Forearm muscles : Tricks to remember

Anterior Forearm (Compartment) Muscles

Total muscles: 8 (4 superficial + 1 intermediate + 3 deep)

Mnemonic: Do it yourself as shown in the figure below! Place your thenar/hypothenar eminence over medial epicondyle and fan out 5 fingers with thumb resting below the 4 fingers. The 4 fingers represent superficial flexors while the thumb represents intermediate/middle flexor. Starting from the index finger count – “Pass, Fail, Pass, Fail, and Fail (at last)” i.e. Pronator teres (PT), Flexor carpi radialis (FCR), Palmaris longus (PL), Flexor carpi ulnaris (FCU) and Flexor digitorum superficialis (FDS) resectively.

superficial flexors mnemonic

Superficial and Middle flexors

Common flexor origin: Medial epicondyle

But remember that the 3 muscles containing “U” have more attachments:

  • Ulnar (deep) head of pronator teres (may be absent): Ulna (coronoid process)
  • Flexor Carpi Ulnaris: Ulna (olecranon) and Ulnar shaft
  • Flexor digitorum sUperficialis: Ulna (coronoid) and Radial shaft

Nerve supply: Median nerve except FCU which is supplied by ulnar nerve

MuscleInsertionFunctionClinical relevance
Pronator teres (PT)Mid-lateral radiusPronate and Flex forearmMedian nerve compression (pronator syndrome)
Flexor carpi raialis (FCR)2nd and 3rd metacarpal baseFlex wrist, radial deviationRadial artery lies between FCR and Brachioradialis
Palmaris longus (PL)Flexor retinaculum/ Palmar aponeurosisFlex wristUsed for tendon transfers
Congenitally absent in 10%
Flexor carpi ulnaris (FCU)Pisiform (sesamoid – developed within tendon of FCU), hook of hamate, 5th metacarpalFlex wrist, ulnar deviationMost powerful flexor of wrist
May compress ulnar nerve between 2 heads
Flexor digitorum superficialis (Sublimis; FDS)Base of middle phalanges (at proximal phalanx splits into medial and lateral slips)Flex Proximal Interphalangeal (PIP) jointSublimis test will isolate and test function
Remember that FCU is a large muscle. Like its origin from large area, it has insertion onto 3 bones on the ulnar aspect of wrist, i.e. pisiform, hamate gook and 5th metacarpal base.
Insertion of FCR on 2nd and 3rd metacarpal base matches the insertion of ECRL and ECRB.

Deep flexors

Mnemonic: All 3 deep flexors have a word starting with “P“.
1. flexor digitorum Profundus
2. flexor Pollicis longus
3. Pronator quadratus

All these 3 are supplied by AIN and can be tested with “OK” sign.

Nerve supply: Anterior interosseous branch of median nerve (AIN) except Flexor digitorum profondus of ring and little fingers which is also supplied by ulnar nerve.

Remember few things:

  • FPL is for thumb, hence originates at the side of thumb (radius and interosseous membrane)
  • FDS is for digits, hence originates at the side of the digits (ulna and interosseous membrane)
  • Pronators, be it “teres” or “quadratus” goes from ulna to radius.
  • “Longus” goes to distal phalanx base.
  • “Superficialis” goes to proximal phalanx base.
MuscleOriginInsertionFunctionClinical relevance
Flexor Digitorum Profundus (FDP)Anterior ulna and interosseous membraneBase of distal phalanges (at proximal phalanx, it passes between 2 slips of FDS – camper’s chiasm)Flex Distal Interphalangeal Joint (DIP)Avulsion: Jersey finger
Profundus test will isolate and test function
Flexor Pollicis Longus (FPL)Anterior radius and interosseous membraneBase of distal phalange of thumbFlex Interphalangeal joint of thumbFDP and FPL are most susceptible to Volkmann’s ischemic contracture (VIC)
Pronator QuadratusMedial distal ulna (oblique ridge)Volar distal radiusPronate forearmPrimary pronator (initiates pronation)

Remember the Rule of three (3):

3 wrist flexors: FCR, PL, FCU
3 finger flexors: FDS, FDP, FPL

Other 2 are pronators: PT, PQ

Posterior Forearm (Compartment) Muscles

Total muscles: 12 (4 Superficial + 3 Mobile wad + 5 Deep)

Superficial Externsors

Mnemonic: Do it yourself as shown in the picture! Hold your elbow with thumbs up and other 4 fingers curling behind the lateral epicondyle. Then go in the sequence of thumb (B-C), little finger (C-D), ring finger (D), middle finger (C) and index finger (A). The thumb is above and represents the origin point as lateral condyle for Brachioradialis and extensor Carpi radialis longus (B-C). All other fingers represent origin point as lateral epicondyle: Little finger – extensor Carpi radialis brevis, extensor Digitorum (C-D); Ring finger – extensor Digitorum minimi (D); Middle finger – extensor Carpi ulnaris; Index finger – Anconeus (A).

forearm extensor mnemonic

Common extensor origin: Lateral epicondyle

  • Brachioradialis and ECRL originates from: Lateral supracondylar ridge

Nerve supply: Radial nerve or one of it’s branches

  • ECRB, EDC, EDM, ECU (lateral epicondyle group) are supplied by raidal nerve branche – PIN (posterior interosseous nerve).


