The scaphoid bone is one of the carpal

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s of the

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

. It is situated between the

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the Koala#Characteristics, koala (which has two thumb#O ...

and

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, techn ...

on the

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

side of the wrist (also called the lateral or radial side). It forms the radial border of the

carpal tunnel In the human body, the carpal tunnel or carpal canal is a flattened body cavity on the flexor ( palmar/volar) side of the wrist, bounded by the carpal bones and flexor retinaculum. It forms the passageway that transmits the median nerve and the ...

. 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 nut.

Structure

The scaphoid is situated between the proximal and distal rows of carpal bones. It is located on the radial side of the wrist, adjacent to the styloid process of the radius. It articulates with the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

lunate Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped lithic flake, flake removed from a stone tool during the process of pressure flaking. In the Natufian cu ...

trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

, trapezium, and capitate. Over 80% of the bone is covered in articular

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

Bone

The palmar surface of the scaphoid is concave, and forming a distal

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projectio ...

, giving attachment to the transverse carpal ligament. The proximal surface is triangular, smooth and convex. 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. The dorsal surface of the bone is narrow, with a groove running the length of the bone and allowing

ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

s 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.

Blood supply

It receives its blood supply primarily from lateral and distal branches of the

radial artery In human anatomy, the radial artery is the main artery of the lateral aspect of the forearm. Structure The radial artery arises from the bifurcation of the brachial artery in the antecubital fossa. It runs distally on the anterior part of the ...

, via palmar and dorsal branches. These provide an "abundant" supply to middle and distal portions of the bone, but neglect the proximal portion, which relies on retrograde flow. The dorsal branch supplies the majority of the middle and distal portions, with the palmar branch supplying only the distal third of the bone.

Variation

The dorsal blood supply, particularly of the proximal portion, is highly variable. Sometimes the fibers of the abductor pollicis brevis emerge from the tubercle.

In animals

In reptiles, birds, and amphibians, the scaphoid is instead commonly referred to as the ''radiale'' because of its articulation with the

Function

The carpal bones function as a unit to provide a bony superstructure for the hand. The scaphoid is also involved in movement of the wrist. It, along with the lunate bone, articulates with the

and

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

to form the major bones involved in movement of the wrist. 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.

Clinical significance

Fracture

Fractures of the scaphoid are the most common of the carpal bone injuries, because of its connections with the two rows of carpal bones. The scaphoid can be slow to heal because of the limited circulation to the

. Fractures of the scaphoid must be recognized and treated quickly, as prompt treatment by immobilization or surgical fixation increases the likelihood of the bone healing in anatomic alignment, thus avoiding mal-union or non-union. Delays may compromise healing. Failure of the fracture to heal ("non-union") will lead to post-traumatic

osteoarthritis Osteoarthritis is a type of degenerative joint disease that results from breakdown of articular cartilage, joint cartilage and underlying bone. A form of arthritis, it is believed to be the fourth leading cause of disability in the world, affect ...

of the carpus. One reason for this is because of the "tenuous" blood supply to the proximal segment. Even rapidly immobilized fractures may require surgical treatment, including use of a headless compression screw such as the Herbert screw to bind the two halves together. Healing of the fracture with a non-anatomic deformity (frequently, a volar flexed "humpback") can also lead to post-traumatic arthritis. Non-unions can result in loss of blood supply to the proximal pole, which can result in avascular necrosis of the proximal segment. Scaphoid fractures may be difficult to diagnose via plain x-ray. A repeat x-ray may be required at a later date, as might cross-sectional imaging via MRI or CT scan.

Other diseases

A condition called scapholunate instability can occur when the scapholunate ligament (connecting the scaphoid to the lunate bone) and other surrounding ligaments are disrupted. In this state, the distance between the scaphoid and

bones is increased. One rare disease of the scaphoid is called Preiser's Disease.

Palpation

The scaphoid can be palpated at the base of the

anatomical snuff box The anatomical snuff box or snuffbox or foveola radialis is a triangular deepening on the radial, dorsal aspect of the hand—at the level of the carpal bones, specifically, the scaphoid and trapezium bones forming the floor. The name originate ...

. 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 The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of muscles of the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex. The w ...

. 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.

Etymology

The word ''scaphoid'' () is derived from the Greek ''skaphos'', which means "a boat", and the Greek ''eidos'', which means "kind". The name refers to the shape of the bone, supposedly reminiscent of a boat. In older literature about

human anatomy Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross ...

, the scaphoid is referred to as the navicular bone of the hand (this time from the Latin ''navis'' for boat); there is also a bone in a similar position in the foot, which is called the navicular. The modern term for the bone in the hand is ''scaphoid''; in human anatomy the term ''navicular'' is reserved for the bone in the foot.

Additional images

File:Scaphoid bone (left hand) - animation01.gif, Scaphoid bone of the left hand (shown in red). Animation. File:Scaphoid bone (left hand) - animation02.gif, Scaphoid bone of the left hand. Close up. Animation. Image:Scaphoid bone1.jpg, Scaphoid bone. File:Gray219 - Scaphoid bone.png, Scaphoid shown in yellow. Left hand. Palmar surface. File:Gray220 - Scaphoid bone.png, Scaphoid shown in yellow. Left hand. Dorsal surface. File:Ospoignet - Scaphoid bone.png, Cross section of wrist (thumb on left). Scaphoid (labelled as "Navicular") shown in red. File:Dissection of the human hand - 01 - scaphoid bone.png, Wrist joint. Deep dissection. Posterior view. File:Slide1dsds - Scaphoid bone.png, Scaphoid forms the radial (thumb-side) border of the

. Wrist joint. Deep dissection. Anterior (palmar) view.

References

{{Authority control Skeletal system Wrist Bones of the hand Carpal bones