Last Updated on May 27, 2025
Forearm muscles are responsible for rotational movements of the forearm [pronation and supination], movements of the wrist and hand. [Just to reemphasize, the flexion-extension movements of the elbow are by muscles of the arm]. The forearm is also called the antebrachium.
The forearm or antebrachium is the region of the upper limb between the elbow and the wrist. It plays a crucial role in nearly every movement of the upper limb. Its muscles control the wrist, fingers, and the rotational actions of pronation and supination, making activities like writing, gripping, and lifting possible.
Structurally, the forearm is supported by two long bones, the radius and ulna, and contains twenty muscles divided into three main compartments:
Understanding the anatomy and function of the forearm muscles is essential to understanding how the hand and arm work together in health and injury.
A clear grasp of these muscles is fundamental for diagnosing and treating conditions such as fractures, tendon injuries, nerve compressions, and overuse syndromes.
This article provides a comprehensive overview of forearm muscle anatomy, their compartmental organization, key actions, nerve supply, and major clinical correlations.
Compartments of the Forearm
The fascia of the forearm or the antebrachial fascia is a continuation of the brachial fascia. It surrounds the musculature of the forearm and divides it into three compartments
- Mobile wad
- Volar compartment
- Dorsal compartments.
Mobile Wad Compartment (Radial Group of Forearm Muscles)
The mobile wad compartment is composed of two wrist extensors and a forearm flexor. These are
- Extensor carpi radialis brevis
- Extensor carpi radialis longus
- Brachioradialis
No major neurovascular structures are located within this compartment.
Volar or Anterior Compartment of Forearm
The volar compartment contains the flexor and pronator muscles. This compartment is divided into superficial and deep parts.
The deep volar compartment contains the flexor digitorum profundus and the flexor pollicis longus muscles.
The superficial group contains the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and flexor digitorum superficialis. Flexor digitorum superficialis is sometimes considered an intermediate volar compartment.
Volar compartment contains the median nerve (and its branch, the anterior interosseous nerve), the ulnar nerve, and the deep branch of the radial nerve. It also has radial and ulnar arteries.
Dorsal Compartment of Forearm
The dorsal compartment contains the wrist and finger extensors. It is also divided into deep and superficial muscle groups.
The deep compartment contains
- Supinator
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus,
- Ex tensor indices
The superficial compartment contains
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
- The anconeus muscle is located in this compartment.
The dorsal compartment contains the posterior interosseous nerve, which is a branch of the radial nerve, and the posterior interosseous artery.
Forearm Muscles of the Mobile Wad Compartment
The mobile wad compartment is also called the radial compartment or lateral compartment. Extensor carpi radialis brevis, extensor carpi radialis longus, and brachioradialis constitute this compartment. Together, these three muscles are called the mobile wad of Henry as they can be easily moved aside during surgery.
Brachioradialis
Origin: From the proximal aspect of the lateral supracondylar ridge of the humerus.
Insertion: Distal radius just before the radial styloid process.
Nerve Supply: Radial nerve (C5-C6)
Action: Elbow flexion, especially in the semipronated forearm.
Extensor Carpi Radialis Longus
Origin: Multiple origins
- Lateral supracondylar ridge of the humerus
- Lateral intermuscular septum
- Lateral epicondyle of the humerus
Insertion: The fibers unite to form a flat tendon at the upper third of the arm, which moves down along the lateral border of the radius (lies between the brachioradialis and the extensor carpi radialis brevis). It is inserted on the dorsoradial surface of the base of the second metacarpal.
Nerve Supply: Radial nerve, direct branch [C6,7]
Action: Extensor of the wrist joint. Also causes radial abduction of the wrist.
Extensor Carpi Radialis Brevis
Origin: Multiple origins from
- Lateral epicondyle of the humerus by the common extensor tendon
- From the radial collateral ligament of the elbow joint
- From the aponeurosis, which covers its surface
- Intermuscular septa between it and the adjacent muscles
Insertion: Its flat tendon courses medial to ECRL and inserts into the dorsoradial surface of the third metacarpal bone. Some fibers also go to the dorsomedial surface of the second metacarpal bone.
