Why care about nerve anatomic anomalies?

  • Affects findings on physical examination.
  • Keep in mind when operating as these may initially be confused for normal anatomic structures.

These anatomic anomalies are often the culprit in a variety of nerve compression syndromes.  While we do not cover all of the anomalies, we will present a few examples to illustrate this point.


  • Extra fascial bands/ligaments:
    • A variety of these may occur and can pose a relatively inflexible anatomic structure that causes nerve compression, for example, of the median nerve in the antecubital area.
  • Extra muscles:
    • Gantzer’s muscle: an extra slip of the flexor pollicis longus that can compress the anterior interosseous nerve in the forearm.
    • A palmaris profundus muscle can compress the median nerve just proximal to the wrist.
    • An accessory palmaris longus or palmaris brevis profundus can compress the ulnar nerve just proximal to the wrist.
  • Abnormalities in muscles:
    • An abnormal/ long lumbrical muscle belly can extend into the carpal tunnel and contribute to median nerve compression at this location.
  • Extra arteries:
    • A persistent median artery can contribute to compression of the median nerve within the carpal tunnel.
  • Extra bones
    • Supracondylar spur bony process coming off the median aspect of the humerus may cause median nerve problems at the arm level (however, this has been noted to be increasingly uncommon).