Final answer:
For shoulder abduction of 180°, the scapulothoracic joint contributes approximately 60° through superior rotation of the scapula. This movement is critical to avoid impingement and allow full overhead reach, indicating that the provided options in the question may be incorrect or the question is meant to be tricky.
Step-by-step explanation:
The question is asking how many degrees of shoulder abduction come from the scapulothoracic region when reaching overhead. When performing a shoulder abduction, movement occurs at two main joints: the glenohumeral joint and the scapulothoracic joint. The typical total range of motion required for overhead abduction is 180°. This movement is not entirely from the glenohumeral joint; it also involves a critical contribution from the scapulothoracic joint.
During shoulder abduction, the scapula undergoes superior rotation so that the arm can clear the acromion process of the scapula without impingement. The scapulothoracic joint contributes about 60° to this movement, which is essential for full abduction to occur. Hence, if the total abduction is 180°, and the scapulothoracic joint contributes 60°, then the remaining 120° comes from the glenohumeral joint. Therefore, the correct answer to the question is that 60° of shoulder abduction comes from the scapulothoracic region, which is not among the options provided, so the question might contain an error or be a trick question.