Approach to Hetrotopic Ossification (HO): Educational Corner

Heterotopic ossification (HO) is a prevalent complication after trauma, injury, or surgery defined by the existence of extraskeletal lamellar type of bone in muscle and soft tissue (1). HO is a disturbance of normal tissue repair. HO also has a genetic form which is rare in comparison to the non-genetic form. HO has a broad spectrum of clinical symptoms, from small lesions to lesions with high morbidity (2). This complication is induced by infiltration of inflammatory cells and osteoinductive growth factors, which are released following an injury and activate an osteochondrogenic program. HO formation takes 6-12 weeks following the operation and ceases after that without any progression. The pathway of bone formation in HO may be either intramembranous or endochondral. HO is classified into four grades based on Brooker’s classification. Most cases of HO are categorized as grade one and grade two, which are asymptomatic and accidentally discovered in radiographic follow-ups. In grades three and four, the patient confronts more pain and reduced range of motion (ROM) (3).