An atavastic belly of the flexor digitorum profundus with absence of tendon of flexor digitorum superficialis to the little finger: Morphological and histological considerations

In this case report, we report the absence of the fourth tendon of flexor digitorium superficialis (FDS) to the little finger with a concurrent anomalous muscular belly of flexor digitorum profundus (FDP) in the palm. The FDS originated from the medial epicondyle, divided into three tendons for the index, middle and ring fingers with the little finger devoid of any attachment. The FDP exhibited a muscular belly which passed deep to the flexor retinaculum (FR) and continued for another 4 cm thereby dividing into four slips for the index, middle, ring and little fingers. The presence of the muscular belly of the FDP lead us to think whether it was an adhesion between the tendons of the FDP, so we proceeded to histological analysis. The tissue was processed and stained with Hematoxylin and Eosin. Abundant longitudinal muscle fibers with peripherally situated nuclei confirmed it to be a skeletal muscle. Absence of the tendon of FDS to little finger may influence the flexion movement in the middle and proximal interphalangeal joints. Presence of anomalous muscle belly of FDP in the palm may mimic any soft tissue tumour, compress neurovascular structures or even pose difficulty while performing tendon transplant surgeries.