A mechanical equinometer to measure the range of motion of the ankle joint: Interobserver and intraobserver reliability

Background: Clinical measurement of passive dorsiflexion of the ankle joint is essential for the diagnosis of various pathologic conditions of the foot and ankle but is of unreliable precision with high interobserver variability in nonweightbearing tests. This work was designed to develop and test a precise, standardized, and reliable technique for measurement of passive and active ankle range of motion. Methods: The proposed measurement tool is composed of two mobile parallelograms, one attached to the tibia, the second one to the plantar surface of the foot. The parallelograms are connected with a hinge with an angular scale to measure the angle between the foot and tibia. Results: Interobserver correlation between clinical measurements for maximal passive foot dorsiflexion were 0.03 with knee extension and 0.38 with knee flexion, while for measurements with the proposed tool they reached 0.89 and 0.97, respectively, with a mean measurement error of 0.9 degrees. Intraobserver correlations reached values of r = 0.98 and 0.99. Conclusions: The proposed tool allows measurement of the ankle range of motion with very high precision and reproducibility far superior to clinical measurements. Clinical Relevance: Precise measurement of ankle range of motion is clinically challenging. With the use of the proposed tool, measurement precision and reliability are decisively improved.