F. Farahmand (Iran)
Joint Modeling, Patello femoral Joint, Total Knee Arthroplasty, Design.
The frequent failure of patellar component in total knee arthroplasty is often referred to the high contact stresses caused by a non-conforming articulation. This work aimed to evaluate the design of conforming patellofemoral joints for total knee prostheses considering their ranges of conforming articulation, contact forces and muscle efficiencies. A computer model of the patellofemoral joint was developed and a fresh cadaver knee, mounted in an Instron machine, was used to produce the input geometry data. Changing the radius and location of articulating arc on the femoral groove and patellar concavity as the design parameters, the resultant joint configuration was studied. Enlargement of the radius of the articulating arc and posterior shift of the patellar concavity with respect to the anatomical geometry, extended the range of conforming articulation slightly in both extension and flexion. Distal shift of the patellar concavity, and proximal and anterior shift of the femoral groove shifted the range of conforming articulation towards extension but limit the conforming articulation in knee flexion. Most of these modifications increased the joint contact force and muscle efficiency, however, muscle efficiency was always considerably lesser than the intact knee near extension. It was concluded that prosthetic patellofemoral designs, which can provide conforming articulation at knee full extension, would suffer from non-anatomical geometry and small muscle efficiency near extension.
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