Femur flap for tibial reconstruction: biomechanical considerations

Free-vascularized fibular flaps have been associated with high risks of graft fracture when used for the reconstruction of discontinuous fractures in the tibia. Plastic surgeons have suggested the use of a free-vascularized femur flap (wedge-shaped bone segment with connected vasculature) from the anterolateral shaft of the contralateral femur as an alternative. The goal of this study was to determine the femur flap size required to provide equivalent support as a fibula flap and to assess the need for intramedullary rod support of the femur following removal of the bone segment. Three-point bending tests were conducted on fibula and femur flaps to characterize the mechanical properties of the bone segments. The average fibular yielding load was 550±175 Newtons. To match this load, 35% of the femur´s circumference must be used. Intact femurs and femurs with 35% flaps removed were tested in compression while being oriented in the anatomical position to simulate the natural compression and beading moments in the femoral diaphysis. The intact femurs failed at 840±297 lbs, while the femurs with the 35% flap removed withstood 810±235 lbs. In conclusion, 35% of the femoral circumference is needed to provide flaps that are equivalent to that of a fibula. The removal of the 35% flap decreases the average maximum strength of the femur, however, the decrease is not statistically significant due to the large standard deviation values. Ongoing analyses of local strain data are being performed to determine whether the procedure requires fixation of the femur.