Biomechanical Study. The Role of Osteoporotic or Osteoarthritic Bone in Determining the Fixation Achieved Within the Femoral Head by the Lag Screw Elements of the Dynamic Hip Screw (DHS) and DHS Blade

Abstract

Objective This study was conducted to investigate the fixation that the lag screw elements of two different implants used in the treatment of intertrochanteric fractures achieve within osteoporotic and osteoarthritic femoral heads, as a practical means of comparing the mechanical properties of osteoporotic bone against those of osteoarthritic bone. Methods The lag screw elements of the Dynamic Hip Screw (DHS) and DHS Blade were the two lag screws that were chosen to conduct this study with. “Pushout” tests were performed as the means to investigate the fixation that each lag screw achieved within the femoral heads, as the most common mode of failure with these devices is ‘cut-out’ Results The results demonstrate that the difference in mechanical properties between osteoporotic and osteoarthritic bone in cadaveric femoral heads mean that the devices used in the fixation of intertrochanteric fractures achieve a much greater fixation within osteoarthritic bone. The results also demonstrate that the overall failure patterns were similar for each device within both the osteoporotic and osteoarthritic bone apart from the large difference in forces achieved. Conclusion The results demonstrate, that as expected when the density of the bone increases, in general the implants achieve better fixation within it. However this study also demonstrates that it is the implant that dictates the pattern of failure and not the bone.