Carpus
Encyclopedia
In tetrapod
s, the carpus is the sole cluster of bone
s in the wrist
between the radius
and ulna
and the metacarpus. The bones of the carpus do not belong to individual fingers (or toes in quadrupeds), whereas those of the metacarpus do. The corresponding part of the foot
is the tarsus
. The carpal bones allow the wrist to move and rotate vertically.
In human anatomy
, the main role of the carpus is to facilitate effective positioning of the hand and powerful use of the extensors and flexors of the forearm, but the mobility of individual carpal bones increase the freedom of movements at the wrist.
, the carpal bones can be classified as belonging to two transverse rows or three longitudinal columns.
The pair of rows together form an arch which is convex proximally and concave distally. On the palmar side, the carpus is concave, forming the carpal tunnel
which is covered by the flexor retinaculum
.
Because the proximal row is simultaneously related to the articular surfaces of the radius and the distal row, it adapts constantly to these mobile surfaces. The bones of this row - scaphoid, lunate, and triquetrum - have their individual movements. The scaphoid contributes to the stability of the midcarpus as it articulates distally with the trapezium and the trapezoid. The distal row is more rigid as its transverse arch moves with the metacarpals.
Biomechanically
and clinically, the carpal bones are better understood as arranged in three longitudinal columns:
In this context the pisiform is regarded as a sesamoid bone
embedded in the tendon of the flexor carpi ulnaris
.
The ulnar column leaves a gap between the ulna and the triquetrum, and therefore, only the radial or scaphoid and central or capitate columns articulate with the radius. The wrist is more stable in flexion than in extension more because of the strength of various capsules and ligaments than the interlocking parts of the skeleton.
(movement towards the radius, so called radial deviation or abduction) of 15 degrees and adduction
(movement towards the ulna, so called ulnar deviation or adduction) of 40 degrees when the arm is in strict supination
and slightly greater in strict pronation
.
Flexion
(tilting towards the palm, so called palmar flexion) and extension
(tilting towards the back of the hand, so called dorsiflexion) is possible with a total range of 170 degrees.
Radial abduction is produced by (in order of importance) extensor carpi radialis longus
, abductor pollicis longus
, extensor pollicis longus
, flexor carpi radialis
, and flexor pollicis longus
.
Ulnar adduction causes a tilting or dorsal shifting of the proximal row of carpal bones.
It is produced by extensor carpi ulnaris
, flexor carpi ulnaris
, extensor digitorum
, and extensor digiti minimi
.
Both radial abduction and ulnar adduction occurs around a dorsopalmar axis running through the head of the capitate bone.
.
Dorsiflexion is produced by (in order of importance) extensor digitorum
, extensor carpi radialis longus
, extensor carpi radialis brevis
, extensor indicis, extensor pollicis longus
, and extensor digiti minimi
. Palmar flexion is produced by (in order of importance) flexor digitorum superficialis
, flexor digitorum profundus
, flexor carpi ulnaris
, flexor pollicis longus
, flexor carpi radialis
, and abductor pollicis longus
.
The superior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated.
The structure in all is similar: cancellous tissue enclosed in a layer of compact bone.
Created from the initial letter of each of the eight carpal bones, in the order most commonly referenced, the sentence "some lovers try positions that they can't handle" is used as a mnemonic
device. Another mnemonic is So Long To Pinky, Here Comes The Thumb
s are found in the carpus, but of more than 20 such described bones, only four (the central, styloid, secondary trapezoid, and secondary pisiform bones) are considered to be proven accessory bones. Sometimes the scaphoid, triquetrum, and pisiform bones are divided into two.
The carpal bones are ossified endochondrally
(from within the cartilage) and the ossific centers appear only after birth.
The formation of these centers roughly follows a chronological spiral pattern starting in the capitate and hamate during the first year of life. The ulnar bones are then ossified before the radial bones, while the sesamoid pisiform arises in the tendon of the flexor carpi ulnaris
after more than ten years.
s, even among those that retain the full set of five digits. In primitive fossil amphibian
s, such as Eryops
, the carpus consists of three rows of bones; a proximal row of three carpals, a second row of four bones, and a distal row of five bones. The proximal carpals are referred to as the radiale, intermediale, and ulnare, after their proximal articulations, and are homologous
with the scaphoid, lunate, and triquetal bones respectively. The remaining bones are simply numbered, as the first to fourth centralia (singular: centrale), and the first to fifth distal carpals. Primitively, each of the distal bones appears to have articulated with a single metacarpal.
