Muscle of Posterior Compartment of the Forearm

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 8 min read
Patient Tools

Read, save, and share this guide

Use these quick tools to make this medical article easier to read, print, save, or share with a family member.

Patient Mode

Understand this article easily

Switch between simple English and easy Bangla patient notes. This is for education and does not replace a doctor consultation.

Muscle of Posterior Compartment of the Forearm is also known as the extensor compartment since the muscles primarily function to extend the wrist and digits of the hand. The posterior compartment of the forearm contains a superficial and deep muscle group. The superficial group includes...

For severe symptoms, danger signs, pregnancy, child illness, or sudden worsening, seek urgent medical care.

বাংলা রোগী নোট এখনো যোগ করা হয়নি। পোস্ট এডিটরে “RX Bangla Patient Mode” বক্স থেকে সহজ বাংলা সারাংশ যোগ করুন।

এই তথ্য শিক্ষা ও সচেতনতার জন্য। এটি ডাক্তারি পরীক্ষা, রোগ নির্ণয় বা প্রেসক্রিপশনের বিকল্প নয়।

Article Summary

Muscle of Posterior Compartment of the Forearm is also known as the extensor compartment since the muscles primarily function to extend the wrist and digits of the hand. The posterior compartment of the forearm contains a superficial and deep muscle group. The superficial group includes the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, and anconeus. These muscles are relatively subcutaneous as there is...

Key Takeaways

  • This article explains Structure and Function in simple medical language.
  • This article explains Blood Supply and Lymphatics in simple medical language.
  • This article explains Nerves in simple medical language.
  • This article explains Muscles in simple medical language.
Educational health guideWritten for patient understanding and clinical awareness.
Reviewed content workflowUse writer and reviewer profiles for stronger trust.
Emergency safety firstUrgent warning signs are highlighted below.

Seek urgent medical care if you notice

These warning signs are general safety guidance. Local emergency numbers and clinical judgment should always come first.

  • Severe symptoms, breathing difficulty, fainting, confusion, or rapidly worsening illness.
  • New weakness, severe pain, high fever, or symptoms after a serious injury.
  • Any symptom that feels urgent, unusual, or unsafe for the patient.
1

Emergency now

Use emergency care for severe, sudden, rapidly worsening, or life-threatening symptoms.

2

See a doctor

Book a professional medical evaluation if symptoms persist, worsen, recur often, affect daily activities, or occur in a high-risk patient.

3

Learn safely

Use this article to understand possible causes, tests, treatment options, prevention, and questions to ask your clinician.

Muscle of Posterior Compartment of the Forearm is also known as the extensor compartment since the muscles primarily function to extend the wrist and digits of the hand. The posterior compartment of the forearm contains a superficial and deep muscle group. The superficial group includes the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, and anconeus. These muscles are relatively subcutaneous as there is usually not much subcutaneous fat on the dorsal aspect of the forearm. The primary function of these muscles is digit and wrist extension, with the extensor carpi ulnaris assisting in ulnar deviation of the wrist during wrist extension. The deep group contains the supinator, abductor pollicis longus, extensor pollicis brevis, and the extensor pollicis longus. The supinator functions to supinates the forearm. Supination is defined as the radius rotating laterally around its longitudinal axis over the ulna, causing the palm to face anteriorly. The remaining deep muscles function to extend and abduct the thumb. The deep compartment also contains the extensor indices whose tendon lays radial to the extensor digitorium tendon to the index finger, and it assists in index finger extension. Similarly, the tendon of the extensor digiti minimi of the superficial posterior compartment travels ulnar to the extensor digitorium tendon the small finger, and assists in small finger extension.

The muscles found in the posterior compartment primarily function to extend the wrists and digits. The muscles are further broken down into deep and superficial groups. The superficial group includes the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The deep group includes the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicia. The mobile wad consists of three muscles: the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis. The anterior compartment contains muscles that act to flex the wrist and digits. The muscles are separated into deep, intermediate, and superficial groups. The superficial compartment contains the pronator teres, the flexor carpi radialis, and the flexor carpi ulnaris. The intermediate compartment contains the flexor digitorum superficially. The deep compartment of the contains the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. 

