Osteokinematic analysis during shoulder abduction using the C-arm

Objective: Despite reliable evidence of abnormal scapular motions increases, there is not yet sufficient evidence of abnormal humeral translations. This study aims to analyze the motion of the humeral head toward the scapula when the shoulder is actively abducted using the C-arm. Design: A case report. Methods: The participant was a healthy man without any limitation and pain during shoulder movement. The participant's shoulder was abducted; this movement in the frontal plane was measured using a C-arm (anterior-posterior view) and was analyzed with computer-aided design. The starting posture was $15^{\circ}$, and as the participant abducted his shoulder measurements were taken and analyzed at $30^{\circ}$, $60^{\circ}$, $90^{\circ}$, $120^{\circ}$, $150^{\circ}$, and ending at $165^{\circ}$. A line was drawn perpendicularly to the line connecting the humeral head axis to the glenoid, and another line was drawn perpendiculary to the line connecting the scapular axis to the glenoid. The distance between the two lines measured is defined as the e value. Results: At the starting posture ($15^{\circ}$), the central axis of the humeral head was located 1.92 mm inferior to the central axis of the scapula. The humeral head was superiorly translated from the starting posture to $120^{\circ}$, and then, showed an inferior translation to the ending posture ($165^{\circ}$). Conclusions: The results of this study showed that the humeral head moved upward from the starting posture ($15^{\circ}$) up to $120^{\circ}$ indicating, superior translation, and it moved downward when the posture was past $120^{\circ}$, indicating inferior translation.