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 osteonecrosis.
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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 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 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. On the radial side it articulates with the trapezoid and trapezium while on the ulnar side it articulates with the capitate.
The medial surface has a smooth concave surface 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
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 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.8
Variant anatomy
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.
The scaphoid may be visualised on a number of series of the distal upper limb including:
Development
Ossification
The scaphoid has a single ossification centre, as do the trapezoid and trapezium. Ossification begins around the 5th year, and completes at 13-15 years of age 7. As with most ossification in the hand and wrist, it tends to occur earlier in females.
History and etymology
Scaphoid means boat-shaped and derives from the Ancient Greek word σκαφη (skaphe) meaning boat 6. Indeed, historically an alternative name for the 'os scaphoideum' was the 'os naviculare manus', meaning navicular bone of the hand. This is not that surprising as navicular is the Latin for boat-shaped. It was decided by anatomists in 1955 to use navicular solely for the foot and scaphoid for the hand, as it was felt confusing and unnecessary to duplicate names of bones in two different parts of the body, as detailed in the Parisiensia Nomina Anatomica, one of the forerunners of the Terminologia Anatomica 9.
More rarely, has been the use of the word scaphoid to refer to the navicular bone of the foot, usually as part of the term "tarsal scaphoid" 10.
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