However, the vast majority of later vertebrates, including modern amphibians, have undergone varying degrees of loss and fusion of these primitive bones, resulting in a smaller number of carpals. Almost all mammals and reptiles, for example, have lost the fifth distal carpal, and have only a single centrale - and even this is missing in humans. The pisiform bone is somewhat unusual, in that it first appears in primitive reptiles, and is never found in amphibians.
Because many tetrapods have less than five digits on the forelimb, even greater degrees of fusion are common, and a huge array of different possible combinations are found. The wing of a modern bird
, for example, has only two remaining carpals; the radiale (the scaphoid of mammals) and a bone formed from the fusion of four of the distal carpals.
In some macropods, the scaphoid and lunar bones are fused into the scaphollunar bone.
In crustacean
s, "carpus" is the scientific term for the claws or "pincers" present on some legs. (See Decapod anatomy
.)
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s, the carpus is the sole cluster of bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s in the wrist
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;...
between the radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
and ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
and the metacarpus. The bones of the carpus do not belong to individual fingers (or toes in quadrupeds), whereas those of the metacarpus do. The corresponding part of the foot
Foot
The foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws...
is the tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
. The carpal bones allow the wrist to move and rotate vertically.
In human anatomy
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
, the main role of the carpus is to facilitate effective positioning of the hand and powerful use of the extensors and flexors of the forearm, but the mobility of individual carpal bones increase the freedom of movements at the wrist.
Etymology
The Latin word "carpus" is derived from Greek καρπὁς meaning "wrist". The root "carp-" translates to "pluck", an action performed by the wrist.As a whole
In human anatomyHuman anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
, the carpal bones can be classified as belonging to two transverse rows or three longitudinal columns.
The pair of rows together form an arch which is convex proximally and concave distally. On the palmar side, the carpus is concave, forming the carpal tunnel
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 middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue...
which is covered by the flexor retinaculum
Flexor retinaculum of the hand
The flexor retinaculum is a strong, fibrous band that arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, the carpal tunnel, through which the Flexor tendons of the digits and the median nerve pass.It is attached, medially, to the pisiform and the...
.
Because the proximal row is simultaneously related to the articular surfaces of the radius and the distal row, it adapts constantly to these mobile surfaces. The bones of this row - scaphoid, lunate, and triquetrum - have their individual movements. The scaphoid contributes to the stability of the midcarpus as it articulates distally with the trapezium and the trapezoid. The distal row is more rigid as its transverse arch moves with the metacarpals.
Biomechanically
Biomechanics
Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells. Perhaps one of the best definitions was provided by Herbert Hatze in 1974: "Biomechanics is the study of the structure and function of biological systems by means of...
and clinically, the carpal bones are better understood as arranged in three longitudinal columns:
- A radial scaphoid column consisting of the scaphoideum, trapezium, and trapezoideum
- A lunate column consisting of the lunate and capitate
- A ulnar triquetral column consisting of the triquetrum and hamatum.
In this context the pisiform is regarded as a sesamoid bone
Sesamoid bone
In anatomy, a sesamoid bone is a bone embedded within a tendon.Sesamoids are found in locations where a tendon passes over a joint, such as the hand, knee, and foot. Functionally, they act to protect the tendon and to increase its mechanical effect. The presence of the sesamoid bone holds the...
embedded in the tendon of the flexor carpi ulnaris
Flexor carpi ulnaris muscle
The flexor carpi ulnaris muscle is a muscle of the human forearm that acts to flex and adduct the hand.-Origin and insertion:Flexor carpi ulnaris muscle arises by two heads - humeral and ulnar, connected by a tendinous arch beneath which the ulnar nerve and ulnar artery pass.* The humeral head...
.
The ulnar column leaves a gap between the ulna and the triquetrum, and therefore, only the radial or scaphoid and central or capitate columns articulate with the radius. The wrist is more stable in flexion than in extension more because of the strength of various capsules and ligaments than the interlocking parts of the skeleton.
