Final answer:
Movement at the sternoclavicular (SC) joint affects the scapula because the clavicle, which connects at the SC joint, also articulates with the scapula at the acromioclavicular (AC) joint, affecting the scapula's position and motion.
Step-by-step explanation:
Movement of the sternoclavicular (SC) joint produces movement at the scapula because the clavicle articulates with the scapula at the acromioclavicular (AC) joint.
This articulation involves the lateral or acromial end of the clavicle and the acromion of the scapula, forming the bony tip of the shoulder.
Therefore, when the SC joint moves, it influences the position and movement of the AC joint which is directly connected to the scapula, thus causing movement of the scapula itself.
The SC joint is the only bony articulation between the pectoral girdle of the upper limb and the axial skeleton, providing a broad range of motion for the clavicle and scapula including upward/downward and anterior/posterior directions.
This joint, along with its ligaments and the associated AC joint, plays an integral role in transmitting forces from the upper limb to the clavicle and further to the trunk of the body.
Such articulations and ligament support are essential for the stability and flexibility of the shoulder girdle during various movements.