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).