Scaphoid

Contents

• Name of bone
• Location/Articulation
• Muscle and ligament attachments
• Surface anatomy
• Clinical significance
• Palpation

Name of bone

Scaphoid

Location/Articulation

The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and the forearm on the thumb side of the wrist (also called the lateral, or radial, side). The scaphoid bone is the largest bone of the proximal row of wrist bones, its long axis being from above downward, lateral, and forward. It is approximately the size and shape of a medium-sized cashew.

Muscle and ligament attachments

Surface anatomy

• The superior surface of the scaphoid is convex, smooth, and of triangular shape; it 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, and the medial, articulating 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.

Figure 1. Scaphoid surface anatomy

Clinical significance

The scaphoid can be slow to heal because of the limited circulation to the bone. It receives its blood supply primarily from lateral and distal branches of the radial artery. 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; improper healing after a fracture increases the likelihood of osteoarthritis and can even lead to avascular necrosis of the proximal segment. Even rapidly immobilized fractures may require surgical treatment, including use of the Herbert screw to bind the two halves together.

A condition called scapholunate instability can occur when the scapholunate ligament (connecting the scaphoid to the lunate bone) is disrupted.

Palpation

The scaphoid can be palpated at the base of the anatomical snuff box. It can also be palpated in the volar (palmar) hand/wrist. Its position is at 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.

Attachments:

scaphoid.png (image/png)