Bilateral extensor pollicis et indicis accessorius: clinical and anatomical perspectives

Historical and contemporary sources differ in defining extensor pollicis et indicis accessorius. Based on a comprehensive literature review and the present bilateral anatomical finding, this report recommends using the term extensor pollicis et indicis accessorius muscle for this configuration and proposes revising existing classification systems to include accessory extensor muscles originating from the extensor pollicis longus muscle, the extensor indicis muscle, or the ulna, rather than limiting them to extensor pollicis longus muscle anomalies.