Accessory Slip of the Extensor Carpi Ulnaris: A Cadaveric Assessment.

Background An accessory slip arising from the extensor carpi ulnaris (ECU) tendon that inserts on the fifth metacarpal bone has been identified. We describe the frequency of this accessory slip arising from the ECU tendon and provide both qualitative and quantitative description of the slip via cadaveric examination. Methods Fifty (28 males and 22 females) cadaveric upper extremity specimens were examined after loupe-aided dissection of the dorsoulnar wrist and hand with identification of the ECU tendon. The presence of an accessory slip arising from the ECU tendon was noted. The insertion and morphology of the accessory slip was also described. Results An accessory slip arising from the ECU tendon at the level of the radiocarpal joint was found to insert on the fifth metacarpal bone in 11 (22%) specimens. Nine accessory slips inserted at the base of the fifth metacarpal (Nakashima Type A) and two inserted at the fifth metacarpal head (Nakashima Type C). Mean width of the accessory slip was 1.2 ± 0.4 mm. No evidence of sexual dimorphism was found regarding the morphology of the accessory slip. Conclusion The current study demonstrates the relative frequency and morphology of the accessory slip arising from the ECU tendon. This variant should be of diagnostic consideration in ailments of the dorsoulnar wrist and hand. Hand surgeons should be aware of this anatomic variant and its potential for clinical manifestation.