The design, manufacture and analysis of a new implant for fracture fixation in human and veterinary orthopaedic surgery: the bone fastenerod
McCartney, William T. (2002) The design, manufacture and analysis of a new implant for fracture fixation in human and veterinary orthopaedic surgery: the bone fastenerod. PhD thesis, Dublin City University.
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Fracture fixation in humans and animals has troubled surgeons and scientists since first it was attempted right up to the present day. At every milestone of achievement in the understanding and practice of fracture repair there has remained a significant problem left unresolved. Of paramount concern is the preservation of blood vessels and soft tissues, avoidance of stress shielding and concentration, promotion. of bone healing and a rapid return to function.
However, matching these principles with the variables of degree and site of fracture/injury, age, size and status of patient, environmental and surgical factors is complex and difficult. To be able to attempt to allow a surgeon to make decisions about every case, knowing that the implant choice does not constrain him but offers flexibility to aim for the ideal fixation for each case, the system must be modular. The objectives were to produce an implant system that would satisfy the most up to date principles of fracture repair through design optimization, mechanical evaluation and testing for specific fracture types. The design was called the bone fastenerod following the optimization and analysis procedures to indicate the origins of its basic formation.
To begin with, the design of the fastenerod had to be optimized and this was achieved using bench testing, initially of selected designs followed by finite element analysis, which allowed a greater number of designs to be processed. Once the optimum design had been found the process of manufacture had to be selected and various possible methods of manufacture were examined until the one most suitable was determined. To analyze the fastenerod, the current industry standard implants that are used in the same clinical type settings were chosen for comparative testing. Testing was performed using static and cyclic loading to failure with wood samples in four point, tensile, side, axial and torsional loading Specific fractures in dog, cat and horse bones were created and repaired using the fastenerod versus the best method currently available and tested in three point, tensile, axial, static loading to failure. Also, specific fractures were created in human mechanical bones and tested using axial, cyclic and four point bending again, comparing the fastenerod w ith the best technology available. The analysis revealed that in static loading the fastenerod was comparable to the industry standards for small implants but not comparable with the large human implants in the specific cases selected However, in the case of the cyclic loading to Mure , the fastenerod performed better than the plate system of similar size, with the ultimate load to failure being higher and no stress concentration leading to implant fracture or failure. Thus, the modular system of the bone fastenerod could now claim to provide fixation that could be flexible, less invasive and destructive to tissues, capable o f greater choice o f screw placement and stiff to level of choice whilst avoiding stress. concentration and shielding On the basis o f this analysis, the fastenerod system can proceed to fu ll c lin ica l trials
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