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The University of Southampton
EngineeringPostgraduate study

EngSci-Bio-01 PhD/EngD Studentship: Imaging and modelling of the interference fit in cementless joint replacement

Cementless fixation relies on achieving good primary stability in order for osseointegration to occur. As well as the shape of the component, the degree of interference between the bone and the implant is key in determining the primary stability. Typical planned interferences between the bone and the implant of up to 1mm are routinely used in clinical practice. However, due to tolerancing of the implant and of the instrumentation and due to the variability in preparation during surgery, the true level of interference can potentially be highly variable. Factors such as the viscoelasticity of bone, and variations in bone quality are also likely to lead to significant variability in the true interference.

Various finite element studies have attempted model interference at the bone-implant interface [1, 2].  These studies have reported that relatively small interferences, of the order of 100-150 microns are all that are necessary to achieve primary stability and that higher interferences lead to substantial yielding of the supporting bone.    This leads to two observations: (i) Current FE models are unable to capture the true nature of the interference and (ii) insertion of the device does not simply elastically/plastically the bone, but probably also continues to rasp the cavity.

The aim of this study is to perform a comprehensive investigation of interference fit in cementless fixation, with a view to providing recommendations for optimal performance.  This will be achieved by developing an in-vitro model based on micro-computed tomography imaging to assess the influence of interference of idealised cementless devices (femoral hip stems and tibial trays), and use the model to explore what factors influence the interference fit. Based on the observations from the in vitro study, develop suitable FE methodologies that are better able to capture the mechanics of interference at the bone-implant interface.

If you wish to discuss any details of the project informally, please contact Martin Browne, Bioengineering research group, Email: doctor@soton.ac.uk , Tel: +44 (0) 2380 593279.

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