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The Sensitivity of Crosslinked UHMWPE to Abrasive Wear: Hips vs. Knees
Good, V., Widding, K., Scott, M., Jani, S.
Introduction
All formulations of commercially available crosslinked andthermally treated UHMWPE (XPE) have demonstrated dramaticreduction in wear compared to conventional UHMWPE (C-PE).A vast majority of these demonstrations have been under "clean&",i.e. non-abrasive conditions. Simulations of abrasive conditionshave been reported for XPE with mixed results possibly dueto the various kinematics of these studies [1-3]. The question,therefore, remains; are contemporary XPE materials suitablefor both hips and knees under abrasive conditions in vivo?These studies examined both XPE (10Mrad, GUR1050) and C-PE(EtO, GUR1050) for hips and knees under clean and abrasiveconditions.
Methods and Results
Studies were conducted with CoCr femoral components on a 12-station(hip) and 6-station (knee) simulator (AMTI, Boston, MA) withinputs as reported previously [4-6]. The femoral componentswere tumbled with plastic cones and alumina powder to createuniform scratching with surface roughness similar to clinical[8, 9]. Both hips and knees showed XPE had lower wear thanC-PE in clean conditions. Under abrasive conditions wear-ratesof XPE and C-PE increased. The trend for lower wear in XPEwas maintained for the hip however for the knees, the XPEshowed greater wear than the C-PE.
Summary
This study shows that both forms of UHMWPE were subject toaccelerated wear under abrasive conditions. The sensitivityto abrasive wear, however, is greater for knees than for hips.The kinematics of the hip (multi-directional) and knee (primarilyuni-directional with some multi-direction) may be the cause.The motion of the hip resulted in lower wear for highly crosslinkedUHMWPE in both conditions. In the knee, with primarily uni-directionalmotion, the high amount of crosslinking was not an advantagein abrasive conditions. These findings need to be taken intoconsideration when developing materials for improved wearresistance in knees.
References
1. Saikko et al, JBMR, 57, 506-512 (2001). 2. McKellop etal, CORR, 369, 73-82 (1999). 3. Marrs et al, Trans 44th ORS,100 (1998). 4. Bergman et al, J Biomechanics, 26, 969-990(1993). 5. Murray, M.P. Am J Phys Med, 46(1), 290-333 (1967).6. Johnston, R.C. and Smidt, G.L. J Bone Joint Surg, 51A(6),1083-1094 (1969). 7. ISO/CD 14242-1.2 Draft Standard, October1997. 8. Bauer et al, CORR, 298, 11-18 (1994). 9. Levesqueet al, Trans ORS, 23, 247 (1988).
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