functional impairment. Surgical excision of the mass as described resulted in a marked functional improvement.