Scaphoid
The scaphoid (also known as the os scaphoideum or - historically - as the navicular) is the largest of the proximal row of carpal bones and forms the radial portion of the carpal tunnel. It is important for stability and movement at the wrist and may be fractured after a fall onto a hyperextended hand. Scaphoid fractures may be radiologically-occult in the acute setting and may result in avascular necrosis.
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Gross anatomy
Osteology
The scaphoid is the largest of the proximal row of carpal bones and sits on the radial side of the lunate. It is a boat-shaped bone that is oriented obliquely with its long axis aligned from the medial portion of the distal radius proximally to the articulation of the 1st and 2nd metacarpals distally.
The scaphoid can be divided into proximal and distal poles. The waist (between the two) is the commonest site of scaphoid fracture. The scaphoid tubercle is a bony prominence on the ventral surface of the lateral portion of the distal pole.
Articulations
The scaphoid articulates with five bones: the radius, trapezoid, trapezium, lunate and capitate.
- proximal surface: radius
- distal surface: laterally with the trapezoid and trapezium; medially with the capitate
- ulnar surface: lunate
Proximally, the smooth convex surface of the scaphoid articulates with the distal radius.
The distal surface is split into two separate articular surfaces by a bony ridge. Radially, it articulates with the trapezoid and trapezium while on the ulnar side, it articulates with the capitate.
The medial surface has a concave appearance and articulates with the lunate.
Attachments
Musculotendinous
There are no musculotendinous attachments to the scaphoid bone.
Ligamentous
- dorsal surface: dorsal radiocarpal ligament
- radial surface: radial collateral ligament
- scapholunate ligament
- radioscapholunate ligament
- scaphocapitate ligament
- transverse carpal ligament 4
Relations
The radial artery crosses the dorsal surface of the scaphoid.
The scaphoid forms the radial portion of the carpal tunnel and is therefore related to the structures that pass through it, namely fibers from flexor digitorum profundus and superficialis, the median nerve, flexor pollicis longus and flexor carpi radialis.
Also located in the vicinity are the muscles of the thumb and associated tendons.
Arterial supply
Approximately 75% of the arterial supply is from branches of the radial artery through vascular perforations on the dorsal surface near the tubercle and waist 2. As the vascular supply to the proximal pole is mainly retrograde, a fracture through the tubercle or the waist places the proximal pole at risk of avascular necrosis.
Variant anatomy
- bipartite scaphoid
- tripartite scaphoid 5
- coalition with neighboring bones (rare)
- scaphoid hypoplasia (as long as not associated with other skeletal dysplasias)
Radiographic features
Plain radiograph
The scaphoid is the most radial of the proximal row of carpals, articulating with the distal radius, lunate and capitate. On the lateral view, it is projected through the carpus.
Development
Ossification
The scaphoid has a single ossification center, as do the trapezoid and trapezium. Ossification begins around the 4th year, and as with most ossification in the hand and wrist, it tends to occur earlier in females.
History and etymology
The term derives from the Ancient Greek word σκαφη (skaphe) meaning boat 6.
Related investigations
Plain radiograph
The scaphoid may be visualized on a number of series of the distal upper limb including:
Cross-sectional imaging
Nuclear medicine
Related pathology
Related Radiopaedia articles
Anatomy: Upper limb
-
skeleton of the upper limb
- clavicle
- scapula
- humerus
- radius
- ulna
- carpal bones (mnemonic)
- metacarpals
- phalanges
- accessory ossicles of the upper limb
- accessory ossicles of the shoulder
- accessory ossicles of the elbow
-
accessory ossicles of the wrist (mnemonic)
- os centrale carpi
- os epilunate
- os epitriquetrum
- os styloideum
- os hamuli proprium
- lunula
- os triangulare
- trapezium secondarium
- os paratrapezium
- os radiostyloideum (persistent radial styloid)
- joints of the upper limb
-
pectoral girdle
-
shoulder joint
- articulations
- associated structures
- joint capsule
- bursae
- ligaments
-
movements
- scapulothoracic joint
- glenohumeral joint
- arm flexion
- arm extension
- arm abduction
- arm adduction
- arm internal rotation (medial rotation)
- arm external rotation (lateral rotation)
- circumduction
- blood supply - scapular anastomosis
- ossification centers
-
shoulder joint
-
elbow joint
- proximal radioulnar joint
- ligaments
- associated structures
- movements
- alignment
- blood supply - elbow anastomosis
- development
-
wrist joint
- articulations
-
ligaments
- intrinsic ligaments
- extrinsic ligaments
- radioscaphoid ligament
- dorsal intercarpal ligament
- dorsal radiotriquetral ligament
- dorsal radioulnar ligament
- volar radioulnar ligament
- radioscaphocapitate ligament
- long radiolunate ligament
- Vickers ligament
- short radiolunate ligament
- ulnolunate ligament
- ulnotriquetral ligament
- ulnocapitate ligament
- ulnar collateral ligament
- associated structures
- extensor retinaculum
- flexor retinaculum
- joint capsule
- movements
- alignment
- ossification centers
-
hand joints
- articulations
- carpometacarpal joint
-
metacarpophalangeal joints
- palmar ligament (plate)
- collateral ligament
-
interphalangeal joints
- palmar ligament (plate)
- collateral ligament
- movements
- ossification centers
- articulations
-
pectoral girdle
- spaces of the upper limb
- muscles of the upper limb
- shoulder girdle
- anterior compartment of the arm
- posterior compartment of the arm
- anterior compartment of the forearm
-
posterior compartment of the forearm (extensors)
- superficial
- deep
- hand (mnemonic)
- accessory muscles
- blood supply to the upper limb
-
arteries
- subclavian artery (mnemonic)
- axillary artery
- brachial artery (proximal portion)
- ulnar artery
- radial artery
- veins
-
arteries
- innervation of the upper limb
- intercostobrachial nerve
-
brachial plexus (mnemonic)
- branches from the roots
- branches from the trunks
- branches from the cords
- lateral cord
- posterior cord
- medial cord
- terminal branches
- lymphatic drainage of the upper limb