Ligaments
There are four groups of ligaments in the region of the wrist:- The ligaments of the wristWristIn 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;...
proper which unite the ulnaUlnaThe ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
and radiusRadius (bone)The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
with the carpus: the ulnarUlnar collateral ligamentUlnar collateral ligament can refer to:* Ulnar collateral ligament * Ulnar collateral ligament * Ulnar collateral ligament...
and radial collateral ligamentRadial collateral ligamentRadial collateral ligament can refer to:* Radial collateral ligament * Radial collateral ligament * Radial collateral ligament...
s; the palmar and dorsal radiocarpal ligamentDorsal radiocarpal ligamentThe dorsal radiocarpal ligament less thick and strong than the volar, is attached, above, to the posterior border of the lower end of the radius; its fibers are directed obliquely downward and medialward, and are fixed, below, to the dorsal surfaces of the navicular , lunate, and triangular, being...
s; and the palmar ulnocarpal ligamentPalmar ulnocarpal ligamentThe palmar ulnocarpal ligament is a ligament in the hand.It consists of ulnolunate, ulnocapitate, and ulnotriquetal ligaments.-External links:* http://classes.kumc.edu/sah/resources/handkines/ligaments/wvdpalmulna.htm...
. - The ligaments of the intercarpal articulations which unite the carpal bones with one another: the radiate carpal ligamentRadiate carpal ligamentThe Radiate carpal ligament is a group of about seven fibrous bands which diverge in all directions on the palmar surface of the carpal bones. The majority of the bands radiate from the capitate to the scaphoid, lunate, and Triquetral bone bones....
; the dorsalDorsal intercarpal ligamentThe dorsal intercarpal ligament consists of a series of fibrous bands that extend transversely across the dorsal surfaces of the carpal bones, connecting them to each other....
, palmarPalmar intercarpal ligamentsThe palmar intercarpal ligaments are fibrous bands that extend transversely across the palmar surfaces of the carpal bones, connecting adjacent carpals. These are the ligaments that define the structure of the palmar arch....
, and interosseous intercarpal ligamentsInterosseous intercarpal ligamentsThe Interosseous intercarpal ligaments are short fibrous bands that connect the adjacent surfaces of the various carpal bones....
; and the pisohamate ligamentPisohamate ligamentThe pisohamate ligament is a ligament in the hand. It is the volar ligament that connects the pisiform to the hamate. It is a prolongation of the tendon of the Flexor carpi ulnaris.It serves as part of the origin for the abductor digiti minimi....
, - The ligaments of the carpometacarpal articulations which unite the carpal bones with the metacarpal bones: the pisometacarpal ligamentPisometacarpal ligamentThe pisometacarpal ligament joins the pisiform to the base of the fifth metacarpal bone.-External links:* http://classes.kumc.edu/sah/resources/handkines/ligaments/wvdpisometa.htm...
and the palmarPalmar carpometacarpal ligamentsThe palmar carpometacarpal ligaments have a somewhat similar arrangement to the dorsal carpometacarpal ligaments, with the exception of those of the third metacarpal, which are three in number:...
and dorsal carpometacarpal ligamentsDorsal carpometacarpal ligamentsThe dorsal carpometacarpal ligaments, the strongest and most distinct carpometacarpal ligaments, connect the carpal and metacarpal bones on their dorsal surfaces.... - The ligaments of the intermetacarpal articulationsIntermetacarpal articulationsIntermetacarpal Articulations - The bases of the second, third, fourth and fifth metacarpal bones articulate with one another by small surfaces covered with cartilage, and are connected together by dorsal, volar, and interosseous ligaments....
which unite the metacarpal bones: the dorsal, interosseous, and palmar metacarpal ligaments
Movements
The hand is said to be in straight position when the third finger runs over the capitate bone and is in a straight line with the forearm. This should not be confused with the midposition of the hand which corresponds to an ulnar deviation of 12 degrees. From the straight position two pairs of movements of the hand are possible: abductionAbduction (kinesiology)
Abduction, in functional anatomy, is a movement which draws a limb away from the median plane of the body. It is thus opposed to adduction.-Upper limb:* of arm at shoulder ** Supraspinatus** Deltoid* of hand at wrist...
(movement towards the radius, so called radial deviation or abduction) of 15 degrees and adduction
Adduction
Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...
