Analysis of the in-vivo failure of the adhesive interlayer for a DLC coated articulating metatarsophalangeal joint

Unwanted physiological reactions, caused by particle release in articulating joints, are still a major concern in total hip arthroplasty. Diamond-like carbon coatings (DLC) show very low wear values in many technical applications. Attempts to transfer these outstanding tribological properties to in-vivo load bearing articulating joints turned out to be extremely problematic. A DLC coated metallic metatarsophalangeal (MTP) prosthesis, with both articulating surfaces coated, was explanted after approximately 4 years. The DLC-coating was removed from the entire face of the phalangeal component and from most of the face of the metatarsal component. It appeared that the coating was scratched and then delaminated parallel to the scratches.To retrospectively investigate the reason for the in-vivo failure, the explanted prosthesis was analyzed by X-ray photoelectron spectroscopy (XPS) depth profiling and cross sectional scanning electron microscope (SEM) analysis. The coating consisted of an approximately 180 nm thick DLC film and a circa 120 nm thick silicon based adhesion promoting interlayer on a CoCrMo base material. SEM observation of transversal cuts showed that the delamination of the DLC-coatings was mainly caused by a slow in-vivo corrosion of the whole Si interlayer due to crevice corrosion. Additionally, a weak mechanical bond between the CoCrMo substrate and the Si-based interlayer further facilitated the access of body liquid below the Si interlayer. The instability of Si toward crevice corrosion was also demonstrated by a separate crevice experiment using silicon single crystals.

► DLC coated Implants having silicon based interlayers will fail in-vivo after some years.
► The build-up of crevice conditions in cavities is promoted by the presence of proteins.
► Coated implant failure by crevice corrosion will not be detected in a simulator test.