Extensor carpi ulnaris

Posterior Interosseus Nerve, Radial Nerve, Posterior Cord, Posterior Division, Upper, Middle and Lower Trunk, C6, C7, C8. 

Palpate the ulna in middle of forearm and insert needle electrode 

If the needle electrode is inserted too radially it will be in the extensor pollicis longus and if inserted too proximally it will be in the 

Common extensor tendon from the lateral epicondyle of humerus. 

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Lateral (wrist extensor) and supinator Supplied by the radial and the posterior interosseous nerve, this group consists of the supinator, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum communis, and the extensor carpi ulnaris. 

Extensor carpi ulnaris extends the wrist and adducts the hand. 

Fig. 10.33 a,b. Schematic drawings illustrate typical sites of overuse tendinopathies in the a dorsal and b ventral wrist, including Ay de Quervain tenosynovitis B, intersection syndrome C,extensor pollicis longus tenosynovitis, ),extensor carpi ulnaris tenosynovitis E, flexor carpi radialis tenosynovitis F, flexor digitorum superficialis and flexor digitorum profundus tenosynovitis Gy flexor carpi ulnaris tendinopathy... 

Fig. 10.41 a,b. Hypertrophic tenosynovitis of the extensor carpi ulnaris in a patient with rheumatoid arthritis, a Short-axis and b long-axis 12-5 MHz US images of the extensor carpi ulnaris tendon (ecu) reveal hypoechoic synovial pannus (arrowheads) which causes abnormal distention of the synovial sheath. The extensor carpi ulnaris is displaced anteriorly because of loosening of the retinaculum. Note the pannus filling the distal radioulnar joint cavity (arrow)... 

The retinaculum most commonly torn at the wrist is that of the sixth osteofibrous tunnel which retains the extensor carpi ulnaris tendon in a correct position during rotation and flexion-extension movements of the forearm. This retinaculum tears... 

Fig. 10.71. Caput ulnae syndrome in rheumatoid arthritis. Schematic drawing of a transverse view through the distal radioulnar joint outlines the rupture of the triangular fibrocartilage (arrowheads) and marginal erosions at the distal radio-ulnar joint level due to intra-articular pannus (asterisks). As a result, the ulna subluxes dorsally (gray arrow). Pannus (star) inside the extensor carpi ulnaris tendon (open arrow) sheath leads to cortical erosions, tear of the retinaculum and tendon thinning and splitting. St, styloid of the ulna Rad, radius...

Fig. 10.72a,b. Caput ulnae syndrome in rheumatoid arthritis, a Longitudinal and b transverse 12-5 MHz US images over the extensor carpi ulnaris tendon (straight arrows) reveal synovial pannus inside the distal radio-ulnar joint (asterisk) and the extensor carpi ulnaris tendon sheath (arrowheads). The tendon is dislocated (curved arrow) out of its ulnar groove due to the tear of the retinaculum. See Fig. 10.20b for comparison with normal findings... 

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