Validity and reliability of clinical tests for assessing passive ankle stiffness

Background: The presence of inadequate levels of passive ankle stiffness have been associated with the occurrence of movement disorders, the development of pathological conditions and the reduction in the performance of functional activities such as walking, running and jumping. Therefore, clinical tests to evaluate ankle stiffness may be useful for the physical therapy assessment. Objectives: To investigate the concurrent validity and the intra- and inter-examiner reliability of clinical measures developed to assess passive stiffness of the ankle joint during dorsiflexion movement. Methods: Fifteen healthy participants underwent to test-retest evaluations of their ankles by two examiners. Two clinical measures were performed: 'position of first detectable resistance' and 'change in passive resistance torque'. The results of these tests were compared to the passive stiffness measured with an isokinetic dynamometer, in which the electromyography activity of specific muscles was monitored to ensure that the test was performed passively (gold standard measure). Results: Pearson correlation coefficients ranged from r=-0.81 to -0.88 (p < 0.001) for the correlation between the passive ankle stiffness measured with the isokinetic dynamometer and the results of the clinical measure 'position of the first detectable resistance'. For the measure of 'change in passive resistance torque', these coefficients ranged from r=0.72 to 0.83 (p < 0.004). The Intraclass Correlation Coefficients (ICCs) for the intra- and inter-examiner reliability ranged from 0.75 to 0.98. Conclusion: The clinical measures presented satisfactory validity and reliability to be used in clinical practice.