A neurologist notes that a patient has weakness when she attempts internal rotation of her right arm at the shoulder. This could be caused by weakness in which of the following muscles?
The subscapularis muscle arises from the anterior surface of the scapula and inses onto the lesser tubercle of the humerus. It is one of the rotator cuff muscles. Its tendon passes on the anterior side of the shoulder joint capsule, where it reinforces the capsule. Contraction of this muscle causes internal rotation of the arm at the shoulder.The infraspinatus muscle arises from the posterior surface of the scapula in the infraspinous fossa and inses on the greater tubercle of the humerus. It is one of the rotator cuff muscles. Its tendon passes along the posterior surface of the shoulder joint capsule, where it reinforces the capsule. Contraction of the infraspinatus causes external rotation of the arm at the shoulder.The pectoralis minor muscle arises from the chest wall and inses onto the coracoid process of the scapula. The pectoralis minor does not attach to the humerus and therefore does not cause movement of the humerus at the shoulder.The supraspinatus muscle arises from the posterior surface of the scapula in the supraspinous fossa and inses onto the greater tubercle. It is one of the rotator cuff muscles. Its tendon passes along the superior surface of the shoulder joint capsule, where it reinforces the capsule. Contraction of the supraspinatus causes abduction of the arm at the shoulder. Ref: Moon D.A., Foreman K.B., Albeine K.H. (2011). Chapter 30. Shoulder and Axilla. In D.A. Moon, K.B. Foreman, K.H. Albeine (Eds), The Big Picture:
Infraspinatus
Pectoralis minor
Subscapularis
Supraspinatus