Nerve Supply: The radial nerve, deep branch (C7-C8)
Action
Extension and abduction of the wrist just similar to extensor carpi radialis longus.
Muscles of the Forearm in the Anterior Compartment
Anterior or volar compartment forearm muscles are responsible for wrist flexion, finger flexion, and forearm pronation.
Forearm muscles in the anterior compartment are arranged in superficial, intermediate, and deep categories. The respective muscles in these compartments are
Overview Table: Anterior Forearm Muscles
| Layer | Muscle Name | Primary Action | Nerve Supply |
|---|---|---|---|
| Superficial | Flexor carpi ulnaris | Wrist flexion, adduction | Ulnar |
| Superficial | Palmaris longus | Weak wrist flexion | Median |
| Superficial | Flexor carpi radialis | Wrist flexion, abduction | Median |
| Superficial | Pronator teres | Pronation, weak elbow flexion | Median |
| Intermediate | Flexor digitorum superficialis | Flexes PIP joints, wrist flexion | Median |
| Deep | Flexor digitorum profundus | Flexes DIP joints, wrist flexion | Median (lateral), Ulnar (medial) |
| Deep | Flexor pollicis longus | Flexes thumb | Median (anterior interosseous) |
| Deep | Pronator quadratus | Pronation | Median (anterior interosseous) |
The muscles of the forearm are arranged in superficial, middle, and deep compartments
The respective muscles in these compartments are
- Superficial compartment [4 muscles]
- Flexor carpi ulnaris
- Palmaris longus
- Flexor carpi radialis
- Pronator teres
- Intermediate Compartment [1 muscle]
- Flexor digitorum superficialis
- Deep compartment [3 muscles]
- Flexor digitorum profundus
- Flexor pollicis longus
- Pronator quadratus
All these muscles originate from the common flexor origin from the medial epicondyle of the humerus.
Flexor Carpi Ulnaris
Origin: From two heads connected by a tendinous arch. Beneath this arch, the ulnar nerve and artery pass.
- The humeral head – Via the common flexor tendon from the medial epicondyle
- The ulnar head – Medial margin of the olecranon of the ulna and upper two-thirds of the dorsal border of the ulna by an aponeurosis.
Insertion: It inserts into
- Pisiform bone
- Hamate bone by the pisohamate ligament
- Fifth metacarpal bone by the pisometacarpal ligament.
Flexor carpi ulnaris is the most medially visible tendon in the forearm.
Action: Flexion and adduction of the wrist joint.
Nerve supply: The ulnar nerve [C8, T1]
Palmaris Longus
Palmaris longus is absent in about 14 percent of people. The distal palmaris longus tendon, if present, can be seen by opposing the fourth finger and thumb and flexing the wrist.
Origin: Common flexor tendon, the adjacent intermuscular septa and from the antebrachial fascia.
The spindle-shaped muscle lies on the medial side of the flexor carpi radialis.
Insertion: The thin, flat tendon passes above the flexor retinaculum of the wrist and inserts on the central part of the flexor retinaculum. It may also send a tendinous slip to the thenar muscles.
Nerve supply: The median nerve (C7, C8)
Action: Weak flexor of the wrist. May assist in thumb abduction movements
Flexor Carpi Radialis
Origin: Common flexor tendon.
Insertion: The muscle runs lateral to the flexor digitorum superficialis and inserts on the anterior aspect of the base of the second metacarpal. Two small slips are sent to the third metacarpal and the tuberosity of the trapezium.
Nerve Supply: Median nerve (C6, C7)
Pronator Teres
The pronator teres forms the medial border of the cubital fossa.
