Flexor digitorum profundus

At a glance

English

Flexor digitorum profundus

Latin (TA2)

Flexor profundus digitorum

System

Muscle

Region

Upper limb

Side

Paired, left and right

Inserts on

The distal phalanx of fourth finger of hand, distal phalanx of second finger of hand and distal phalanx of third finger of hand

About the flexor digitorum profundus

Flexor digitorum profundus is a large, thick muscle in the deep layer of the front of the forearm. It lies on the ulna, under flexor digitorum superficialis, with flexor pollicis longus beside it on the radial side.

It arises from the front and inner surfaces of the upper three quarters of the ulna, from the interosseous membrane and from the deep fascia of the forearm. In the lower forearm it forms four tendons. The tendon to the index finger usually separates early, while the other three stay partly linked, which limits independent bending of the ring and little fingers. All four pass through the carpal tunnel behind the superficialis tendons. In the palm each tendon gives origin to a lumbrical muscle, then enters the fibrous sheath of its finger, passes through the split in the superficialis tendon and attaches to the front of the terminal phalanx base.

The muscle bends the distal interphalangeal joints, and as it continues to pull it also flexes the middle and knuckle joints and the wrist. It is the main muscle of a strong fist and of hooking with the fingertips. It has a double nerve supply: the part for the index and middle fingers is served by the anterior interosseous branch of the median nerve, and the part for the ring and little fingers by the ulnar nerve. Its blood comes from the anterior interosseous and ulnar arteries.

Its tendon can be torn off the distal phalanx when a player grabs a shirt, a jersey finger, most often in the ring finger. Each tendon is tested by holding the middle joint straight and asking the patient to bend the fingertip.

Attachments, action and supply

Origin

Front and inner surfaces of the upper three quarters of the ulna, the interosseous membrane and the deep forearm fascia.

Insertion

Palmar bases of the distal phalanges of the index, middle, ring and little fingers.

Action

Flexes the distal interphalangeal joints, then the proximal interphalangeal and metacarpophalangeal joints and the wrist.

Nerve supply

Lateral part by the anterior interosseous nerve from the median nerve; medial part by the ulnar nerve (both C8, T1).

Blood supply

Anterior interosseous artery and muscular branches of the ulnar artery.