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Evaluating the Local Release, Systemic Transport, and Biological Significance of CoCr Debris in TKR
Start Date: 9/3/2020Start Time: 9:00 AM
End Date: 9/3/2020End Time: 11:00 AM

Event Description
BIOMED PhD Thesis Defense
Evaluating the Local Release, Systemic Transport, and Biological Significance of Cobalt-Chromium (CoCr) Debris in Total Knee Replacement (TKR)

Christina M. Arnholt, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Steven M. Kurtz, PhD
Research Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Total knee arthroplasty (TKA) is one of the most commonly performed orthopedic surgeries during which a tibial tray, either titanium (Ti) or cobalt-chromium (CoCr) alloys, a polyethylene insert, and a cobalt-chromium alloy femoral component are implanted. Sensitivity to metal debris re-emerged as a concern in arthroplasty, with relatively little research focused on metal release in TKA. The overall focus of this work was to describe the potential biological burden of metallic debris from TKA. This dissertation investigated TKA devices, and tissues collected from routine revision and post-mortem TKA retrievals.

The causes of damage to the metal components which lead to metallic release were evaluated, specifically looking at third-body damage using a semiquantitative method. This method was used to determine the severity and coverage of third-body damage on the bearing surface of femoral components. Using the semiquantitative third-body damage score, total knee arthroplasty components could be observed at multiple retrieval centers and compared.

Secondly, metal debris and its characteristics (tissue metal concentration, particle size, and particle shape) were studied to determine if they were uniform throughout the knee joint capsule. The relationship between metal debris and observed damage to the femoral component or observed biological reactions were also analyzed. The analysis of different regions within the joint capsule provided evidence that the chosen tissues for model analysis represent the entire joint capsule. Additionally, observations of metallic debris observed from the joint capsule could describe the characteristic shapes and sizes expected from total knee arthroplasty.

Finally, we used a biokinetic model to discuss the mobility of cobalt metal ions through the body. This approach involved the study of peripheral blood metal concentration and peri-prosthetic tissue metal concentration. The local movement of cobalt from the joint capsule into the bloodstream was modeled as debris movement directly from the synovial fluid to the bloodstream as a corrosion byproduct. Additionally, this model included a second transport of bearing surface debris movement from the synovial fluid to the joint capsule and then to the bloodstream. The remaining portions of the model originated from a biokinetic model of inorganic cobalt circulation with the exposure point of ingestion linked through an ailment track model. This model was altered so that the exposure point was the joint capsule, and the model was then calibrated to the periprosthetic tissue and blood of 7 retrieved TKA devices. The use of blood and peri-prosthetic tissues for metallic concentration measurements allowed the created model to be calibrated to total knee arthroplasty patients. With this calibrated model, the cobalt movement could describe an average TKA patient.  With this model, the burden of metallic debris released from TKA could begin to be described.

The execution of these aims provided an assessment of total knee arthroplasty components, an assessment of debris regarding dose, shape, size, material, and an assessment of the mobility of cobalt from the joint capsule.
Contact Information:
Name: Natalia Broz
Email: njb33@drexel.edu
Christina Arnholt
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