Heterotopic bone formation (HO) is a potentially serious complication of hip surgery. HO, defined as the formation of normal bone in an abnormal soft tissue location, results from alteration in the normal regulation of skeletogenesis. Although most patients remain asymptomatic despite HO development, two articles that included 10,826 patients from 37 studies suggest HO may be associated with substantial compromise of function and range of motion even at low grades.In a large pooled incidence study, HO was estimated to be 43% in 59,121 patients undergoing total hip arthroplasty, and 51% in 998 patients after acetabular trauma.