Bone:Carpal bones:Names of all bones

The eight bones forms a semicircle. The convexity is proximal and articulates with the forearm. The distal row articulates with the metacarpal bases. Flexor surface is deeply concave to accommodate for flexor tendons. The extensor surface is convex for the extensor tendons to pass across it. The bones lie in two rows from lateral to medial: proximally- scaphoid, lunate and triquetrum and pisiform. Distally trapezium, trapezoid, capitate and hamate.

The **scaphoid bone**is the largest of the proximal row of carpal bones and forms the radial portion of the carpal tunnel.

The scaphoid on the lateral 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 by the waist.

* The waist, the commonest site of scaphoid fracture, is in the mid lateral portion and location for vascular channel and ligament attachment.
* 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: smooth convex surface for distal radius
* distal surface: laterally with the trapezoid and trapezium; medially with the capitate, separated by a bony ridge
* ulnar surface: concave for 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 ventral 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 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. 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.

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.

Variant anatomy

* bipartite/tripartite scaphoid
* coalition with neighbouring bones (rare) - lunate, radius, capitate etc.
* scaphoid hypoplasia (as long as not associated with other skeletal dysplasias)
* accessory osscles, e.g. os centrale, os radiale externum

The **lunate** is one of the carpal bones and forms part of the proximal carpal row. it has a crescent-shape with a proximal convex articular facet and a distal concave articular facet. On the medial surface is a square-shaped facet and on the lateral surface is a semilunar facet. It is broader anteriorly than it is posteriorly.

Articulations

* along with the scaphoid and triquetrum forms the distal articular surface of the radiocarpal joint
* intercarpal articulations
	+ scaphoid (lateral)
	+ capitate (distal)
	+ triquetrum (medial)
	+ hamate (distal and medial)
* articulates with the triangular fibrocartilage complex

Attachments

Musculotendinous

* nil

Ligamentous

* scapholunate ligament
* lunotriquetral ligament

Blood supply

* branches from the dorsal radiocarpal arch and dorsal intercarpral arch supply the lunate via the dorsal and palmar surfaces (80%) or palmar surface only (20%)

Ossification

Ossification typically begins at age four and is complete by age six or seven.

Variant anatomy

* bipartite/tripartite
* variation in articular facets. The classification proposed by Veigas et al is arguably the most relevant:
	+ **type I lunates**: single distal articular facet for the capitate
	+ **type II lunates**: additional distal articular facet medially for the hamate
* lunotriquetral coalition (fusion)
* associated accessory ossicles
	+ os epilunatum (dorsal to lunate)
	+ os hypotriquetrum

**Other variants:**

lateral intercarpal space

ossicle for trapezoid/trapezium

Splitting of trapezoid

**Ossification of all carpal bones**

 Start in capitate, skips pisiform, and start at counterclockwise direction on volar surface of right carpus).

* capitate: 1-3 months
* hamate:  2-4 months
* triquetral: 2-3 years
* lunate: 2-4 years
* scaphoid: 4-6 years
* trapezium: 4-6 years
* trapezoid: 4-6 years
* pisiform: 8-12 years