24 The APL muscle belly lies just distal to the supinator in the extensor compartment in the mid forearm. 29.3 ), all of which are innervated by the posterior interosseous nerve, from nerve roots C7 and 8. Intersection syndrome: the intersection (at an angle of around 60°) of the musculotendinous junctions of the first and second extensor compartment tendons leading to tenosynovitis of 2nd compartment due to friction from the overlying 1st compartment. The extensor tendons of the thumb are the APL, the EPB, and the EPL ( Fig.DeQuervain’s tenosynovitis (modified Eichoff’s test or Finkelstein’s test) – most common extensor compartment tenosynovitisĬompartment 2: ECRL (Extensor Carpi Radialis Longus) and ECRB (Extensor Carpi Radilis Brevis).Remember: These form the lateral border of Anatomical Snuff box.The EPL winds around Lister tubercle and occupies the third extensor compartment. These structures are known as the extensor tendons (diagram below). The first compartment contains the APL and EPB tendons and the second contains the ECRL and ECRB tendons. The tendons on the dorsal (top) side extend the fingers and wrist. It shares a common synovial tendon sheaths along with other extensor muscles which helps to reduce friction between the tendon and the surrounding structures. The number of tendons passinf thorugh the compartments (radial to ulnar) can be remembered using the mnemonic: 2-2-1-2-1-1.Ĭompartment 1: APL (Abductor Pollicis Longus radial frequently has multiple slips) and EPB (Extensor Pollicis Brevis ulnar) At the wrist, the tendons of the extensor muscles run under the extensor retinaculum and are separated into six compartments (five fibro-osseous and one fibrous). The extensor digitorum communis is a superficial extensor muscle located in the posterior compartment of the forearm.