Editing Carpal bones

{{short description|Eight small bones that make up the wrist (or carpus) that connects the hand to the forearm}}
{{Infobox bone
| Name        = Carpal bones
| Latin       = os carpale<br>pl. ossa carpi
| Image       = Xray hand with color.jpg
| Caption     =
| Image2      = 3D Medical Animation Human Wrist.jpg
| Caption2    = Labelled image showing the eight carpal bones.
}}

The '''carpal bones''' are the eight small [[bone]]s that make up the [[wrist]] (carpus) that connects the [[hand]] to the [[forearm]]. The terms "carpus" and "carpal" are derived from the [[Latin]] [[wikt:carpus#Latin|carpus]] and the [[Greek language|Greek]] [[wikt:καρπός#Ancient Greek|καρπός]] (karpós), meaning "wrist". In [[human anatomy]], the main role of the carpal bones is to [[joint|articulate]] with the [[radius (bone)|radial]] and [[ulnar]] heads to form a highly mobile [[condyloid joint]] (i.e. [[wrist joint]]),<ref name="Kingston-126">Kingston 2000, pp 126-127</ref> to provide attachments for [[thenar]] and [[hypothenar]] muscles, and to form part of the rigid [[carpal tunnel]] which allows the [[median nerve]] and [[tendon]]s of the [[anterior compartment of the forearm|anterior forearm muscles]] to be transmitted to the hand and [[finger]]s.

In [[tetrapod]]s, the '''carpus''' is the sole cluster of bones in the wrist between the [[radius (bone)|radius]] and [[ulna]] and the [[metacarpus]]. The bones of the carpus do not belong to individual [[finger]]s (or toes in quadrupeds), whereas those of the metacarpus do. The corresponding part of the [[foot]] is the [[Tarsus (skeleton)|tarsus]]. The carpal bones allow the wrist to move and rotate vertically.<ref name="Kingston-126"/>

==Structure==
===Bones===
The eight carpal bones may be conceptually organized as either two transverse rows, or three longitudinal columns.

When considered as paired rows, each row forms an arch which is convex proximally and concave distally. On the palmar side, the carpus is concave and forms the [[carpal tunnel]], which is covered by the [[Flexor retinaculum of the hand|flexor retinaculum]].<ref name="Platzer-124">Platzer 2004, p 124</ref> The proximal row comprises the [[scaphoid bone|scaphoid]], [[lunate bone|lunate]], [[triquetral bone|triquetral]], and [[Pisiform bone|pisiform bones]] which articulate with the surfaces of the radius and distal carpal row, and thus constantly adapts to these mobile surfaces. Within the proximal row, each carpal bone has slight independent mobility.  For example, the scaphoid contributes to midcarpal stability by articulating distally with the trapezium and the trapezoid. In contrast, the distal row is more rigid as its transverse arch moves with the [[Metacarpal bones|metacarpals]].<ref name="Schmidt-29">Schmidt-Lanz 2003, p 29</ref>

[[Biomechanics|Biomechanically]] and clinically, the carpal bones are better conceptualized as three longitudinal columns:<ref name="Thieme-Atlas-224">''Thieme Atlas of Anatomy'' 2006, p 224</ref>
# Radial scaphoid column: scaphoid, trapezium, and trapezoid
# Lunate column: lunate and capitate
# Ulnar triquetral column: triquetrum and hamate
In this context the pisiform is regarded as a [[sesamoid bone]] embedded in the tendon of the [[Flexor carpi ulnaris muscle|flexor carpi ulnaris]].<ref name="Thieme-Atlas-224" /> 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.<ref name="Schmidt-29" />

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]].

===Joints===
{{image frame|width=255
|content={{Human hand bones|width=250}}
|caption=Carpal bones and their articulations. Carpal bones are shown in violet. Human left hand, anterior (palmar) view.
}}
{| class="wikitable"
|+ What each carpal bone joints to<ref name="Platzer-126">Platzer 2004, p 126</ref>
! Name !! Proximal/radial<br />articulations !! Lateral/medial<br />articulations !! Distal/metacarpal<br />articulations
 |-
 ! colspan="4" | Proximal row
 |-
 | [[Scaphoid bone|Scaphoid]] || [[radius (bone)|radius]] || capitate, lunate || trapezium, trapezoid
 |-
 | [[Lunate bone|Lunate]] || radius, articular disk || scaphoid, triquetral || capitate, hamate (sometimes)
 |-
 | [[Triquetrum bone|Triquetrum]] || articular disk || lunate, pisiform || hamate
 |-
 | [[Pisiform bone|Pisiform]] || &nbsp; || triquetral || &nbsp;
 |-
 ! colspan="4" | Distal row
 |-
 | [[Trapezium (bone)|Trapezium]] || scaphoid  || trapezoid || [[first metacarpal bone|first]] and [[second metacarpal bone|second metacarpal]]
 |-
 | [[Trapezoid bone|Trapezoid]] || scaphoid || trapezium, capitate || second metacarpal
 |-
 | [[Capitate]] || scaphoid, lunate || trapezoid, hamate || [[third metacarpal bone|third]], partly second<br />and [[fourth metacarpal bone|fourth metacarpal]]
 |-
 | [[Hamate]] || triquetral, lunate || capitate || fourth and [[fifth metacarpal bone|fifth]]
|}

=== Accessory bones ===

[[Image:Carpalia accessoria cropped.jpg|thumb|Location of the accessory ossicles of the carpals]]
Occasionally [[accessory bone]]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.
<ref name="Platzer-124" />

