Flexor Digitorum Profundus

Origin	Proximal 3/4 of medial and anterior surfaces of ulna and interosseous membrane
Insertion	Base of the distal phalanx of digits 2 – 5
Action	Flexes distal phalanges at distal interphalangeal joints of medial four digits; assists with flexion of hand
Innervation	Medial part: ulnar nerve (C8 and T1); Lateral part: anterior interosseous branch of median nerve (C8 and T1) (C8, T1)
Arterial Supply	Ulnar and anterior interosseous arteries

Overview

Flexor digitorum profundus is a muscle in the forearm that plays an essential role in finger flexion. It is one of the deep muscles of the anterior compartment of the forearm and is responsible for flexing the distal interphalangeal (DIP) joint of the fingers.

The flexor digitorum profundus muscle originates from the upper three-quarters of the anterior and medial surfaces of the ulna, the interosseous membrane, and the deep fascia of the forearm. The muscle fibers then travel through the carpal tunnel and divide into four tendons, which pass through the palm of the hand and attach to the distal phalanges of the four fingers (index, middle, ring, and little fingers).

Relations

The flexor digitorum profundus muscle is surrounded by other muscles and structures in the forearm, wrist, and hand. Here are some of its relations:

1. Superficial muscles: The flexor digitorum profundus muscle lies deep to the flexor carpi ulnaris, flexor carpi radialis, and pronator teres muscles in the forearm.
2. Other deep muscles: The flexor digitorum profundus muscle is adjacent to the flexor pollicis longus and pronator quadratus muscles in the distal forearm.
3. Tendons: The four tendons of the flexor digitorum profundus muscle pass through the carpal tunnel along with the median nerve and the flexor digitorum superficialis tendons. In the palm of the hand, the flexor digitorum profundus tendons run along with the lumbrical muscles and the flexor digitorum superficialis tendons.
4. Nerves: The flexor digitorum profundus muscle is innervated by the anterior interosseous nerve (a branch of the median nerve) in the anterior compartment of the forearm and the ulnar nerve in the palm of the hand.
5. Blood vessels: The blood supply to the flexor digitorum profundus muscle comes from the ulnar artery and the anterior interosseous artery.
6. Bones: The flexor digitorum profundus muscle originates from the ulna and the interosseous membrane in the forearm and inserts into the distal phalanges of the four fingers.

Innervation

The flexor digitorum profundus muscle is innervated by two nerves in different parts of the forearm and hand:

1. Anterior interosseous nerve: The anterior interosseous nerve is a branch of the median nerve that arises in the proximal forearm. It runs through the anterior compartment of the forearm alongside the flexor digitorum profundus muscle and innervates it. The anterior interosseous nerve also innervates the flexor pollicis longus and pronator quadratus muscles.
2. Ulnar nerve: The ulnar nerve is a branch of the brachial plexus that arises in the arm and runs through the posterior compartment of the forearm. In the hand, it divides into a deep branch and a superficial branch. The deep branch runs through the hypothenar muscles and the interossei muscles and innervates the medial two lumbrical muscles and the deep muscles of the hand, including the flexor digitorum profundus muscle to the ring and little fingers. The superficial branch innervates the skin on the palmar and dorsal aspects of the hand, as well as the skin on the medial one and a half fingers.

The innervation of the flexor digitorum profundus muscle by both the median and ulnar nerves is important for finger flexion, as it allows for coordinated and precise movement of the fingers.

Blood supply

The blood supply to the flexor digitorum profundus muscle comes from the ulnar artery and the anterior interosseous artery, which are branches of the brachial artery.

1. Ulnar artery: The ulnar artery runs down the forearm and enters the hand through the Guyon’s canal, where it gives off several branches to supply the deep muscles of the hand, including the flexor digitorum profundus muscle.
2. Anterior interosseous artery: The anterior interosseous artery arises from the ulnar artery in the proximal forearm and runs alongside the anterior interosseous nerve through the anterior compartment of the forearm. It supplies the deep muscles of the forearm, including the flexor digitorum profundus muscle.

These arteries provide oxygenated blood and nutrients to the flexor digitorum profundus muscle, which is essential for its proper function. In addition to the ulnar artery and the anterior interosseous artery, the muscle is also supplied by small branches of the radial and interosseous arteries.

Studies

1. Anatomy: Studies have investigated the morphology and variations of the flexor digitorum profundus muscle, including the number and arrangement of its tendons, its attachment sites, and its relationships with other muscles and structures in the forearm and hand.
2. Biomechanics: Studies have examined the role of the flexor digitorum profundus muscle in finger flexion, grip strength, and hand function, as well as its activation patterns and force generation properties during different types of finger movements.
3. Clinical relevance: Studies have explored the clinical significance of the flexor digitorum profundus muscle in various conditions such as tendon injuries, nerve compression syndromes, and congenital anomalies. For example, tendon injuries can lead to impaired finger flexion, while ulnar nerve compression can cause weakness or numbness in the ulnar aspect of the hand and the fifth digit.

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