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.

Effect of axis alignment on in vivo shoulder kinematics.

BACKGROUND. To describe 3D shoulder joint movements, the International Society of Biomechanics (ISB) recommends using segment coordinate systems (SCSs) on the humerus, scapula and thorax, and joint coordinate systems (JCSs) on the shoulder. However, one of the remaining problems is how to define the zero angles when the arm is in an initial reference position. The aim of this paper is to compare various methods of determining the JCSs of the shoulder that make it possible to define the zero angles of the arm in the resting position. METHODS. Able-bodied subjects performed elevation movements in the scapular plane, specifically neutral, internal and external rotations of the humerus. The initial humerus position (at the beginning of the arm movement) and range of motion were analysed for the purpose of clinical interpretation of arm attitude and movement. The following four different JCSs were explored: (1) the standard JCS, defined as recommended by the ISB, (2) a first aligned JCS, where the humerus SCS is initially aligned with the scapula SCS, (3) a second aligned JCS, where the opposite operation is performed and 4) a third aligned JCS, where both the humerus and the scapular SCS are initially aligned with the thorax SCS. FINDINGS. The second aligned JCS was the only method that did not produce any exaggerated range of movement in either anatomical plane. INTERPRETATION. Mathematical JCS alignment allows clearer clinical interpretation of arm attitude and movement.