This study examined whether TiNbN surface characteristics can reduce corrosion and wear of Chrome Cobalt Molybdenum Metal-on Metal bearings.

Two series of patients had plasma concentrations of chromium and cobalt at intervals following surgery. The First Series comprised a retrospective analysis of 52 consecutive cases (49 patients, 73–96 months following operation; age at surgery: 33–78) who had undergone an ACCIS (Implantcast, Germany) Modular Large Head hip replacement. The Second Series comprised a prospective, consecutive series of 125 cases (109 patients, 1–61 months following operation; age at surgery: 24–75) who had undergone an ACCIS Resurfacing Hip Replacement in whom pre-operative samples and periodic post-operative metal ion analysis was obtained. Cup inclination and anteversion angles, patient outcome and Harris hip scores at last follow-up were also recorded.

The first series revealed medians for [Cr] of 1.2 (range <0.5–2.4) ug/l and [Co] of 3.3 (range <0.15–8.18) ug/l. Four patients were not available for measurement. The second series gave one year [Cr] of 0.8 (range <0.5–1.6) ug/l and [Co] of 0.2 (range <0.15–0.9) ug/l and at two years [Cr] of 0.2 (range <0.5–1.5) ug/l and [Co] of 0.8 (range <0.15–1.0) ug/l. There was no correlation with cup inclination (38° to 62°) or anteversion (0° to 32°) in either group. Mean Harris Hip Scores were 80.9 and 92.3 respectively.

Low median levels of metal ions were found in the First Series (despite differing stem type usage). The low median ion levels were more consistent in the Resurfacing patients of the Second Series. The Titanium Niobium Nitride Ceramic Surface Engineering Metal-on-Metal bearing implants appear to protect against raised plasma [Cr] and [Co] both over time and with outlying cup positions. The Harris Hip Scores suggest a good patient outcome for the hip replacements in both series. Further study by a randomised controlled prospective analysis is suggested.