The flexor retinaculum thickens at the level of its attachments to the hamate and trapezium, which is also where the carpal tunnel is narrowest. The flexor retinaculum, which is generally considered synonymous with the transverse carpal ligament, extends in a proximal to distal direction from the distal radius to the base of the third metacarpal and attaches to the four bony prominences mentioned above. Tendons passing through the carpal tunnel are secured in place by the flexor retinaculum, which forms the volar margin of the carpal tunnel. This arch forms the dorsal margin of the carpal tunnel demarcated by four bony prominences: the pisiform and scaphoid tubercle proximally and the hook of the hamate and tubercle of the trapezium distally 1. The median nerve is indicated (asterisk). The flexor pollicis longus tendon (star) is positioned at the radial aspect of the tunnel, separated from the flexor carpi radialis tendon (curved arrow) by a ligamentous reflection of the transverse carpal ligament. At the radial aspect of the carpal tunnel, the flexor digitorum tendons are arranged in two rows (separated by dotted line), the profundus tendons deep to the superficialis tendons. The transverse carpal ligament (short arrows) extends from the hook of the hamate (long arrow) to the tubercle of the trapezium (arrowhead), forming the floor of the carpal tunnel. In the axial plane, the carpus forms an arch that is concave on the palmar side.Ī fat-suppressed T1-weighted axial image from an MR arthrogram of the wrist in a healthy 24-year-old man. The other nine flexor tendons pass through the carpal tunnel, a fibro-osseous tunnel defined by the carpal bones dorsally and the flexor retinaculum volarly. Of the 12 flexor tendons normally found at the level of the wrist, only three do not traverse the carpal tunnel: (1) the palmaris longus tendon, superficial to the tunnel (2) the flexor carpi radialis tendon, radial to the tunnel and (3) the flexor carpi ulnaris tendon, on the ulnar side of the tunnel. In contrast to the extensor tendons of the wrist, which are segregated into six extensor compartments, the flexor tendons observe a simpler organizational scheme. To properly characterize such diseases, the radiologist should be familiar with the relevant anatomy and its implications on patterns of disease progression. On the flexor side, these synovial sheaths consist of the two palmar bursae-the ulnar bursa and the radial bursa-and the digital flexor tendon sheaths. The differential diagnosis will be discussed in subsequent sections.Ī variety of infectious and noninfectious diseases involve the synovial sheaths of the hand and wrist. There is no involvement of the flexor tendon sheaths of the index, long, and ring fingers (2, 3, 4).Ĭlassic ‘horseshoe abscess’ (in this case, related to atypical mycobacteria) that has spread through communicating synovial pathways, which include the ulnar and radial bursae proximally and the flexor tendon sheaths of the thumb and little finger distally. A fat-suppressed T1-weighted post-contrast axial image at the level of the metacarpal heads showing extension of synovitis into the digital flexor tendon sheaths of the thumb (1) and little finger (5).
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