New Method for Measuring the Achilles Tendon Length by Ultrasonography

Since tendons store and release elastic energy, changes in tendon length are important in the performance of human movements. Various methods have been used for evaluating changes in the Achilles tendon length in both static and dynamic conditions. However, thus far, a direct measurement of changes in the Achilles tendon length during dynamic movements has not been performed. In this review article, we discuss the availability of a new method for measuring the Achilles tendon length, which can be potentially applied to dynamic movements due to high time resolution. In this method, both ends of the Achilles tendon were detected using ultrasonographic images. In addition, the path of the Achilles tendon was tracked by placing markers on the skin over the Achilles tendon. Using the three-dimensional coordinates of these markers and the ultrasonographic images, the Achilles tendon length was calculated at 20° dorsiflexion, 0° plantar flexion, and 20° plantar flexion. For this new method, high repeatability (day-to-day) and validity (compared to the Achilles tendon length obtained by magnetic resonance imaging that is considered the golden standard) were confirmed. Therefore, we consider that it would be useful for measuring the Achilles tendon length. Further, since this method allows sufficient time resolution unlike the magnetic resonance imaging method, it would allow the direct measurement of the Achilles tendon length during not only static but also dynamic conditions. This method is expected to improve our understanding of the contribution of the Achilles tendon to the performance of human movements. Keywords: Magnetic resonance imaging, medial gastrocnemius, muscle-tendon unit, three-dimension, triceps surae, ultrasonography.