The six synovial tunnels deep to the extensor retinaculum and their tendons
Mnemonic
Six compartments under the extensor retinaculum, with the tendon counts 2, 2, 1, 2, 1, 1:
- Abductor pollicis longus and extensor pollicis brevis - the site of de Quervain’s tenosynovitis
- Extensor carpi radialis longus and brevis
- Extensor pollicis longus - hooks around Lister’s tubercle
- Extensor digitorum and extensor indicis
- Extensor digiti minimi
- Extensor carpi ulnaris
“2, 2, 1, 2, 1, 1” covers the counts.
Compartment 1 gives de Quervain’s, diagnosed by Finkelstein’s test: ulnar deviation with the thumb clasped in the fist reproduces the pain. Common in new mothers and after repetitive thumb use.
Extensor pollicis longus is the one that ruptures, because it turns sharply around Lister’s tubercle with a watershed blood supply, classically after a distal radius fracture, even an undisplaced one treated conservatively.
The anatomical snuffbox is bounded by compartment 1 tendons laterally and extensor pollicis longus medially.
Expansion
From lateral (radial) to medial (ulnar):
- Abductor pollicis longus and extensor pollicis brevis
- Extensor carpi radialis longus and extensor carpi radialis brevis
- Extensor pollicis longus
- Extensor digitorum and extensor indicis
- Extensor digiti minimi
- Extensor carpi ulnaris