Scaphoid bone

The scaphoid bone is the largest bone of the proximal carpal row of the wrist, named for its elongated, boat-like (navicular) or twisted peanut three-dimensional shape. It occupies a radial position in the proximal row and functions as the key mechanical link bridging the proximal and distal carpal rows, making it central to wrist stability, load transmission, and coordinated motion (flexion, extension, and radial/ulnar deviation).

Structure. It is described in three regions—a proximal pole, a waist (isthmus), and a distal pole bearing a palmar tubercle—along with a dorsal ridge. Roughly 80% of its surface is covered by articular cartilage, which limits the areas available for ligamentous attachment and vascular entry.

Articulations. The scaphoid articulates with five bones: the scaphoid fossa of the distal radius proximally, and the lunate, capitate, trapezium, and trapezoid.

Blood supply. Vascularization derives principally from dorsal and palmar branches of the radial artery, entering at the dorsal ridge and distal pole and perfusing the bone in a retrograde (distal-to-proximal) direction. This retrograde pattern leaves the proximal pole dependent on distal inflow, predisposing proximal and waist fractures to nonunion and avascular necrosis.

Clinical relevance. It is the most commonly fractured carpal bone, typically after a fall on an outstretched hand, and its fragile blood supply and cartilage-dominated surface underlie its notable risk of delayed union, nonunion, and osteonecrosis.

Gray's description:

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

• 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 trapezium, the medial with the trapezoid.

• 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 forwardand 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.