Origin: It arises by two heads
- Humeral head (Larger and superficial)
- Medial supracondylar ridge immediately proximal to the medial epicondyle of the humerus
- Common flexor tendon
- Ulnar head (Thin fasciculus)
- From the medial side of the coronoid process of the ulna
Insertion: The ulnar head joins the humeral head at an acute angle. The median nerve enters the forearm between the two heads. The ulnar head separates ulnar artery from the median nerve.
The muscle passes obliquely across the forearm and inserts on the rough impression on the radial shaft on the lateral side about the middle, just distal to the insertion of the supinator.
Nerve supply: Median nerve (C6, C7)
Action: Pronates the forearm. The pronator teres muscle is aided by the pronator quadratus. Pronator teres also acts as a weak flexor of the elbow.
Flexor Digitorum Superficialis
This muscle belongs to the intermediate volar compartment of the forearm and is sole muscle of the compartment. Some authors prefer to club it with superficial muscles.
Origin: Flexor digitorum superficialis has two origins.
- Humeroulnar
- Medial epicondyle of the humerus (common flexor tendon)
- Coronoid process of the ulna.
- Ulnar collateral ligament of elbow
- Radial
- from the oblique line on the radial shaft
Insertion: This muscle lies medial to the flexor carpi radialis in the forearm. Near the wrist, this gives off four long tendons that travel under the flexor retinaculum along with tendons of flexor digitorum profundus and are enclosed by the common flexor sheath
The tendons of flexor digitorum superficialis are attached to the anterior margins on the bases of the middle phalanges of the four fingers.
At the insertion, the tendon splits to let the tendons of flexor digitorum profundus pass. This split is called Camper’s Chiasm.
Nerve Supply: Median nerve (C7, C8, T1)
Action: Flexion of the middle phalanges of the four fingers at the proximal interphalangeal joints. However, with continued action, it also flexes the metacarpophalangeal joints.
It also acts as a weak wrist flexor.
The deep compartment of the anterior forearm contains three muscles- flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.
Flexor Digitorum Profundus
Flexor digitorum profundus, flexor pollicis longus, and pronator quadratus are deep muscles lying in the deep anterior compartment of the forearm.
Origin: The upper three–fourths of the anterior and medial surface of the ulna along with the interosseous membrane and deep fascia of the forearm
Insertion: Flexor digitorum profundus lies deep to the flexor digitorum superficialis muscle and ends in four tendons, one to each of the second to fifth fingers. Each slip inserts on the base of the distal phalanx on the palmar aspect after passing through Camper’s chiasm as described above.
Nerve supply:
- Dual nerve supply
- Ulnar nerve supplies the medial part of the muscle that acts on the ring and little finger [C8, T1]
- The median nerve supplies the lateral half of the muscle acting on the index and ring finger.[C8, T1]
Action: Flexes the distal interphalangeal joints of the fingers. It also causes flexion of the metacarpophalangeal joints and the wrist.
Flexor Pollicis Longus
Origin: The anterior surface of the radius from immediately below the radial tuberosity and oblique line, along with the surrounding interosseous membrane
Sometimes, slips from the coronoid process and medial epicondyle may also contribute.
Insertion: This muscle lies laterally to the flexor digitorum profundus. It is inserted into the base of the distal phalanx of the thumb on the palmar aspect.
Pronator Quadratus
It is a square-shaped muscle that lies deep to the tendons of the flexor digitorum profundus and flexor pollicis longus.
Origin: Anterior distal aspect of the distal diaphysis of the ulna. The fibers run perpendicular to the forearm.
Insertion:
- Superficial fibers insert into the anterior distal diaphysis of the radius and the anterior metaphysis.
- Deep fibers insert proximal to the ulnar notch.
Nerve Supply: Median nerve (C7, C8) via anterior interosseous branch.
Action: Pronates the forearm
Forearm Muscles in the Posterior Compartment
Forearm muscles in the posterior compartment, in general, function to extend the wrist and the fingers.
Some of the muscles also function to supinate the forearm. All of these muscles are innervated by the radial nerve.
The muscles of the forearm in the posterior compartment can be clubbed into two layers – superficial and deep.
The layers are separated by a fascia.
