The three-dimensional (3D) kinematics of the scapula were analyzed in vivo in 10 patients with scapular and 10 patients with clavicular fracture. Both the injured shoulder and normal contralateral shoulder were evaluated by computed tomography in the neutral and fully elevated positions. 3D rotational and translational movements of the scapula relative to the thorax during arm elevation were analyzed. A computer simulation program was used to compare rotational elevation/depression in the coronal plane, anterior/posterior tilting in the sagittal plane and protraction/retraction in the axial plane between the normal and affected sides. Anterior/ posterior translational movement along the X-axis, upward/downward movement along the Y-axis, and lateral/ medial movement along the Z-axis in the Euler space during forward elevation were also compared. In scapular fracture, rotational elevation of the scapula decreased in the coronal plane and posterior tilting of the scapula increased in the sagittal plane. Anterior and superior translation were higher in scapular fracture than in the corresponding normal sides. However, no significant abnormal rotational and translational kinematic changes were observed during elevation in clavicular fracture. In vivo 3D computerized motion analysis was useful for evaluating scapular dyskinesis. Scapular fracture can cause scapular dyskinesis, but not all clavicular fractures alter scapular motion biomechanics.
Keywords: 3-dimensional motion analysis; clavicle; fracture; scapula; scapular dyskinesis.