WBR0552

Author	[[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::A 22-year-old college baseball pitcher presents to his sports medicine physician for left shoulder weakness and pain. He reports feeling a sharp pain in his right posterior shoulder one day after throwing a fastball. The pain was followed by numbness and tingling down his right arm, which persisted for several hours. On physical examination, the patient reports pain as he attempts to laterally rotate the left shoulder against the physician's resistance. All other shoulder maneuvers do not elicit any pain. Which of the following muscles in most likely injured in this patient?]]
Answer A	AnswerA::Infraspinatus
Answer A Explanation	[[AnswerAExp::The infraspinatus is a muscle of the rotator cuff that is responsible for lateral rotation of the arm. Injuries of the infraspinatus and its tendon are common among baseball pitchers.]]
Answer B	AnswerB::Subscapularis
Answer B Explanation	[[AnswerBExp::The subscapularis is a large flat muscle that overlies the anterior surface of the scapula (subscapular fossa). It aids in medial rotation and adduction of the arm.]]
Answer C	AnswerC::Supraspinatus
Answer C Explanation	[[AnswerCExp::The supraspinatus is a muscle of the rotator cuff that is responsible for the first 15 degrees of shoulder abduction. Injuries of the supraspinatus are the most common cause of rotator cuff injuries. Typically, patients with supraspinatus injuries cannot initiate arm abduction.]]
Answer D	AnswerD::Teres minor
Answer D Explanation	[[AnswerDExp::The teres minor is a rotator cuff muscle that is responsible for adduction and lateral rotation of the arm. It is innervated by the posterior branch of the axillary nerve (C5-C6).]]
Answer E	AnswerE::Teres major
Answer E Explanation	[[AnswerEExp::The teres major not a rotator cuff muscle. It is a large, flat muscle that medially rotates and adducts the humerus. It is innervated by the subscapular nerve (C5-C6).]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::The hallmark of rotator cuff injuries is the combination of pain that accompanies shoulder weakness. The patient in this vignette has injured his infraspinatus muscle as a result of large rotational forces during pitching. The infraspinatus muscle is a rotator cuff muscle that is responsible for lateral rotation of the arm. It is innervated by the suprascapular nerve, which originates from the superior trunk of the brachial plexus (C5-C6). Injuries to the infraspinatus muscle and tendon are common among individuals who perform pitching sports. Although injury to the muscle is immediate, pain becomes more apparent when the muscle activity rests a few hours following the initial insult. Because the infraspinatus muscle is responsible for lateral rotation exclusively, attempt to laterally rotate the arm against resistance typically elicits pain on physical examination. In contrast, other maneuvers that do not involve lateral rotation of the arm do not cause contraction of the infraspinatus muscle and thus do not elicit pain. MRI of the shoulder is often required to confirm the suspicion of infraspinatus muscle or tendon injury. The rotator cuff is composed of 4 muscles: Subscapularis, Infraspinatus, Teres minor, Suprascapularis (SITS). When patients are suspected to have rotator cuff injuries, provocative testing may be performed to further localize the injury. Although rotator cuff injuries often require MRI to identify the location of the injury, clinical tests may be helpful to evaluate for specific rotator cuff injuries: Empty can test: Patient pushes against physician resistance while arm in 90 degree abduction with thumb pointing down. Pain suggests tear to the supraspinatus muscle or tendon. Full can test: Patient pushes against physician resistance while arm abducted 45-90 degrees and shoulder externally rotated. Pain suggests tear to the supraspinatus muscle or tendon. Neer's test: Patient places the arm in forced flexion with arm in full pronation. Pain suggests subacromial impingement due to pinching under the coracoacromial arch. Hawkin's test: Patient elevates the arm forward to 90 degrees while internally rotating the shoulder. Pain suggests subacromial impingement or rotator cuff tendonitis. Drop-arm test: Patient passively abducts involved shoulder, then slowly lowers the arm to the waist. Sudden arm drop suggests supraspinatus injury. Cross-arm test: Patient raises arm to 90 degrees and adducts forcibly the acromion into distal end of clavicle. Pain suggests acromioclavicular joint involvement. Educational Objective: The infraspinatus is a muscle of the rotator cuff that is responsible for lateral rotation of the arm. Injuries of the infraspiantus muscle and its tendon are common among baseball pitchers. References: Woodward TW, Best TM. The painful shoulder: part I. clinical evaluation. Am Fam Physician. 2000;61(10):3079-88. First Aid 2014 page 411]]
Approved	Approved::Yes
Keyword	WBRKeyword::Scapula, WBRKeyword::Rotator cuff, WBRKeyword::Upper limb, WBRKeyword::Arm, WBRKeyword::Muscle, WBRKeyword::Tendon, WBRKeyword::Infraspinatus, WBRKeyword::Infraspinatus muscle, WBRKeyword::Rotator cuff injury, WBRKeyword::Shoulder pain, WBRKeyword::Shoulder, WBRKeyword::Shoulder weakness
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