At the wrist, the extensor forearm muscles are compartmentalized in six osteofascial compartments [see later section- Arrangement of Forearm Muscles and Tendons in the Wrist]
The superficial layer of the posterior forearm contains four muscles.
- Extensor digitorum
- Extensor carpi ulnaris
- Extensor digiti minimi
- Anconeus
There are five deep muscles in the deep compartment of the forearm.
- Supinator
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
- Extensor indicis
Extensor Digitorum
The extensor digitorum muscle is the main extensor of the fingers.
Origin:
- The lateral epicondyle via the common extensor tendon on the lateral epicondyle of the humerus
- Intermuscular septa between it and the adjacent muscles
- Antebrachial fascia or fascia of the forearm
Insertion: Near the wrist, it divides into four tendons, which together with that of the extensor indicis pass through the extensor tendon compartment.
After crossing the metacarpophalangeal joint, it forms a broad aponeurosis called dorsal digital expansion[reinforced by interossei and lumbricals] that covers the surface of the first phalanx.
At the proximal interphalangeal joint, the aponeurosis divides into three slips.
The middle is inserted into the base of the middle phalanx. The two lateral slips travel further to insert into the dorsal surface of the last phalanx.
Fasciculi are given from tendons at the metacarpophalangeal and interphalangeal joints, which act as dorsal ligaments.
Nerve Supply: Radial nerve [deep branch]
Action: Extention of fingers at the metacarpophalangeal and interphalangeal joints. It also contributes to wrist extension.
Extensor Digiti Minimi
The extensor digiti minimi is a slender extensor muscle for the little finger. In some people, it is fused with the extensor digitorum.
Origin: Common extensor origin and lies medially to the extensor digitorum.
Insertion: The tendon passes posterior to the distal radioulnar joint and divides into two slips that join the extensor digitorum tendon.
All three slips attach to the dorsal digital expansion of the little finger.
Nerve Supply: Radial nerve, deep branch (C7, C8)
Action: It causes extension of the little finger. It also contributes to the extension at the wrist.
Extensor Carpi Ulnaris
Origin: Lateral epicondyle of the humerus
Insertion: It attaches to the base of the fifth metacarpal.
Nerve Supply: Radial nerve, deep branch (C7, C8).
Action: Extension and adduction of the wrist.
Anconeus
The anconeus is present on the medial aspect of the extensor region near the elbow and is often indistinguishable from the triceps muscle because the fibers blend with the triceps muscle.
Origin: The lateral epicondyle.
Insertion: Posterior and lateral part of the olecranon.
Nerve Supply: Radial nerve (C6-C8)
Action: The Anconeus muscle extends and stabilizes the elbow joint. It also abducts the ulna during pronation of the forearm.
Supinator
This belongs to a deep dorsal compartment along with four other muscles
Origin: Originates from two heads [the deep branch of the radial nerve passes between the two heads]
- Lateral epicondyle of the humerus
- Deep muscular head
- The posterior surface of the ulna [supinator crest]
- Radial collateral ligament
- Annular radial ligament
Insertion:
- Superficial fibers – the lateral edge of the radial tuberosity and the oblique line of the radius.
- The deep fibers form a sling-like fasciculus that encircles the neck of the radius above the tuberosity and inserts into
- The posteromedial surface of the radial tuberosity of its medial surface
- Posterior dorsal and lateral surfaces of the radial shaft in the middle between the oblique line and the head
Nerve Supply: Deep branch of radius (C7, C8)
[After it leaves the supinator, the deep branch of the radial nerve is also called the posterior interosseous nerve].
Action: Supinates the forearm
Abductor Pollicis Longus
Abductor pollicis longus is an abductor muscle that is situated immediately distal to the supinator muscle in the deep dorsal compartment. Distally, its tendon forms the anterior border of the snuffbox.
[Another abductor of the thumb, abductor pollicis brevis is a thenar muscle]
Origin: The posterior surface of the shaft below the insertion of the anconeus, interosseous membrane, and the middle third of the posterior surface of the radius.
