The Development and Biomechanical Study of Novel Dynamic Hip Screws- Blade Dhs, Expansive Dhs and Perforated Dhs

This study aims to develop the novel dynamic hip screws (DHS) for treatment of unstable interochanteric fractures with osteoporosis. The application of the novel DHSs is expected to improve the screw fixation strength and hence, increase the successful rate of surgery. The DHS has been widely used as the implant in the treatment of interochanteric fractures. However, in unstable fractures, the most common complications is inadequate bone anchorage of the lag screw, resulting in upward migration of the lag screw, and even cutout of the lag screw. Previous reports have addressed the perforated screws capable of cement-injection and expansive screws effectively enhance the screw holding power for spinal fusion surgery. The perforated screw allows for the injection of cement through the perforation to achieve the improvement of screw anchoring strength. Whereas the expansive screw allows for flange expansion at the screw tip and, hence, increases the screw holding power. In the author’s opinion, these concepts could be applied for treatment of unstable trochanteric fractures with osteoporosis. In our previous experience, besides the perforated and expansive screws, a prototype of the novel blade DHS had been developed, which was modified from conventional DHS by adding a ring-shape blade to the existing lag screw, and our preliminary results have demonstrated the feasibility of its function. To prevent the common surgical complications of unstable intertrochanteric fractures in elderly patients, this three-year study aims to develop three novel DHS systems (Blade-DHS, Expansive-DHS and Perforated-DHS) to enhance the DHS fixation strength. The mechanical performance of the novel DHS systems will be compared to the conventional DHS using in vitro experiment and finite element analysis. The contents of this three-year study are summarized as follows: A. The first-year study: Design and manufacture of the novel DHS systems All novel DHSs will be designed based on existing conventional lag screw. For blade-DHS, four designs of blade-DHS will be employed: 2 blades and 4 blades with a blade length of 20 mm or 30 mm. For expansive-DHS, two expansive-screw designs will be employed: expansive-DHS with a slit length of 12 mm (larger expansion range) or 20 mm (Smaller expansion range). For perforated-DHS, two perforated-screw designs will be employed: perforated-screw with 2 or 4 radial holes. B. The second-year study: In vitro experiment) Commercially available test blocks with different density (7.5 lbm/ft3, 10 lbm/ft3, and 12.5 lbm/ft3) will be used as a substitute for human osteoporotic cancellous bones. Mechanical tests involving: (1). Screw pullout, (2). screw cut-out, and (3). screw torsion will be performed according to the related ASTM testing standards (F543-02 and F2193-02) using MTS testing machine. The biomechanical performance for various DHD under different loading modes will be evaluated and compared. C. The third-year study: Finite element analysis Computed tomography (CT) image data of a standard composite femur will be used to create the 3-D intact femur solid model. FEM models of femur instrumented with various DHS will be created based on identical screw design parameters as described previously. Stress distribution for all models will be compared under loading condition simulating single leg stance.

Project ID:PC10408-1267
External Project ID:MOST104-2221-E182-030