(movement towards the ulna, so called ulnar deviation or adduction) of 40 degrees when the arm is in strict supination
Supination
Supination is a position of either the forearm or foot; in the forearm when the palm faces anteriorly, or faces up . Supination in the foot occurs when a person appears "bow-legged" with their weight supported primarily on the anterior of their feet.The hand is supine in the anatomical position...
and slightly greater in strict pronation
Pronation
In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
.
Flexion
Flexion
In anatomy, flexion is a position that is made possible by the joint angle decreasing. The skeletal and muscular systems work together to move the joint into a "flexed" position. For example the elbow is flexed when the hand is brought closer to the shoulder...
(tilting towards the palm, so called palmar flexion) and extension
Extension (kinesiology)
In kinesiology, extension is a movement of a joint that results in increased angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed elbow. Straightening of...
(tilting towards the back of the hand, so called dorsiflexion) is possible with a total range of 170 degrees.
Radial abduction/ulnar adduction
During radial abduction the scaphoid is tilted towards the palmar side which allows the trapezium and trapezoid to approach the radius. Because the trapezoid is rigidly attached to the second metacarpal bone to which also the flexor carpi radialis and extensor carpi radialis are attached, radial abduction effectively pulls this combined structure towards the radius. During radial abduction the pisiform traverses the greatest path of all carpal bones.Radial abduction is produced by (in order of importance) extensor carpi radialis longus
Extensor carpi radialis longus muscle
Extensor carpi radialis longus is one of the five main muscles that control movements at the wrist. This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the second metacarpal bone .-Function:As the name suggests, this muscle is an extensor at the...
, abductor pollicis longus
Abductor pollicis longus muscle
The abductor pollicis longus muscle is one of the extrinsic muscles of the hand. It lies immediately below the supinator muscle and is sometimes united with it.-Origin and insertion:...
, extensor pollicis longus
Extensor pollicis longus muscle
In human anatomy, the extensor pollicis longus is a skeletal muscle located dorsally on the forearm. It is much larger than the extensor pollicis brevis, the origin of which it partly covers, and acts to stretch the thumb together with this muscle....
, flexor carpi radialis
Flexor carpi radialis muscle
In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and abduct the hand.-Origin and insertion:This muscle originates on the medial epicondyle of the humerus...
, and flexor pollicis longus
Flexor pollicis longus muscle
The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb...
.
Ulnar adduction causes a tilting or dorsal shifting of the proximal row of carpal bones.
It is produced by extensor carpi ulnaris
Extensor carpi ulnaris muscle
In human anatomy, the extensor carpi ulnaris is a skeletal muscle located on the ulnar side of the forearm. It acts to extend and adduct at the carpus/wrist.Being an extensor muscle, extensor carpi ulnaris is on the posterior side of the forearm....
, flexor carpi ulnaris
Flexor carpi ulnaris muscle
The flexor carpi ulnaris muscle is a muscle of the human forearm that acts to flex and adduct the hand.-Origin and insertion:Flexor carpi ulnaris muscle arises by two heads - humeral and ulnar, connected by a tendinous arch beneath which the ulnar nerve and ulnar artery pass.* The humeral head...
, extensor digitorum
Extensor digitorum muscle
The extensor digitorum muscle is a muscle of the posterior forearm present in humans and other animals...
, and extensor digiti minimi
Extensor digiti minimi muscle
The extensor minimi digiti is a slender muscle of the forearm, placed on the ulnar side of the Extensor digitorum communis, with which it is generally connected....
.
Both radial abduction and ulnar adduction occurs around a dorsopalmar axis running through the head of the capitate bone.
Palmar flexion/dorsiflexion
During palmar flexion the proximal carpal bones are displaced towards the dorsal side and towards the palmar side during dorsiflexion. While flexion and extension consist of movements around a pair of transverse axes — passing through the lunate bone for the proximal row and through the capitate bone for the distal row — palmar flexion occurs mainly in the radiocarpal joint and dorsiflexion in the midcarpal jointMidcarpal joint
The midcarpal joint is formed by the scaphoid, lunate, and triquetral bones in the proximal row, and the trapezium, trapezoid, capitate, and hamate bones in the distal row. The distal pole of the scaphoid articulates with two trapezial bones as a gliding type of joint...
.
Dorsiflexion is produced by (in order of importance) extensor digitorum
Extensor digitorum muscle
The extensor digitorum muscle is a muscle of the posterior forearm present in humans and other animals...
