A 12-year-old boy is brought to the emergency department by his mother due to right hand clumsiness. Several hours ago he attempted to climb a tree with a friend but lost his balance and fell from a branch. The boy tried to break the fall by grabbing the tree branch with his right hand. He landed safely on his feet with no head injury or loss of consciousness. On physical examination, he has difficulty performing fine finger movements with the right hand. Which of the following structures is most likely injured in this patient?

Question

A 12-year-old boy is brought to the emergency department by his mother due to right hand clumsiness.  Several hours ago he attempted to climb a tree with a friend but lost his balance and fell from a branch.  The boy tried to break the fall by grabbing the tree branch with his right hand.  He landed safely on his feet with no head injury or loss of consciousness.  On physical examination, he has difficulty performing fine finger movements with the right hand.  Which of the following structures is most likely injured in this patient?

Quizplus · Accepted Answer

11ec160b_3598_f259_9249_b546445bd760_MD0001_00 Sudden upward jerking of the arm at the shoulder can cause injury to the lower trunk of the brachial plexus. The lower trunk carries nerve fibers from the C8 and T1 spinal levels that ultimately contribute to the median and ulnar nerves. Together, these nerves innervate all of the intrinsic muscles of the hand (eg, lumbricals, interossei, thenar, hypothenar). Injury to the lower trunk of the brachial plexus may cause paralysis of all the intrinsic hand muscles (Klumpke's palsy). Weakness of lumbricals causes impaired flexion of the metacarpophalangeal joints and impaired extension of the interphalangeal joints. Relative sparing of the extrinsic flexors and extensors of the hand contributes to the total claw hand deformity seen in this condition. Sensory loss can also occur over the medial aspect of the hand/forearm. Involvement of the T1 nerve root proximal to the sympathetic trunk may cause concomitant Horner's syndrome (eg, ipsilateral ptosis, miosis, anhidrosis). (Choice A) Shoulder dislocations or fractures of the proximal humerus can cause axillary nerve injury, which results in weakness of the deltoid and teres minor muscles. (Choice B) Long thoracic nerve injury classically occurs during axillary lymph node dissection and results in paralysis of the serratus anterior muscle, leading to winging of the scapula. (Choice D) Injury to the musculocutaneous nerve causes weakened elbow flexion because the nerve innervates the biceps brachii and brachialis muscles. (Choice E) Fractures at the midshaft of the humerus commonly cause radial nerve injury. Patients may experience posterior forearm and dorsolateral hand numbness with paralysis of the wrist and finger extensors (wrist drop). (Choice F) The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. Nerve injury may result in problems with abduction and lateral rotation of the arm, respectively. Educational objective: The lower trunk of the brachial plexus carries nerve fibers from the C8 and T1 spinal levels that are responsible for innervating all of the intrinsic muscles of the hand (via the median and ulnar nerves). Sudden upward stretching on the arm at the shoulder can damage the lower trunk, resulting in finger clumsiness with total claw hand deformity. __________ References: Brachial plexopathy: a review of traumatic and nontraumatic causes. (http://www.ncbi.nlm.nih.gov/pubmed/24370167)

A 12-Year-Old Boy Is Brought to the Emergency Department by His