A 15-year-old boy comes to the office due to right arm numbness. He plays on his high school baseball team and has been intensively practicing his pitching for an upcoming game. For the past several weeks, the patient has had fluctuating tingling and numbness involving the right shoulder, arm, and hand. He also has recently developed dull pain in the right little finger and hand. The symptoms worsen with overhead activities and when throwing a baseball. The patient has no medical problems other than being told that he has an extra rib. On examination, there is right-sided weakness of the intrinsic hand muscles. Which of the following muscles is most likely contributing to this patient's condition?

Question

A 15-year-old boy comes to the office due to right arm numbness.  He plays on his high school baseball team and has been intensively practicing his pitching for an upcoming game.  For the past several weeks, the patient has had fluctuating tingling and numbness involving the right shoulder, arm, and hand.  He also has recently developed dull pain in the right little finger and hand.  The symptoms worsen with overhead activities and when throwing a baseball.  The patient has no medical problems other than being told that he has an extra rib.  On examination, there is right-sided weakness of the intrinsic hand muscles.  Which of the following muscles is most likely contributing to this patient's condition?

Quizplus · Accepted Answer

11ec160b_35f4_3285_9249_8505f6586b6a_MD0001_00 This patient's upper extremity neurologic symptoms in the setting of an extra rib are highly suggestive of thoracic outlet syndrome (TOS). The thoracic outlet refers to the region above the first rib and behind the clavicle that is bordered by the cervical vertebral bones and the sternum. Compression of the brachial plexus as it passes through the thoracic outlet can cause upper extremity numbness, tingling, and weakness (most often in an ulnar distribution due to compression of the lower trunk). Involvement of the subclavian vein and artery can also occur and lead to upper extremity swelling and exertional arm pain. TOS most commonly occurs due to compression of the brachial plexus within the scalene triangle, which is formed by the anterior and middle scalene muscles and the first rib. The anterior scalene muscle originates from the C3-C6 transverse processes and attaches to the scalene tubercle of the first rib. The middle scalene originates from the C2-C7 transverse processes and inserts into the posterior portion of the first rib. The brachial plexus trunks and subclavian artery pass between the anterior and middle scalenes; the subclavian vein runs anterior to the anterior scalene. The presence of an anomalous cervical rib or scalene muscular anomalies can predispose to TOS. Affected patients typically have a history of trauma or repetitive overhead arm movements (eg, swimming, stacking boxes). (Choice A) The coracobrachialis originates from the coracoid process of the scapula and acts to flex the arm at the glenohumeral joint. The musculocutaneous nerve pierces the muscle near its insertion into the humerus; overuse of the coracobrachialis (eg, excessive bench pressing) can cause entrapment of the musculocutaneous nerve, causing impaired elbow flexion and lateral forearm sensory loss. (Choice C) The subscapularis muscle originates in the subscapular fossa of the scapula and inserts into the lesser tubercle of the humerus. It acts to adduct and internally rotate the humerus. (Choices D and E) The teres major muscle and long head of the triceps brachii form the inferior and medial borders of the quadrangular space through which the axillary nerve passes. Entrapment of the axillary nerve within the quadrangular space can cause sensory loss over the lateral shoulder and impair shoulder abduction. Educational objective: Thoracic outlet syndrome (TOS) is most often caused by compression of the brachial plexus as it passes through the scalene triangle, the space bordered by the anterior and middle scalene muscles and the first rib. Symptoms typically include upper extremity numbness, tingling, and weakness that worsen with repetitive overhead arm movements. The presence of an anomalous cervical rib is a risk factor for TOS. __________ References: Understanding thoracic outlet syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/25140278)

A 15-Year-Old Boy Comes to the Office Due to Right