MSK The carpal tunnel & anatomical snuffbox Flashcards
What are the borders of the carpal tunnel?
The carpal tunnel is formed by 2 layers:
A deep carpal arch
- formed laterally by scaphoid and trapezium
- formed medially by hook of hamate and pisiform
A superficial flexor retinaculum
- thick CT
- turns carpal arch into tunnel by bridging the medial and lateral parts of the arch (originates lateral and inserts medial)
What are the contents of the carpal tunnel?
9 tendons and the median nerve
- flexor pollicis longus tendon (own sheath)
- 4 tendons of flexor digitorum profundus
- 4 tendons of flexor digitorum superficialis
(8 surrounded by single synovial sheath)
What is the function of the median nerve in the hand?
Once is passes through the carpal tunnel the median nerve divided into 2 branches - recurrent branch and palmar digital nerves
Palmar digital nerves:
sensory to palmar skin and nail beds of lateral 3 1/2 digits
motory to lateral 2 lumbricals
Recurrent branch:
supplies the thinner muscle group
What is carpal tunnel syndrome?
Compression of the medial nerve due to thickened ligaments and tendon sheaths.
If untreated leads to atrophy of thenar muscles
Symptoms inc numbness, tingling, pain, radiates into forearm, pain wakes them at night, worse in mornings
How to test for carpal tunnel syndrome:
- Tinels test, tap distal wrist and proximal hand to induce pain in median nerve distribution (3 1/2 digits)
- Phelans test, holding wrist in flexion for 90 secs to induce numbness and pain in 1st 3 1/2 digits
Treatment - splint to hold hand in dorsiflexion overnight, corticosteroid injections to wrist, surgical decompression
What are the borders, floor and roof of the anatomical snuffbox?
Ulnar border: tendon of extensor pollicis longus
Radial border: tendon of extensor pollicis brevis + abductor pollicis longus
Proximal border: styloid process of radius
Floor: scaphoid and trapezium
Roof: Skin
What are the contents of the anatomical snuffbox?
Radial artery - crosses the floor, runs deep to the extensor tendons
Branch of radial nerve - runs across the roof and sensory to lateral 3 1/2 digits and palm
Cephalic vein - superficially
What happens where there is a fracture of the scaphoid?
In the snuffbox the scaphoid and radius articulate
A fall on an outstretched hand can fracture the scaphoid - localised pain in the snuffbox
Scaphoid has unique blood supply - distal to proximal
Fracture can disrupt proximal blood supply (emergency( can lead to avascular necrosis and future arthritis
