Flexor Digitorum Superficialis Muscle Anatomy

The Flexor Digitorum Superficialis Muscle is the largest superficial muscle in the forearm that originates from the common flexor tendon and cross the elbow and wrist to insert onto middle phalanges of fingers.

The Flexor Digitorum Superficialis actually forms an intermediate layer between the superficial and deep groups of forearm muscles. The median nerve and ulnar artery enter the forearm by passing between its humero-ulnar and radial heads.

Near the wrist, the FDS gives rise to four tendons, which pass deep to the flexor retinaculum through the carpal tunnel to the fingers. The four tendons are enclosed (along with the four tendons of the flexor digitorum profundus) in a synovial common flexor sheath.

The FDS flexes the middle phalanges of the medial four fingers at the proximal interphalangeal joints. In continued action, the FDS also flexes the proximal phalanges at the metacarpophalangeal joints and the wrist joint. The FDS is capable of flexing each finger it serves independently.

See Also: Forearm Muscles Anatomy

Flexor Digitorum Superficialis Muscle Anatomy

Origin

The FDS has a dual origin:

• Humeroulnar head: It arises from the medial epicondyle of the humerus, the ulnar collateral ligament, and the coronoid process of the ulna.
• Radial head: It originates from the superior half of the anterior border of the radius.

Insertion

The muscle extends distally, giving rise to four tendons near the wrist. These tendons pass deep to the flexor retinaculum, through the carpal tunnel, and insert into the bodies of the middle phalanges of the four fingers (digits 2-5).

Actions

The primary function of the FDS is to flex the middle phalanges at the proximal interphalangeal (PIP) joints of the medial four fingers. Additionally, it plays a significant role in:

• Flexing the proximal phalanges at the metacarpophalangeal (MCP) joints.
• Contributing to wrist flexion.

Remarkably, the FDS is capable of flexing each finger it serves independently, a unique feature among the flexor muscles of the forearm.

Innervation

The FDS is innervated by the median nerve, specifically the C7, C8, and T1 nerve roots. This innervation is crucial for the muscle’s function and coordination during finger and wrist movements.

See Also: Hand Nerves and Blood Supply

Arterial Supply

The primary blood supply to the FDS is provided by the ulnar artery, ensuring adequate oxygenation and nutrient delivery essential for muscle performance and endurance.

Clinical Significance

To test the flexor digitorum superficialis, one finger is flexed at the proximal interphalangeal joint against resistance and the other three fingers are held in an extended position to inactivate the flexor digitorum profundus.

References & More

1. Clinically Oriented Anatomy – 8th Edition
2. Okafor L, Varacallo M. Anatomy, Shoulder and Upper Limb, Hand Flexor Digitorum Superficialis Muscle. [Updated 2022 Oct 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: Pubmed