Figure 8.12 Movement at the AC joint. (A) The axes of rotation of the AC joint are oriented in the scapular planes rather than the cardinal planes. (B) Upward and downward scapular rotation at the AC joint. (C) Lateral view of anterior and posterior tipping of the scapula that occurs at the AC joint during arm motion. (D) Superior view of scapular medial and lateral rotation that occurs at the AC joint. (E) Summary of motions that occur at the AC joint.