FRETTING WEAR IN A MODULAR NECK HIP-PROSTHESIS

In vitro cyclic load fretting tests were conducted on a prototype of a cementless, modular neck, hip prosthesis. The study had three major o bjectives: to determine the amount of fretted material in the tapered- neck joint under various load cycle amplitudes, to determine the frett ing damage evolution, and to determine the effect of different-sized s tem bodies on the production of debris. All the tests produced some fr etting microdamage on the tapered surface although the extent was quit e different among test groups. The amount of abraded material increase d almost linearly with the applied load magnitude but not with the num ber of load cycles. The amount of weight loss was higher in the large stem bodies than in the small ones. Weight loss ranged from 0.28 +/- 0 .10 mg for small stem bodies loaded 5.5 million times up to 2300N to 2 .54 +/- 0.53 mg for large stem bodies located 20 million times up to 3 300N. Considering the large-size stem results, and assuming one millio n load cycles between 300N and 3300N to be the average yearly load his tory, the modular neck tapered joint would produce 0.6 mg/year of meta l debris. The clinical impact of this observation is unknown; however, some of the literature on the presence of metal in patient tissues an d fluids supports the hypothesis that a normal and stable prosthesis i s likely to produce less than 10 mg/year of metal debris. Thus, a furt her production of 0.6 mg/year due to the modular neck should not have any significant effect. (C) 1997 John Wiley & Sons, Inc.