تنشهاي تماسي مفصل تيبيوفمورال در مفاصل مصنوعي كامل زانو

Contact stresses of the tibio-femoral joint in total knee prostheses

A major cause of early failure of prosthetic joints, particularly total knee prostheses, has been reported to be wear of the articulating surfaces and release of wear debris in patient ʹs body, which is mostly related to the joint contact stresses. In previous studies, the variation of the contact area has been always analyzed in knee extension and semi flexion positions. We studied the contact area of femoral and tibial components of a commercial total knee prosthesis across the whole range of knee flexion, including deep flexion, using casting technique. The femoral component was fixed rigidly on a horizontal shaft beneath of a compression testing machine, being able to rotate with the shaft and provide a full range of knee flexion angles. The tibial component was mounted, with enough laxity for abduction -adduction rotation, on the end of a vertical rod at the moving cross head of the testing machine. At each flexion angle, the surfaces ofʹ the femoral and tibial components were covered with silicon rubber solution, then a compressive load of 2000 N was applied to the joint for 5 minutes and removed following the setting of the silicon. The silicon casts were then photographed to obtain the contact areas of the tibio-femoral joint at different flexion angles. The contact area appeared to be almost consistent between 0 to 90 degrees knee flexion with a mean of 173 mm^2. The maximum and minimum contact areas were found to be 247 mmʹ and 72 mm^2, occurring at 120 degrees and 140 degrees of knee flexion, respectively. The mean contact stresses were obtained across the range of knee flexion, using the measured contact areas and appropriate. force data from the literature. The contact stress had a maximum of 7 MPa at early knee flexion and 21 MPa at semi flexion, but increased to more than 68 MPa at 140 degrees knee flexion. These results approve the clinical suggestion that the physiological activities which include deep knee flexion are critical for knee arthroplasty patients.