EXTENSOR TENDON INJURIES

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 proximalphalanx  Rarely multiple slips• Second compartment  Extensor carpi radialis longus(ECRL)  Inserts into base of index fingermetacarpal  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 apparatusABFig. 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 withsubluxation of ECUINTRINSICS n Dorsal interossei: Fourmuscles, bipennate (Fig. 70-2) • Innervated by ulnarnerve • Act to abductfingers, 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).