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 for cementless hip stems and pegs/keels in cementless tibial trays. 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 achieved is likely to be less than planned and potentially highly variable. Due to the viscoelastic nature of bone, the degree of interference is likely to decay in the first few days following surgery. Variations in bone quality are therefore likely to lead to significant variability in the true interference that will ultimately determine the primary stability required in the first 4-6 weeks of arthroplasty for osseointegration to occur.
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 forming computational models to assess the influence of interference of idealised cementless devices (femoral hip stems and tibial trays). Micro-computed tomography data will be used to visualise the insertion process and to analyse the response of the bone at the bone-implant interface. Once inserted, mechanical testing protocols will evaluate the primary stability of the bone-implant construction.