| Summary: | 碩士 === 長庚大學 === 醫療機電工程研究所 === 101 === Background: Dynamic hip screw (DHS) is widely accepted as an efficient fixation device in treatment of unstable intertrochanteric fractures. Although clinical outcome with satisfactory results are achieved, postoperative incidence such as screw loosening or screw cutout are often found for patients with osteoporosis. Many efforts have been made in modifying the DHS system to improve the postoperative stability.
Methods: Based on the conventional DHS lag screw, this study aims to develop a new DHS system with expandable blades to treat the intertrochanteric fractures with osteoporosis. Both in vitro experiment and finite element analysis (FEA) are conducted to explore the effect of the design parameters including blade number (2 or 4), blade length (20 mm or 30 mm), blade design (with or without leading edge) on the postoperative stability of the femoral constructs. For the in vitro experiment, with use of a material test machine, axial compression and torsion tests are performed following the insertion of the newly designed DHS into test blocks with different density. For FEA, three dimensional finite element models simulating one lag stance are established using CT images of an artificial femur. Stress distribution and the axial displacement difference between the femoral head and lag screw are compared for femora implanted with the conventional and newly designed DHS.
Results: The results from in vitro experiment reveal that a higher expansion angle is found for the new DHS with leading edge design. The increase of blade number and blade length would improve both compression and torsion resistances. New DHS with four 30 mm blades exhibits the highest compressive stiffness (149.42 N/mm) and torsion stiffness (55.7±5.35 N*mm); wheras the conventional DHS exhibits the lowest compressive stiffness (49.28 N/mm) and torsion stiffness (20.9±2.37 N*mm). The FEA results indicate that, a decrease of von Mises stress surrounding femoral neck is found for newly designed DHS femur as compared to the conventional DHS femur. Additionally, the axial displacement difference between the femoral head and lag screw for conventional DHS and newly designed DHS femora are 1.55 mm and 0.43 mm, respectively. This imply that femur with intertrochanteric fractures implanted with newly designed DHS could efficiently reduce the risk of screw cutout.
Conclusion: The new DHS system with expandable blades can efficiently improve the postoperative stability and reduce the incidence of screw cut-out, which provide an alternative choice for treatment of unstable intertrochanteric fractures.
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