An anatomical study of additional radial wrist extensors including a unique extensor carpi radialis accessorius.

BACKGROUND: In this study, 82 forearms from 41 cadavers were dissected to establish the incidence of variant additional radial wrist extensors. Three variants have been described in the literature: extensor carpi radialis intermedius (ECRI), extensor carpi radialis accessorius (ECRA) and extensor carpi radialis tertius (ECRT). MATERIALS AND METHODS: Of the 41 cadavers studied, 5/41 (12%) had an additional radial wrist extensor. Of these 5 individuals, 2 had bilateral additional muscles and 3 were unilateral. Of the 82 forearms, 7/82 (9%) had additional radial wrist extensors. RESULTS: We found 4 examples of ECRI and 3 examples of ECRA. We did not find any examples of ECRT. One specimen of ECRA had an atypical, previously undescribed, course. CONCLUSIONS: These accessory muscles are of clinical relevance, as they may be a contributing factor in tennis elbow and nerve entrapment, or cause diagnostic confusion, especially in ultrasound scans. However, they may also be used for tendon transfer. Of the 7 muscles found in the current study, 3 would have been suitable for such procedures.