WBR0496

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles
Prompt	[[Prompt::A 17 year old male is brought to the emergency room following trauma to his arm when he was struck with by another player during a lacrosse game. He reports 7/10 pain for which he took ibuprofen en route to the hospital. An X-ray of the arm is shown below. Which of the following is most likely impaired in this patient?]]
Answer A	AnswerA::Adduction of the thumb
Answer A Explanation	AnswerAExp::'''Incorrect:''' The ulnar nerve is responsible for adduction of the thumb.
Answer B	AnswerB::Forearm pronation
Answer B Explanation	AnswerBExp::'''Incorrect:''' The radial nerve is responsible for innervating the supinators of the forearm.
Answer C	AnswerC::Raising the arm between 15 and 90 degrees
Answer C Explanation	AnswerCExp::'''Incorrect:''' The deltoid muscle is responsible for raising the arm between 15 and 90 degrees. The deltoid is innervated by the axillary nerve which can be lesioned by fractures at the surgical head of the humerus.
Answer D	AnswerD::Wrist extension
Answer D Explanation	AnswerDExp::'''Correct:''' The radial nerve is responsible for innervating the extensors of the wrist. The radial nerve is damaged by midshaft fractures of the humerus such as the one pictured above.
Answer E	AnswerE::Wrist flexion
Answer E Explanation	AnswerEExp::'''Incorrect:''' The median and ulnar nerves are responsible for wrist flexion.
Right Answer	RightAnswer::D
Explanation	[[Explanation::: The above image shows a mid-shaft fracture of the humerus. This injury is associated with radial nerve damage. The radial nerve is responsible for the innervating the extensors of the wrist. Educational Objective: The radial nerve is responsible for innervating the extensors of the wrist. The radial nerve is damaged by midshaft fractures of the humerus such as the one pictured above. References: First Aid 2012 page 409. Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Arm, WBRKeyword::Humerus, WBRKeyword::Fracture, WBRKeyword::Nerve, WBRKeyword::Radial Nerve, WBRKeyword::Brachial, WBRKeyword::Brachial plexus
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