Influence of implant design on the method of failure for three implants designed for use in the treatment of intertrochanteric fractures: the dynamic hip screw (DHS), DHS blade and X-BOLT.

BACKGROUND: The dynamic hip screw (DHS) has been widely adopted as the implant of choice in the treatment of intertrochanteric fractures. There have been attempts over the years to improve on the DHS lag screw design in order to reduce failure in the form of "cut out". The purpose of this study was to investigate how two new design variations of the DHS, the DHS blade and the X-BOLT, behave within bone, and if these design modifications do indeed improve the fixation achieved and lead to a reduction in failure due to cut out. METHODS: "Pushout" tests were chosen as the means of investigating the failure modes and patterns for these implants that lead to cut out. These pushout studies were performed in artificial bone substrate in the form of polyurethane foam blocks and in cadaveric femoral heads. RESULTS: The results demonstrated that each individual implant produces its own specific distinct force-displacement curve or pattern of failure, and that despite the very different implant designs and methods of fixation, all of the implants tested reached very similar peak forces in each of the test materials used. CONCLUSION: The results demonstrated that implant design only influences the pattern of failure, and that the peak forces reached by each implant are determined by the quality of the bone or test material into which they are placed. However, altering the force-displacement curve or pattern of failure may be enough to improve the fixation achieved and to provide an increased resistance to cut out.