Heterotopic ossification (HO) is the process by which bone tissue forms outside of the skeleton.
Causes
Heterotopic ossification of varying severity can be caused by surgery or trauma to the hips and legs. About every third patient who has total hip arthoplasty (joint replacement) or a severe fracture of the long bones of the lower leg will develop heterotopic ossification. Between 50% and 90% of patients who developed heterotopic ossification following a previous hip arthoplasty will develop additional heterotopic ossification.