Comprehensive Guide to Forearm Myology

Anatomy of the Anterior Region of the Forearm: Flexors and Pronators

The anterior region of the forearm consists of muscles primarily responsible for the flexion of the wrist and fingers, as well as the pronation of the forearm. These muscles are generally organized into layers. The superficial and intermediate layers include several key muscles that mostly originate from the medial epicondyle of the humerus.

The Pronator Teres (Pronador redondo) is a key muscle for forearm rotation. Its origin is dual, arising from the medial epicondyle of the humerus and the coronoid process of the ulna. It inserts into the lateral surface of the middle third ($1/3$) of the radius.

The Flexor Carpi Radialis (Flexor radial del carpo) serves to flex and abduct the wrist. It originates from the medial epicondyle of the humerus and inserts into the base of the $2^{nd}$ and $3^{rd}$ metacarpals.

The Palmaris Longus (Palmar largo) is a slender muscle that originates at the medial epicondyle of the humerus. Its insertion point is the palmar aponeurosis. This muscle is sometimes absent in a percentage of the population.

The Flexor Carpi Ulnaris (Flexor cubital del carpo) is responsible for wrist flexion and adduction. It has a broad origin including the medial epicondyle of the humerus and the olecranon of the ulna. It inserts into the pisiform bone, the hamate (ganchoso), and the base of the $5^{th}$ metacarpal.

The Flexor Digitorum Superficialis (Flexor superficial de los dedos) is an intermediate muscle. It originates from the medial epicondyle, the oblique line of the radius, and the coronoid process. It inserts into the middle phalanges of the fingers ranging from the $2^{nd}$ to the $5^{th}$ digit.

Deep Layer of the Anterior Forearm

The deep plane of the anterior forearm consists of three specific muscles that provide fine motor control and power for the digits and forearm positioning.

The Flexor Digitorum Profundus (Flexor profundo de los dedos) originates from the anterior and medial surfaces of the ulna and the interosseous membrane. Its insertion reaches the distal phalanges of the $2^{nd}$ to the $5^{th}$ fingers. It is the primary muscle for flexing the distal interphalangeal joints.

The Flexor Pollicis Longus (Flexor largo del pulgar) originates from the anterior surface of the radius and the interosseous membrane. It inserts specifically into the distal phalanx of the thumb (pulgar).

The Pronator Quadratus (Pronador cuadrado) is a deep, rectangular muscle located near the wrist. It originates from the distal third ($1/3$) of the anterior surface of the ulna and inserts into the distal third ($1/3$) of the anterior surface of the radius.

Anatomy of the Posterior Region of the Forearm: Extensors and Supinators

The posterior compartment of the forearm contains muscles that extend the wrist and fingers and supinate the forearm. These are largely divided into superficial and deep layers.

The Brachioradialis (Braquiorradial) is a unique muscle that acts as a flexor of the elbow despite its posterior location. It originates from the lateral supracondylar ridge of the humerus and inserts into the styloid process of the radius.

The Extensor Carpi Radialis Longus (Extensor radial largo del carpo) originates from the lateral supracondylar ridge of the humerus and inserts into the base of the $2^{nd}$ metacarpal.

The Extensor Carpi Radialis Brevis (Extensor radial corto del carpo) originates from the lateral epicondyle of the humerus and inserts into the base of the $3^{rd}$ metacarpal.

The Extensor Digitorum (Extensor de los dedos) is the primary extensor of the fingers. It originates from the lateral epicondyle of the humerus and inserts into the extensor expansions of the $2^{nd}$ through the $5^{th}$ fingers.

The Extensor Digiti Minimi (Extensor del meñique) provides independent extension for the little finger. It originates from the lateral epicondyle of the humerus and inserts into the extensor expansion of the $5^{th}$ finger.

The Extensor Carpi Ulnaris (Extensor cubital del carpo) originates from the lateral epicondyle of the humerus and the posterior border of the ulna. Its insertion is at the base of the $5^{th}$ metacarpal.

The Anconeus (Ancóneo) is a small muscle that assists in elbow extension. It originates from the lateral epicondyle of the humerus and inserts into the olecranon and the posterior surface of the ulna.

Deep Layer of the Posterior Forearm

The deep plane of the posterior forearm contains five muscles primarily involved with the thumb, the index finger, and forearm supination.

The Supinator (Supinador) originates from multiple points: the lateral epicondyle of the humerus, the radial collateral ligament, and the supinator crest of the ulna. It inserts into the proximal part of the lateral surface of the radius.

The Abductor Pollicis Longus (Abductor largo del pulgar) originates from the posterior surfaces of the ulna, the radius, and the interosseous membrane. It inserts into the base of the $1^{st}$ metacarpal.

The Extensor Pollicis Brevis (Extensor corto del pulgar) originates from the posterior surface of the radius and the interosseous membrane. Its insertion is the base of the proximal phalanx of the thumb.

The Extensor Pollicis Longus (Extensor largo del pulgar) originates from the posterior surface of the ulna and the interosseous membrane, inserting into the base of the distal phalanx of the thumb.

The Extensor Indicis (Extensor del índice) provides independent extension for the index finger. It originates from the posterior surface of the ulna and the interosseous membrane, inserting into the extensor expansion of the $2^{nd}$ finger.