Upper limb

Flexor Digitorum Profundus

Musculus flexor digitorum profundus

Origin

Proximal three-quarters of the anterior and medial surface of the ulna, and the interosseous membrane

Insertion

Base of the distal phalanges of fingers 2 through 5

Function

Flexes the DIP joints (and to a lesser extent the PIP, MCP joints and wrist) of fingers 2–5

Innervation

Lateral half (index/middle finger): median nerve (anterior interosseous nerve); medial half (ring/little finger): ulnar nerve

Movement & chain

The only muscle that can actively flex the DIP joints. When making a fist, it works together with flexor digitorum superficialis, which stabilizes the PIP joints first.

Palpation

Difficult to distinguish directly from the superficial finger flexor; the tendons can be felt distally on the palmar side of the fingers during active DIP flexion.

Clinical

Avulsion of the tendon at the distal phalanx (known as 'jersey finger') causes loss of active DIP flexion. Tendon injuries in the fingers are classified according to flexor tendon zones (zone II is notorious for adhesions).

Segmental innervation

C7–T1, via the median and ulnar nerves.

In clinical practice

Testing isolated DIP flexion while the examiner holds the PIP joint in extension is a standard part of the physical examination to detect an injury to this tendon.

Region in the model

Upper limb