Biomechanical Evaluation of Novel Expansive Dhs Screws for Treatment of Osteoporotic Unstable Intertrochanteric Fractures - the Effects of Screw Design and Cement Augmentation

This study aims to develop a novel expansive dynamic hip screw system (Expansive-DHS) with mechanical performance superior to the conventional DHS for treatment of osteoporotic unstable intertrochanteric fractures. The DHS has been widely used as the fixation device for treatment of intertrochanteric fractures. However, in unstable fractures with osteoporosis, complications such as upward migration of the lag screw, and even cutout of the lag screw are not uncommon due to inadequate bone anchorage of the lag screw. To enhance screw anchoring power, the author’s previous reports have demonstrated that expansive screws can effectively improve the screw holding power for spinal fusion surgery (Plos One, 10(12), 2015). The expansive screw allows for flange expansion at the screw tip and, hence, increases the screw holding power. Particularly, an enormous increase of screw fixation strength can be achieved when expansive screw is used accompanied with cement augmentation. Furthermore, in another author’s previous study, a novel blade-DHS was developed for enhancing DHS fixation strength. The novel blade-DHS was modified from standard DHS by adding a ring-shape blade to the existing lag screw. With use of an expanding tool, the ring-shape blades can effectively expand to improve the screw fixation strength. The results from in vitro experiments and finite element analysis had demonstrated that the novel blade-DHS has fixation strength superior to the conventional DHS.In author’s opinion, these concepts can be applied for treatment of osteoporotic unstable trochanteric fractures. Therefore, this three-year study intends to link up previous experience to further develop novel expansive-DHS to enhance the DHS fixation strength. With use of in vitro experiment and finite element analysis, the mechanical performance of the novel DHS systems will be evaluated and compared to the standard DHS. A. The first-year study: Static tests of single lag screw using test blocksFour types of expansive screws will be studied: 4-slit or 6-slit with 12-mm or 18-mm EELs (effective expansion length). Three types of low-density synthetic bones (test blocks) simulating different degree of osteoporosis are used as substitutes for human bones. Five groups of lag screws are studied (standard and 4 types of expansive screws). Each group is divided into two subgroups based on two different augmentation techniques (cemented and cementless). Mechanical tests involving: (1). screw pullout, (2). screw cut-out, and (3). screw torsion will be performed using MTS testing machine. B. The second-year study: Static and dynamic tests of femoral constructs using osteoporotic composite femurOsteoporotic composite femora will be used as substitute for cadaveric osteoporotic femur. Both static and dynamic tests of femoral constructs will be conducted following DHS instrumentation identical with the aforementioned conditions. The biomechanical performance of integral femoral construct on combinations of screw design and cement augmentation will be evaluated and compared.C. The third-year study: Finite element analysis of femoral constructsFinite element analysis will be conducted to evaluate the stress and strain distribution of femoral constructs. CT images of the osteoporotic composite femur is used to create 3-D FE models. The results will be compared with those of biomechanical experiments.

Project ID:PB10907-3475
External Project ID:MOST109-2221-E182-007-MY3