High wear resistance of femoral components coated with titanium nitride: a retrieval analysis

Abstract

Purpose The objective of this study was to evaluate the in vivo wear resistance of cobalt-chromium femoral components coated with titanium nitride (TiN). Our null hypothesis was that the surface damage and the thickness of the TiN coating do not correlate with the time in vivo.Methods Twenty-five TiN-coated bicondylar femoral retrievals with a mean implantation period of 30.7 ± 11.7 months were subjected to an objective surface damage analysis with a semi-quantitative assessment method. A visual examination of scratches, indentations, notches and coating breakthroughs of the surfaces was performed. The roughness and the coating thickness of the TiN coating were evaluated in the main articulation regions.ResultsNarrow scratches and indentations in the range of low flexion angles on the retrieval surfaces were the most common modes of damage. There was no evidence of delamination on the articulation surface but rather at the bottom of isolated severe indentations or notches. An analysis of three retrievals revealed a coating breakthrough in the patellofemoral joint region, resulting from patella maltracking and a dislocation. The arithmetical mean roughness of the TiN surface slightly increased with the implantation period. In contrast, the maximum peak height of the roughness profile was reduced at the condyles of the retrieved components in comparison with new, unused surfaces. No significant association between the coating thickness and implantation period was determined. Moreover, the measured values were retained in the range of the initial coating thickness even after several years of in vivo service.ConclusionsAs was demonstrated by the results of this study, the surface damage to the TiN coating did not deteriorate with the implantation period. The calculated damage scores and the measured coating thickness in particular both confirmed that the TiN coating provides low wear rates. Our findings support the use of wear-resistant TiN-coated components in total knee arthroplasty with the objective of reducing the risk of aseptic loosening. However, in terms of TiN-coated femoral components, particular attention should be paid to a correct patellar tracking in order to avoid wear propagation at the implant.

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

“…Since some studies demonstrated that implants with Ti(Nb)N and similar coatings have decreased allergenic potential in comparison to CoCrMo implants, they are an attractive alternative in metal sensitive patients (Lachiewicz et al, ; Reich et al, ; Thienpont, ; Thomsen et al, ). In such applications the durability of the coating is of critical importance, and one retrieval study demonstrated little wear of TiN coatings in femoral components (Fabry et al, ). However, it did not include tibial components and implant examination was limited to semiquantitative wear scoring and optical microscopy.…”

“…It is very difficult to collect such retrievals because TiN coated implants are not routinely used in large groups of patients (Breugem et al, ; Buechel Sr et al, ; Buechel Sr et al, ; Park et al, ; Thienpont, ; Van Hove et al, ). This is reflected by lack of registry data and a small body of literature regarding Ti(Nb)N coated arthroplasties, and retrieval studies focused on such implants also involved small sample numbers (Bone & Naylor, ; Fabry et al, ; Harman et al, ; Khatkar et al, ; Łapaj et al, ; Łapaj, Markuszewski, et al, ; Malviya et al, ; Raimondi & Pietrabissa, ). An inherent limitation of this, as well as other retrieval studies, is that only prematurely revised components were examined, which do not exactly represent well‐functioning knee replacements (Anderson et al, ; Fabry et al, ; Heyse, Elpers, Nawabi, Wright, & Haas, ).…”

“…After retrieval of all metal implants, poly liners were cleaned in a mild detergent using a soft nylon brush, disinfected by submersion in 70% ethanol for 72 hr, dried and stored in plastic containers. First, they were examined using a stereo‐light microscope to determine surface damage of tibial and femoral components using a modified Brandt scale as described by Fabry et al (). Briefly, this semiquantitative scoring system evaluated the extent of damage caused by the presence of scratches (>2 mm) in the direction of implant movements, coating breakthrough (destruction of coating caused by wear), indentations (small pits) and notches (plastic deformation of substrate material and coating).…”

“…The area score quantified the estimated area covered by a given type of damage mark; 0 to 10 points were assigned for damage present in 0%, 0–10%, 10–20% … 90–100%. The severity of damage was quantified as 0, 0.33, 0.66, and 1 corresponding to no, mild, pronounced and severe damage as described in detail by Fabry et al (). This scoring system was designed for femoral components of TKRs and included evaluation of both condyles in areas corresponding to 0°, 45°, and 90° of flexion (six areas per component).…”

“…The only retrieval analysis conducted so far used semiquantitative damage scoring and optical microscopy examination. It demonstrated good wear resistance of TiN coated femoral components; however it did not include any tibial components (Fabry et al, ). Conflicting results were presented in a simulator study where severe wear of the TiNbN coating was observed on femoral components during 5 million cycles of testing (Haider et al, ).…”