MSK 4d: the wrist and carpal tunnel Flashcards
What are the articulations of the wrist joint?
Distal radius and articular disc articulate with the proximal row of carpal bones, except pisiform (i.e. scaphoid, lunate and triquetrium)
ULNA NOT INVOLVED
Pisiform acts as a sesamoid bone to increase leverage of flexor carpi ulnaris
Describe the wrist’s joint capsule
Fibrous layer: attached to distal radius and ulna and S,L&tri carpals
Synovial membrane: lines internal surface of fibrous layer and is attached to margins
What type of joint is the wrist?
Synovial condyloid/ellipsoidal
can move in 2 axes
Name the carpal bones
(from lateral to medial)
Proximal: Scaphoid, Lunate, Triquetrium, Pisiform
Distal: Trapezium, Trapezium, Capitate, Hamate
What ligaments are involved in the wrist?
Radial and ulnar collateral ligaments
Palmar radiocarpal ligament: ensures the hand follows the radius in supination
Dorsal radiocarpal ligament: ensures the hand follows the radius in pronation
Describe the movements at the wrist and which muscles are involved for each
FLEXION: flexor carpi radialis, flexor carpi ulnaris. Synergists: digit and thumb flexors (FDP, FDS, FPL) and APL and palmaris longus
EXTENSION: extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris. Synergists: some digit and thumb extensors
ABDUCTION: radial deviation. Abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus and brevis
ADDUCTION: extensor carpi ulnaris and flexor carpi ulnaris
How can anterior dislocation on lunate occur and what are the complications?
From falling on a dorsiflexed wrist
Lunate forced anteriorly and compresses the carpal tunnel, so may cause carpal tunnel syndrome
Scaphoid fracture?
Fall on to outstretched hand
Tenderness over anatomical snuffbox, as scaphoid forms the base
Scaphoid gets distal blood supply, so in non-union may lead to avascular necrosis
Colle’s fracture?
FOOSH-forced extension of hand
Fracture to distal radius causing posterior displacement of distal radial fragment. Transverse fracture of the distal 2cm of radius; often comminuted (broken into pieces). Ulnar styloid process often avulsed
Characteristic extended “dinner fork deformity”: posterior angulation occurs in forearm just proximal to wrist due to the displacement of the distal radial fragment
Smith’s fracture?
Direct trauma on distal forarm
Fracture to distal radius causing anterior displacement of the distal fragments
State the borders of the carpal tunnel
Carpal arch: deep concave on palmar side, formed laterally by scaphoid and trapezium tubercles and medially by hook of hamate and pisiform
Flexor retinaculum: superificial thick connective tissue that turns the carpal arch into a carpal tunnel by bridging the space between the medial and lateral parts of the arch. Originates on the lateral side and inserts on the medial side of the arch
State the contents of the carpal tunnel
Tendons of:
- Flexor pollicis longus (own synovial sheath)
- 4 tendons of flexor digitorum profundus + 4 tendons of flexor digitorum superficialis (share a single synovial sheath)
Median nerve-after the tunnel divides into the recurrent and palmar digital branches
What does the median nerve divide into at the carpal tunnel, and what do these supply?
Recurrent branch: supplies the thenar muscles
Palmar digital branch: sensory innervation to the palmar skin and dorsal nail beds of the lateral 3.5 digits, and motor innervation to the lateral 2 lumbricals
What are the risk factors for carpal tunnel syndrome?
Myxoedema (hypthyroidism) Edema (oedema) Diabetes Idiopathic Amyloidoses Neoplasm Trauma Rheumatoid arthritis Acromegaly Pregnancy
Symptoms of carpal tunnel sydrome?
Paraesthesia (tingling) and hypoesthesia (loss of sensation) that often wakes the patient, in the lateral 3.5 digits (no change in centre of palm)
Wasting of the thenar eminence
Pain in the distribution of the median nerve
Inability to oppose thumbs
