In vivo quantification of the Achilles tendon moment arm

Introduction The Achilles' tendon moment arm (ATma) is a critical quantity in that it defines the triceps surea's ability to generate a moment on the calcaneus, which is then transferred to the foot. In the past this measure has been primarily acquired statistically, in 2D, without muscle activation, and in small populations. Thus, the primary purpose of this study was to establish the first in vivo threedimensional measures of the ATma, measured non-invasively and in vivo during dynamic activity in a large normative population (n = 19) using a dynamic MRI technique. The ATma was defined as the shortest distance between the finite helical axis (FHA) of the calcaneal-tibial joint and the AT line of action.