Metal-on-metal bearings surfaces: Materials, manufacture, design, optimization, and alternatives

Abstract

When first introduced, total hip replacements offered pain relief and improved mobility in elderly patients. The success of this procedure in terms of long-term durability and restoration of function has led to its use in younger, more active patients. This has resulted in a commensurate increase in patient expectation regarding longevity and the degree to which function and lifestyle is restored. The bearing surface is a key feature of the performance of replacement joints. It is generally accepted that excessive amounts of wear debris preclude their long-term survivorship and hence there is an ongoing requirement for bearing surfaces which minimize debris generation. The purpose of this paper is to review the factors which affect the performance of so-called metal-on-metal bearings, to compare their performance with that of the other commonly used contemporary alternatives, metal and ceramic articulating against highly cross-linked polyethylene, and ceramic-on-ceramic, and finally to consider the potential solutions offered by new developments such as ceramic-on-metal and coatings applied to metal-on-metal bearings.

Reduced Articular Surface of One-piece Cups: A Cause of Runaway Wear and Early Failure

“…Improved metal implant manufacturing techniques with better tolerance, roundness, and metallurgy, however, have led to recent increases in the use of metalon-metal bearings. Metal-on-metal articulations are associated with a very low wear rate and as a result of the tribology of the materials, unlike metal-on-polyethylene articulations, the wear rate improves as the head size increases [6,7,9,14]. This combination of low wear and large head sizes with metal-on-metal bearings has prompted the resurgence of hip resurfacing arthroplasty [3,18].…”

The development of a small-scale wear test for CoCrMo specimens with human synovial fluid

“…The first generation hip joint was the Metal-on-Polymer (MoP) however they gave poor longevity due to polyethylene wear and particle debris resulting in osteolysis [3]. Implant lifespans of only 12-15 years made the implant suitable solely for older patients.…”

“…Implant lifespans of only 12-15 years made the implant suitable solely for older patients. Designs switched to the MoM prosthesis where both bearing surfaces are made from Cobalt-Chromium-Molybdenum (CoCrMo) Alloys [3]. Although the volumetric wear of the joint was reduced there was an increase in the number of wear particles causing metallosis damaging the periarticular bone and soft tissue eventually requiring implant revision [4,5].…”

The Hard on Hard Bearings in THA – Current concepts

“…Consequently, relatively polar contact is preferred. 20 For MOM bearings, in distinction from PE bearings, larger diameters can actually produce lower wear rates for similar manufacturing parameters. 21 It appears that a patient with normal renal function is capable of clearing cobalt and chromium ions.…”