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Stability analysis of implants for reverse obliquity hip fractures

The objective of this project was the development of the methodology to quantify the stability of fixation devices used to treat reverse obliquity intertrochanteric hip fractures. Determination of the optimal implant design to treat these types of fractures might help to decrease the high rate of unsuccessful recovery typically seen with these types of injuries. The objective of this research was to design a test apparatus and procedure to simulate the physiological behavior of human femurs. In addition, a data acquisition system for recording displacements and strains experienced by the femur was developed. Stability analysis was performed on both an intact sawbone femur and a fractured femur, fixated with a Gamma Nail implant, in order to verify the methodology and also to provide information on the stability of Gamma Nail implants. According to the stability criteria used in this research, the Gamma Nail specimen was observed to have adequate properties for stabilizing reverse obliquity intertrochanteric hip fractures.

That is, for a compressive cyclic loading of up to 3000N, the Gamma Nail specimen experienced a femoral head movement of 18mm along the fracture surface in comparison to an acceptable movement of 25mm. However, a femoral head rotation at the point of fracture produced a 7mm gap between the two fracture surfaces, which is obviously undesirable since it would hinder the healing process. Furthermore, instability occurred at a compressive static loading of 4500N; although, both the femur and the Gamma Nail implant remained intact. In addition, when compared with the control specimen, the Gamma Nail specimen experienced a reduction of strain levels of 79 and 89, at femur neck and shaft, respectively. These reductions in strain provided evidence that the Gamma Nail implant acted as a load-bearing member to assist in minimizing the stresses exerted on the femur. Further investigation is needed in order to determine whether other fixation devices would provide better stability for treating reverse obliquity intertrochanteric hip fractures.