Assessment of an electronic goniometer designed to measure equinus contracture

To achieve more objective and repeatable measurements of equinus contracture, we developed the equinometer, a device that allows the measurement of ankle range of motion under controlled torque conditions. This study assessed its accuracy across different subjects and examiners. Two examiners used the equinometer to measure the angle of ankle dorsiflexion at 15 N x m torque on five subjects. Accounting for variation in measurements because of subjects, examiners, and placement of device, we used linear mixed-effects models. Accounting for the variation because of subject, different placements of the equinometer within each subject and the adjustment for the effects of examiner and trial sequence, the standard deviation was 0.94 degrees, 95% confidence interval (0.79 degrees, 1.13 degrees). An upper standard deviation of 1.36 degrees is felt to be acceptable for clinical investigation.