Fretting wear in a modular neck hip prosthesis

Abstract

In vitro cyclic load fretting tests were conducted on a prototype of a cementless, modular neck, hip prosthesis. The study had three major objectives: to determine the amount of fretted material in the tapered-neck joint under various load cycle amplitudes, to determine the fretting damage evolution, and to determine the effect of different-sized stem bodies on the production of debris. All the tests produced some fretting microdamage on the tapered surface although the extent was quite different among test groups. The amount of abraded material increased almost linearly with the applied load magnitude but not with the number of load cycles. The amount of weight loss was higher in the large stem bodies than in the small ones. Weight loss ranged from 0.28 +/- 0.10 mg for small stem bodies loaded 5.5 million times up to 2300N to 2.54 +/- 0.53 mg for large stem bodies located 20 million times up to 3300N. Considering the large-size stem results, and assuming one million load cycles between 300N and 3300N to be the average yearly load history, the modular neck tapered joint would produce 0.6 mg/year of metal debris. The clinical impact of this observation is unknown; however, some of the literature on the presence of metal in patient tissues and fluids supports the hypothesis that a normal and stable prosthesis is likely to produce less than 10 mg/year of metal debris. Thus, a further production of 0.6 mg/year due to the modular neck should not have any significant effect.

Proximal Component Modularity in THA—At What Cost?: An Implant Retrieval Study

“…Third, we did not perform in vitro testing to elucidate the mechanism of fretting, micromotion, or corrosion peculiar to each of the modular designs. This type of testing is technically challenging, however, and commonly such in vitro studies have concluded modular-junction degradation is of little clinical relevance [17,18,22,25], which contrasts to the findings of this retrieval study. Finally, we could not retrospectively collate metal ion levels, which may indicate the degree of systemic metal exposure.…”

“…Clinical advantages of modular necks include the adjustment of leg length and offset via the head-neck taper, femoral anteversion via the neck-stem taper, easier revision when there is no clinical need to revise a well-fixed stem, and optimal restoration of soft tissue tension and patient biomechanics [7]. As a consequence of introducing a second taper junction, it has been reported, in single-patient case studies, multiple modular taper junctions present an additional site for failure [1,11,[23][24][25][26].…”

Metal release and corrosion effects of modular neck total hip arthroplasty

“…Compared to other studies the titanium release of all systems investigated in this study is low. A similar study on a modular neck hip implant design made of a titanium alloy revealed material loss of between 280 and 1,640 µg after 5.5×10 6 loading cycles [22]. Another study on a titanium plate-screw connection resulted in a titanium release of 849 µg after 1.2×10 6 loading cycles [13].…”

High Risk of Failure With Bimodular Femoral Components in THA

“…However, failures of these components have been reported [2,7,15,27,28,30,31]; thus long-term survivorship of and complications associated with bimodular femoral neck components must be assessed to determine if the benefits outweigh the risks of failure. In our retrospective study, we evaluated a series of bimodular femoral neck implants used for primary THA to determine survivorship, main causes of failure, and the risk factors associated with them.…”

“…Failures of bimodular necks have been reported, including bimodular neck fracture and corrosion with pseudotumor and periprosthetic loosening [2,7,15,27,28,30,31]. 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].…”