, extensor carpi radialis longus
Extensor carpi radialis longus muscle
Extensor carpi radialis longus is one of the five main muscles that control movements at the wrist. This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the second metacarpal bone .-Function:As the name suggests, this muscle is an extensor at the...
, extensor carpi radialis brevis
Extensor carpi radialis brevis muscle
The Extensor carpi radialis brevis is shorter and thicker than the extensor carpi radialis longus. The longus muscle can be found above the distal end of the Extensor carpi radialis brevis.-Origin and insertion:...
, extensor indicis, extensor pollicis longus
Extensor pollicis longus muscle
In human anatomy, the extensor pollicis longus is a skeletal muscle located dorsally on the forearm. It is much larger than the extensor pollicis brevis, the origin of which it partly covers, and acts to stretch the thumb together with this muscle....
, and extensor digiti minimi
Extensor digiti minimi muscle
The extensor minimi digiti is a slender muscle of the forearm, placed on the ulnar side of the Extensor digitorum communis, with which it is generally connected....
. Palmar flexion is produced by (in order of importance) flexor digitorum superficialis
Flexor digitorum superficialis muscle
Flexor digitorum superficialis is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints....
, flexor digitorum profundus
Flexor digitorum profundus muscle
- References :...
, flexor carpi ulnaris
Flexor carpi ulnaris muscle
The flexor carpi ulnaris muscle is a muscle of the human forearm that acts to flex and adduct the hand.-Origin and insertion:Flexor carpi ulnaris muscle arises by two heads - humeral and ulnar, connected by a tendinous arch beneath which the ulnar nerve and ulnar artery pass.* The humeral head...
, flexor pollicis longus
Flexor pollicis longus muscle
The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb...
, flexor carpi radialis
Flexor carpi radialis muscle
In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and abduct the hand.-Origin and insertion:This muscle originates on the medial epicondyle of the humerus...
, and abductor pollicis longus
Abductor pollicis longus muscle
The abductor pollicis longus muscle is one of the extrinsic muscles of the hand. It lies immediately below the supinator muscle and is sometimes united with it.-Origin and insertion:...
.
Combined movements
Combined with movements in both the elbow and shoulder joints, intermediate or combined movements in the wrist approximate those of a ball-and-socket joint with some necessary restrictions, such as maximum palmar flexion blocking abduction.Accessory movements
Anteroposterior gliding movements between adjacent carpal bones or along the midcarpal joint can be achieved by stabilizing individual bones while moving another (i.e. gripping the bone between the thumb and index finger).Individual bones
Almost all carpals (except the pisiform) have six surfaces. Of these the palmar or anterior and the dorsal or posterior surfaces are rough, for ligamentous attachment; the dorsal surfaces being the broader, except in the lunate.The superior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated.
The structure in all is similar: cancellous tissue enclosed in a layer of compact bone.
| Name | Proximal/radial articulations | Lateral/medial articulations | articulations | radius Radius (bone) The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally... |
capitate, lunate | >- | radius, articular disk | scaphoid, triquetral | >- | articular disk | lunate, pisiform | >- | triquetral | >- | scaphoid | trapezoid | first First metacarpal bone The first metacarpal bone or the metacarpal bone of the thumb is the first bone of the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpophalangeal joint.... and second metacarpal >- | Trapezoid Trapezoid bone The trapezoid bone is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the palmar surface; and by its having four articular facets touching each... |
scaphoid | trapezium, capitate | >- | scaphoid, lunate | trapezoid, hamate | third Third metacarpal bone The third metacarpal bone is a little smaller than the second.The dorsal aspect of its base presents on its radial side a pyramidal eminence, the styloid process, which extends upward behind the capitate; immediately distal to this is a rough surface for the attachment of the extensor carpi... , partly second and fourth metacarpal Fourth metacarpal bone The fourth metacarpal bone is shorter and smaller than the third.The base is small and quadrilateral; its superior surface presents two facets, a large one medially for articulation with the hamate, and a small one laterally for the capitate.On the radial side are two oval facets, for articulation... >- | Hamate |
triquetral, lunate | capitate | fourth and fifth Fifth metacarpal bone The fifth metacarpal bone is the most lateral metacarpal.-Surfaces:It presents on its base one facet on its superior surface, which is concavo-convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal.On its ulnar side is a prominent tubercle... |
|---|
Created from the initial letter of each of the eight carpal bones, in the order most commonly referenced, the sentence "some lovers try positions that they can't handle" is used as a mnemonic
Mnemonic
A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...
