Reliability of the Passive Knee Flexion and Extension Tests in Healthy Subjects

ObjectiveInformation on the reliability of the passive knee extension (PKE) and passive knee flexion (PKF) tests is still incomplete. Moreover, standardization of the 2 test procedures could be enhanced. The present study investigates interrater and test-retest reliability of the modified versions of the PKE and PKF tests to establish whether the level of reliability is sufficiently high to justify their use in scientific studies and clinical practice.MethodsA total of 14 healthy subjects met the selection criteria. The 2 tests were carried out successively by each of the 3 clinicians/raters involved in the study, and each test was repeated 3 times. Two series of such measurements were performed. To evaluate interrater and test-retest reliability of the 2 tests, we calculated the intraclass correlation coefficients (ICCs), the standard errors of measurement, and the smallest detectable differences.ResultsThe PKE and PKF tests showed excellent and good reliability, respectively. Mean ICCs for the PKE were greater than those for the PKF. Mean ICCs for the interrater reliability (0.88-0.93) were higher than those for test-retest reliability (0.84-0.93). No mean ICCs lower than 0.84 were found (test-retest for PKF). The lowest ICCs of 0.73 and 0.75 were registered for the test-retest reliability of PKF in the case of rater 1.ConclusionThese results show excellent and good interrater and test-retest reliability of the PKE and PKF, respectively. The PKE test seems to be slightly more reliable. These findings may help clinicians when using these tests. For research purposes, investigators must critically evaluate whether the presented amount of error is acceptable for a specific setting.