Isolated laceration to the deep motor branch of the ulnar nerve by a retained foreign body.

This report describes an isolated laceration to the deep motor branch of the ulnar nerve by a retained foreign body. The patient sustained a laceration on the ulnar, volar aspect of his palm after a fall on gravel. He presented to the emergency room with motor deficits but a normal sensory examination. No foreign bodies were identified on initial wound exploration or review of plain radiographs, and the patient's wound was sutured closed without diagnosing the nerve injury or the retained foreign body. Confusion over the patient's intact sensory examination and lack of awareness of the complex distal anatomy of the ulnar nerve contributed to the misdiagnosed nerve lesion. Isolated injuries of the deep motor branch are very rare, but increased awareness and understanding of the complex ulnar nerve distal anatomy will help avoid future delays in diagnosis and treatment.