A 46-year-old man comes to the office due to right shoulder pain. The pain started 2 months ago after the patient began working at a new warehouse where he frequently moves heavy boxes. He has been taking over-the-counter analgesics and has continued to work. Past medical history is not significant. On physical examination, external rotation of the right shoulder against resistance is painful, but there is no weakness. MRI reveals near complete tear of the right infraspinatus muscle. The absence of weakness in this patient is best explained by compensatory hypertrophy of which of the following muscles?

Question

A 46-year-old man comes to the office due to right shoulder pain.  The pain started 2 months ago after the patient began working at a new warehouse where he frequently moves heavy boxes.  He has been taking over-the-counter analgesics and has continued to work.  Past medical history is not significant.  On physical examination, external rotation of the right shoulder against resistance is painful, but there is no weakness.  MRI reveals near complete tear of the right infraspinatus muscle.  The absence of weakness in this patient is best explained by compensatory hypertrophy of which of the following muscles?

Quizplus · Accepted Answer

11ec160b_35f1_4c4f_9249_c9735d73ffa7_MD0001_00 The rotator cuff muscles originate from the scapula and insert onto the proximal humerus; they stabilize the shoulder joint and move the arm at the shoulder. Overuse (eg, heavy lifting) can lead to rotator cuff injury, resulting in shoulder pain and possible weakness; the specific symptoms depend on which muscle is involved. Resistance added by the examiner when testing muscle function increases tendon loading, eliciting pain when tendon pathology is present. This patient has pain on resisted external rotation, suggesting pathology of the infraspinatus or teres minor, the two rotator cuff muscles responsible for this function. The infraspinatus is the main external rotator when the arm is adducted (eg, by the side), whereas teres minor is the main external rotator when the arm is abducted. When the infraspinatus tendon is torn, there is often compensatory hypertrophy of the teres minor, thereby preserving the strength of external rotation. (Choice A) Latissimus dorsi is a broad muscle in the mid- and low back. It originates from the spinous processes of T7 to L5, iliac crest, thoracolumbar fascia, inferior angle of the scapula, and the lower 3 or 4 ribs. It inserts onto the bicipital groove of the humerus and adducts, extends, and internally (not externally) rotates the arm. (Choice B) Serratus anterior is a fan-shaped muscle in the lateral thorax. It originates from the first 8 or 9 ribs and inserts onto various sections of the scapula. It is responsible for anterolateral and rotational movements of the scapula. When the long thoracic nerve is damaged, the muscle becomes paralyzed, resulting in winged scapula. (Choice C) Subscapularis originates from the subscapular fossa of the scapula and inserts onto the lesser tubercle of the humerus. It adducts and internally (not externally) rotates the arm. (Choice D) Supraspinatus originates from the supraspinatus fossa of the scapula and inserts onto the superior aspect of the greater tubercle of the humerus. It abducts the arm. Educational objective: The rotator cuff muscles attach to the proximal humerus and move the arm at the shoulder. Infraspinatus and teres minor are primarily responsible for external rotation. When one is torn, the other hypertrophies to compensate, resulting in preserved strength in external rotation. __________ References: Acute shoulder injuries in adults. (http://www.ncbi.nlm.nih.gov/pubmed/27419328)

A 46-Year-Old Man Comes to the Office Due to Right