Failure analysis of explants retrieved during revision surgeries in Hip and Knee Arthroplasty
In 2020, the European Federation of Orthopaedics and Traumatology launched in cooperation with the German Society of Orthopaedics an “Implant & Patient Safety Initiative”. One part of this initiative is the identification of factors responsible for clinical failure of hip and knee endoprostheses (Morlock et al., 2022). The German Arthroplasty Register EPRD attributes about 2% of all revision surgeries to implant failure. This does not sound much but amounts to about 1.000 cases for the 50.000 revision surgeries performed in Germany alone in 2019.
In a pilot phase, 15 hospitals with large volumes of revision surgeries were asked to provide explants from cases, in which the reason for revision is suspected to be directly related to mechanical failure or wear of the implant. Explants are only included in the study if they are previously reported to the responsible regulatory body (BfArM) and to the manufacturer, as required by German law. Each explant is analysed by one of the four participating University laboratories with research focused on Biomechanics and Implant Development (TU Hamburg, Uni Heidelberg, LMU Munich, Uni Rostock). The study is coordinated by TU Hamburg.
First results indicate that most submitted cases originate from re‐revision surgeries, i.e. surgeries which were performed to revise an already performed first revision in a patient.
Mechanical overload of the implant was identified as reason for failure in 60% of the implants analysed. During revision surgery, anatomical structures such as bone and soft tissue are damaged much more as during primary surgery due to the removal process of the originally implanted endoprosthesis components. Revision endoprostheses have such to take over the function of the removed tissue, which is associated with much higher mechanical loading. Increasing the strength of revision endoprostheses, however, is only possible to a certain amount due to the limited dimensions inside the long bones, in which endoprostheses are anchored. Implant failure can for example occur if the bone support for the implant is reduced over time (see Figure 1). Other reasons include increased patient weight with concurrent increasing activity levels. Surgeons and patients have to be made aware of this problem after revision surgery in order to act accordingly.
Figure 1: Failure of the femoral component of a revision //
left: X‐ray after implantation of the revision knee endoprosthesis after a
failed primary knee endoprosthesis //
middle: X‐ray 9 years later with a fracture of the taper connection (red arrow)
to the prosthesis stem //
right: The fractured taper after revision
Prof. Michael Morlock, Institut für Biomechanics, morlock(a)tuhh.de
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