Anomaly originated flexor digitorum superficialis muscle of the small finger: A case report

We present a clinical case of flexor digitorum superficialis (FDS) muscle belly of the small finger originating from the palm of a patient undergoing carpal tunnel surgery with a literature review. PATIENTS CONCERN: A 28-year-old right-handed woman visited our hospital with a chief complaint of a continuous tingling sensation and weakness in the right hand, which began after the volar side of her wrist was crushed by a machine during work 2 weeks prior. The patient complained of a continuous tingling sensation in the thumb, index, and middle fingers. The patient had a positive result on Tinel test of the median nerve of the wrist. As electromyography and nerve conduction velocities showed signs of severe injury in the right median nerve, exploration and carpal tunnel release were planned. DIAGNOSIS: Carpal tunnel release was performed under regional anesthesia using the classical open approach. The median nerve in the distal forearm and distal portion of the flexor retinaculum appeared to be narrowed and compressed. An anomalous muscle originating from the flexor retinaculum is also observed. INTERVENTION: The FDS muscle of the small finger was excised at the flexor retinaculum and musculotendinous junction and sutured to the flexor digitorum profundus tendon. OUTCOME: At the 37-month follow-up, the patient did not experience any tingling sensation or weakness. She showed excellent range of motion of the right small finger. The grip strength was 20 kg on both the right and left sides. Quick disabilities of the arm, shoulder, and hand score was 2.3. CONCLUSION: Asymptomatic small finger FDS muscle anomalies can occur, as demonstrated in this case study. Thus, physicians should familiarize themselves with small finger FDS muscle anomalies during interactions with patients to facilitate future treatments of patient complaints related to the hand, as well as wrist laceration or trauma requiring hand exploration.