Extensor pollicis et indicis communis or extensor indicis radialis muscle.

Anatomical variations of the fingers extensor tendons are not uncommon and have been described by several authors. Participation of intertendinous band of fascia in this kind of variation can change muscle functionality. However, this element is scarcely described in the literature. In this case report, we describe the finding of an accessory tendon located between the extensor digitorum communis muscle tendon, destined for the index finger, and the extensor pollicis longus tendon. In an anatomical analysis, we observed a connection between the radial portion of the accessory tendon and the ulnar portion of the extensor pollicis longus tendon by intertendinous fascia. This finding corresponds anatomically to the supernumerary muscle denominated extensor indicis radialis, but due to the fascial connections observed with the extensor pollicis longus, this muscle would behave functionally as a supernumerary muscle denominated extensor pollicis et indicis communis. This report suggests that participation of fascia in muscular variation in this anatomical segment is essential to establish the correct morpho-functional denomination of muscular variants.