Rotation sequence as an important factor in shoulder kinematics.

BACKGROUND The International Society of Biomechanics has proposed a standardization recommendation for motion recordings of the upper extremity defining the set of bony landmarks, local coordinate systems and joint coordinate systems. The aim of our study was to verify the clinical interpretation of the proposed rotation sequence for the glenohumeral joint and to compare it with other sequences. METHODS Fifteen glenohumeral movements in their maximal ranges were tested on five healthy subjects. The movements were separated into five groups (flexion, extension, abduction, horizontal flexion and circumduction) with three humeral rotation positions (full external, full internal and neutral). Four glenohumeral rotation sequences were constructed using YXY, YXZ, ZXY and XZY orders and angle amplitudes were examined in terms of gimbal lock and amplitude coherence. FINDINGS The results of the gimbal lock incidence and amplitude coherence should be taken into account together. Therefore, the suitable rotation sequences for all rotation variations of abduction and extension were found and no tested rotation sequence was found to be clinically interpretable for all tested movements. INTERPRETATION Before glenohumeral three-dimension experiments the choice of the rotation sequence should be made in agreement with the no-gimbal lock incidence and amplitude interpretability of the performed movements.