Reproducibility of the Knee Signature System

Abstract

To assess trial-to-trial, installation-to-installation, and day-to-day effects of the Knee Signature System, we studied anterior/posterior translation measurements in six normal subjects. The protocol consisted of testing both knees on 6 days with three installations per day and three trials per installation. We recorded anterior, posterior, and total anterior/posterior translation at ±20 and ±40 pounds of force at 30° of flexion. Addi tionally, after measuring anterior/posterior translation during passive knee extension, active extension, and active extension with 15 pounds of weight at the ankle, we calculated the difference in anterior translation at 30° of flexion between each of these three conditions. We analyzed the size of the effects and computed 90% confidence limits using analysis of variance.

Means and 90% confidence limits for total anterior/ posterior translation measured at ±20 pounds of force were: right knee, 6.8 ± 2.3; left knee, 8.2 ± 2.0; and right/left difference, 1.5 ± 2.7 mm. Left knee translation means were significantly greater than right knee means in all tests. Day-to-day effects, while statistically signif icant for right and left knee measurements, showed no significant effects for right/left differences. Trial-to-trial and installation-to-installation effects were not signifi cant for any parameter. Right/left differences during knee extension testing were smaller than for the stress test, measuring 0.1 mm or less, but confidence limits were larger, being ±3.7 mm for active extension-pas sive knee extension, ±1.5 mm for 15 pounds of weight at the ankle-active extension, and ±4.6 mm for 15 pounds of weight at the ankle-passive knee extension. Active extension produced 6.3 mm more anterior trans lation at 30° of flexion than passive extension. Active