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

摘要

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. Introduction Previous studies by Li, B., Aspden et al [1] and Shih-Sheng Sun et al [2] have been conducted to compare the actual values for the mechanical properties of bone from osteoporotic femoral heads against those of bone from osteoarthritic femoral heads, however our study was performed with a difference perspective, to investigate what this recognised difference in the mechanical properties between osteoarthritic and osteoporotic bone has in practical terms, in relation to implant fixation. Femoral heads were again chosen as the medium to conduct this study in, as they are available post total hip replacement or hemiarthroplasty. Two implants used in the treatment of Intertrochanteric fractures were chosen as the means of testing fixation because even though the majority of intertrochanteric fractures occur with osteoporotic bone, some also have been reported with osteoarthritic bone.[3] Another factor worth noting is that there is no one clearly defined value for osteoporosis. Osteoporosis is a metabolic disease characterised by low bone mass and micro-architectural changes of bone that predispose it to fragility fractures [4]. In essence osteoporosis is a multifactorial chronic disease that may progress silently for decades until characteristic fractures occur late in life.[5] Patients with a bone mineral density of 2.5 standard deviations less than the average value for young adults are said to be opteoporotic.[6] Therefore osteoporosis can exist within a spectrum of values below a certain defined value in the literature.[6] In conducting this experiment with both osteoporotic and osteoarthritic femoral heads, it may help to demonstrate the role that bone density has on the mechanical properties of bone and ultimately on the fixation achieved within it.‘Cut out’ is the most common mode of failure with the implants chosen for this study. [7] Pushout studies, as previously documentated in the literature,[8,9,10] were chosen as the method of testing to represent ‘Cut out.’ Therefore the purpose of this study was to determine the difference in the mechanical properties between osteoporotic and osteoarthritic femoral heads in practical terms, in relation to the fixation achieved within them by the lag screw elements of two different implants used in the treatment of intertrochanteric fractures. Methods The implants chosen to conduct the study with were the lag screw elements of the Dynamic Hip Screw (DHS) and DHS Blade, as they are both are placed within the femoral head during the treatment of an intertrochante