Identification of a flexor digitorum accessorius longus muscle with unique distal attachments.

During a cadaver dissection in a gross anatomy course, a flexor digitorum accessorius longus (FDAL) muscle was identified. The FDAL was a unilateral, two-headed, multipennate muscle originating from the flexor retinaculum, deep fascia, and calcaneus. The muscle bodies fused into one tendon and coursed distally where slips were observed inserting into the flexor digitorum longus tendon and the flexor hallicus longus tendon. A survey of the literature revealed that an FDAL may be present in approximately 15% of the general population. Our results concerning the FDAL suggest the need for clinicians to recognize the occurrence and variability of accessory leg and ankle muscles, and to use available technology such as MRI to assist with the diagnosis and treatment of compressive neuropathies of the foot.