Anatomy Muscles of the Rotator Cuff Questions and Answers — Questions and Answers
Question 1: A patient presents with significant weakness in initiating arm abduction (the first 0-15 degrees) and pain over the superior aspect of the shoulder. An MRI confirms a full-thickness tear of a rotator cuff tendon. Which muscle is most likely affected?
- Infraspinatus
- Supraspinatus (Correct answer)
- Teres Minor
- Subscapularis
Correct answer: Supraspinatus
The supraspinatus muscle is responsible for the initial 0-15 degrees of arm abduction. It is also the most commonly torn rotator cuff muscle, and its location superior to the glenohumeral joint aligns with the described pain.
Question 2: Which rotator cuff muscle is unique in that it inserts on the lesser tubercle of the humerus, while the other three insert on the greater tubercle?
- Teres Minor
- Infraspinatus
- Supraspinatus
- Subscapularis (Correct answer)
Correct answer: Subscapularis
The subscapularis muscle is the only rotator cuff muscle that inserts on the lesser tubercle of the humerus. The supraspinatus, infraspinatus, and teres minor all have tendinous insertions on the greater tubercle.
Question 3: A physical examination reveals a patient has marked weakness in external (lateral) rotation of the shoulder. An injury to which pair of rotator cuff muscles would best explain this finding?
- Supraspinatus and Subscapularis
- Infraspinatus and Teres Minor (Correct answer)
- Subscapularis and Teres Minor
- Supraspinatus and Infraspinatus
Correct answer: Infraspinatus and Teres Minor
The infraspinatus and teres minor are the primary external (lateral) rotators of the humerus among the rotator cuff muscles. Weakness in this specific action strongly suggests dysfunction of this pair.
Question 4: A patient is diagnosed with quadrangular space syndrome, causing compression of the axillary nerve. In addition to the deltoid muscle, which rotator cuff muscle would most likely demonstrate atrophy and weakness?
- Teres Minor (Correct answer)
- Supraspinatus
- Subscapularis
- Infraspinatus
Correct answer: Teres Minor
The axillary nerve passes through the quadrangular space and provides motor innervation to both the deltoid and the teres minor muscles. Therefore, compression in this space would affect the teres minor.
Question 5: Which of the following is the largest and most powerful of the rotator cuff muscles, primarily responsible for medial (internal) rotation of the arm?
- Infraspinatus
- Supraspinatus
- Subscapularis (Correct answer)
- Teres Minor
Correct answer: Subscapularis
The subscapularis is the largest and strongest of the four rotator cuff muscles and is the primary medial (internal) rotator of the humerus. It originates from the subscapular fossa on the anterior surface of the scapula.
Question 6: A collegiate baseball pitcher presents with posterior shoulder pain. An MRI reveals inflammation and a partial tear of the muscle that originates in the infraspinous fossa of the scapula and inserts on the middle facet of the greater tubercle. Which muscle has been injured?
- Supraspinatus
- Teres Minor
- Subscapularis
- Infraspinatus (Correct answer)
Correct answer: Infraspinatus
The infraspinatus muscle originates from the infraspinous fossa of the scapula and inserts on the middle facet of the greater tubercle of the humerus. It is a key muscle for decelerating the arm in overhead throwing athletes, making it susceptible to injury.
Anatomy Muscles of the Rotator Cuff Questions and Answers
A patient presents with significant weakness in initiating arm abduction (the first 0-15 degrees) and pain over the superior aspect of the shoulder.
An MRI confirms a full-thickness tear of a rotator cuff tendon.
Which muscle is most likely affected?