A 19-year-old woman is evaluated in the clinic due to right hand clumsiness. The patient injured the right upper extremity after falling off her bicycle 6 months ago. She has since had a "pins and needles" sensation in the right hand associated with mild weakness. The patient is worried as these symptoms are interfering with her piano lessons and she has an upcoming recital in 3 weeks. Physical examination shows decreased sensation over the fifth digit and a flattened hypothenar eminence. Triceps reflexes are 2+ and symmetric bilaterally. The nerve affected in this patient is commonly injured at which of the following locations?

Question

A 19-year-old woman is evaluated in the clinic due to right hand clumsiness.  The patient injured the right upper extremity after falling off her bicycle 6 months ago.  She has since had a "pins and needles" sensation in the right hand associated with mild weakness.  The patient is worried as these symptoms are interfering with her piano lessons and she has an upcoming recital in 3 weeks.  Physical examination shows decreased sensation over the fifth digit and a flattened hypothenar eminence.  Triceps reflexes are 2+ and symmetric bilaterally.  The nerve affected in this patient is commonly injured at which of the following locations?

Quizplus · Accepted Answer

11ec160b_35f7_b4f7_9249_e5d2a47fb854_MD0001_00 This patient's presentation is consistent with ulnar neuropathy. The ulnar nerve is a branch of the medial cord of the brachial plexus derived from the C8-T1 ventral rami. It enters the forearm after passing behind the medial epicondyle of the humerus. Within the forearm, it innervates the flexor carpi ulnaris and the medial portion of the flexor digitorum profundus. The nerve then enters the wrist between the hook of the hamate and the pisiform bone in a fibroosseous tunnel known as Guyon's canal. Here, it divides into a superficial branch that provides sensation over the medial 1½ digits and hypothenar eminence and a deep motor branch that supplies most of the intrinsic muscles of the hand. The ulnar nerve is most commonly injured at the elbow ("funny bone") due to trauma or nerve compression, but it can also be injured at the wrist as it runs through Guyon's canal. Nerve damage may cause sensory loss in the ulnar distribution with weakness on wrist flexion/adduction, finger abduction/adduction, and flexion of the fourth/fifth digits. The hypothenar eminence can appear flattened due to denervated muscle atrophy. Weakness of the lumbricals in the fourth/fifth digits may also produce an "ulnar claw" deformity during finger extension. (Choice A) Carpal tunnel syndrome can result from any condition that reduces the size of the carpal tunnel and compresses the median nerve (eg, pregnancy, hypothyroidism). Patients typically have pain/paresthesias affecting the first 3½ digits. Thenar atrophy with weakness on thumb abduction/opposition may also be seen. (Choice B) The coracobrachialis muscle lies deep to the biceps brachii and is perforated and innervated by the musculocutaneous nerve. Nerve injury may result in decreased strength on forearm flexion and sensory loss over the lateral forearm. (Choice C) Subluxation of the radial head can injure the deep branch of the radial nerve during its passage through the supinator canal, leading to weakness during finger and thumb extension ("finger drop"). (Choice E) Fracture of the midshaft of the humerus typically results in radial nerve injury leading to paralysis of the hand and finger extensor muscles ("wrist drop") with sensory loss over the posterior forearm and dorsolateral hand. (Choice F) Fracture of the surgical neck of the humerus may cause axillary nerve injury leading to paralysis of the deltoid and teres minor muscles with sensory loss over the lateral upper arm. Educational objective: The ulnar nerve can be injured at the medial epicondyle of the humerus ("funny bone") or in Guyon's canal near the hook of the hamate and pisiform bone in the wrist. Patients often have sensory loss over the medial 1½ digits and hypothenar eminence, and weakness on wrist flexion/adduction, finger abduction/adduction, and flexion of the fourth/fifth digits. The hypothenar eminence may flatten due to muscle atrophy. __________ References: Ulnar neuropathy at the wrist. (http://www.ncbi.nlm.nih.gov/pubmed/19506968) Diagnosis and Treatment of Work-Related Ulnar Neuropathy at the Elbow. (http://www.ncbi.nlm.nih.gov/pubmed/26231962)

A 19-Year-Old Woman Is Evaluated in the Clinic Due to Right