Accessory Extensor Pollicis Longus Tendon Classification Modification.

Supernumerary extensor pollicis longus (EPL) and extensor indicis proprius tendons are infrequently reported. There are few case reports on more than one accessory tendon in one individual. As a result, they are not represented in previously described classifications for variations in extensors to the thumb. Elective surgery was performed on a 57-year-old right-handed female. Within the fourth compartment, two anomalous accessory tendons were present. These tendons were identified as an accessory EPL tendon and an accessory extensor indicis proprius tendon. The normal EPL tendon occupied the third compartment ulnar to Lister's tubercle, as usual. The previous classification system for anomalous EPL tendons is useful in the organization and description of thumb extensor tendon variations. However, it is not a complete representation of the anomalies identified, including the one in this report. We have proposed an additional category for this classification system to better encompass the variation in anomalous tendon anatomy.