Effects of heterotopic bone formation on outcome after hip arthroplasty

Background: Heterotopic bone formation (HBF) is well established as a frequent complication of major hip surgery, but its importance as a cause of impaired postoperative outcome is uncertain. Methods: A systematic overview of all studies that reported the association of HBF with the risk of impaired range of movement, pain or poor function, late after hip arthroplasty. Results: A computer-based search identified 37 relevant studies that included 10 826 individuals. There were 30 studies (8305 participants) that assessed the association between HBF and range of movement, 14 studies (7420 participants) that assessed the association between HBF and pain and 16 studies (5918 participants) that assessed the association between HBF and function. Overall, there was a clear positive association of HBF with the risk of an impaired range of movement at the hip joint and with the risk of a poor functional outcome. The association of HBF with pain was unclear. There was evidence of effects of mild-to-moderate HBF on the postoperative range of movement. Conclusions: These results suggest that mild-to-moderate HBF, not just severe HBF, can influence outcome after major hip -surgery. HBF may therefore be a more frequent cause of postoperative symptomatology than is generally believed. It is possible that effective prophylactic regimens will improve outcomes in large numbers of patients.