Structure and Function

The mobile wad contains three muscles. The brachioradialis originates over the proximal two-thirds of the lateral supracondylar ridge of the humerus, while both extensor carpi radialis longus and extensor carpi radialis brevis originate over the distal lateral supracondylar ridge. The brachioradialis inserts just proximal the radial styloid. The brachioradialis which is the strongest flexor of the forearm. The extensor carpi radialis longus and extensor carpi radialis brevis insert on the second and third metacarpal base respectively. Of note, the mobile wad is occasionally included as part of the posterior compartment.

The anterior compartment is known as the flexor compartment since the muscles primarily function to flex the wrist and digits. The anterior compartment consists of a deep and superficial layer. The superficial compartment contains the pronator teres, the flexor carpi radialis, and the flexor carpi ulnaris. The palmaris longus is also present in the superficial compartment but is often absent in many people. All these muscles originate as part of the common flexor origin at the medial epicondyle. The intermediate compartment contains the flexor digitorum superficialis. The deep compartment of the contains the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The pronator trees and pronator quadratus assist in pronation of the forearm. Pronation is defined as the radius pulling medially along its longitudinal axis over the ulna, causing the palm to face posteriorly. The carpal tunnel consists of nine tendons and the median nerve. It includes four tendons of the flexor digitorum profundus, four tendons of the flexor digitorum superficialis, and one tendon from flexor pollicis longus.

The interosseous membrane of the forearm is a Z shaped fibrous sheet that connects the radius and ulna forming a syndesmosis. The membrane divides the forearm into the anterior and posterior compartments and is the site of attachment for many muscles. Its main function is to transfer forces from the radius, ulna, and humerus. The lateral intermusclar septum is an additional structure that helps delineate the compartments of the forearm.

Blood Supply and Lymphatics

The forearm has a vast vascular network. The brachial artery divides at the elbow giving rise to the ulnar and radial arteries which are located along the ulnar and radial aspects of the anterior forearm compartment. The radial artery supplies the posterolateral forearm and courses lateral to the flexor carpi radialis. The ulnar artery supplies the anteromedial aspect of the forearm and gives rise to the anterior and posterior interosseous arteries which course in the deep anterior and posterior compartments respectively bringing supply to deeper structures of the forearm.

The venous drainage of the arm consists of 3 superficial veins. The dense vascular network found in the forearms drains towards these 3 main veins. The cephalic vein is found on the lateral aspect of the arm. The basilic vein is located on the medial aspect of the arm. The median cubital vein connects the two structures and is commonly found in the antecubital fossa.

The lymphatic drainage of the forearm uses a lymphatic plexus which originates on the distal extremity that flows proximally to superficial lymphatic vessels towards the axillary lymph nodes.

Nerves

Three primary nerves supply the majority of muscles in the forearm. The radial nerve and its branches supply the mobile wad of Henry and the dorsal compartment. The ulnar nerve and median nerve, and their respective branches supply the volar compartment. The radial nerve provides innervation to the anconeus, brachioradialis, and extensor carpi radialis longus. The posterior interosseous nerve, a branch of the radial nerve provides innervation to the rest of the muscles in the dorsal compartment of the forearm. The ulnar nerve provides innervation to the flexor carpi ulnaris and ulnar half of the flexor digitorum profundus. The median nerve provides innervation to the palmaris longus, flexor carpi radialis, pronator teres, and flexor digitorum superficialis. The anterior interosseous nerve, a branch of the median nerves supplies flexor pollicis longus, radial half of the flexor digitorum profundus, and pronator quadratus.

The cutaneous nerves provide the dermatome pattern of the forearm. The lateral aspect is covered by the C5 and C6 nerve roots while the medial side is covered by the C8 and T1 nerve roots. Cutaneous nerves of the forearm include the posterior cutaneous nerve of the arm, lateral cutaneous nerve of the forearm, and medial cutaneous nerve of the forearm.

