Scaphoid

Original Editor

Top Contributors - Nina Myburg, Kim Jackson, Chrysolite Jyothi Kommu, Nikhil Benhur Abburi and Vidya Acharya

Description

The navicular bone is the largest bone of the proximal row, and has received its name from its fancied resemblance to a boat. It 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 articulateswith 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 navicular articulates with five bones: the radius proximally, greater and lesser multangulars distally, and capitate and lunate medially.

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

The scaphoid is situated between the proximal and distal rows of carpal bones. It is located on the radial side of the wrist, and articulates with the radius, lunate, trapezoid, trapezium and capitate.^[1]:176 Over 80% of the bone is covered in articular cartilage.^[2]

Bone[edit]

The palmar surface of the scaphoid is concave, and forming a tubercle, giving attachment to the transverse carpal ligament. The proximal surface is triangular, smooth and convex, and articulates with the radius and adjacent carpal bones, namely the lunate, capitate, trapezium and trapezoid.^[2] The lateral surface is narrow and gives attachment to the radial collateral ligament. The medial surface has two facets, a flattened semi-lunar facet articulating with the lunate bone, and an inferior concave facet, articulating alongside the lunate with the head of the capitate bone.^[3]

The dorsal surface of the bone is narrow, with a groove running the length of the bone and allowing ligaments to attach, and the surface facing the fingers (anatomically inferior) is smooth and convex, also triangular, and divided into two parts by a slight ridge.^[3]

Blood supply[edit]

It receives its blood supply primarily from lateral and distal branches of the radial artery, via palmar and dorsal branches. These provide an "abundant" supply to middle and distal bone, but neglects the proximal portion, which relies on retrograde flow.^[1]:189 The dorsal branch supplies the majority of the middle and distal portions, with the palmar branch supplying only the distal third of the bone.^[2]

Variation[edit]

The dorsal blood supply, particularly of the proximal portion, is highly variable.^[1]:189 Sometimes the fibers of the abductor pollicis brevis emerge from the tubercle.^[3]

In animals[edit]

In reptiles, birds, and amphibians, this bone is instead commonly referred to as the radiale because of its articulation with the radius.

Function[edit]

The carpal bones function as a unit to provide a bony superstructure for the hand.^[4]:708 The scaphoid is also involved in movement of the wrist.^[1]:6 It, along with the lunate, articulates with the radius and ulna to form the major bones involved in movement of the wrist.^[4]The scaphoid serves as a link between the two rows of carpal bones. With wrist movement, the scaphoid may flex from its position in the same plane as the forearm to perpendicular.^{[1]:176–177}

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 the intersections of the long axes of the four fingers while in a fist, or the base of the thenar eminence. When palpated in this position, the bone will be felt to slide forward during radial deviation (wrist abduction) and flexion.

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

The etymology of the scaphoid bone (Greek: σκαφοειδές) is derived from the Greek skaphos, which means "a boat," and the Greek eidos, which means "kind".^[5] The name refers to the shape of the bone, supposedly reminiscent of a boat. In older literature about human anatomy,^[3] the scaphoid is referred to as the navicular bone of the hand (this time from the latin word “navis” = boat), since there is also a bone in a similar position in the foot which is called the navicular.