The Journal of Bone and Joint Surgery, Vol 60, Issue 3 342-348, Copyright © 1978 by Journal of Bone and Joint Surgery, Inc
The influence of design on the transmission of torque across knee prostheses
F Werner, D Foster and DG Murray
Knee prostheses of eight different designs were tested experimentally to
determine the axial torque necessary to rotate the tibial component
relative to the femoral component with the prosthesis positioned at or near
full extension. The results represent transmitted torque as a function of
axial rotation. For six designs, the transmitted torque was 11.3
newton-meters (100 inch-pounds) or greater at 6 degrees of rotation, with
an axial load of 1556.8 newtons (350 pounds). These prostheses either had
close conformation between femoral and tibial components, or were
mechanically linked. In these prostheses, the geometry of the articulating
surfaces was the primary determinant of torque. For the other two types,
under similar loading conditions the transmitted torques were 2.5
newton-meters (twenty-two inch-pounds) at 6 degrees of rotation. These
prostheses were designed to allow greater freedom for rotation, and hence
for them the primary determinant of torque was friction between the
articulating surfaces. The predictive value of this torque characteristic
relative to the incidence of loosening will have to be determined by
comparison with clinical experience.
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