Joint Contact Characteristics in Agility Total Ankle Arthroplasty

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High component contact pressures in total joint prostheses can lead to particle wear debris and prosthesis loosening. The contact pressures in the Agility total ankle prosthesis have not been investigated. In the current study, a cadaveric model was used to evaluate contact characteristics (average contact area, contact pressure, and contact peak pressures) for the Agility total ankle system. Ten cadaveric specimens were implanted with the Agility total ankle and axially loaded to 700 N. The average contact pressure of the system was 5.6 MPa with mean peak pressures of 21.2 MPa. In a separate phase of the study, contact characteristics with applied loads for each of the six component sizes showed a significant effect of component size on contact characteristics. When physiologic ankle forces are considered for normal patient activity, peak pressures observed in the current study may exceed recommended contact pressures (10 MPa) and the compressive yield point (13–22 MPa) for polyethylene. A heavy patient with a small ankle would not be expected to have a good outcome based on the current contact pressures data, whereas a heavy patient with a larger ankle might be a better candidate for surgery.

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