TRIBOLOGY LOADING CAPACITY OF UHMWPE FROM TOTAL JOINT REPLACEMENTS

Andrei TUDOR

tudor@meca.omtr.pub.ro

Georgiana BOSOI

Felix PARVU

"Politehnica" University of Bucharest, ROMANIA

Abstract. The wear rate of ultra-high molecular polyethylene (UHMWPE) total joint prosthesis is known to be influenced by various factors such as material and design. However, it is not known if these factors affect the size or morphology of the wear particles. It is known that the molecular chain structure at the articulating surface of UHMWPE undergoes a re-organization process due to strain accumulation caused by surface traction. A theoretical model of wear particle that is based of intimate conical asperity interactions is proposed to account for the observed differences in sliding and rolling wear. Cyclic plastic strain accumulation is identified as the common cause for wear debris generation in sliding and rolling joints, as examples being hip and knee replacements. In the case of acetabular cup wear (sliding velocity), the scale of plastic deformation is limited to the sites of intimate conical-asperity contacts and the wear is defined by a critical strain criterion. In the case of tibial component wear (rolling velocity), however, plastic deformation spreads into the subsurface to the site of macro-asperity contact, and material can be removed by subsurface cracking and delamination. In both cases, the wear rate is strongly affected by the ultimate tensile strength and breaking elongation of UHMWPE material.
 

Keywords: wear debris, UHMWPE, sliding joint, rolling joint, conical asperity

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