Abstract
Although good clinical results for modern metal-on-metal total hip endoprostheses are reported, in some cases early loosening is encountered. Such loosening may lead to revision surgeries, which raise some concern on the functionality of that pairing. The study contains 17 early-revised uncemented metal-on-metal (Co28Cr6Mo, ASTM F799) total hip arthroplasties from one manufacturer (Plus Endoprothetik, Switzerland) with a mean of 29 months in-situ (12–58) from 16 patients (seven male, nine female); mean age at revision surgery was 57 years (41–72). The reason for revisions was aseptic loosening of implants with increasing pain (13 stems and seven metal cups were revised). The tribologic assessment of all 17 metal pairings is conducted by 3 dimensional measurements of the metal ball heads and inlays according to ISO and through scanning electron microscopy (SEM) inspection of the articulating surfaces. Additional metal ion content (Cr, Co, Mo, Ti,Al, Nb, Ni) of selected tissue samples and synovial fluid is quantified by inductively coupled plasma – atomic emission spectrometry (ICP-AES).
The mean wear rate of both, the femoral ball head and the acetabular inlay, is 7.3um/a (2.8 – 29.4) based on the time in-situ with a mean clearance of 42.8um (32 – 56um). Adhesive and abrasive wear traces as well as third body wear particles (aluminum oxide Al2O3) are identified on all bearing surfaces only to an extent, which is typical for metal pairings. Corrosive attack is visible on one pairing as a smoky area.
Tribologic results do not indicate a significant contribution of wear due to the Al2O3-particles. The amount of wear does not seem increased and is comparable to previously published data for metal-on-metal pairings and simulator studies. Analytic results indicate a relatively high Al content from all retrieved tissue areas. The investigations on the surfaces of all 17 metal-on-metal articulations indicate no material failure that might have led to the necessity of early revision.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
