Poster AA7 - Compression Stability of Three Fixation Modes for Intraoperative Femoral Condyle Fractures During Knee Replacement

Introduction: Total knee arthroplasty (TKA) is one of the most performed surgeries to reduce the pain and disability associated with end stage knee osteoarthritis. In total knee replacement surgery, the incidence of intraoperative periprosthetic fracture varies between 0.3% to 4% depending on the patient's risk factors and implants used [1]. Among the fracture types, medial femoral condyle intraoperative fracture is the most common and requires fixation of the fracture [2]. A stable intraoperative fracture fixation is desirable to allow minimal modification to standard total knee replacement protocol. There are various fixation options, but the three commonly used techniques are: (1) Reduce the fracture, fix with screws, and use standard femoral component; (2) reduce the fracture, fix it with plates and screws, and then implant standard component; (3) reduce the fracture and fix it with screws and use a femoral component with a stem attached to the component. The choice of fixation is often determined by surgeon preference with no specific clinical or biomechanical data to support the selection. In this study, we performed incremental cyclic compression testing to assess the mechanical stability of three fixation options.

Materials and

Methods: Denuded human right femurs were obtained from Science Care (Phoenix, AZ). Those cadaver femurs are from a similar age range (Male, 65 to 75), with similar size, fresh and no abnormality, and no treatment. Standard knee implants, stem knee implants, bone screws, and locking plates were obtained from Stryker (Addison, TX). With the right femur bones procured and the knee prostheses ready, medial femoral condyle fractures had been created before implantation of the femoral prosthetic component. The fracture had been fixed with three different fixation options, i.e., (1) standard implants with screws alone, (2) Standard implants with locking plate-screws, and (3) Stemmed implants with screws. Instron Machine (Model: 5965) was used for this study. With its TestProfiler software, Instron Machine can apply cyclic loading and unloading, step-by-step loading patterns to mimic the functional use of orthopedic devices. Incremental cyclic compressive loading-unloading protocol up to 1.5 kN (337 lbs) was then programmed to assess the fixation stability and its resistance to cyclic compressive loading.

Results, Conclusions, and Discussions: The mechanical results demonstrated different performances of three fixation options. (1) The locking plate-screws fixation demonstrated the best stability and resistance to cyclic compressive loading. (2) The bone screw-only fixation was able to achieve stability and resistance to cyclic compressive loading similar to the locking plate-screws fixation, only showing slightly lower stability and resistance. (3) The stemmed implants with screws showed the worst stability and resistance to cyclic compressive loading among three fixation options. These important observations point out, under the cyclic axial compressive loading (the dominant, physiologically-relevant loading pattern), the stemmed implants have the worst stability and compressive resistance, the locking plate-screw fixation has the best stability and compressive resistance, and the bone screw only fixation achieves a stability and compressive resistance only slighter lower than the locking plate-screws fixation and might be the most cost-effective fixation option. Furthermore, our observation indicates that the routine use of stemmed implants might not be needed since (i) it is not a stable fixation; (ii) it has disadvantages such as increased bone loss, longer operative time, and higher cost.

Acknowledgements (Optional): Department of Veterans Affairs NTX Investigator Grant: NIP549

[1] Lombardi AV, et al., J Arthroplasty, 10:643-650, 1995.
[2] Bennett CG, et al., Arthroplasty Today. 3(4):253-256, 2017.