Muscles

Posterior Compartment

Superficial Muscles

Extensor digitorum communis
  • Origin: lateral epicondyle of humerus
  • Insertion: extensor hood of digits
  • Action: extension of the wrist and extension of the MCP and IP joints of the digits
  • Innervation: posterior interosseous nerve
Extensor digiti minimi
  • Origin: lateral epicondyle of humerus
  • Insertion: extensor hood of 5th digit
  • Action: extension of the wrist and extension of MCP and IP of the 5th digit
  • Innervation: posterior interosseous
Extensor carpi ulnaris
  • Origin: lateral epicondyle of humerus and ulna
  • Insertion: base of 5th metacarpal
  • Action: extension and adduction of the wrist
  • Innervation: posterior interosseous nerve
Anconeus
  • Origin: lateral epicondyle of the humerus
  • Insertion: lateral surface of the olecranon
  • Action: extension of the forearm and stabilization of the elbow joint
  • Innervation: radial nerve

Deep Muscles

Supinator
  • Origin: lateral epicondyle of humerus
  • Insertion: proximal radius
  • Action: supination of the forearm
  • Innervation: posterior interosseous nerve
Abductor pollicis longus
  • Origin: ulna, radius, interosseous membrane
  • Insertion: 1st metacarpal
  • Action: extension of the wrist, abduction of the thumb, and extension of the CMC joint
  • Innervation: posterior interosseous nerve
Extensor pollicis brevis
  • Origin: radius and interosseous membrane
  • Insertion: phalanx of 1st digit
  • Action: extension of the wrist, extension of the thumb and the CMC joint
  • Innervation: posterior interosseous nerve
Extensor pollicis longus
  • Origin: ulna and interosseous membrane
  • Insertion: phalanx of first digit
  • Action: extension of the wrist and extension thumb at IP, MCP, and CMC joints
  • Innervation: posterior interosseous nerve
Extensor indicis
  • Origin: ulna and interosseous membrane
  • Insertion: phalanx of first digit
  • Action: extension of the wrist and extension thumb at IP, MCP, and CMC joints
  • Innervation: posterior interosseous nerve

Anterior Compartment

Superficial Muscles

Pronator teres
  • Origin: 2 heads; medial epicondyle via common flexor tendon and coronoid process
  • Insertion: lateral radius
  • Action: pronation and flexion of forearm
  • Innervation: median nerve
Flexor carpi radialis
  • Origin: medial epicondyle of humerus via common flexor tendon
  • Insertion: base of 2nd metacarpal
  • Action: flexion and abduction of the hand
  • Innervation: median nerve
Flexor carpi ulnaris
  • Origin: medial epicondyle of humerus via common flexor tendon and olecranon
  • Insertion: isoform, hook of hamate, 5th metacarpal
  • Action: flexion and adduction of the wrist
  • Innervation: ulnar nerve
Palmaris longus
  • Origin: medial epicondyle of humerus via common flexor tendon
  • Insertion: palmar aponeurosis and flexor retinaculum
  • Action: flexion of the hand
  • Innervation: median nerve

Intermediate Muscles

Flexor digitorum superficialis
  • Origin: two heads; medial condyle of the humerus and radius
  • Insertion: middle phalanges of digits 2-5
  • Action: flexion of the metacarpophalangeal and proximal interphalangeal joints of digits 2-5
  • Innervation: median nerve

Deep Muscles

Flexor digitorum profundus
  • Origin: ulna and interosseous membrane
  • Insertion: base of phalanges
  • Action: flexion DIP joints of digits
  • Innervation: digits 2-3: median nerve; digits 4-5: ulnar nerve
Flexor pollicis longus
  • Origin: radius and interosseous membrane
  • Insertion: distal phalanx of thumb
  • Action: flexion of the wrist and flexion of the MCP and IP joints of the digits
  • Innervation: median nerve
Pronator quadratus
  • Origin: distal ulna
  • Insertion: distal radius
  • Action: pronation of the forearm
  • Innervation: median nerve

Mobile Wad Muscles

Brachioradialis
  • Origin: lateral supracondylar ridge of humerus and lateral intermuscular septum
  • Insertion: styloid process of the radius
  • Action: flexion of the forearm
  • Innervation: radial nerve

Extensor carpi radialis longus

  • Origin: lateral supracondylar ridge of humerus
  • Insertion: base of 2nd metacarpal
  • Action: extension and abduction of the wrist
  • Innervation: radial nerve
Extensor carpi radialis brevis
  • Origin: lateral epicondyle of humerus
  • Insertion: base of 3rd metacarpal
  • Action: extension and abduction of the wrist
  • Innervation: radial nerve

