ABSTRACT
The rotational constraint characteristics of 4 commercially available posterior-stabilized
implants (Triathlon, NexGen, PFC, and Genesis II) were determined. The torques required
to achieve up to ±20° of internal and external rotation were quantified at hyperextension,
0°, 15°, 60°, and 90° of flexion. The effect of lubrication was tested by comparing
the torque values generated in dry and serum environments. Results indicated that
substantially higher torques were generated in the dry environment, compared with
the serum environment. In extension, the principal design features influencing the
torques were interaction of the box and post, as well as the insert anterior lip.
In higher flexion angles, the amount of rollback, coupled with the posterior lip geometry,
most heavily influenced the generation of torque. Comparison of the 4 designs showed
that the Triathlon generated the least torques to ±10° of rotation, whereas the PFC
and Genesis II were the most constrained.
