Flexor Digitorum Profundus

Origin

The flexor digitorum profundus muscle originates from the:

- medial aspect of the coronoid process of ulna;

- superior three quarters of the anterior and medial surfaces of the body of ulna;

- anterior surface of the adjacent interosseous membrane of forearm.

Insertion

The fibers of the flexor digitorum profundus muscle travel inferiorly to the hand and insert onto the palmar aspects of the bases of distal phalanges of the index, middle, ring, and little fingers.

Key Features & Anatomical Relations

The flexor digitorum profundus muscle is one of the muscles of the deep part of the anterior compartment of the forearm. It is a thick, fusiform type of skeletal muscle that divides into four tendons. The tendon for the index finger separates from the other tendons in the forearm, while the others separate in the hand. In the forearm and hand, each of these tendons travels deep to the tendons of the flexor digitorum superficialis muscle. At the wrist, the tendons of both muscles travel together, deep to the flexor retinaculum of the hand, where they pass through the common flexor sheath. The tendons of both muscles travel through the fibrous sheaths that are found along the palmar aspects of each finger. Along each proximal phalanx, the tendons of the flexor digitorum profundus pass through the tendons of the flexor digitorum superficialis, then travel to their insertion sites.

For descriptive purposes, the flexor digitorum profundus muscle is divided into two parts:

- a medial part, which refers to the two tendons that attach to the distal phalanges of the ring and little fingers, along with the portion of the muscle belly that controls them;

- a lateral part, which refers to the two tendons that attach to the distal phalanges of the index and middle fingers, along with the portion of the muscle belly that controls them.

The flexor digitorum profundus muscle is located:

- anterior (superficial) to the ulna, interosseous membrane of forearm, and the pronator quadratus muscle;

- posterior (deep) to the flexor digitorum superficialis muscle;

- lateral to the ulnar artery and ulnar nerve.

Within the palm of the hand, each of the four lumbrical muscles of the hand originates from each of the four tendons of the flexor digitorum profundus.

Actions & Testing

The flexor digitorum profundus muscle is involved in multiple actions:

- flexes the distal phalanges at the distal interphalangeal joints of the index, middle, ring, and little fingers;

- assists in flexion of the middle phalanges at the proximal interphalangeal joints of the same fingers;

- assists in flexion of the proximal phalanges at the metacarpophalangeal joints of the same fingers;

- assists in flexion of the hand at the radiocarpal (wrist) joint.

This muscle is capable of flexing the index finger independently of the other fingers.

The flexor digitorum profundus muscle can be tested by flexing the distal phalanx at the distal interphalangeal joints while its corresponding middle phalanx is held in its extended position (Standring, 2016).

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.