Humero-ulnar head of flexor digitorum superficialis

At a glance

English

Humero-ulnar head of flexor digitorum superficialis

Latin (TA2)

Caput humeroulnare musculi flexoris digitorum superficialis

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the humero-ulnar head of flexor digitorum superficialis

Flexor digitorum superficialis is the largest of the superficial flexors on the front of the forearm, though it lies in an intermediate layer, under the muscles that cover it and above the deep finger flexor. It arises by two heads, one from the humerus and ulna and one from the radius, which are linked by a fibrous arch.

This head takes origin from the medial epicondyle through the common flexor tendon, from the ulnar collateral ligament of the elbow, and from the medial edge of the coronoid process of the ulna. It runs down and joins the radial head beneath the arch. The muscle then forms four tendons, arranged in two layers at the wrist: those for the middle and ring fingers lie in front of those for the index and little fingers. They pass through the carpal tunnel, enter the fibrous sheaths of the fingers and each splits into two slips. The deep tendon passes through the gap, and the slips reunite behind it before attaching to the sides of the middle phalanx.

The muscle flexes the proximal interphalangeal joints of the four fingers, and with further pull the knuckle joints and the wrist. Each finger part can act fairly independently. It is innervated by the median nerve, which branches to it in the upper forearm, and its blood comes from the ulnar artery with help from the radial artery.

The median nerve and the ulnar artery pass behind the arch between the two heads and then run down under the muscle. The nerve can be pinched here. Each tendon is tested by holding the other fingers straight and asking the patient to bend the free finger at its middle joint.

Attachments, action and supply

Origin

Medial epicondyle of the humerus by the common flexor tendon, the ulnar collateral ligament of the elbow and the medial border of the coronoid process.

Insertion

With the radial head, by four split tendons into the sides of the middle phalanges of the index, middle, ring and little fingers.

Action

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

Nerve supply

Median nerve (C8, T1).

Blood supply

Ulnar artery, with branches from the radial artery.