Scaphoid_bone

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Scaphoid bone

The scaphoid bone (hand navicular) of the wrist is found on the thumb side of the hand, within the anatomical snuffbox. It is known as the "navicular" in older texts, from its fancied resemblance to a boat. In modern usage, when used without modifiers, navicular refers to a bone in the tarsus.

It is approximately the size and shape of a cashew.

The scaphoid is the largest bone of the proximal row. It is situated at the radial side of the carpus, its long axis being from above downward, lateralward, and forward.

The etymology derives from the Greek skaphe which means "a boat," and the Greek eidos which means "form".

Surfaces

The superior surface is convex, smooth, of triangular shape, and articulates with the lower end of the radius.

The inferior surface, directed downward, lateralward, and backward, is also smooth, convex, and triangular, and is divided by a slight ridge into two parts, the lateral articulating with the greater multangular, the medial with the lesser multangular.

On the dorsal surface is a narrow, rough groove, which runs the entire length of the bone, and serves for the attachment of ligaments.

The volar surface is concave above, and elevated at its lower and lateral part into a rounded projection, the tubercle, which is directed forward and gives attachment to the transverse carpal ligament and sometimes origin to a few fibers of the Abductor pollicis brevis.

The lateral surface is rough and narrow, and gives attachment to the radial collateral ligament of the wrist.

The medial surface presents two articular facets; of these, the superior or smaller is flattened of semilunar form, and articulates with the lunate bone; the inferior or larger is concave, forming with the lunate a concavity for the head of the capitate bone.

The distal convex surface articulates with trapezium and trapezoid.

Clinical significance

It can be slow to heal because of the limited circulation to the bone. Fortunately, it is relatively difficult to break, but is the most commonly fractured bone in the carpus, particularly because of its unique anatomy and position within the wrist. Approximately 60% of carpal fractures are scaphoid fractures.

Fractures of the scaphoid must be recognized and treated quickly, as prompt treatment is the key to proper healing. Delays may complicate healing. Even rapidly immobilized fractures may require surgical treatment, including use of the Herbert screw to bind the two halves together.

Palpation

Other than the obvious anatomical snuff box position, the scaphoid can be palpated in the volar (palmar) hand/wrist. Its position is the intersections of the long axes of the four fingers while in a fist, or the base of the thenar eminence. When felt in this position, the bone will feel to slide forward during radial deviation (wrist abduction), and flexion.

Clicking of the scaphoid, or no anterior translation can indicate scapholunate instability.