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Anatomic Anomalies

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).