Insertion: The muscle passes downward and laterally to end in a tendon that runs along the groove on the lateral side of the lower end of the radius the extensor pollicis brevis tendon. It is inserted in two parts
- Distal superficial part- radial side of the base of the first metacarpal bone
- Deep part- trapezium, along with its joint capsule and ligaments, some slips to abductor pollicis brevis and opponens as well
Nerve Supply: Radial nerve (posterior interosseous branch). – (C7, C8)
Action: Abducts the thumb.
Extensor Pollicis Brevis
A deep extensor muscle that lies medial and deep to the abductor pollicis longus.
Origin: Posterior surface of the radius, interosseous membrane, and the ulna distal to the abductor pollicis longus.
Insertion: Base of the proximal phalanx of the thumb.
Action: Extends the metacarpophalangeal joint and carpometacarpal joints of the thumb.
Nerve Supply: Radial nerve, posterior interosseous branch (C7, C8)
Extensor Pollicis Longus
This muscle is also in the deep dorsal compartment of the forearm. Its tendon forms the medial border of the anatomical snuffbox in the wrist.
Origin: Posterior surface of the ulna and interosseous membrane.
Insertion:
It reaches the narrow, oblique groove on the back of the lower end of the radius, where it turns towards the thumb using Lister’s tubercle on the distal end of the radius as a pulley.
It attaches to the distal phalanx of the thumb.
Nerve Supply: Radial nerve, posterior interosseous branch (C7,C8).
Action: Extends all joints [carpometacarpal, metacarpophalangeal, and interphalangeal] of the thumb.
Extensor Indicis Proprius
This, another deep compartment muscle, is an independent extensor muscle of the index finger.
Origin: Posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus.
Insertion: It runs through the fourth tendon compartment in the wrist together with the extensor digitorum. It attaches to the extensor hood of the index finger.
Nerve Supply: Radial nerve, posterior interosseous branch (C7, C8).
Action: Extends the index finger.
Quick Summary of Posterior Compartment Muscles
| Layer | Muscle Name | Primary Action | Nerve Supply |
|---|---|---|---|
| Superficial | Brachioradialis | Flexes elbow (paradoxical muscle) | Radial |
| Extensor carpi radialis longus | Wrist extension, abduction | Radial | |
| Extensor carpi radialis brevis | Wrist extension, abduction | Radial (deep) | |
| Extensor digitorum | Extends fingers, wrist | Radial (deep) | |
| Extensor digiti minimi | Extends little finger | Radial (deep) | |
| Extensor carpi ulnaris | Wrist extension, adduction | Radial (deep) | |
| Anconeus | Extends and stabilizes elbow | Radial | |
| Deep | Supinator | Supination of forearm | Radial (deep) |
| Abductor pollicis longus | Abducts thumb | Radial (post. interosseous) | |
| Extensor pollicis brevis | Extends thumb (MCP joint) | Radial (post. interosseous) | |
| Extensor pollicis longus | Extends thumb (all joints) | Radial (post. interosseous) | |
| Extensor indicis | Extends index finger | Radial (post. interosseous) |
Arrangement of Forearm Muscles and Tendons in the Wrist
Here is a cross-section of the wrist showing the arrangement of tendons in the wrist and their relations to other structures.
On the extensor side, the retinaculum sends down septa which are attached to the longitudinal ridges on the posterior surface of the lower end of the radius. This creates six osteofascial compartments as shown in the cross-section above.
The structures passing through each compartment, from lateral to medial side, are listed below.
- Compartment I: Abductor pollicis longus, Extensor pollicis brevis
- Compartment II: Extensor carpi radialis longus, Extensor carpi radialis brevis
- Compartment III: Extensor pollicis longus
- Compartment IV: Extensor digitorum, Extensor indicis, Posterior interosseous nerve, and anterior interosseous artery are also present in this compartment.
- Compartment V: Extensor digiti minimi
- Compartment VI: Extensor carpi ulnaris
A synovial sheath lines each compartment.
