Retrieval analysis of TiN (titanium nitride) coated knee replacements: Coating wear and degradation in vivo.

Abstract

Titanium nitride (TiN) coatings are used in joint arthroplasty to minimize wear and reduce the allergenic potential of metal implants, yet little is known about their performance in knee arthroplasty. This retrieval study examined TiN coated knee replacements to verify in vivo wear and degradation of the coating. This study included total and unicompartmental mobile bearing knee replacements retrieved from five patients (eight components) after 13-21 months due to aseptic loosening or infection. Implants were examined using scanning (SEM) and optical microscopy, surface damage was assessed using a semiquantitative scoring system, adhesion was determined using indentation technique testing, surface roughness was measured using contact profilometry. Although good coating adhesion and no gross failure were observed on all retrievals, coating wear and roughening were evident on tibial bearing surfaces. Multiple microscopic defects (pinholes, craters, titanium droplets) were observed on all samples in SEM studies. Microscopic wear scars indicated that particulate defects significantly contributed to coating wear, acting as third bodies. TiN coatings of knee replacements undergo wear and degradation related to presence of third bodies and microscopic defects on their surface. Since coating integrity may be compromised in vivo, such implants should be used with caution in metal sensitive patients.