WBR0551

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::An 18-year-old female softball player presents to her primary care physician with right shoulder pain and weakness. The pain becomes much worse when the patient performs over-the-head activities with her right shoulder and is often relieved by maintaining arm adduction and with NSAID administration. The patient informs the physician that she has been preparing for an upcoming championship and has been practicing several hours a day for the past few weeks. On physical examination, the patient reports pain when she attempts to elevate her arm against the physician's resistance while abducting the shoulder to 90 degrees in forward flexion with her thumb pointing downward. Which of the following muscle is most likely injured in this patient?]]
Answer A	AnswerA::Deltoid
Answer A Explanation	AnswerAExp::While the deltoid is responsible for shoulder abduction, the deltoid is not responsible for initiating shoulder abduction. Instead, the deltoid primarily responsible for abduction greater than 30 degrees from the body.
Answer B	AnswerB::Infraspinatus
Answer B Explanation	AnswerBExp::The infraspinatus is a muscle of the rotator cuff that is responsible for lateral rotation of the arm. The infraspinatus and its tendon are commonly injured in baseball pitchers.
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. The supraspinatus sits atop the scapula in the supraspinous fossa and its tendon proceeds through the under the acromion to attach to the lateral head of the humerus. Contraction of the supraspinatus abducts the arm in the manner seen in the animation below.]]
Answer D	AnswerD::Teres Major
Answer D Explanation	AnswerDExp::The teres major is large, flat muscle that medially rotates and adducts the humerus. It is innervated by the subscapular nerve (C5,C6).
Answer E	AnswerE::Teres Minor
Answer E Explanation	AnswerEExp::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).
Right Answer	RightAnswer::C
Explanation	[[Explanation::The hallmark of rotator cuff injuries is the combination of pain that accompanies shoulder weakness. The patient in this vignette has injured her supraspinatus muscle, the most commonly injured muscle in rotator cuff injuries. The supraspinatus originates on the medial edge of the supraspinous fossa, where it proceeds to pass under the cover of the acromion to attach to the lateral aspect of the head of the humerus. The supraspinatus is innervated by the suprascapular nerve, which originates from the superior trunk of the brachial plexus (C5-C6). It is responsible for initiating arm abduction (initial 15 degrees of abduction). Beyond 15 degrees, the deltoid muscle, which is innervated by the axillary nerve (C5-C6), becomes more effective in arm abduction. When patients are suspected to have rotator cuff injuries, provocative testing may be performed to further localize the injury. The following tests may be used clinically to evaluate for specific rotator cuff injuries: 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. Cross-arm test: Mnemonic: Rotator cuff muscles = SITS (Subscapularis, Infraspinatus, Teres minor, Suprascapularis). Educational Objective: The supraspinatus is responsible for initiating shoulder abduction. References: First Aid 2014 page 411]]
Approved	Approved::Yes
Keyword	WBRKeyword::Scapula, WBRKeyword::Brachial, WBRKeyword::Brachial plexus, WBRKeyword::Rotator cuff, WBRKeyword::Rotator, WBRKeyword::Cuff, WBRKeyword::Shoulder, WBRKeyword::Arm, WBRKeyword::Upper Limb
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::