Wear of surface engineered metal-on-metal hip prostheses

Abstract

The wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/million cycles) is much lower than the more widely used polyethylene-on-metal bearings (30-100 mm3/million cycles). However, there remain some potential concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically in the human body. The aim of this study was to investigate the wear, wear debris and ion release of fully coated surface engineered MOM bearings for hip prostheses. Using a physiological anatomical hip joint simulator, five different bearing systems involving three thick (8-12 microm) coatings, TiN, CrN and CrCN, and one thin (2 microm) coating diamond like carbon (DLC) were evaluated and compared to a clinically used MOM cobalt chrome alloy bearing couple. The overall wear rates of the surface engineered prostheses were at least 18-fold lower than the traditional MOM prostheses after 2 million cycles and 36-fold lower after 5 million cycles. Consequently, the volume of wear debris and the ion levels in the lubricants were substantially lower. These parameters were also much lower than in half coated (femoral heads only) systems that have been reported previously. The extremely low volume of wear debris and concentration of metal ions released by these surface engineered systems, especially with CrN and CrCN coatings, have considerable potential for the clinical application of this technology.

Diamond like carbon coatings for potential application in biological implants—a review

“…5 [38]. Fracture and cracking was noted along the wear scars by Fisher et al [42], shown in Fig. 6, suggesting early delamination in the coating around the contact points.…”

“…A number of papers do not state the type of DLC used [4,[40][41][42][43][46][47][48], while those that do state they are using ta-C or a-C:H, they fail to mention the composition ratio. While the manufacturing method and the source material enable an estimation of the composition, without knowing the exact conditions during the deposition, it remains little more than a guess.…”

“…Some of the earliest tests (Dowling [40]and Lapalainen et al [44]) provide some of the most positive results compared to the later tests (Fisher et al [42]). However, as Fisher does not mention the coating used, or any interlayers it could be possible that none were used, which could show that the advancements in coatings are improving the performance of the coating.…”

“…The results showed similarities, with all 3 tests showing a reduction in wear compared to uncoated tests, however to different levels. Tiainen [27] showed a reduction in wear by a factor of 10 5 -10 6 , Lappalainen et al [39] only showing a reduction of 10 2 -10 4 and Fisher et al [42] only showing a wear rate reduction of 26.The only notable differences between these tests is that Fisher et al tested the DLC coating against a different hard coating (CrN) not a 2nd DLC surface and a slightly different testing rig Papers that use DLC on UHMWPE(Saikko et al [43], Affatato et al [41] and Dowling et al [40]) use similar testing periods and testing solutions. However, Affatato et al [41] used double the test load that Saikko et al [43] employed.…”

“…Out of 14 reports [4,27,[39][40][41][42][43][44][45][46][47][48][49][50] there appeared to be no standardisation between choice of testing conditions and counter surface.…”