The cutaneous innervation of the palm: an anatomic study of the ulnar and median nerves.

Twenty-five fresh-frozen cadaveric hands without obvious deformity were dissected using 3.5x loupe magnification. Median and ulnar nerves were identified in the proximal forearm and dissected distally to the midpalm. Cutaneous branches of median and ulnar nerves were described relative to an incision for carpal tunnel release. The palmar cutaneous branch of the median nerve was present in all 25 specimens. In a single specimen, the palmar cutaneous branch of the median nerve was isolated as it crossed the incision, and in another two specimens, the terminal branches of the nerve were identified at the margin of the incision. In 4 hands, a classic palmar cutaneous branch of the ulnar nerve was found an average of 4.9 cm proximal to the pisiform. In 10 specimens, a nerve of Henle arose an average of 14.0 cm proximal to the pisiform and traveled with the ulnar neurovascular bundle to the wrist flexion crease. In 24 specimens, at least one-usually multiple-transverse palmar cutaneous branch was identified originating an average of 3 mm distal to the pisiform within Guyon's canal. The origin and destination of these nerves was highly variable. In 16 specimens, an incision in the axis of the ring finger would likely have encountered at least one branch of the ulnar-based cutaneous innervation to the palm. Cutaneous branches of the ulnar nerve would be expected to cross the line of dissection frequently during open carpal tunnel release. Decreased levels of discomfort in patients undergoing endoscopic and subcutaneous types of carpal tunnel release may be in part due to the preservation of the crossing cutaneous nerves with these procedures.