Repeatability of the KT-1000 arthrometer in a normal population

Despite its popularity, the MEDmetric KT-1000 arthro meter's reliability remains inadequately documented. We conducted this study to determine the magnitude of trial-to-trial (within installation), installation-to-instal lation (within day), and day-to-day (between day) vari ability of anterior/posterior translation measurements in normal knees. We selected six normal subjects, three males and three females, and tested each on 6 consecutive days with three separate installations per day. We recorded the total anterior/posterior translation at ±89 and ±134 N force at 25° of flexion during three consecutive trials in a single installation. Analysis of variance showed that no significant differ ence existed between trials (within installation) or be tween installations (within day) for all parameters. How ever, we did find a significant difference between days for individual right and left knee translation measure ments at 89 and 134 N force. More importantly, no significant difference existed between days for right to left differences at both force levels. The magnitude of the expected measurement varia bility was expressed by computing 90% confidence limits for total anterior/posterior translation at ±89 N force. These were ±1.5 mm for the right knees, ±1.4 mm for the left knees, and ±1.6 mm for the right-left differences. Fischer's protected least significant differ ence post hoc test revealed that for all parameters, the 1 st day measurements were significantly less than those on following days, suggesting that patient and examiner adjust to the testing procedure. We conclude that the standard KT-1000 evaluation should report paired differences rather than individual knee measurements. Additionally, initial evaluation should be supplemented by follow-up examinations for verifying translation values.