Development of a novel orthopedic microfastener
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Over the last decade, biodegradable screws and plates have received wide acceptance over metallic fasteners for orthopedic fracture fixation. A biodegradable fastener would gradually "disappear" during healing of a fractured bone or tissues, therefore avoiding a secondary operation to remove that fastener. When using a metal fastener, the current approach requires manual threading on a large bone fragment for fixation. This technique is difficult when it is required to fixate a small bone fragment. This study puts forth the development of a threadless, polymer based orthopedic fastener for small fragment fixation which would provide stability and interfragmental compression to the fracture site. The fastener was designed with ratchets on its surface, which deflect during insertion into the drilled hole in the bone and subsequently stiffen to hold the bone fragments in place due to interference. The head of the fastener was developed analogous to a Belleville washer which deflects during insertion of the fastener and subjects the bone fragments to interfragmental compression. Finite element analysis (FEA) was conducted to design the fastener profile and assess its performance. The push-in and pull-out forces predicted by FEA were comparable to the experimental results for the prototype of the microfasteners. The push-in force was found to increase with increasing insertion depth and radial interference. The force required to initiate pull-out was maximum and was reduced with reducing fastener bone contact. An analytical model was proposed to explain the fastener bone interaction. It was found to be in good agreement with the FEA and experimental results at low levels of interference.
Agnihotri, Mukul Mukund (2005). Development of a novel orthopedic microfastener. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from