The forgotten forearms (Anterior compartment)

The forgotten forearms (Anterior compartment)

The lower “arm” is called the forearm. The forearm contains many muscles, including the flexors and extensors of the digits, a flexor of the elbow (brachioradialis), and pronators and supinators that turn the hand to face down or upwards, respectively. In cross-section, the forearm can be divided into two fascial compartments. The posterior compartment contains the extensors of the hands, which are supplied by the radial nerve. The anterior compartment contains the flexors, and is mainly supplied by the median nerve. Let´s focus on this one.

Superficial anterior compartment

Pronator teres pronates the forearm, turning the hand posteriorly. If the elbow is flexed to a right angle, then pronator teres will turn the hand so that the palm faces inferiorly. It is assisted in this action by pronator quadratus.

It also weakly flexes the elbow, or assists in flexion at the elbow when there is strong resistance.

Pronator teres syndrome is one cause of wrist pain. It is a type of neurogenic pain.

  • Patients with the pronator teres syndrome have numbness in median nerve distribution with repetitive pronation/supination of the forearm, not flexion and extension of the elbow.
  • Early fatigue of the forearm muscles is seen with repetitive stressful motion, especially pronation.
  • EMG may show only mildly reduced conduction velocities.
  • despite their anatomic proximity, patients with pronator teres syndrome do not have a higher incidence of AIN syndrome.

Pronator teres

Origin:

  1. Humeral head:

A. upper portion of medial epicondyle via the CFT (common flexor tendon).

B. medial brachial intermuscular septum.

2. Ulnar head – coronoid process of ulna.

3. Antebrachial fascia.

Insertion:

Lateral aspect of radius at the middle of the shaft (pronator tuberosity).

Flexor carpi radialis is a muscle of the human forearm that acts to flex and (radial) abduct the hand. It is a superficial muscle that becomes very visible as the wrist comes into flexion. The flexor carpi radialis muscle is located close to the palm side of the arm, which allows it to bend the wrist on its side. This helps to reduce the angle between the forearm and the thumb. The wrist remains straight and does not extend or bend backwards.

Flexor carpi radialis

Origin:

  1. Medial epicondyle via the CFT (common flexor tendon).
  2. Antebrachial fascia.

Insertion:

Base of the 2nd and sometimes 3rd metacarpals

Palmaris longus serves no apparent function in humans.For this reason, it is actually very popular with reconstructive surgeons because they can “harvest” the tissue or the tendon and use it to rebuild other useful muscles. What is even more interesting is the fact that the muscle is completely or partially absent in about 14 percent of the population.

Palmaris longus

 Origin:

  1. Medial epicondyle via the CFT (common flexor tendon).
  2. Antebrachial fascia.

Insertion:

  1. Central portion of the flexor retinaculum.
  2. Superficial portion of the palmar aponeurosis.

The flexor carpi ulnaris muscle works in tandem with the extensor carpi ulnaris. These muscles flex the wrist and adduct it (move it laterally in the direction of ulnar).

Flexor carpi ulnaris

Origin:

  1. Humeral head – medial epicondyle via the CFT (common flexor tendon).
  2. Ulnar head:
  • Medial aspect of olecranon.
  • Proximal 3/5 of dorsal ulnar shaft.
  • Antebrachial fascia.

Insertion:

  1. Pisiform & hamate bones (via the pisohamate ligament).
  2. Base of the 5th metacarpal (via the pisometacarpal ligament).

The flexor digitorum superficialis is an extrinsic muscle that allows the four medial fingers of the hand to flex. It flexes the middle phalanges of the fingers at the proximal interphalangeal joints, however under continued action it also flexes the metacarpophalangeal joints and wrist joint. The secondary role of the muscle is to flex the metacarpophalangeal joints. These are located between the proximal phalanges and the metacarpal bones of the palm.

Flexor digitorum superficialis

Origin:

  1. Humeral-ulnar head:
  • Medial epicondyle via the CFT (common flexor tendon).
  • Medial boarder of base of coronoid process of ulna.
  • Medial (ulnar) collateral ligament.
  • Antebrachial fascia.

2. Radial head: oblique line of radius along its upper anterior boarder.

Insertion:

Both sides of the base of each middle phalanx of the 4 fingers

Deep anterior compartment

The pronator quadratus is a muscle that is near the lower part of the radius. It is the only muscle attached only to the radius at one end and the ulna at the other.

Its function is to rotate the forearm and keep the proper distance and rotation between the ulna and radius. It is also used to turn the wrist and palm of the hand. When pronator quadratus contracts, it pulls the lateral side of the radius towards the ulna, thus pronating the hand. Its deep fibers serve to keep the two bones in the forearm bound together.

Pronator quadratus

Origin:

Distal 1/4 anteriomedial surface of ulna.

Insertion:

Distal 1/4 anteriolateral surface of radius.

The flexor digitorum profundus belly is located in the forearm. However, it is considered a hand muscle because it is primarily used for hand functionality. The muscle’s long tendons extend over the wrist and the metacarpals of the hand.

It is a flexor of the wrist and helps flex the fingers.

Flexor digitorum profundus 2

Origin:

  1. Anterior & medial surface of upper 3/4 ulna.
  2. Adjacent interosseous membrane.

Insertion:

Distal phalanx of medial 4 digits (through FDS tunnel).

The flexor pollicis longus muscle is located in the lower half of the arm, from the elbow down. It is an anatomical part that is unique to humans.

The flexor pollicis longus is a flexor of the phalanges of the thumb; when the thumb is fixed, it assists by flexing the wrist.

Flexor pollicis longus

Origin:

  1. Middle anterior surface of the radius.
  2. Interosseous membrane.
  3. (may also originate from lateral boarder of coronoid process.
  4. or medial epicondyle).

Insertion:

Palmar aspect of base of the distal phalanx of thumb (deep to flexor retinaculum).

5 thoughts on “The forgotten forearms (Anterior compartment)”

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