Upper limb
Tendon sheath of third extensor compartment (EPL)
Vagina tendinis musculi extensoris pollicis longi
- Origin
- Third dorsal compartment looping acutely around the medial side of Lister's tubercle
- Insertion
- Invests the extensor pollicis longus (EPL) tendon extending to the distal phalanx of the thumb
- Function
- Acts as a biomechanical pulley redirecting EPL vector across Lister's tubercle to enable thumb hyperextension
- Innervation
- Posterior interosseous nerve (C7–C8)
- Movement & chain
- Experiences significant directional angular shear during thumb retroflexion and extension
- Palpation
- Palpable along the ulnar border of the anatomical snuffbox and Lister's tubercle
- Clinical
- Delayed spontaneous EPL tendon rupture following non-displaced distal radius fractures due to watershed ischemia or callus abrasion; treated via extensor indicis proprius (EIP) tendon transfer
- Segmental innervation
- C7–C8 spinal segments
- In clinical practice
- Early detection of thumb extensor weakness post-wrist fracture; patient counseling and surgical tendon transfer rehabilitation
- Region in the model
- Upper limb