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As total knee arthroplasty (TKA) patients are getting more active, heavier and younger and structural material fatigue and delamination of tibial inserts becomes more likely in the second decade of good clinical performance it appears desirable to establish advanced pre-clinical test methods better characterizing the longterm clinical material behaviour. The questions of our study were 1) Is it possible to induce subsurface delamination and striated pattern wear on standard polyethylene TKA gliding surfaces? 2) Can we distinguish between γ-inert standard polyethylene (PEstand.30kGy) as clinical reference and vitamin E stabilised materials (PEVit.E30kGy & PEVit.E50kGy)? 3) Is there an influence of the irradiation dose (30 vs 50 kGy) on oxidation and wear behaviour? Clinical relevant artificial ageing (ASTM F2003; 2 weeks) of polyethylene CR fixed TKA inserts and oxidation index measurements were performed by Fourier transform infrared spectroscopy prior testing. The oxidation index was calculated in accordance with ISO 5834-4:2005 from the area ratio of the carbonyl peak (between 1650 and 1850 cm −1 ) to the reference peak for polyethylene (1370 cm −1 ). Highly demanding patient activities (HDA) measured in vivo were applied for 5 million knee wear cycles in a combination of 40% stairs up, 40% stairs down, 10% level walking, 8% chair raising and 2% deep squatting with up to 100° flexion. After 3.0 mc all standard polyethylene gliding surfaces developed noticeable areas of progressive delamination. Cumulative gravimetric wear was 355.9 mg for PEstand.30kGy, 28.7 mg for PEVit.E30kGy and 26.5 mg for PEVit.E50kGy in HDA knee wear simulation. Wear rates were 12.4 mg/mc for PEstand.30kGy in the linear portion (0–2 mc), 5.6 mg/mc for PEVit.E30kGy and 5.3 mg/mc for PEVit.E50kGy. In conclusion, artificial ageing of standard polyethylene to an oxidation index of 0.7–0.95 in combination with HDA knee wear simulation, is able to create subsurface delamination, structural material fatigue in vitro, whereas for the vitamin-E-blended materials no evidence of progressive wear, fatigue or delamination was found. Statement of Significance As total knee arthroplasty patients are getting more active, heavier and younger and structural material fatigue and delamination of polyethylene tibial inserts becomes more likely in the second decade of good clinical performance, it appears desirable to establish advanced pre-clinical test methods better characterizing the longterm clinical material behaviour. Various studies reported in literature attempted to artificially create delamination during in vitro knee wear simulation. We combined artificial ageing to clinically observed oxidation of gamma inert and vitamin E stabilised polyethylene inserts and highly demanding patient activities knee wear simulation based on in vivo load data. With this new method we were able to create clinically relevant subsurface delamination and structural material fatigue on standard polyethylene inserts in vitro. [ABSTRACT FROM AUTHOR]

The article discusses a study evaluating tibiofemural contact forces during cycling in vivo and to quantify the influences of power, pedaling cadence, and seat height on it. The findings revealed that tibiofemural contact forces were smaller during cycling than during walkin, and increased linearly with cycling power. Cycling with moderate power levels is suitable for those with osteoarthritis and rehabilitation.

The long term performance of total knee arthroplasty (TKA) with regards to the bearing materials is related to the aging behaviour of these materials. The use of highly crosslinked materials in hip arthroplasty improved the clinical outcome. Nevertheless, the outcome for these materials compared to conventional UHMWPE (ultra-high molecular weight polyethylene) remains controversial in TKA and alternative bearing materials may be advantageous to improve its outcome in the second and third decade. The aim of this study is the evaluation of the influence of radiation conditions on the wear behaviour of Vitamin E blended UHMWPE gliding components for TKA by simulation of extended aging and high demanding daily patient activities. For a medium radiation dose (30 kGy), the influence of the irradiation type (E-beam or Gamma radiation) and the thermal conditions (room temperature (RT) or heated to 115 °C) are evaluated in comparison to non-irradiated material. Significant influences on the wear behaviour were found for the radiation source and temperature during irradiation. Furthermore, no relevant degradation of the tested materials was observed after extended artificial aging. There was a good correspondence between the wear pattern in this study and retrievals. [ABSTRACT FROM AUTHOR]