Determination of functional rotation axes during elevation of the shoulder complex.
METHODS
A cross-sectional, descriptive study of shoulder movements conducted on nonimpaired subjects.


OBJECTIVE
To investigate whether a single functional rotation axis about the shoulder complex can be determined during elevation in the coronal or sagittal planes, and to identify their location.


BACKGROUND
Accurate measurement of isokinetic torques about a joint requires alignment of the dynamometer axis with an assumed rotation axis of the joint. To assess shoulder function on a dynamometer, the location of a single rotation axis is not evident because the shoulder joint motion is based on several anatomical joints. Therefore, the rotation axis where humerothoracic movements occur should be judged as a functional rotation axis.


METHODS
During slow elevation movements in the sagittal and coronal plane, the position of the epicondyle and acromion were recorded with a motion analysis system. The motion trajectory of the elbow coordinates was fitted to a circle and considered an estimate of the functional shoulder joint rotation axis in the specified plane.


RESULTS
The fitted trajectory appeared to be very accurate (root-mean-square error < 2%; N = 7). In the sagittal plane, the estimated functional rotation axis was found at the humeral head; in the coronal plane, it was located about 13 centimeters medial relative to the acromion.


CONCLUSIONS
The shoulder complex of nonimpaired subjects can act as a hinge joint of the upper arm relative to the thorax during elevation in each measured plane.
Doorenbosch
C A
CA
Department of Rehabilitation Medicine, University Hospital Vrije Universiteit, Amsterdam, The Netherlands. cam.doorenbosch@azvu.nl
Mourits
A J
AJ
Veeger
D H
DH
Harlaar
J
J
van der Helm
F C
FC
D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D009068:Movement / Q000502:physiology; D011597:Psychomotor Performance; D016059:Range of Motion, Articular; D012785:Shoulder Joint / Q000502:physiology*; D014102:Torsion Abnormality