Abstract
Introduction
One unpredictable clinical risk with THA may be impingement of a metal cup rim against a metal femoral-neck, with concomitant release of metal particles. Our objective was to determine if metal debris could be one trigger for catastrophic MOM wear.
Patients/Materials & Methods
To simulate release of metal debris, we added metal particles (CoCr #230, Ti6Al4V #340) to six 38mm MOM bearings at beginning of each simulator test interval. The weekly 500,000 cycle intervals were replicated 10 times to acquire 5-million duty cycles. Flakes of polymerized bone cement (PMMA) were scraped from a retrieved TKR and used as control debris (N = 1,300 particles; 3 MOM).
Results
Metal debris turned all lubricants black within first hour of test, and consistently over the study. Cement flakes elicited no such lubricant changes. MOM wear-rates using PMMA, CoCr, and Ti64 debris were 0.3, 4.1, and 6.4 cubic millimetes per million cycles, respectively, revealing statistically significant differences. The CoCr debris allotment produced ×30 times its weight in surface wear; the Ti6Al4V debris produced ×50 times its weight in CoCr wear.
Discussion
Successful MOM bearings were reputed to have low friction due to fluid-film lubrication. Nevertheless, any THA impingement that can release metal debris may compromise such thin films. This simulator study of MOM bearings running under abrasive conditions revealed that MOM wear-rates with CoCr and Ti6Al4V debris were raised ×14 and ×23 times greater than that of PMMA debris.
Conclusion
The insertion of metal debris, simulating just one impingement episode in 500,000 gait cycles, created a ×30–50 times multiplier effect in production of CoCr debris. The resulting black lubricants may be directly analogous to the black tissues noted around high-wearing MOM bearings. Thus the nemesis of MOM THA may be an extreme sensitivity to 3rd-body wear particles.
