ABSTRACT
Extrinsic tEndons n Innervated by the radial nerve n Cross the wrist under extensor retinaculum, which is divided into six compartments (Fig. 70-1)
• First compartment Abductor pollicis longus (APL)
Inserts into base of thumb metacarpal Almost always multiple slips
Extensor pollicis brevis (EPB) Inserts into base of thumb proximal
phalanx Rarely multiple slips
• Second compartment Extensor carpi radialis longus
(ECRL) Inserts into base of index finger
metacarpal Extensor carpi radialis brevis (ECRB)
Inserts into base of middle finger metacarpal
• Third compartment Extensor pollicis longus (EPL)
Inserts into base of thumb distal phalanx
Relative independence of action across all three joints because of multiple attachments to dorsal apparatus
A
B
Fig. 70-1 Extensor compartments. (APL, Abductor pollicis longus; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; EDC, extensor digitorum communis; ECU, extensor carpi ulnaris; EDM, extensor digiti minimi; EIP, extensor indicis proprius; EPB, extensor pollicis brevis; EPL, extensor pollicis longus.)
• Fourth compartment Extensor digitorum communis (EDC)
Often has two slips to ring finger Slip to small finger absent in up to 56% of population
Extensor indicis proprius (EIP) Ulnar to EDC of index finger Most distal myotendinous junction
• Fifth compartment Extensor digiti minimi (EDM); also called extensor digiti quinti (EDQ)
Two slips in 80% of population • Sixth compartment Extensor carpi ulnaris (ECU)
Only extensor tendon with a true sheath Tear of sheath: Leads to ulnar-sided wrist pain and popping sensation with
subluxation of ECU
INTRINSICS n Dorsal interossei: Four
muscles, bipennate (Fig. 70-2) • Innervated by ulnar
nerve • Act to abduct
fingers, flex metacarpophalangeal (MP) joints, and extend interphalangeal (IP) joints (only with MP joints flexed)
n Palmar (volar) interossei: Three muscles, unipennate (see Fig. 70-2) • Innervated by ulnar nerve • Act to adduct fingers, flex MPs, extend IPs (only with MP joints flexed)
TIP: The function of the interossei can be remembered by the mnemonics DAB (dorsal abduct) and PAD (palmar adduct).