References

Patient safety assistant

Check your symptom safely

Hi, I am RX Symptom Navigator. I can help you understand what to read next and what warning signs need care.
Warning: Do not use this in emergencies, pregnancy, severe illness, or as a substitute for a doctor. For children or teens, use with a parent/guardian and clinician.
A rural-friendly guide: warning signs, when to see a doctor, related articles, tests to discuss, and OTC safety education.
1 Symptom 2 Severity 3 Safe guidance
First safety question

Is there chest pain, breathing trouble, fainting, confusion, severe bleeding, stroke-like weakness, severe injury, or pregnancy danger sign?

Choose quickly

Browse by body area
Start here: Write or select a symptom. The guide will show warning signs, doctor guidance, diagnostic tests to discuss, OTC safety education, and related RX articles.

Important: This tool is educational only. It cannot diagnose, treat, or replace a doctor. OTC information is not a prescription. In an emergency, contact local emergency services or go to the nearest hospital.

Doctor visit helper

Prepare before seeing a doctor

A simple rural-patient checklist to help you explain symptoms clearly, ask better questions, and avoid unsafe self-treatment.

Safety note: This is not a prescription or diagnosis. For severe symptoms, pregnancy danger signs, children with serious illness, chest pain, breathing difficulty, stroke-like weakness, or major injury, seek urgent care.

Which doctor may help?

Start with a registered doctor or the nearest qualified health center.

What to tell the doctor

  • Write when the problem started and how it changed.
  • Bring old prescriptions, investigation reports, and current medicines.
  • Write allergies, pregnancy status, diabetes, kidney/liver disease, and major past illnesses.
  • Bring one family member if the patient is weak, elderly, confused, or a child.

Questions to ask

  • What is the most likely cause of my symptoms?
  • Which danger signs mean I should go to hospital quickly?
  • Which tests are necessary now, and which can wait?
  • How should I take medicines safely and what side effects should I watch for?
  • When should I come for follow-up?

Tests to discuss

  • Vital signs: temperature, pulse, blood pressure, oxygen saturation
  • Basic physical examination by a clinician
  • CBC, urine test, blood sugar, or imaging only when clinically needed

Avoid these mistakes

  • Do not use antibiotics, steroid tablets/injections, or strong painkillers without proper medical advice.
  • Do not hide pregnancy, kidney disease, ulcer, allergy, or blood thinner use.
  • Do not delay emergency care when danger signs are present.

Medicine safety and first-aid guide

This section is for patient education only. It does not replace a doctor, pharmacist, or emergency care.

Safe first steps

  • Rest, drink safe water, and observe symptoms carefully.
  • Keep a written note of symptoms, duration, temperature, medicines already taken, and allergy history.
  • Seek medical care quickly if symptoms are severe, worsening, or unusual for the patient.

OTC medicine safety

  • For mild pain or fever, ask a registered pharmacist or doctor before using common over-the-counter pain/fever medicines.
  • Do not combine multiple pain medicines without advice, especially if you have kidney disease, liver disease, stomach ulcer, asthma, pregnancy, or take blood thinners.
  • Do not give adult medicines to children unless a qualified clinician advises it.

Avoid these mistakes

  • Do not start antibiotics without a proper medical decision.
  • Do not use steroid tablets or injections casually for quick relief.
  • Do not delay emergency care because of home remedies.

Get urgent help if

  • Severe symptoms, confusion, fainting, breathing difficulty, chest pain, severe dehydration, or sudden weakness need urgent medical care.
Medicine names, dose, and timing must be decided by a qualified clinician or pharmacist after checking age, pregnancy, allergy, other diseases, and current medicines.

For rural patients and family caregivers

Patient health record and symptom diary

Write your symptoms, medicines already taken, test results, and questions before visiting a doctor. This note stays on your device unless you print or copy it.

