Characterization of protein degradation in serum-based lubricants during simulation wear testing of metal-on-metal hip prostheses

Wear Simulation of Ceramic-on-Crosslinked Polyethylene Hip Prostheses: A New Non-Oxide Silicon Nitride versus the Gold Standard Composite Oxide Ceramic Femoral Heads

The purpose of the present study was to compare the wear behavior of ceramic-on-vitamin-E-diffused crosslinked polyethylene (Vit-E XLPE) hip bearings employing the gold standard oxide ceramic, zirconia (ZrO₂)-toughened alumina (Al₂O₃) (ZTA, BIOLOX^®delta) and a new non-oxide ceramic, silicon nitride (Si₃N₄, MC^2®). In vitro wear test was performed using a 12-station hip joint simulator. The test was carried out by applying the kinematic inputs and outputs as recommended by ISO 14242-1:2012. Vitamin-E-diffused crosslinked polyethylene (Vit-E XLPE) acetabular liners (E1^®) were coupled with Ø28-mm ZTA and Si₃N₄ femoral heads. XLPE liner weight loss over 5 million cycles (Mc) of testing was compared between the two different bearing couples. Surface topography, phase contents, and residual stresses were analyzed by contact profilometer and Raman microspectroscopy. Vit-E XLPE liners coupled with Si₃N₄ heads produced slightly lower wear rates than identical liners with ZTA heads. The mean wear rates (corrected for fluid absorption) of liners coupled with ZTA and Si₃N₄ heads were 0.53 ± 0.24 and 0.49 ± 0.23 mg/Mc after 5 Mc of simulated gait, respectively. However, after wear testing, the ZTA heads retained a smoother topography and showed fewer surface stresses than the Si₃N₄ ones. Note that no statistically significant differences were found in the above comparisons. This study suggests that the tribochemically formed soft silica layer on the Si₃N₄ heads may have reduced friction and slightly lowered the wear of the Vit-E XLPE liners. Considering also that the toughness of Si₃N₄ is superior to ZTA, the present wear data represent positive news in the future development of long-lasting hip components.

Chrome nitride coating reduces wear of small, spherical CrCoMo metal-on-metal articulations in a joint simulator

Metal-on-metal articulations have fallen out of favour in larger joint replacements, but are still used in smaller joints. Coating the articulation has been suggested as one way of reducing wear. We compared a standard 6 mm CrCoMo articulation designed for the carpometacarpal joint of the thumb with a chromium nitride-coated version after 512,000 cycles in a joint simulator. A total of 6 articulations in each group were tested with a unidirectional load of 5 kg in Ringer's solution. We found a statistically significant reduction in weight loss, amount of metallic wear produced and volumetric wear for the chromium nitride-coated articulation. Our findings support the use of chromium nitride coating in order to minimize the amount of metallic wear produced.

Metal-on-metal total hip arthroplasty: is there still a role in 2016?

The use of metal-on-metal (MoM) bearings in total hip arthroplasty (THA) was popularized due to its enhanced wear profile and the ability to use large femoral heads to reduce post-operative instability. However, enthusiasm for the bearing declined following serious complications encountered at the primary articulation. This review discusses the development of MoM and the subsequent unexpected downstream challenges, most notably elevated serum metal ion levels, aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL), pseudotumor formation, and subsequent soft tissue and bone destruction. Both patient centered risk factors as well as component design led to high early failure rates resulting in product recalls and an overall decline in the use of MoM. In 2016, there is not a role for large-head MoM bearing in THA. Alternatively, the bearing has shown promise in hip resurfacing procedures for carefully selected patients.

CoCrMo metal-on-metal hip replacements

After the rapid growth in the use of CoCrMo metal-on-metal hip replacements since the second generation was introduced circa 1990, metal-on-metal hip replacements have experienced a sharp decline in the last two years due to biocompatibility issues related to wear and corrosion products. Despite some excellent clinical results, the release of wear and corrosion debris and the adverse response of local tissues have been of great concern. There are many unknowns regarding how CoCrMo metal bearings interact with the human body. This perspective article is intended to outline some recent progresses in understanding wear and corrosion of metal-on-metal hip replacement both in vivo and in vitro. The materials, mechanical deformation, corrosion, wear-assisted corrosion, and wear products will be discussed. Possible adverse health effects caused by wear products will be briefly addressed, as well as some of the many open questions such as the detailed chemistry of corrosion, tribochemical reactions and the formation of graphitic layers. Nowadays we design almost routinely for high performance materials and lubricants for automobiles; humans are at least as important. It is worth remembering that a hip implant is often the difference between walking and leading a relatively normal life, and a wheelchair.