Flexor tendons are more voluminous and centrally placed. On the flexor side, the arrangement in the proximal wrist is from radial to ulnar side is
- Flexor carpi radialis
- Flexor pollicis longus
- Palmaris longus (subcutaneous or superficial)
- Flexor digitorum superficialis (superficial) and flexor digitorum profundus (deep)
- Flexor carpii ulnaris
Clinical Significance of Forearm Muscles
Anatomical Landmarks
Anatomical landmarks are used in locating the lesion or structure during clinical examination or surgery. Important landmarks formed by forearm muscles and/or their tendons are
- Flexor digitorum superficialis is important during surgery. The median nerve and ulnar artery pass between its two heads and then travel posteriorly.
- In the distal forearm, the radial artery and nerve are sandwiched between the brachioradialis and the deep flexor muscles.
- Anteriorly, proximal to the wrist, the flexor carpi radialis is the most lateral tendon visible when the wrist is brought into flexion.
- Abductor pollicis longus forms the lateral border of the anatomical snuffbox.
Common Clinical Conditions
Golfer’s Elbow and Tennis Elbow
These are commonly used names for medial epicondylitis and lateral epicondylitis of the humerus, respectively. As we know medial epicondyle is the origin of many flexors, and the lateral epicondyle is the origin site for extensors.
Overuse of the respective muscles is one of the important causes of these conditions.
Cubital tunnel syndrome
Cubital tunnel syndrome may be caused by the aponeurosis of the two heads of the flexor carpi ulnaris muscle compressing the nerve. Numbness, tingling, and weakness in the ulnar hand.
Pronator Teres syndrome
Pronator teres syndrome is a type of neurogenic pain caused by compression of the median nerve by the pronator teres muscle in the forearm.
Compartment Syndrome
Compartment syndrome is a serious condition that can develop when increased pressure within the tightly bound muscle compartments. It is most commonly seen in the leg and forearm.
It is most commonly triggered by trauma such as fractures, crush injuries, or reperfusion after vascular compromise, it can affect any of the forearm’s compartments.
Early signs include severe pain disproportionate to the injury, pain on passive stretch of fingers, tense swelling, and neurological deficits. It is a surgical emergency that threatens the viability of the tissues affected.
Learn more about Compartment syndrome
Tendon transfers
In various tendon injuries of the limb or paralytic disorders resulting in loss of movements, tendon transfer surgeries using expendable working tendons are conducted to provide the maximum possible movement outcome.
Palmaris longus is completely expendable and is often used in various tendon transfers or as a tendon graft.
Tendons for transfer are decided on an individual basis, depending on the tendons available and the type of movement lost.
Summary
The forearm muscles are intricately organized into anterior (flexor-pronator) and posterior (extensor-supinator) compartments, each with distinct layers, functions, and clinical relevance. Their primary roles include enabling fine wrist, hand, and finger movements as well as forearm rotation (pronation and supination).
Understanding the detailed anatomy—including compartmentalization, nerve supply, and arrangement at the wrist—forms the basis for accurate clinical assessment, diagnosis, and management of common conditions such as epicondylitis, nerve entrapments, and traumatic injuries.
Knowledge of muscle landmarks and tendon pathways is essential for surgical planning, targeted injections, and interpreting physical examination findings. The expendable nature of certain muscles (like palmaris longus) also underpins reconstructive surgical techniques, especially tendon transfers.
References
- Standring, S., & Gray, H. (2021). The muscles and fasciae of the forearm. In Gray’s Anatomy: The Anatomical Basis of Clinical Practice (42nd ed., pp. 869–882). Elsevier.
- Mitchell B, Whited L. Anatomy, Shoulder and Upper Limb, Forearm Muscles. [Updated 2023 Jun 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536975/
- Klausmeyer MA, Mudgal C. Exposure of the forearm and distal radius. Hand Clin. 2014 Nov;30(4):427-33, v. [PubMed]
