The accessory tendon of the extensor indicis muscle.

The extensor indicis and the extensor pollicis longus muscles differentiates from the extensor digitorum profundus muscle. The extensor indicis muscle is an unstable muscle concerning its variations. Kosugi (1989) found the frequency of variations of this muscle to be 20% and described 18 different types of variations of this muscle. This study describes a rare case of the extensor indicis muscle. The extensor indicis muscle develops an accessory tendon in between the extensor indicis and extensor pollicis longus muscle. It passes under the extensor retinaculum. At the level of 2nd metacarpal bone, the accessory extensor indicis tendon is connected to the tendon of the extensor pollicis longus muscle by a intertendinous connection.