Flexor digitorum profundus muscle (hand, anatomy)

Flexor digitorum profundus is one of the forearm flexor muscles of the hand and fingers.

Its origin is from the proximal three quarters of the anterior surface of the ulna. It extends medially to the interosseous membrane. From this point it divides into four tendons which pass distally. The tendons pass deep to those of flexor digitorum superficialis at the wrist and as they enter each digital sheath.

It inserts into the palmar base of the distal phalanges of the ulnar four digits. Usually, the tendon to the index finger separates at a more proximal point than the other tendons.

Flexor digitorum has a double innervation but this can be very variable:

• supply to the muscles moving the two ulnar fingers (ring and little) is from the ulnar nerve (C8,T1)
• supply to the muscles moving the index and middle fingers is from the anterior interosseous branch of the median nerve (C8, T1)

The actions of flexor digitorum profundus are:

• uniquely flexes the distal interphalangeal joint of the ulnar four fingers
• flexes all the joints crossed by its tendon: wrist, metacarpal and two interphalangeal