The scaphoid bone is one of the

carpal The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, the ...

bone A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...

s of the

wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, 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 ...

. It is situated between the hand 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 most often used to describe the entire appendage of the upper limb, but which in ...

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

radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance, a directional coordinate in a polar coordinate system * Radial set * A bearing f ...

border of the

carpal tunnel In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the hand. The tunnel is bounded by the bones of the wrist and flexor retinaculum from connective tissue. Norma ...

. 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.

Structure

The scaphoid is situated between the proximal and distal rows of

carpal bone The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, t ...

s. It is located on the radial side of the wrist, and articulates with the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

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

trapezoid A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium (). A trapezoid is necessarily a Convex polygon, convex quadri ...

, trapezium, and

capitate The capitate bone is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone (the middle finger) and forms the third carpomet ...

. Over 80% of the bone is covered in articular cartilage.

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 projection ...

, giving attachment to the

transverse carpal ligament The flexor retinaculum (transverse carpal ligament, or anterior annular ligament) is a fibrous band on the palmar side of the hand near the wrist. It arches over the carpal bones of the hands, covering them and forming the carpal tunnel. Structur ...

. 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 the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal li ...

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 f ...

, 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 The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb. Structure The abductor pollicis brevis is a flat, thin muscle located just under the skin. It is a thenar muscle, and therefore contributes to th ...

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

, articulates with the

and

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

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 (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...

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 The Herbert screw (invented by Timothy Herbert) is a variable pitch cannulated screw typically made from titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, i ...

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 Post-traumatic arthritis (PTA) is a form of osteoarthritis following an injury to a joint. Classification Post-traumatic arthritis is a form of osteoarthritis and the former can occur after the latter. However, post-traumatic arthritis can also ...

. Non-unions can result in loss of blood supply to the proximal pole, which can result in

avascular necrosis Avascular necrosis (AVN), also called osteonecrosis or bone infarction, is death of bone tissue due to interruption of the blood supply. Early on, there may be no symptoms. Gradually joint pain may develop which may limit the ability to move. C ...

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 The scapholunate ligament is a ligament of the wrist. Rupture of the scapholunate ligament causes scapholunate instability, which, if untreated, will eventually cause a predictable pattern of wrist osteoarthritis called scapholunate advanced coll ...

(connecting the scaphoid to the

lunate bone The lunate bone (semilunar bone) is a carpal bone in the human hand. It is distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row carpal bones, which lie between the ulna and radius and the h ...

) 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 Palpation is the process of using one's hands to check the body, especially while perceiving/diagnosing a disease or illness. Usually performed by a health care practitioner, it is the process of feeling an object in or on the body to determine ...

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 originates ...

. 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 word ...

. 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 etymology of the scaphoid bone () 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, the scaphoid is referred to as the

navicular bone The navicular bone is a small bone found in the feet of most mammals. Human anatomy The navicular bone in humans is one of the tarsal bones, found in the foot. Its name derives from the human bone's resemblance to a small boat, caused by th ...

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. The medical term for the bone is the scaphoid, as the term "navicular" is solely reserved for the bone located in the tarsals of the human body.

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