device. Another mnemonic is So Long To Pinky, Here Comes The Thumb
Accessory bones
Occasionally accessory boneAccessory bone
An accessory bone is a bone which does not occur frequently in the body but is still present in a significantly large number of people.- Examples :...
s are found in the carpus, but of more than 20 such described bones, only four (the central, styloid, secondary trapezoid, and secondary pisiform bones) are considered to be proven accessory bones. Sometimes the scaphoid, triquetrum, and pisiform bones are divided into two.
Ossification
| Bone | Average | Variation |
|---|---|---|
| Capitate | 2.5 months | 1–6 months |
| Hamate | 4-5.5 months | 1–7 months |
| Triquetrum | 2 years | 5 months to 3 years |
| Lunate | 5 years | 2-5.5 years |
| Trapezium | 6 years | 4–8 years |
| Trapezoid | 6 years | 4–8 years |
| Scaphoid | 6 years | 4–7 years |
| Pisiform | 12 years | 8–12 years |
The carpal bones are ossified endochondrally
Endochondral ossification
Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...
(from within the cartilage) and the ossific centers appear only after birth.
The formation of these centers roughly follows a chronological spiral pattern starting in the capitate and hamate during the first year of life. The ulnar bones are then ossified before the radial bones, while the sesamoid pisiform arises in the tendon of the flexor carpi ulnaris
Flexor carpi ulnaris muscle
The flexor carpi ulnaris muscle is a muscle of the human forearm that acts to flex and adduct the hand.-Origin and insertion:Flexor carpi ulnaris muscle arises by two heads - humeral and ulnar, connected by a tendinous arch beneath which the ulnar nerve and ulnar artery pass.* The humeral head...
after more than ten years.
Evolutionary variations
The structure of the carpus varies widely between different groups of tetrapodTetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s, even among those that retain the full set of five digits. In primitive fossil amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, such as Eryops
Eryops
Eryops meaning "drawn-out face" because most of its skull was in front of its eyes is a genus of extinct, semi-aquatic amphibian found primarily in the Lower Permian-aged Admiral Formation of Archer County, Texas, but fossils are also found in New Mexico and parts of the eastern United...
, the carpus consists of three rows of bones; a proximal row of three carpals, a second row of four bones, and a distal row of five bones. The proximal carpals are referred to as the radiale, intermediale, and ulnare, after their proximal articulations, and are homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
with the scaphoid, lunate, and triquetal bones respectively. The remaining bones are simply numbered, as the first to fourth centralia (singular: centrale), and the first to fifth distal carpals. Primitively, each of the distal bones appears to have articulated with a single metacarpal.
However, the vast majority of later vertebrates, including modern amphibians, have undergone varying degrees of loss and fusion of these primitive bones, resulting in a smaller number of carpals. Almost all mammals and reptiles, for example, have lost the fifth distal carpal, and have only a single centrale - and even this is missing in humans. The pisiform bone is somewhat unusual, in that it first appears in primitive reptiles, and is never found in amphibians.
Because many tetrapods have less than five digits on the forelimb, even greater degrees of fusion are common, and a huge array of different possible combinations are found. The wing of a modern bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
, for example, has only two remaining carpals; the radiale (the scaphoid of mammals) and a bone formed from the fusion of four of the distal carpals.
In some macropods, the scaphoid and lunar bones are fused into the scaphollunar bone.
In crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, "carpus" is the scientific term for the claws or "pincers" present on some legs. (See Decapod anatomy
Decapod anatomy
The decapod crustacean, such as a crab, lobster, shrimp or prawn, is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess one pair of appendages, although in various groups these may be reduced or missing...
.)
See also
- Bone terminology
- Terms for anatomical location
- Carpal tunnelCarpal tunnelIn 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 middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue...
- Carpal tunnel syndromeCarpal tunnel syndromeCarpal Tunnel Syndrome is an entrapment idiopathic median neuropathy, causing paresthesia, pain, and other symptoms in the distribution of the median nerve due to its compression at the wrist in the carpal tunnel. The pathophysiology is not completely understood but can be considered compression...