A 25-year-old man fractures his right tibia in a motor vehicle accident. His right leg is fixed in a cast and he requires underarm crutches to ambulate. Two weeks later, he comes to the clinic with right upper-extremity weakness and numbness. He has no neck or arm pain. The patient is concerned because he is right handed and cannot perform his duties as an electrician. On neurologic examination, there is diminished strength on extension of the right wrist with an absent triceps reflex. Injury to which of the following nerves is most likely responsible for this patient's symptoms?

Question

A 25-year-old man fractures his right tibia in a motor vehicle accident.  His right leg is fixed in a cast and he requires underarm crutches to ambulate.  Two weeks later, he comes to the clinic with right upper-extremity weakness and numbness.  He has no neck or arm pain.  The patient is concerned because he is right handed and cannot perform his duties as an electrician.  On neurologic examination, there is diminished strength on extension of the right wrist with an absent triceps reflex.  Injury to which of the following nerves is most likely responsible for this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_35c0_ed07_9249_9380f8aca5ea_MD0001_00 The radial nerve is derived from the C5-T1 spinal nerves and is one of the two final branches of the posterior cord of the brachial plexus. The nerve initially courses medial to the surgical neck of the humerus inferior to the teres major muscle within the axilla before entering the posterior arm to course between the long head of the triceps brachii and the posterior humerus. Proximal radial nerve injury can occur at the nerve's superficial location within the axilla by repetitive pressure/trauma caused by an ill-fitting crutch ("crutch palsy") or if an individual sleeps with the arm over a chair ("Saturday night palsy"). Injury to the nerve at this location may cause weakness or paralysis of the forearm, hand, and finger extensor muscles (eg, wrist drop, absent triceps reflex). Sensory loss may also be observed over the radial nerve distribution. Injuries to the proximal radial nerve as it crosses the posterior humerus (eg, midshaft humeral fractures) spare the triceps brachii, as the fibers innervating this muscle leave the nerve before it enters the radial groove. (Choice A) The spinal accessory nerve (CN XI) exits the skull through the jugular foramen and courses over the levator scapulae muscle to innervate the sternocleidomastoid and trapezius muscles. (Choice B) Fracture of the surgical neck of the humerus and anterior dislocation of the glenohumeral joint can cause injury to the axillary nerve. The resultant paralysis of the deltoid and teres minor muscles causes weakness on arm abduction. Sensory loss over the deltoid may also be evident. (Choice C) Damage to the long thoracic nerve causes paralysis of the serratus anterior muscle and winging of the scapula. This nerve is often injured during lymph node dissection in patients undergoing radical mastectomy. (Choice D) Proximal median nerve injury often occurs with supracondylar humerus fractures. This results in sensory loss over the palmar aspect of the first 3 digits and impairment of thumb flexion/opposition, flexion of the second/third digits, and wrist flexion/abduction. (Choice F) The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. These muscles function to abduct and laterally rotate the arm, respectively. Educational objective: Radial nerve injury can occur with repetitive pressure/trauma at the axilla (eg, improperly fitted crutches). Findings include weakness of the forearm, hand, and fingers extensors (eg, wrist drop, absent triceps reflex) and sensory loss over the posterior arm and forearm, dorsolateral hand, and dorsal thumb. More distal lesions spare the triceps brachii. __________ References: Clinical features of wrist drop caused by compressive radial neuropathy and its anatomical considerations. (http://www.ncbi.nlm.nih.gov/pubmed/24851150) Anatomical, clinical, and electrodiagnostic features of radial neuropathies. (http://www.ncbi.nlm.nih.gov/pubmed/23177029)

A 25-Year-Old Man Fractures His Right Tibia in a Motor