Hand Extensor Indicis Muscle – Anatomy, Nerve Supply

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 4 min read

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Hand Extensor Indicis Muscle is a narrow, elongated muscle found in the posterior compartment of the forearm. It belongs to the deep extensors of the forearm, together with supinator, abductor pollicis longus, extensor pollicis longus, and extensor pollicis brevis muscles. Extensor indicis can be palpated by...

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

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Article Summary

Key Takeaways

This article explains Structure of Hand Extensor Indicis Muscle in simple medical language.
This article explains Origin and Insertion of Hand Extensor Indicis Muscle in simple medical language.
This article explains Nerve Supply 0f Hand Extensor Indicis Muscle in simple medical language.
This article explains Blood supply of Hand Extensor Indicis Muscle in simple medical language.

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Seek urgent medical care if you notice

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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.

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

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Hand Extensor Indicis Muscle is a narrow, elongated muscle found in the posterior compartment of the forearm. It belongs to the deep extensors of the forearm, together with supinator, abductor pollicis longus, extensor pollicis longus, and extensor pollicis brevis muscles. Extensor indicis can be palpated by applying deep pressure over the lower part of the ulna while the index finger is extended.

The main function of extensor indicis involves the extension of the index finger at the metacarpophalangeal and interphalangeal joints. As the index finger is one of the few fingers that have their own separate extensor muscle, it is able to extend independently from other fingers. Additionally, extensor indicis muscle produces a weak extension of the wrist.

Extensor indices is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm, placed medial to, and parallel with, the extensor pollicis longus. Its tendon goes to the index finger, which it extends.

Structure of Hand Extensor Indicis Muscle

It arises from the distal third of the dorsal part of the body of ulna and from the interosseous membrane. It runs through the fourth tendon compartment together with the extensor digitorum, from where it projects into the dorsal aponeurosis of the index finger. ^[rx]

Opposite the head of the second metacarpal bone, it joins the ulnar side of the tendon of the extensor digitorum which belongs to the index finger.

Like the extensor digiti minimi (i.e. the extensor of the little finger), the tendon of the extensor indicis runs and inserts on the ulnar side of the tendon of the common extensor digitorum.^[rx] The extensor indicis lacks the juncturae tendinum interlinking the tendons of the extensor digitorum on the dorsal side of the hand. ^[rx]

Origin and Insertion of Hand Extensor Indicis Muscle

Extensor indicis is a narrow muscle that originates mainly from the ulna, arising from the posterior two-thirds of its distal surface, distal to extensor pollicis longus muscle. Some fibers also stem from the adjacent interosseous membrane. It extends inferiorly and narrows into a tendon that passes deep to the extensor retinaculum. Beneath the retinaculum, the tendon is invested within a tendinous sheath with the tendons of extensor digitorum muscle.

As it courses in the hand, the tendon of extensor indicis passes obliquely over the carpal bones and joins the ulnar side of the tendons of extensor digitorum, opposite to the head of the second metacarpal. Here, the tendon of extensor indicis inserts at the extensor expansion on the back of the proximal phalanx of the index finger.

At times, extensor indicis gives off several accessory slips to the extensor tendons of other digits. In addition, it can contain an additional muscle belly on the dorsum of the hand called extensor indicis brevis manus, although this occurs rarely.

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

Nerve Supply 0f Hand Extensor Indicis Muscle

Extensor indicis receives its nervous supply from posterior interosseous nerve, a branch of the radial nerve derived from spinal roots C7 and C8. The skin overlying the muscle is supplied by the same nerve, with fibers that stem from the spinal roots C6 and C7.

Blood supply of Hand Extensor Indicis Muscle

The superficial surface of the extensor indicis receives arterial blood supply from posterior interosseous branch of the ulnar artery, whereas its deep surface receives blood from perforating branches of the anterior interosseous artery.

Function of Hand Extensor Indicis Muscle

Extensor indicis acts at the metacarpophalangeal and interphalangeal joints to extend the index finger. Unlike most of the other fingers of the hand, the index finger has its own separate extensor, which enables it to extend independently from other fingers. In addition, as it crosses the wrist, this muscle produces a weak extension of this joint.

References

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?

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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?
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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.
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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.
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Avoid these mistakes

Do not start antibiotics without a proper medical decision.
Do not use steroid tablets or injections casually for quick relief.
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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.

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.

Step 1
Check danger signs first
If danger signs are present, seek emergency care and do not wait for online information.
Step 2
Record the symptom story
Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.
Step 3
Visit a qualified clinician
A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.
Step 4
Do only useful tests
Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.
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.

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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.