The reliability of a new device designed to assess gastrocnemius contracture

Gastrocnemius contracture may be a significant cause of many foot disorders. Gastrocnemius tension can be estimated clinically by measuring maximum ankle dorsiflexion during full knee extension. Such measurements, when made with currently available goniometric devices, are subject to high levels of intra- and inter-observer variability. We have designed a device to more consistently measure ankle dorsiflexion, using three dimensional tracking sensors on the leg and foot. The applied dorsiflexion torque is kept constant by a computer, and the computer also monitors hindfoot position to maintain a neutrally aligned foot during testing. Repeated measurements on 26 feet were taken to determine the consistency of the device. The correlation coefficient for the measurements was 0.96, indicating very low intra-observer variability. The standard deviation of the repeated measures was 2 degrees. Based on the 95% confidence interval, the device can be considered accurate to within 4 degrees. Given this accuracy, this instrument could be used to assess gastrocnemius tension, its role in foot pathology, and the effectiveness of surgical lengthening. Compared to other currently available measuring devices, this instrument is the most reliable in estimating ankle dorsiflexion, since it is capable of controlling hindfoot position and applied dorsiflexion torque, and it can be easily constructed by other laboratories.