Joint replacements wear factor

The derived wear factor (k) for the Freeman-Swansog and Leeds knee joints tested in the simulator for about 10 cycles are both interesting and similar. The ln-vlvo Freeman-Swanson joint was kindly made available by Professor S.A.V. Swanson and the conditions of service were not known with any certainty. The joint had functioned in an elderly patient for some four years, with a light to medium level of walking activity. It was therefore assumed that /PdX remained constant at 47.7 Nm/cycle and that the patient achieved 6000 strides or 3000 loading cycles per day. These assumptions are consistent with a subsequent study of the walking activity of patients fitted with total replacement joints reported by Wallbrldge and Dowson, but considerable scope for errors... 

Since 1962, UHMWPE also has been used in orthopedics as a bearing material in artificial joints. Each year, about 1.4 million joint replacement procedures are performed aroimd the world. Despite the success of these restorative procedures, UHMWPE implants have only a finite lifetime. Wear and damage of the UHMWPE components is one of the factors limiting implant longevity. 

Vassiliou K, Unsworth A. Is the wear factor in total joint replacements dependent on the nominal contact stress in ultra-high molecular weight polyethylene contacts Proc InstMech Eng, PartH J Eng Med 2004 218 101-7. 

The major factors limiting the effective life of a total replacement synovial joint are loosening of one or more of the prosthetic components, a variety of medical problems (e g. infection) and wear. Most internal prostheses now consist of metallic and polymeric components and it is the penetration of the former into the latter which is the subject of this paper. 

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