Varus-valgus and rotational stability in rotationally unconstrained total knee arthroplasty.

This study was designed to test the ability of the ligaments to restore rotational stability to the knee after rotationally unconstrained anterior cruciate-sacrificing total knee arthroplasty (TKA). Rotational and varus-valgus stability both were returned to near-normal values, and the normal screw home pattern of coupled external rotation with extension was restored when the ligaments were correctly tensioned. When the ligaments were tensioned so that the knee was either too loose or too tight, both varus-valgus and rotational laxity were affected equally. Rotational constraint is not necessary in a TKA system to achieve normal rotational stability of the knee, as long as normal varus-valgus stability is restored.