What muscle participates in horizontal abduction of the shoulder joint?

The posterior deltoid is the muscle responsible for horizontal abduction of the shoulder joint. When the arm is lifted to the side and moved horizontally away from the body, the posterior fibers of the deltoid contract to facilitate this movement. This muscle's anatomical position and fiber orientation allow it to effectively perform this action, making it a primary mover in horizontal abduction.

In contrast, the other muscles listed either do not play a significant role in this specific movement or primarily function in other actions. The coracobrachialis assists with flexion and adduction of the shoulder but is not involved in horizontal abduction. The pectoralis major, particularly its clavicular head, primarily contributes to flexion and horizontal adduction rather than abduction. The anterior deltoid aids in flexion and internal rotation of the shoulder but does not contribute to horizontal abduction either. Therefore, the posterior deltoid clearly stands out as the key player in executing horizontal abduction.