Extensor pollicis et indicis communis with triple slips in a bilateral case of accessory muscles of the hand.

The presence and disposition of supernumerary tendons in the fourth extensor compartment of the wrist have been described by several authors. The aim of this communication was to describe a finding in a study of an anatomical dissection of an adult cadaver that presents a rare disposition of extensor tendons in the fourth extensor compartment of both wrists. In the right wrist, we found an extensor pollicis et indicis communis with three slips: two toward the index finger and one toward the thumb. We found no similar reports in a review of the literature. Additionally, we found an extensor indicis radialis in the left wrist. In both hands, the course of accessory slips was modified by fiber derived from intertendinous fascia. Although this represents a small percentage of the distribution of tendons of the dorsal hand, knowledge of these anatomical variations and their relationships to intertendinous fascia is critical for clinical decisions because this area is used frequently in treatments related to tendon graft, transfer, and transplantation.