Modular titanium alloy neck adapter failures in hip replacement - failure mode analysis and influence of implant material

Abstract

BackgroundModular neck adapters for hip arthroplasty stems allow the surgeon to modify CCD angle, offset and femoral anteversion intraoperatively. Fretting or crevice corrosion may lead to failure of such a modular device due to high loads or surface contamination inside the modular coupling. Unfortunately we have experienced such a failure of implants and now report our clinical experience with the failures in order to advance orthopaedic material research and joint replacement surgery.The failed neck adapters were implanted between August 2004 and November 2006 a total of about 5000 devices. After this period, the titanium neck adapters were replaced by adapters out of cobalt-chromium. Until the end of 2008 in total 1.4% (n = 68) of the implanted titanium alloy neck adapters failed with an average time of 2.0 years (0.7 to 4.0 years) postoperatively. All, but one, patients were male, their average age being 57.4 years (36 to 75 years) and the average weight 102.3 kg (75 to 130 kg). The failures of neck adapters were divided into 66% with small CCD of 130° and 60% with head lengths of L or larger. Assuming an average time to failure of 2.8 years, the cumulative failure rate was calculated with 2.4%.MethodsA series of adapter failures of titanium alloy modular neck adapters in combination with a titanium alloy modular short hip stem was investigated. For patients having received this particular implant combination risk factors were identified which were associated with the occurence of implant failure. A Kaplan-Meier survival-failure-analysis was conducted. The retrieved implants were analysed using microscopic and chemical methods. Modes of failure were simulated in biomechanical tests. Comparative tests included modular neck adapters made of titanium alloy and cobalt chrome alloy material.ResultsRetrieval examinations and biomechanical simulation revealed that primary micromotions initiated fretting within the modular tapered neck connection. A continuous abrasion and repassivation process with a subsequent cold welding at the titanium alloy modular interface. Surface layers of 10 - 30 μm titanium oxide were observed. Surface cracks caused by fretting or fretting corrosion finally lead to fatigue fracture of the titanium alloy modular neck adapters. Neck adapters made of cobalt chrome alloy show significantly reduced micromotions especially in case of contaminated cone connection. With a cobalt-chromium neck the micromotions can be reduced by a factor of 3 compared to the titanium neck. The incidence of fretting corrosion was also substantially lower with the cobalt-chromium neck configuration.ConclusionsFailure of modular titanium alloy neck adapters can be initiated by surface micromotions due to surface contamination or highly loaded implant components. In the present study, the patients at risk were men with an average weight over 100 kg. Modular cobalt chrome neck adapters provide higher safety compared to titanium alloy material.

High Risk of Failure With Bimodular Femoral Components in THA

“…Chemomechanical stress is reported to be higher in titanium modular necks compared with cobalt-chromium bimodular necks. This also is true in femoral stems used for primary THA compared with stems used in revisions owing to the longer and larger anchorage cones of revision stems [7,9,11,16,33].…”

“…Because of a substantial rate of loosening by subsidence with the bimodular PROFEMUR 1 E, in 2006 the bimodular PROFEMUR 1 Z stem was chosen for use. Because of reports of fracture of the bimodular neck, use of PROFEMUR 1 stems that accommodated the bimodular neck was abandoned [5,7,13,16,28,32,33]. Bearing surface…”

“…Mechanical analyses have suggested that corrosion-assisted fatigue is an important mechanism of failure, and design choices in metallurgy, offset, caput-column diaphysis angle, and mechanical stresses of physical activity are factors contributing to corrosion [7,11,16,33]. As with any new technology, the risk-benefit analysis must show that the advantages of modularity outweigh the risks.…”

What is the Trouble With Trunnions?

“…Large-diameter femoral heads and trunnion geometry were common features identified in the studies that associated elements of implant design with tribocorrosion in taper junctions [7,18,19,32]. Larger head sizes increase torsional forces at the trunnion [9], and this may be a contributing factor in the increased failure rates seen metalon-metal (MoM) THAs [17,22], which have a high revision rate of 19% after 12 years [2].…”

Comparative Effectiveness of Ceramic-on-Ceramic Implants in Stemmed Hip Replacement

“…The interaction terms were based on time intervals of zero to two, two to four, four to six, and six to eight years. A test of the interaction terms was nonsignificant (x 2 [3] = 0.84, p = 0.84); therefore, these terms were removed. The iterated model indicated that the overall head size effect was nonsignificant, with the point estimate favoring a harmful effect of small-head-size C-C implants (b = 0.097, SE = 0.221).…”