National Physical Therapy Examination (NPTE) Practice Exam

Which muscle weakness is likely to cause decreased scapular upward rotation during shoulder abduction?

1. Upper trapezius

2. Posterior deltoid

3. Rhomboids

4. Teres major

The correct answer is: Upper trapezius

Decreased scapular upward rotation during shoulder abduction is primarily associated with weakness in the upper trapezius muscle. The upper trapezius plays a crucial role in the upward rotation and elevation of the scapula, especially during movements like shoulder abduction. This muscle works in conjunction with the lower trapezius and serratus anterior to facilitate the necessary scapular motion, allowing the glenohumeral joint to abduct properly and maximizing range of motion. When the upper trapezius is weak, the ability to effectively elevate and rotate the scapula is compromised, which can result in a compensatory mechanism during shoulder movements. This may lead to reduced functional ability and potential subsequent shoulder impingement, as the humerus does not have the desired clearance under the acromion during abduction. Thus, when considering the impact of muscle weakness on scapular movement, the upper trapezius is a key contributor, making it the correct choice in this context.