  • ECU is a large muscle like FCU and has origin on posterior ulna too.
  • ECRL and ECRB like FCR insert into 2nd and 3rd metacarpal base respectively.
  • ECU like FCU inserts on 5th metacarpal base.
MuscleInsertionFunctionClinical relevance
Brachioradialis (BR)Lateral distal radius/styloidFlex forearmDeforming force in distal radius fracture;
Radial artery lies medially
Extensor carpi radialis longus (ECRL)2nd Metacarpal baseExtend wrist
Extensor carpi radialis brevis (ECRB)3rd Metacarpal baseExtend wristDegenerates in tennis elbow
AnconeusProximal dorsal ulnaExtend forearmMuscular plane in Kocher approach
Extensor digitorum (EDC)MCP (Metacarpophalangeal joint): Saggital band
P2 (middle phalanx): Central slip
P3 (distal phalanx): Lateral slip unite
Extend digitsTendon avulsion:
P2 – Boutonniere
P3 – Mallet finger
Extensor digitorum minimi – 2 tendons (EDM/EDQ)As above but in little fingerExtend little fingerMedial to EDC to little finger
Extensor carpi ulnaris (ECU)5th Metacarapal baseExtend/adduct handCan cause painful snapping over ulna

Brachioradiailis, ECRL and ECRB are the components of Mobile wad of Henry. These structures can be grasped between thumb and index finger just distal to lateral epicondyle. Brachioradialis is a paradoxical muscle. Its origin and innervation are characteristic of a extensor muscle, but it is actually a strong flexor of forearm.

posterior compartment of forearm

Deep Extensors

Mnemonic: Like the deep flexor muscles, all the extensor muscles that have “P” in them are deep extensors –
1. abductor Pollicis longus (APL)
2. extensor Pollicis brevis (EPB)
3. extensor Pollicis longus (EPL)
4. extensor indicis Proprius (EIP)
5. PIN – supply all these muscles
6. SuPinator

Nerve supply: Radial nerve – PIN

Remember few things:

  1. Supinator like Pronator teres has also origin from the epicondyle (lateral epicondyle in contrast to medial epicondyle in pronator teres)
  2. Remember the 6 extensor compartments of wrist. The 1st compartment muscle (APL and EPB), they originate from radius and interosseous membrane.
  3. The 3nd and 4th compartment muscle (EPL and EIP respectively) originate from ulna and interosseous membrane.
MuscleOriginInsertionFunctionClinical relevance
SupinatorPosterior medial ulna including supinator crestProximal lateral radiusSupinate forearmPIN can be compressed as it pierces the muscle
Abductor Pollicis Longus (APL)Dorsal ulna and radius1st Metacarpal baseAbduct and extend thumb (CMCJ)deQuervain’s tenosynovitis (may have multiple slips)
Extensor Pollicis Brevis (EPB)Dorsal radius and interosseous membrane (below APL)Base of proximal phalanx of thumbMetacarpo-phalangeal (MCP) joint extension of thumbRadial border of snuffbox
Extensor Pollicis Longus (EPL)Posterior ulna and interosseous membrane (below APL)Base of distal phalanx of thumbInterphalangeal joint (IPJ) extension of thumbTendon turns 45 degrees on Lister’s tubercle
Extensor Indicis Proprius (EIP)Posterior ulna and interosseous membrane (below EPL)Same as EDCExtension of index fingerUlnar to EDC tendon; last PIN muscle

From superior to inferior, origin of muscles are:
a. APL (radius and ulna) – remember A for Above
b. EPL (ulna) and EPB (radius)
d. EIP (ulna)

As in flexors, we have rule of threes (3) for extensors as well:

3 muscles for wrist extension: ECRB, ECRL, ECU
3 muscles for finger extension: EDC, EIP, EDM
3 muscles for thumb: EPL, EPB, APL

longus brevis mnemonic

Another handy relation to keep in the back of head is: longus, brevis, longus, brevis (longus is lateral to brevis)

In the distal forearm, APL and EBP crosses from medial to lateral over ECRL and ECRB. APL and EPB enter 1st extensor compartment at wrist while the ECRL and ECRB enter the 2nd.

Recommended reading: Netter’s atlas for images

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