WBR0552

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Musculoskeletal/Rheumatology, SubCategory::Vascular
Prompt	[[Prompt::A 22-year-old college baseball pitcher presents to his sports medicine physician for shoulder weakness and pain. The patient reports feeling a sharp pain in his right posterior shoulder after throwing a fastball. The pain was followed by numbness and tingling down his right arm, which persisted for several hours after the injury. Physical exam reveals pain with passive internal rotation of the arm, and weakness in external rotation of the arm. 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. The infraspinatus and its tendon are commonly injured in 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 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 infraspinatus are the most common cause of rotator cuff injuries, but would present with inability to initiate abduction of the arm.]]
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 is 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 patient in this vignette has injured his infraspinatus muscle as a result of large rotational forces during pitching. The infraspinatus 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). Mnemonic: Rotator cuff muscles = SITS (Subscapularis, Infraspinatus, Teres minor, Suprascapularis). Educational Objective: 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. References: First Aid 2014 page 411 Rotator Cuff Review Overview of the shoulder joint]]
Approved	Approved::Yes
Keyword	WBRKeyword::Scapula, WBRKeyword::Rotator cuff, WBRKeyword::Shoulder, WBRKeyword::Upper limb, WBRKeyword::Arm, WBRKeyword::Muscle, WBRKeyword::Tendon
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::