As a result of chronic stress associated with an intense high school weight-lifting program, a 15-year-old boy suffers an avulsion fracture of the greater tubercle of the humerus. In the ER, he displays difficulty initiating abduction of the upper limb. Which muscles was involved in this fracture?

The correct answer is: supraspinatus.

Explanation:

Many muscles insert in the humerus - in its greater tubercle, where the fracture took place, is where three of the four rotator cuff muscles insert: supraspinatus, infraspinatus, and teres minor. Avulsion of the greater tubercle could result in detachment of any of these 3 muscles but if we take into account that the 15-year-old boy had difficulty initiating abduction of the upper limb, we can infer that the damaged muscle is the supraspinatus because its main action is to start the abduction the upper limb.