The role of muscular trauma in the development of heterotopic ossification after hip surgery: An animal-model study in rats

Abstract Background Heterotopic ossification (HO), the formation of bone in soft tissues, is a frequent complication after surgery of the hip and the pelvis. Although the pathophysiological entities responsible for the formation of HO remain largely unclear, muscle trauma is alleged to play a central role in the pathogenic mechanisms underlying HO. However, for this observation, made by many surgeons for decades, no objective evidence has been provided yet. Methods Fifty male Wistar rats were subjected to surgery of the right hip. The femoral canal was reamed in three steps up to 2mm. Animals formed 2 groups: in group 1 (25 animals) every effort was taken not to injure the muscles. In contrast, in the rats of group 2 (25 animals), an additional muscle lesion was created. Twelve weeks after surgery, the amount of heterotopic bone was assessed using micro-computed tomography, and classified using a modified Brooker classification system. A chi-square test was used to assess the statistical hypothesis comparing both groups. Results A significant higher amount of heterotopic bone was observed in animals that underwent additional muscular trauma. Conclusion According to our data, muscle trauma seems to play an important role in the development of HO after hip surgery. Hence, during surgery, particular care not to injure the surrounding muscular tissue should be taken.