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Hip fractures : understanding the mechanism and seeking prevention through prophylactic augmentation of the proximal femur

University of British Columbia

Introduction: In addition to having increased mortality and decreased mobility, hip fiacture patients are more likely to sustain a second hip fracture than people who have never fractured a hip. There is currently no surgical technique that can be used to instantly strengthen the contralateral femur. Objectives: The primary objective was to evaluate the mechanical feasibility of augmenting the proximal femur with a novel implant to prevent hip fracture. This involved developing implants to prevent proximal femur fracture and quantifying the effect of the implants on the propensity of femurs to fracture. The secondary objective was to describe the initiation and progression of proximal femur failure during hip fracture to better understand the injury mechanism. Methods: Four cadaveric femurs were fractured in a fall configuration while being filmed with a high-speed camera. Visual analysis of the video images was used to describe the initiation and progression of fracture. Eight implant designs were developed and assessed with a finite-element model of a proximal femur. Of these designs, the Carbon Sleeve and Gamma Nail implants underwent a preliminary experimental assessment using a single pair of femurs. The Neck- Contouring Composite was further investigated using four pairs of femurs to compare to the Femoroplasty concept, which was assessed with three pairs of femurs. Results: In the hip fracture mechanism experiments, the four femurs were found to fail in a two stage process, with fracture initiating in the superior neck followed by a second failure in the inferior neck or intertrochanteric region. The preliminary experimental assessment of the Carbon Sleeve a nd Gamma Nail implants found that neither had a large effect on femur strength, with differences in failure load between control and augmented femurs of -8% and +1% respectively. The Femoroplasty implants had failure loads that were 24% higher that controls (p = 0.071). The Neck-contouring Composite implants had failure loads that were 18% higher than controls (p = 0.095). Summary and Conclusion: Hip fractures were seen to occur in a two stage process with failure initiating in the superior neck. Although only four specimens were tested, these experiments point to the superior neck as a region of interest for the development of screening tools for hip fracture risk assessment, targeted therapy for bone strengthening and surgical prophylaxis. The augmentation experiments found that it was possible to increase in the strength of the proximal femur by up to 24%.

Text

2010-01-08

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http://hdl.handle.net/2429/17891

Mechanical Engineering

University of British Columbia

UBCV

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