Intra-articular kinematics of the normal glenohumeral joint in the late preparatory phase of throwing: Kaltenborn's rule revisited

A new method to quantify intra-articular relationships between articular su rfaces of the glenohumeral joint during discrete poses representing the lat e preparatory phase of throwing is presented. This method is based on 3D bo ne reconstructions from medical imaging data processed into finite helical axis parameters. With the shoulder moving in the anatomical planes from 90 degrees abduction and 90 degrees external rotation into the apprehension te st pose, the centre of the humeral head posteriorly translated on the gleno id and rotated about a finite helical axis, which was positioned at the joi nt contact. The data are contrasted with Kaltenborn's convex-concave rule e xplaining intra-articular kinematics of the glenohumeral joint as a ball-an d-socket joint. The data show at all conditions that the glenohumeral joint does not act as a ball-and-socket joint. Consequently, the mobilization te chniques used in manual therapy, which are based on this convex-concave rul e, should be adapted.