Doctor to discuss: Doctor / qualified healthcare provider
Tests to discuss with doctor
  • Basic vital signs: temperature, pulse, blood pressure, oxygen level if needed
  • Relevant blood, urine, imaging, or specialist tests only after clinical assessment
Questions to ask
  • What is the most likely cause of my symptoms?
  • Which warning signs mean I should go to emergency care?
  • Which tests are really needed now?
  • Which medicines are safe for my age, pregnancy status, allergy, kidney/liver/stomach condition, and current medicines?

Emergency warning signs such as chest pain, severe breathing difficulty, sudden weakness, confusion, severe dehydration, major injury, or loss of bladder/bowel control need urgent medical care. Do not wait for online information.

Safe pathway to proper treatment

Patient care roadmap

Use this simple roadmap to understand the next safe steps. It is educational and does not replace examination by a doctor.

Go to emergency care if you notice:
  • Severe or rapidly worsening symptoms
  • Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration
Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. Step 5

    Follow up and return early if worse

    If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips
  • Take a written symptom diary and all previous prescriptions/test reports.
  • Do not hide medicines already taken, even herbal or over-the-counter medicines.
  • Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

RX Patient Help

Ask a health question safely

Write your symptom story. A health professional or site editor can review it before any answer is prepared. This box is not for emergency care.

Emergency first: Severe chest pain, breathing trouble, unconsciousness, stroke signs, severe injury, heavy bleeding, or rapidly worsening symptoms need urgent local medical care now.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area from the RX Article Professional Blocks panel.

More from this topic
  1. Antenatal Abnormality

    Antenatal abnormality means a problem in the baby that starts before birth and is found during pregnancy. Doctors often use this term for a structural problem,...

    April 7, 2026 • Rx Pregnancy, Baby & Mom Care
  2. Enlarged Adenoids

    Enlarged adenoids mean the adenoid tissue at the back of the nose has become bigger than normal. The adenoids are part of the body’s immune system....

    April 4, 2026 • Rx ENT, Oral and Dental Health (A - Z)
  3. Congenital Epstein–Barr Virus Infection

    Congenital? Epstein–Barr virus infection? means a baby is thought to get Epstein–Barr virus, or EBV, before birth while still inside the mother’s womb. EBV is also...

    April 4, 2026 • Rx Blood, Metabolism, and Infectious Diseases (A - Z)
  4. Congenital Enterovirus Infectious Disease

    Congenital? enterovirus infectious disease means an enterovirus infection? that is already present in the baby before birth or becomes apparent at birth or in the first...

    April 4, 2026 • Rx Blood, Metabolism, and Infectious Diseases (A - Z)
  5. Congenital Enterovirus Infection

    Congenital? enterovirus infection? means a baby is infected with an enterovirus before birth or around the time of birth from the mother. In very simple words,...

    April 3, 2026 • Rx Blood, Metabolism, and Infectious Diseases (A - Z)
  6. Congenital Enterocyte Heparan Sulfate Deficiency

    Congenital? enterocyte heparan sulfate deficiency is a very rare, severe, genetic intestinal disease. In this condition, the small bowel lining cells, called enterocytes, do not show...

    April 3, 2026 • Rx Autoimmune, Genetic and Rare Diseases (A - Z)
  7. Congenital Enterocyte Heparan Sulfate Deficiency

    Congenital? enterocyte heparan sulfate deficiency is a real but ultra-rare genetic intestinal disease. It causes the small-intestine lining cells, called enterocytes, to lack heparan sulfate on...

    April 3, 2026 • Rx Blood, Metabolism, and Infectious Diseases (A - Z)
  8. Undescended Shoulder Disease

    Undescended shoulder disease is not the usual medical name. Doctors usually call this condition Sprengel deformity, Sprengel shoulder, congenital? high scapula, or congenital? elevation of the...

    April 3, 2026 • Degenerative Bones, Joints, and Spine Care (A - Z)
  9. Sprengel Deformity

    Sprengel deformity is a birth condition in which one shoulder blade, called the scapula, stays higher than normal because it does not move down to its...

    April 2, 2026 • Degenerative Bones, Joints, and Spine Care (A - Z)
  10. High Shoulder Blade

    A high shoulder blade usually means one shoulder blade sits higher than normal from birth. The medical name is Sprengel deformity or congenital? high scapula. “Scapula”...

    April 2, 2026 • Degenerative Bones, Joints, and Spine Care (A - Z)