A Variant Accessory Belly of Extensor Indicis Muscle: An Anatomical Variation

Muscular variations of the extensor compartment of the forearm are generally encountered during surgical and dissection procedures. Additional bellies, extra tendons, and abnormal attachment are such reported variations. Knowledge of these kinds of variation are important for hand surgeons to plan the surgical procedure and modify their approach to that case, or the surgeon can take the advantage of these variations during muscle graft and tendon transplantation procedures. Here we report a case of an additional belly of the extensor indicis muscle. The additional belly arose from the interosseous membrane. Its tendon passed through the fourth compartment deep into the extensor retinaculum and divided into two tendinous slips on the dorsum of the hand. One of these slips attached to the ulnar side of the tendon of the extensor digitorum for the middle finger; the other slip was merged with fascia over the dorsum of the hand. The additional belly was supplied by the posterior interosseous nerve