104 Relative and Absolute Reliability of the KT-2000 Arthrometer for Uninjured Knees Testing at 67, 89, 134, and 178 N and Manual Maximum Forces J. William Myrer,*&dagger; PhD, Shane S. Schulthies,* PhD, PT, ATC, and Gilbert W. Fellingham,&Dagger; PhD From the *Physical Education Department and &Dagger;Statistics Department, Brigham Young University, Provo, Utah ABSTRACT We assessed the reliability of the KT-2000 knee ar- thrometer at 67, 89, 134, and 178 N and at manual maximum forces on 30 college students who were free from present or previous knee injuries. Two examiners tested all subjects on two occasions. Anterior laxity (P < 0.0001) and side-to-side difference ( P < 0.05) sig- nificantly increased as force increased. There was a significant difference ( P < 0.0001) between testers for anterior laxity but not for side-to-side difference. We used intraclass correlation coefficients to estimate rel- ative reliability. Anterior laxity intraclass correlation co- efficients (2,1) between testers ranged from 0.81 to 0.86 and within tester correlations ranged from 0.92 to 0.95. Intraclass correlation coefficients for between testers for side-to-side differences ranged from 0.38 to 0.58 and within tester correlations ranged from 0.53 to 0.64. Subject-to-subject variability needs to be taken into account when interpreting intraclass correlation coefficient values. Our absolute reliability estimates (95% confidence intervals) were small, indicating little variability. Our data demonstrate the KT-2000 arthrom- eter to be reliable. Researchers should present both relative and absolute reliability estimates, although we believe absolute estimates are of greater clinical value. Side-to-side differences are better discriminators than individual absolute values. We recommend that a <3 mm side-to-side difference be used to indicate stable knees. Clinicians diagnose knee ligament sprains and evaluate progress after surgery and rehabilitation by assessing the limits of joint motion.2-9,11,13-17,19-26,28-31 Subjective clinical examination and evaluation of cruciate ligament integrity is generally thought to be accurate among individual experienced examiners. There are, however, appreciable differences between examiners.5,6,23 Re- searchers have stated a need to develop standardized methods of quantifying knee stability. 15,21,23,26 This has led to the development of various devices designed to objectively quantify the amount of tibial translation.4, 7,9,17,20,22,24,30,31 Daniel et a1.7 developed a knee arthrometer known as the KT-1000 (MEDmetric Corp., San Diego, California) to measure tibial translations at varying anterior forces. Re- cent advances to the KT arthrometer allow the examiner to test the anterior-posterior displacement of the knee at 67, 89, 134, and 178 N of force and obtain a hard copy of both the displacement in millimeters and the force in pounds. Several researchers have found the KT arthrometer to be both reliable and valid at 67 and 89 N of force. 2,3,6,7,11, 15,17,22,31 Only five studies have investi- gated the KT arthrometer at 134 N of force, and no studies have been done on testing at 178 N. g, 16, 22, 29, 31 We designed this study to provide clinicians with addi- tional information on uninjured knees that will enable them to more accurately interpret their KT arthrometer results for 67, 89, 134, and 178 N and manual maximum forces. MATERIALS AND METHODS Thirty healthy students volunteered as subjects (13 women, age, 22.2 ± 1.5 years; weight, 57.5 ± 5.5 kg; t Address correspondence and repnnt requests to J William Myrer, PhD, 221-D Richards Building, Physical Education Department, Bngham Young Umversity, Provo, UT 84602 No author or related institution has received any financial benefit from research in this study.