Scaphoid
Updates to Article Attributes
The scaphoid bone (os scaphoideum)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 hyper-extended hand. Scaphoid fracture may be radiologically occult in the acute setting and may result in avascular necrosis.
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 orientated 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 the 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 forms articulation with the distal radius.
The distal surface is split into two separate articular surfaces by a bony ridge. Radially, it articulates the 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
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, fibres from flexor digitorum produndus and superficialis, the median nerve, flexor pollicis longus and flexor carpi radialis.
Also located in the vicinity are the muscles of the thumbs and associated tendons.
Blood supply
Approximately 75% of blood supply is from branches of the radial artery through vascular perforations on the dorsal surface near the tubercle and waist 2. Because there is mainly retrograde vascular supply to the proximal pole, a fracture through the tubercle or the waist puts the proximal pole at risk of avascular necrosis.
Variant anatomy
- bipartite scaphoid
- coalition with neighbouring bones (rare)
- scaphoid hypoplasia (as long as not associated with other skeletal dysplasias)
Radiographic features
Plain film
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 centre, 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 Greek word "skaphe" meaning boat.
Related investigations
Plain film
The scaphoid may be visualised on a number of series of the distal upper limb including:
Cross-sectional imaging
Nuclear medicine
Related pathology
-<li><a href="/articles/hand-radiograph">hand radiograph</a></li>-<li><a href="/articles/scaphoid-radiograph-series">scaphoid radiograph series</a></li>-<li><a href="/articles/wrist-radiograph">wrist radiograph</a></li>-<li><a href="/articles/forearm-radiograph">forearm radiograph</a></li>- +<li><a title="Hand series" href="/articles/hand-series">hand radiograph</a></li>
- +<li><a href="/articles/scaphoid-series">scaphoid radiograph series</a></li>
- +<li><a title="Wrist series" href="/articles/wrist-series">wrist radiograph</a></li>
- +<li><a title="Forearm series" href="/articles/forearm-series">forearm radiograph</a></li>