Highest are
(1) 2 muscles: anconeus (superficial) and supinator (deep).
From lateral humerus ¨
(2) 3 muscles along radial border (ECRL and ECRB and brachioradialis)
(3) 3 muscles along posterior surface of forearm. (ED, EDM, ECU)
These two groups separated lower down by:
(4) 3 muscles emerging between them going to thumb (AbPL, EPL and EPB)
(5) 1 muscle for forefinger passes deeply to back of hand (extensor indices)
Nerve of extensor compartment = posterior interosseus; reaches it by curling around radius.
Artery = posterior interosseous; a ÒfailureÓ which is reinforced by its anterior colleague distally.
Note there isnÕt enough room at the extensor origin for 6 muscles, hence two start higher at the supracondylar ridge and lateral intermuscular septum.
Arises: upper 2/3 of lateral supracondylar ridge ¨ along preaxial border; = lat border of cubital fossa.
Inserts: overlies radial nerve & artery. ¨ into radial styloid process.
- lower tendon covered by AbPL, EPB as they spiral down to thumb.
Innervation: radial nerve C5,6 from above elbow before posterior interosseous nerve given off.
Action: flexes elbow jt, most powerful in semi-pronation
Arises: lower 1/3 of supracondylar ridge ¨ base of 2nd MC. Runs post to brachioradialis.
Innervation: radial nerve C6,7 from above elbow before posterior interosseous nerve given off.
Action: wrist extensor and abductor, assists in elbow flexion. Makes a fist, synergist to finger flexion.
- if forearm flexors paralysed, can be transplanted to take over FDP.
Test: perform action against resistance, palpate it.
Smooth area on anterior aspect of lateral epicondyle of humerus ¨ fused tendons of ECRB, ED, EDM and ECU all pass to posterior aspect of forearm.
- in supination / extension, a pit forms posterior to them ¨ head of radius palpable here.
- In working position (semiflexion, semipronation), they run straight over lateral epicondyle.
In order from radial ¨ ulanr side:
Passes posterior and deep to ECRL ¨ inserts: base of 3rd MC (it and ECRL mirror FCR)
Tendon crossed by 3 thumb extensors.
Innervation: posterior interosseous nerve (C7,C8) from branch in cubital fossa.
Action: wrist extensor, helps make a fist.
Diverges from above 3 muscles so that distally thumb extensor flesh separates them.
¨ 4 tendons passing under extensor retinaculum crowding over indices tendon ¨ insert into fingers;
- Ring & little tendons often fused; Tendon to little finger overlies MC of ring finger.
- Other bands join adjacent finger tendons in a variable manner.
Innervation: posterior interosseous nerve (C7,C8)
Action: extends ICP, MCP and wrist joints.
Test: forearm in pronation, fingers extended, pt tries to keep fingers extended.
Common origin with ED ¨ become separate bellies & passes under extensor retinaculum.
Inserts: tendon splits into 2 and passes to little finger, often joined by band to little finger tendon of ED.
Innervation: posterior interosseous nerve (C7,C8)
Action: assists extensor digitorum; extension of little finger / wrist
Arises: common extensor origin and subcutaneous border of ulna (latter in common with FCU origin)
Inserts: tendon grooves ulnar styloid ¨ base of 5th MC.
Symmetrical insertion with FCU which acts on 5th MC via pisometacarpal ligament.
Innervation: posterior interosseous nerve (C7,C8), in forearm
Action: extensor / adductor of wrist; synergist in finger flexion, making a fist.
Test: Perform action, palpate.
From lateral epicondyle ¨ lateral aspect of olecranon.
Innervation: radial nerve (C7,8) by branch at level of spiral groove (a branch of triceps)
Action: abductor of ulna during pronation.
Two parts with different origins, running in different directions, with posterior interosseous nerve passing between.
