Thumb extensor mechanism

The thumb extensor tendons are maintained in a central position at the metacarpophalangeal joint level by radial and ulnar attachments to the Sagittal bands. At this level, the extensor pollicis brevis lies radial to the extensor pollicis longus and attaches to the dorsal base of the proximal phalanx. Radial and ulnar tendon slips from the Abductor Pollicis Brevis and the Adductor Pollicis muscles, respectively, and the extensor pollicis longus join the extensor hood to form the Terminal tendon. This crosses the dorsal surface of the interphalangeal joint to attach to the dorsal base of the distal phalanx.