Improving the long-term performance of modular connections in artificial joints

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Artificial joints have been used in increasing numbers since the middle of the last century to treat patients with diseased joints. Early on, mainly hip and knee joints were treated, and the devices were rarely implanted in persons younger than 60 years, as the implant survival rate was typically less than 15 years. Artificial joints have improved much in the last 50 years, so that a survival rate of 90% or more can be expected after 15 years, in spite of the fact that they are increasingly being implanted in younger and more active patients. Improvements that were introduced in the last few years included more modular designs, which allow surgeons intra-operatively to optimally adjust the articulation, geometric features and fixation to an individual patient. Despite enormous efforts using computer modeling and elaborate near physiological testing, it appears that some of these new designs develop problems at their modular connections. More frequently, there is an increase in corrosion at the modular head-neck interface of hip joints, especially in hips with larger heads that can lead to adverse tissue reactions such as the formation of cysts, pseudotumors and muscle damage. The long term goal of this industry independent research is to improve the performance of modular connections in artificial joints to achieve a reduction of revisions due to fractures, corrosion and adverse tissue reactions. The proposed work will look at modular connections through the failure analysis of explanted joints, computer modeling and in vitro testing of improvements of modular connections resulting from this research program. A key outcome will be the development of a novel fatigue test that includes corrosion of modular connections between large heads and the neck of hip implants. The expected reduction of revisions will increase the successful long-term performance of artificial joints benefiting the patients, and reduce the costs to health care. Training of HQP in this area of expertise at the University of Manitoba and the Concordia Hip and Knee Institute will support the growth of the medical device industry in Canada.