A 36-year-old construction worker comes to the emergency department after falling 3 meters (~10 ft) from a ladder. The patient braced his fall with outstretched hands and experienced severe pain in the left wrist immediately on impacting the ground. On examination, the left wrist is swollen, with no lacerations. A strong radial pulse is present, and the fingers are well perfused. There is a palpable mass just proximal to the left palm. X-ray of the left wrist reveals a lunate dislocation without evidence of a distal radius fracture, as seen in the exhibit.

The patient is at greatest risk for impairment of which of the following hand functions?

Question

A 36-year-old construction worker comes to the emergency department after falling 3 meters (~10 ft) from a ladder.  The patient braced his fall with outstretched hands and experienced severe pain in the left wrist immediately on impacting the ground.  On examination, the left wrist is swollen, with no lacerations.  A strong radial pulse is present, and the fingers are well perfused.  There is a palpable mass just proximal to the left palm.  X-ray of the left wrist reveals a lunate dislocation without evidence of a distal radius fracture, as seen in the exhibit.

The patient is at greatest risk for impairment of which of the following hand functions?

Quizplus · Accepted Answer

11ec160b_35f9_62aa_9249_11dc42037d29_MD0001_00 This patient who experienced a high-energy fall onto an outstretched hand now has a volar lunate dislocation, with the displaced lunate now palpable in the patient's proximal palm and visualized on lateral x-ray of the wrist ("spilled teacup" sign). Lunate dislocation requires a high-energy force to disrupt the numerous ligaments (eg, scapholunate, capitolunate, lunotriquetral) that typically stabilize the lunate. When severe ligamentous injury occurs, the lunate can dislocate volarly from its normal position within the floor of the carpal tunnel and compress and/or injure the median nerve. Median nerve injury at the level of the carpal tunnel may result in both sensory and motor deficits in the distribution of the median nerve's distal branches: Prompt reduction of the dislocated lunate is required to prevent permanent damage to the median nerve. (Choices A and D) The deep motor branch of the ulnar nerve is responsible for both finger abduction due to innervation of the dorsal and volar interossei and thumb adduction due to innervation of the adductor pollicis. The ulnar nerve is susceptible to acute compression at the wrist (ie, Guyon canal syndrome) when the hook of the hamate is fractured. (Choice B) Branches of the median and ulnar nerves in the forearm innervate the flexor digitorum superficialis and profundus muscles that control finger interphalangeal joint flexion. These branches arise and innervate their respective muscles prior to the carpal tunnel and Guyon canal and would not be affected by wrist trauma. (Choice E) The radial nerve innervates the extensor pollicis longus and brevis, which control thumb extension. All radial nerve-innervated muscles are located proximal to the wrist and therefore would not be affected by lunate dislocation. Educational objective: Volar dislocation of the lunate from its normal position within the floor of the carpal tunnel can cause median nerve compression and/or injury. Median nerve injury at the level of the carpal tunnel may result in weakness of thumb abduction, flexion, and opposition. __________ References: Lunate dislocation causing median nerve entrapment. (http://www.ncbi.nlm.nih.gov/pubmed/28123252) Evaluation, management, and outcomes of lunate and perilunate dislocations. (http://www.ncbi.nlm.nih.gov/pubmed/30403823)

A 36-Year-Old Construction Worker Comes to the Emergency Department After