A 23 year old male presents to the emergency department, with extensive laceration to his left forearm from a motorcycle accident. In addition to the pain of the laceration, he feels numb in his little finger, with tingling in his ring finger, and tingling in a part of the palm of his left hand.
Sensory and motor functions of the hand arise from innervation by the median, radius and ulnar nerves. Examination of the hand should always include checking motor function as well as pin prick, light touch and two-point discrimination. Normal two-point discrimination will increase with age and neuropathic disease, but is considered approximately 4-5 mm.
Bassett, RE et al. Finger and thumb anatomy. UpToDate, July 2016.
On examination of this patient’s left hand, he is found to have decreased sensation in the 5th digit, ulnar aspect of the 4th digit and weakness with extension of the digits and wrist. This raises the concern for injury to the ulnar nerve associated with the forearm laceration.
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Nathan Whittaker, MD