A non-invasive protocol to determine the personalized moment arms of knee and ankle muscles

One difficulty that comes with predicting muscular forces is the accuracy of experimental data, particularly the assessment of muscle moment arms with respect to each joint rotation axis. This paper presents a non-invasive experimental protocol to obtain the personalized muscle moment arms with respect to the ankle and knee joints. A specific pointer is used by a specialist of lower limb anatomy in order to define the local portion of the line of action of the different muscles closed to the joint on the standing subject's lower limb. With this pointer, the three-dimensional coordinates of several points representing the line of action of 12 ankle and knee muscles are collected by a Motion Analysis system. The collection is done five times by the same operator and one time by two different operators. From this data, the intra and inter operator repeatabilities are tested. Relative (ICC) and absolute (SEM) reliabilities are determined in order to evaluate the intra operator repeatability of this non-invasive protocol. The ICC values obtained are higher than 0.91 for 10 among 12 muscles. The intra operator repeatability is thus confirmed. From the records realized by the two operators, the differences are negligible. Thus, the inter operator repeatability is also confirmed. The moments arms obtained using this non-invasive experimental protocol are compared with those calculated from origin and insertion points reported in the literature, according to the work of Whites, Pierrynowskis and Kepples, respectively. The estimations obtained using the non-invasive experimental protocol are found, for some muscles, more realistic than those calculated using the literature data and are always coherent with the role of the muscles described in anatomical books.