Intertester reliability of measurements obtained with the KT-1000 on patients with reconstructed anterior cruciate ligaments.

Clinicians frequently measure anterior tibial displacement on patients following surgical reconstruction for a torn anterior cruciate ligament (ACL). Little is known about the reliability of measurements of anterior tibial displacement obtained on patients following an ACL reconstruction. The purpose of this study was to describe the degree of error associated with repeated measurements of anterior tibial displacement on patients with reconstructed ACLs. Random pairs of physical therapists used the KT-1000 to measure the anterior tibial displacement of 30 subjects. Each pair of examiners took measurements according to the manufacturer's instructions. Examiners took three sets of measurements while applying 6.8, 9.1, and 13.6 kg (15, 20, and 30 lbs) of force to the handle of the KT-1000. Intraclass correlation coefficients (ICC 2,1) and the standard error of the difference (SED) were calculated to describe the intertester reliability of the mean of three measurements of anterior tibial displacement at each force level and of the individual measurements at each force level. The SED was then multiplied by 2 to provide a 95% confidence estimate of the magnitude of error present with KT-1000 measurements. The SED estimates the magnitude of change in anterior tibial displacement necessary to infer that a real change in anterior tibial displacement has occurred. Clinicians can be 95% confident that changes in anterior tibial displacement of greater than 5 mm (+/- 2 SED) during KT-1000 tests at 6.8, 9.1, or 13.6 kg (15, 20, or 30 lbs) of force indicate that a true change in anterior tibial displacement has occurred.