From supinator crest & fossa of ulna ¨ horizontally around radius to area between anterior & posterior oblique lines. They wrap around the proximal third of the shaft
From distal border of lateral epicondyle & radial collateral ligament ¨ downwards to overlie deep fibres & insert into radius above anterior oblique line.
Innervation: branch of posterior interosseous nerve in cubital fossa (C6,C7)
Action: fixes the forearm in supination, much weaker than biceps unless elbow completely extended.
Arises: radius, ulna and interosseous membrane ¨ spirals around ECRL, ECRB & B-R.
Inserts: base of 1st MC and trapezium (divides into two slips)
Innervation: posterior interosseous nerve (C7,C8)
Action: extends thumb (radial abduction); can help abduct & flex wrist.
Test: Radial abduct against resistance; can see the tendon at most radial side of snuffbox (there are 2 radial snuffbox tendons)
Arises: from radius and interosseous membrane, below AbPL.
Inserts: (also spirals around ECRL, ECRB, B-R) ¨ base of proximal phalanx.
Innervation: posterior interosseous nerve (C7,C8)
Action: extends CMC and MCP jts of thumb; helps in threading a needle.
Test: extend thumb at MCP jt against resistance; tendon in radial snuffbox next to APL.
Arises: from ulna distal to AbPL (\ higher in forearm than EPB);
- tendon forms ulnar border of snuffbox; hooking around dorsal tubercle (of Lister) of radius
- here supplied by anterior interosseus artery branches; in CollesÕ these may be disrupted ¨ necrosis ¨ tendon rupture ¨ Ôhammer thumbÕ
Inserts: base of distal phalanx (\ more distal in thumb than EPB).
- note there is no extensor expansion of thumb; some expansions from AbPB and Adductor pollicis add to stability.
Innervation: posterior interosseous nerve (C7,C8).
Action: extends terminal phalanx of thumb, assists in wrist extension & abduction.
Test: thumb extends against resistance; tendon at ulnar border of snuff-box.
Arises: ulna distal to EPL ¨ passes below ED tendons (& shares their synovial sheath)
Inserts: ¨ dorsum of index finger MC (ulnar aspect of ED tendon) ¨ dorsal expansion of index finger. Innervation: posterior interosseous nerve (C7,8)
Action: extends indicis, as in pointing.
Terminal cutaneous branch (still called radial nerve) runs down under brachialis ¨ brachioradialis ¨ ECR ¨ run across snuffbox.
Radial border: AbPL + EPB. Ulnar border: EPL.
1) Cephalic vein begins in snuffbox.
2) Cutaneous (terminal) branches of radial nerve cross it and the EPL tendon.
3) Radial artery lies in floor.
4) Palpable bones: base of 1st MC, radial styloid, scaphoid and trapezium.
Passes between heads of supinator & winds around radius to appear in extensor compartment
¨ passes down over APL then dips deep to reach interosseus membrane
¨ ends at wrist joint as small nodule supplying wrist joint.
Supplies all muscles from common extensor origin, and deep extensor compartment muscles.
No cutaneous branch.
From ulnar artery, passing over oblique cord to reach interosseus membrane
Accompanies posterior interosseous nerve, strongly reinforced by branches of its anterior colleague, which pierces interosseous membrane above PQ
¨ ends on back of wrist in dorsal carpal anastomosis.
Band-like fascial thickening 2.5cm wide, obliquely across extensor surface of wrist.
Proximal attachment: anterolat border of radius above styloid
- not attached to ulnar (else would go all floppy in pronation)
Distal attachment: to pisiform and triquetral bones
Fibrous septae: pass to bones, dividing into 6 compartments:
i) most radial: APL, EPLB (separate sheaths)
ii) to dorsal tubercle: ECRL ECRB (separate sheaths)
iii) groove ulnar to tubercle: EPL (sheath)
iv) to border of radius: all ED tendons, and indicis, (single sheath)
v) over radioulnar jt: EDM (sheath)
vi) groove at ulnar styloid base: ECU (sheath)