The innovation trap: modular neck in total hip arthroplasty
Background: Innovations play the key role in the success of orthopaedic surgery. However, even minor modifications in the established concepts and proven designs may result in disasters. The endemic of modular femoral neck fracture (24 cases of about 4000 implanted) in fully modular total hip arthroplasty, popular in our country for the last 20 years, seems to challenge us with such an unfortunate consequences. The aim of this report was to analyze the extent and the causes of the problem on the one hand and to propose possible solutions on the other.
Methods: Literature search for problems associated with Profemur Z (or earlier versions with the same taper-cone design) fully-modular femoral stem made of titanium alloy (Ti6Al4V) was performed, and hip arthroplasty registries were searched to evaluate the failure rates of the mentioned design. Mechanisms of failure were studied to get in-depth understanding of this particular hip reconstruction device.
Results: Since 2010 onwards, several case reports on catastrophic modular femoral neck fractures of Profemur Z were published. Te frst Slovenian case was described in 2012. The first two larger series with modular femoral neck fractures were published in 2016. Te Australian Joint Replacement Registry was the first to discover increased revision rates due to fractures of this hip reconstruction system. Public Agency of the Republic of Slovenia for Medicinal Products and Medical Devices (JAZMP) received frst two reports regarding Profemur Z modular neck complication from abroad in 2010, the first Slovenian report was received in 2012, and altogether 7 reports from Slovenian hospitals were received until December 2016. Corrosion at the neck-taper interface, where two equal or diﬀerent materials are subject to constant wear in the presence of body ﬂuids, is assumed to be responsible for the unacceptable high failure rate.
Conclusions: Manufacturers are responsible to produce and market only safe devices. However, orthopaedic surgeons should carefully monitor any adverse eﬀect of innovations. JAZMP took adequate measures only after having received an urgent field safety corrective notice from the manufacturer in 2015 indicating that all lots of long modular necks made from cobalt-chromium alloy should be withdrawn. Tis should be viewed in concordance with the fact that the regulatory agency of the Republic of Slovenia was not receiving vigilance reports accurately and was thus unaware of the extent of this complication. A national arthroplasty registry would probably warn orthopaedic community on this questionable innovation earlier. Regulatory bodies should therefore establish such a registry as soon as possible, for the benefit of our patients.
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