[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › Extensor digitorum [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Extensor digitorum The extensor digitorum runs down the back of the forearm with tendons to four fingers; it straightens the fingers and helps lift the wrist. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=extensor_digitorum&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The main finger-straightening muscle on the back of the forearm. ## What it does Straightens the fingers and helps lift the wrist. ## Key points - Extends mainly the MCP joints; IP extension also needs the lumbricals and interossei through the extensor mechanism, which explains the claw hand - Juncturae tendinum link its tendons on the back of the hand, so a cut proximal to them can be masked by partial extension - Fourth extensor compartment with extensor indicis; the end of the posterior interosseous nerve runs in its floor ## Key facts **Origin** Lateral epicondyle **Insertion** Extensor expansions of digits 2–5 **Action** Extends the fingers (mainly at the MCP joints) and the wrist **Nerve** Posterior interosseous nerve (C7–C8) **Blood supply** Posterior interosseous artery ## Relations **Lateral** [Extensor carpi radialis brevis](https://durgical.com/en/anatomy/extensor-carpi-radialis-brevis/) (ECRB) **Medial** [Extensor digiti minimi](https://durgical.com/en/anatomy/extensor-digiti-minimi/), then the [extensor carpi ulnaris](https://durgical.com/en/anatomy/extensor-carpi-ulnaris/) (ECU) **Deep** The deep extensor layer: [supinator](https://durgical.com/en/anatomy/supinator/), APL, EPB, EPL and [extensor indicis](https://durgical.com/en/anatomy/extensor-indicis/), with the [posterior interosseous nerve](https://durgical.com/en/anatomy/posterior-interosseous-nerve/) and artery between the layers **Course** Through the fourth compartment and across the back of the hand; over each finger it forms the extensor mechanism, with a central slip to the middle phalanx and lateral bands to the distal phalanx ## How to find it With the fingers straightened at the knuckles against resistance, its tendons fan out visibly on the back of the hand; the belly is felt in the middle of the back of the forearm below the lateral epicondyle. ## Examination - Resisted MCP extension: loss of finger extension with preserved, radially deviated wrist extension (finger drop without wrist drop) indicates posterior interosseous nerve palsy - Elson test: with the PIP joint bent over a table edge, resisted PIP extension that makes the fingertip rigid indicates a central slip rupture ## On imaging Ultrasound shows its tendons in the fourth extensor compartment and over the metacarpal heads, centred by the sagittal bands; making a fist shows a tendon slipping off the knuckle after a sagittal band tear (boxer's knuckle). In mallet finger a lateral finger radiograph looks for a fragment from the distal phalanx base; ultrasound or MRI for tears. ## Clinical notes - Central slip injury leads to a boutonnière deformity; loss of the terminal tendon to a mallet finger - Sagittal band rupture lets the tendon slip off the knuckle toward the ulnar side (seen after punching); in rheumatoid arthritis it adds to ulnar drift - In permanent [radial nerve](https://durgical.com/en/anatomy/radial-nerve/) palsy, finger extension is restored by transferring FCR or FCU to its tendons ## Anatomical variants - Tendon slips are often doubled or missing; the little-finger tendon may be absent, replaced by a junctura, leaving extension to extensor digiti minimi - [Extensor digitorum brevis](https://durgical.com/en/anatomy/extensor-digitorum-brevis/) manus, a small accessory muscle on the back of the hand, can be mistaken for a ganglion ## Development Comes from the dorsal muscle mass of the limb bud. When the [upper limb](https://durgical.com/en/anatomy/region/upper-limb/) turns outward by about 90° in week 7, this mass ends up on the back of the forearm and the thumb on the lateral side, so the extensors lie posterior and take the radial nerve. ## Related conditions - [Lateral epicondylitis (tennis elbow)](https://durgical.com/en/conditions/lateral-epicondylitis/) - [Humeral shaft fracture](https://durgical.com/en/conditions/humeral-shaft-fracture/) ## Test yourself Think of the answer, then tap the question to see it. ## Which joints does the extensor digitorum mainly extend, and what else is needed for IP extension? Mainly the MCP joints; IP extension also needs the lumbricals and interossei through the extensor mechanism. ## What is the pattern of posterior interosseous nerve palsy at the extensor digitorum? Finger drop without wrist drop: loss of MCP extension with preserved, radially deviated wrist extension. ## Which deformity follows a central slip injury of the extensor digitorum mechanism? A boutonnière deformity; loss of the terminal tendon gives a mallet finger. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/extensor-digitorum/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** extensor digitorum TA2 2500 **Official Spanish (DeCS)** Músculo extensor de los dedos **English (TA2)** Extensor digitorum ## Related - [Posterior interosseous nerve](https://durgical.com/en/anatomy/posterior-interosseous-nerve/) - [Interosseous arteries](https://durgical.com/en/anatomy/interosseous-arteries-of-the-forearm/) - [Humerus](https://durgical.com/en/anatomy/humerus/) - [Common extensor tendon](https://durgical.com/en/anatomy/common-extensor-tendon/) - [Extensor tendons](https://durgical.com/en/anatomy/extensor-digitorum-tendons/) Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Hand Compartments](https://www.ncbi.nlm.nih.gov/books/NBK532942/); [Anatomy, Shoulder and Upper Limb, Wrist Extensor Muscles](https://www.ncbi.nlm.nih.gov/books/NBK534805/); [8.5 Development of the Appendicular Skeleton](https://openstax.org/books/anatomy-and-physiology-2e/pages/8-5-development-of-the-appendicular-skeleton) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/extensor-digitorum/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/extensor-digitorum/