Anatomical snuffbox
Boundaries
Radial – tendons of abductor pollicis longus, extensor pollicis brevis
Ulnar – tendon of externsor pollicis longus
Floor – scaphoid, trapezium, base of first metacarpal, radial styloid
Roof – skin
Contents – radial nerve(roof), radial artery, cephalic vein(roof)
Bony features of the radius and ulna
Radius
Radial head
Radial fossa
Neck
Radial tuberosity – attachment of biceps brachii
Shaft
Radial styloid
Ulna notch
Articulates with scaphoid and lunate
Ulna
Trochlea fossa
Olecranon – triceps
Coronoid
Radial notch
Tuberosity of Ulna – brachialis
Shaft
Ulna styloid
Mechanism of pronation and supination of the forearm
Proximal and distal radio-ulnar joints – pivot joints. Distal has a fibrocartilagenous articular disc
Axis of movement is through styloid of ulna and head of radius.
Radius moves on Ulna, a small amount of movement only by ulna
Pronators – pronator quadratus, pronator teres
Supinators – supinator, biceps brachii
Model of flexor or extensor forearm.
Flexors and pronators are in anterior compartment – communicates with central compartment of palm through carpal tunnel.
Superficial – all attach to medial epicondyle via the common flexor tendon
Pronator teres – lateral radius
Flexor carpi radialis – base of 2nd metacarpal
Palmaris longus – flexor retinaculum and palmar aponeurosis
Flexor carpi ulnaris – pisiform, hook of hamate, 5th metacarpal.
Intermediate layer
FDS – flex middle phalynx – from medial epicondyle, coronoid and superior half of radius -> middle phalanges. Tendons act independently.
Deep layer – do not cross the elbow joint.
FDP – flex distal phalynx – proximal ant and medial surface of ulna and IO membrane–> distal phalynx
Flexor policis longus – ant radius and IO membrane –> distal phalynx of thumb(own sheath)
Pronator quadratus – between distal ulna and radius. Prime pronator.
EXCEPTION – brachiradialis
Main action is to flex forearm
Radial nerve supply
Posterior compartment
Extensors and supinators are in posterior compartment
Superficial – all attach to lateral epicondyle via common extensor tendon.
Extensor carpi radialis brevis – base of 3rd metacarpal
Extensor digitorum – extensor expansion
Extensor digiti minimi – extensor expansion of 5th
Extensor carpi ulnaris – base of 5th metacarpal
Other superficial – attach to lateral supraepicondylar ridge and Iat intermusc septum
Brachioradialis – lateral distal radius
Extensor carpi radialis longus – base of 2nd metacarpal
Deep
Supinator – lateral epicondyle to lateral and ant surface of prox radius.
Extensor indicis – posterior distal ulna –> ext enxpansion of 2nd finger
Outcropping
Abductor pollicis longus – proximal 1/2 of ulna and radius –> base of first metacarpal
Extensor pollicis longus – middle 1/3 of ulna and IO membrane –> base of distal phalynx of thumb
Extensor pollicis brevis – distal 1/3 of radius and IO membrane –> base of proximal phalynx of thumb
Arrangement of the superficial veins of the forearm.
Fascial plane is between intermediate and deep layer of muscles – neurovasc bundle.
Superficial veins
Variable
Cephalic and basalic
Deep veins
Follow arteries
Superficial and deep palmar arches
Ulna and radial veins connecting to brachial vein.
Course of the ulnar / radial / median nerve through the forearm.
Median nerve and ulnar artery pass under two heads of FDS to enter forearm
Ulnar
Passes between two heads of flexor carpi ulnaris
Goes posterior to medial epicondyle
Descends between FDP and FCU
Superficial in distal forearm
Radial
Between brachioradialis and brachialis
Anterior to lateral epicondyle
Divides into superficial and deep branches.
Median
Medial to brachial artery
Passes between tw heads of pronator teres
Descends between FDP and FDS
Deep to palmaris longus
Enters carpal tunnel.
Ditto with radial / ulnar artery.
Both arise at neck of radius from brachial artery
Radial artery
Lies on supinator, pronator teres tendon, FDS, FPL
Runs inferolaterally Under brachioradialis
Lateral to FCR in distal forearm
Winds around lateral aspect of radius and crosses anatomical snuffbox and pierces 1st dorsal interosseous muscle.
Deep branch pierces supinator and goes to posterior compartment and runs between superficial and deep extensor compartments.
Ulna artery
FCU and median nerve medially
Runs between intermediate and deep layer of muscles medially in forearm
Finishes medially and passes superficial to flexor retinaculum
Under Guyon canal to enter hand
Attachments of Extensor retinaculum and contents.
Attached to lateral margin of radius to triquetrum and pisiform medially.
1st – Abductor policis longus and extensor policis brevis)
2nd – Extensor carpi radialis longus and brevis
Dorsal radial tubercle
3rd – extensor pollicis longus – changes direction after tubercle
4th – extensor digitorum and extensor indicis
5th – extensor digiti minimi (posterior to distal radio-ulnar joint)
6th – extensor carpi ulnaris (on ulna)
Clinical aspects
- Colles fracture – A Colles’ fracture, is a fracture of the distal radius in theforearm with dorsal (posterior) and radial displacement of the wrist and hand.
- Smith fractue – opposite of Colles – The distal fracture fragment is displaced volarly.
- Monteggia’s Fracture – Usually caused by a force from behind the ulna. The proximal shaft of ulna is fractured, and the head of the radius dislocates anteriorly at the elbow.
- Galeazzi’s Fracture – A fracture to the distal radius, with the ulna head dislocating at the distal radio-ulnar joint.