WBR0328
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| Author | [[PageAuthor::Serge Korjian M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Anatomy |
| Sub Category | SubCategory::Head and Neck |
| Prompt | [[Prompt::A 42-year-old man presents to the physician's office with complaints of right shoulder pain radiating to the neck and upper back for the past 3 weeks. He reports that the pain started after getting hit on the neck during a recent basketball game. Physical exam reveals normal passive motion but limited sustained abduction and elevation of the shoulder. Which other finding is most likely to be present in this patient?]] |
| Answer A | AnswerA::Inability to laterally flex the neck |
| Answer A Explanation | AnswerAExp::Cranial nerve (CN) XI or the spinal accessory nerve innervates the sternocleidomastoid, which is the muscle responsible for ipsilateral neck flexion and contralateral head rotation. |
| Answer B | AnswerB::Inability to open his jaw |
| Answer B Explanation | AnswerBExp::The lateral pterygoid is the main muscle responsible for opening the jaw. All jaw muscles are innervated by the trigeminal nerve - the mandibular branch (CN V3). |
| Answer C | AnswerC::Inability to protrude his tongue |
| Answer C Explanation | AnswerCExp::The CN XII or the hypoglossal nerve innervates the tongue. |
| Answer D | AnswerD::Inability to abduct arm |
| Answer D Explanation | AnswerDExp::Arm abduction relies on the deltoid muscles and the supraspinatus muscle. The deltoid muscle is innervated by the axillary (C5-C6) nerve. The supraspinatus muscle is innervated by the suprascapular (C5-C6) nerve. |
| Answer E | AnswerE::Inability to swallow |
| Answer E Explanation | AnswerEExp::Swallowing involves several cranial nerves most importantly CN IX or the glossopharyngeal nerve. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The patient in this scenario likely suffered an injury to his spinal accessory nerve secondary to neck trauma. The spinal accessory nerve is the eleventh cranial nerve that arises mostly from the spinal cord. Only a small portion of the spinal accessory nerve originates from the nucleus ambiguus and eventually joins the vagus nerve. The spinal portion arises from a column of nuclei in the ventral medulla. The nerve supplies both the sternocleidomastoid (SCM) and trapezius muscles. The sternocleidomastoid muscles originate from the sternum and clavicle and inserts on the mastoid process. The SCM rotates the head contralaterally and flexes the neck ipsilaterally. Patients with accessory nerve injury classically present with shoulder pain, weakness with sustained shoulder abduction, and difficulty shrugging shoulder. Signs in the SCM include weakness with ipsilateral neck flexion and contralateral head rotation. Educational Objective: The spinal accessory nerve (CN XI) supplies the sternocleidomastoid (SCM) muscles responsible for ipsilateral neck flexion and contralateral head rotation, and the trapezius muscles responsible for shoulder elevation. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Trapezius, WBRKeyword::Sternocleidomastoid, WBRKeyword::SCM, WBRKeyword::Cranial nerves, WBRKeyword::CNXI, WBRKeyword::Cranial nerve injuries |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |