Design and development of an adaptive external bone fracture fixation system

Herbert, Christopher

Design and development of an adaptive external bone fracture fixation system

Master Thesis

2019

Abstract

External fixation is a surgical treatment primarily utilised for long bone fracture stabilisation. External fixation, through either pin or wire insertion, is done by constraining bone fragments and providing support to the injury via external scaffolding built across the fracture., but it can also be used to solve both traumatic and congenital bony deformities. Certain devices, particularly the Ilizarov Ring Fixator, can employ external bone fixation to create a biomechanical environment to gradually correct deformities (comprised of: translation, rotation and angulation). A typical application for deformity correction is the fixation of lower leg fractures, particularly tibial fractures, which have been recognised as the most common incident in long bone fractures. External ring fixators have become more developed; manufactured from sophisticated materials; or designed to incorporate computational support, to achieve accurate correction, however these factors have created limitations regarding their accessibility, complexity and ease in application. In addition, standard systems are not as versatile or correctively exact as required to prove their cost of use, creating reluctance as well as added bias towards the more developed devices. Threedimensional and multi-planar deformity correction has become major factors for current devices, yet the feasibility to use such expensive and complex devices may not be beneficial for all parties. External Fixation Systems are considered operationally expensive. Standard systems still utilise expensive and cumbersome setups, while developed devices require computational consultation and extensive training. With such complex procedural actions required to facilitate multi-planar correction, most devices utilise computational support, which in turn minimizes the clinician’s control. The current study aims to design a light-weight Adaptive External Bone Fracture Fixation System that can offer definite treatment and full clinical control over the injury. The system is to be able to stabilise and offer correction of planar bony deformities via controlled shape change. The functional verification of the device was limited to (according to the scope) stress testing. The proposed device consists of hinge systems capable of allowing for full assembly expansion to permit quick installation for various injury structures or states. In addition, the design possesses longitudinal elements that can offer both rapid and finite lengthening (with lock-and-switch) to offer both rapid and gradual system shape change, improving the control over the injury fixation. The device stress testing had revealed limited capabilities in providing enough scaffolding stability for a certain directional stress condition. To determine the quality of its structural integrity, the device was loaded under direct compressive and tensile load. The strain generated was measured and analysed using a Load-Deformation Curve. The device could support tension close to [3.5 kN], equivalent to standard models, whilst unable to support compression for loads close to [1.2 kN]. The conclusive points that were made had detailed that it was limited by its structural integrity, however the design was evaluated as functionally versatile as and should be further developed. Future recommendations proposed include the addition of constrained joints; improved locking capabilities; implementation of failure modes for hinges and lastly improved structural integrity by using sophisticated materials to further validate the skeletal structure of the fixation system.

Keywords

Biomedical Engineering

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