Abstract
The ACCIS system comprises a bearing of a 5 micron surface ceramic upon a Chrome Cobalt Molybdenum (CrCoMo) substrate which allows for a homogeneous couple. The Titanium Niobium Nitride (TiNbN) microceramic applied by Plasma Vapour Deposition. In comparison with CrCoMo alloy, TiNbN gives a hard (2800 vs 489V), smooth (0.23 vs 0.55Rz), low friction (0.079–0.1 vs 0.11–0.56mu pin on disk test), wetable surface which when combined allows for the potential of gaining fluid film lubrication (lambda>3) on a smaller head diameter than an untreated surface. These properties are postulated to reduce wear and hence lower the release of Cr and Co ions in vivo. The surface microceramic also prevents exposure to release of Cr and Co by corrosion. The surface modified implants were first used in 2003 in large head arthroplasty and later in 2005 with resurfacing implants. Two series of patients implanted by a single surgeon were examined to elucidate the metal ion release of the ACCIS system. The first series retrospectively examined 52 consecutive Large Head Arthroplasty cases for [Cr], [Co] and [Mo] levels. A mean follow-up time of 7.5 yrs (77–101mths) with 9 patients being lost to revision and death by the time of the study. Median levels of [Cr] 1.6, [Co] 4.76 and [Mo] 2.5 µg/l were obtained. The second series prospectively examined the [Cr] and [Co] levels with the pre-operative values as controls in 125 resurfacing cases with the ACCIS microceramic. The second series gave no rising trend observed at up to 5 years ([Cr & Co] (range < 0.5–1.6 µg/l). It is postulated that the ACCIS surface microceramic reduces wear and also reduces the effective patch size for a given load thus allowing for a greater Patch to Edge Distance allowing a greater tolerance to cup positioning. A RCT is currently underway.
