Movements of the human upper extremity are difficult to measure due to the specific structure of the limb, but they all involve a combination of movements of the humerus relative to a moveable base: the scapula. The scapula can translate and rotate relative to the thorax surface. Measuring such movements, however, are strongly hampered by the fact that the scapula moves underneath the skin. Consequently, the scapula cannot be followed in the traditional manner, i.e. by following the course of movements by placing markers on the skin. A second complicating factor is that a superficial proximal landmark on the humerus is difficult to define, which directly affects an accurate description of the movements of that segment.

To solve these problems, special measurement procedures have been developed involving general or individualized regression equations for determining scapulo-thoracic movements [1,2,3]. In addition, the proximal landmark for the humerus can be determined using either regression equations or screw-axes [4,5]. This procedure is now applied in several experiments, such as measuring the daily activities of patients with shoulder endoprostheses or wheelchair users. The method has proven successful and has been proposed by the International Shoulder Group as a standard procedure to the International Society of Biomechanics.

References

1. Veeger, H.E.J.; Helm, F.C.T. v. d.; et al. (1993). Orientation of the scapula in a simulated wheelchair push. Clinical Biomechanics, 8, 81-90.
2. Groot, J.H.d. (1998). The shoulder: a kinematic and dynamic analysis of motion and loading. Delft University of Technology.
3. Pascoal, A.G.; Helm, F.C.T. v.d.; et al. (2000). Effects of different arm external loads on the scapulo-humeral rhythm. Clinical Biomechanics, 15, S21-S24.
4. Stokdijk, M.; Nagels, J.; et al. (2000). The glenohumeral joint rotation centre in vivo. Journal of Biomechanics, 33(12), 1629-1636.
5. Veeger, H.E.J. (2000). The position of the rotation center of the glenohumeral joint. Journal of Biomechanics, 33(12), 1711-1715.

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