Wear simulation in total knee arthroplasty (TKA) is currently based on the most frequent activity – level walking. A decade ago multi-station knee wear simulators were introduced leading to optimisations of TKA designs, component surface finish and bearing materials. One major limitation is that current wear testing is mainly focused on abrasive-adhesive wear and in vitro testing does not reflect “delamination” as an essential clinical failure mode. The objective of our study was to use a highly demanding daily activities wear simulation to evaluate the delamination risk of polyethylene materials with and without vitamin E stabilisation. A cruciate retaining fixed bearing TKA design (Columbus CR) with artificially aged polyethylene knee bearings (irradiation 30±2 kGy) blended with and without 0.1% vitamin E was used under medio-lateral load distribution and soft tissue restrain simulation. Daily patient activities with high flexion (2×40% stairs up and down, 10% level walking, 8% chair raising, 2% deep squatting) were applied for 5 million cycles. The specimens were evaluated for gravimetric wear and analysed for abrasive-adhesive and delamination wear modes.Background
Methods
Spines are often stabilised posteriorly by internal fixation and anteriorly by a bone graft. The effect of an autologous bone graft from the iliac crest on implant loads is unknown. We used an internal spinal fixation device with telemetry to measure implant loads for several body positions and activities in nine patients before and after anterior interbody fusion. With the body upright, implant loads were often higher after than before fusion using a bone graft. Distraction of the bridged region led to high implant loads in patients with a fractured vertebra and to marked changes in load in those with degenerative instability. Leaving the lower of the bridged intervertebral discs intact led to only small changes in fixator load after anterior interbody fusion. A bone graft alone does not guarantee a reduction of implant loads.