==Development==

{| class="wikitable" align="right"
|+ Appearance of ossification centers of carpal bones<ref name="Schmidt-Lanz-6">{{cite book
 | url = https://books.google.com/books?id=L7a1tkBU8eMC
 | title = Surgical Anatomy of the Hand | page = 7
 | first1 = Hans-Martin | last1 = Schmidt | first2 = Ulrich | last2 = Lanz
 | publisher = Thieme | year = 2003
 | isbn = 1-58890-007-X
}}</ref><ref name=CHLT>{{cite journal|last1=Balachandran|first1=Ajay|last2=Kartha|first2=Moumitha|last3=Krishna|first3=Anooj|last4=Thomas|first4=Jerry|last5=K|first5=Prathilash|last6=TN|first6=Prem|last7=GK|first7=Libu|last8=B|first8=Krishnan|last9=John|first9=Liza|title=A Study of Ossification of Capitate, Hamate, Triquetral & Lunate in Forensic Age Estimation|journal=Indian Journal of Forensic Medicine & Toxicology|date=2014|volume=8|issue=2|pages=218–224|doi=10.5958/0973-9130.2014.00720.8|url=http://www.indianjournals.com/ijor.aspx?target=ijor:ijfmt&volume=8&issue=2&article=052|access-date=18 August 2014|issn=0973-9130|archive-date=25 January 2020|archive-url=https://web.archive.org/web/20200125215740/http://www.indianjournals.com/ijor.aspx?target=ijor:ijfmt&volume=8&issue=2&article=052|url-status=live|url-access=subscription}}</ref>
|-
! Bone !! Average !! Variation<ref name="Schmidt-Lanz-6"/> !! Variation<ref name=CHLT/>
|-
| [[Capitate]] || 2.5&nbsp;months || 1–6&nbsp;months || 1–5&nbsp;months
|-
| [[Hamate]] || 4–5.5&nbsp;months || 1–7&nbsp;months || 1–12&nbsp;months
|-
| [[Triquetrum bone|Triquetrum]] || 2&nbsp;years || 5&nbsp;months to 3&nbsp;years || 9&nbsp;months to 4&nbsp;years and 2&nbsp;months
|-
| [[Lunate bone|Lunate]] || 5&nbsp;years || 2–5.5&nbsp;years || 18&nbsp;months to 4&nbsp;years and 3&nbsp;months
|-
| [[Trapezium (bone)|Trapezium]] || 6&nbsp;years || 4–8&nbsp;years ||
|-
| [[Trapezoid bone|Trapezoid]] || 6&nbsp;years || 4–8&nbsp;years || 
|-
| [[Scaphoid]] || 6&nbsp;years || 4–7&nbsp;years ||
|-
| [[Pisiform]] || 12&nbsp;years || 8–12&nbsp;years ||
|}
The carpal bones are [[Endochondral ossification|ossified endochondrally]] (from within the cartilage) and the ossific centers appear only after birth.
<ref name="Platzer-126" />
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 muscle|flexor carpi ulnaris]] after more than ten years.
<ref name="Schmidt-Lanz-6" /> The commencement of ossification for each bone occurs over period like other bones. This is useful in forensic age estimation.<ref name=CHLT/>

==Function==

=== Ligaments ===
[[File:Braus 1921 201.png|thumb|500px|Four groups of ligaments in the region of the wrist (shown in four different colors.)]]
There are four groups of ligaments in the region of the wrist:<ref name="Platzer-130">Platzer 2004, p 130</ref>
# The ligaments of the [[wrist]] proper which unite the [[ulna]] and [[radius (bone)|radius]] with the carpus: the [[Ulnar collateral ligament of wrist joint|ulnar]] and [[Radial collateral ligament of wrist joint|radial collateral ligament]]s; the [[palmar radiocarpal ligament|palmar]] and [[dorsal radiocarpal ligament]]s; and the [[palmar ulnocarpal ligament]]. (Shown in blue in the figure.)
# The ligaments of the [[intercarpal articulations]] which unite the carpal bones with one another: the [[radiate carpal ligament]]; the [[dorsal intercarpal ligament|dorsal]], [[palmar intercarpal ligaments|palmar]], and [[interosseous intercarpal ligaments]]; and the [[pisohamate ligament]]. (Shown in red in the figure.)
# The ligaments of the [[carpometacarpal articulations]] which unite the carpal bones with the metacarpal bones: the [[pisometacarpal ligament]] and the [[palmar carpometacarpal ligaments|palmar]] and [[dorsal carpometacarpal ligaments]]. (Shown in green in the figure.)
# The ligaments of the [[intermetacarpal articulations]] which unite the metacarpal bones: the dorsal, interosseous, and palmar metacarpal ligaments. (Shown in yellow in the figure.)

=== Movements ===
{{Main|Anatomical terms of motion#Special motions of the hands and feet}}
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&nbsp;degrees. From the straight position two pairs of movements of the hand are possible: [[Abduction (kinesiology)|abduction]] (movement towards the radius, so called radial deviation or abduction) of 15&nbsp;degrees and [[adduction]] (movement towards the ulna, so called ulnar deviation or adduction) of 40&nbsp;degrees when the arm is in strict [[supination]] and slightly greater in strict [[pronation]].
<ref name="Platzer-132">Platzer 2004, p 132</ref>
[[Flexion]] (tilting towards the palm, so called palmar flexion) and [[Extension (kinesiology)|extension]] (tilting towards the back of the hand, so called dorsiflexion) is possible with a total range of 170&nbsp;degrees.
<ref name="Platzer-134">Platzer 2004, p 134</ref>

==== Radial abduction/ulnar adduction ====
[[File:Braus 1921 210.png|thumb|'''Left''': Ulnar adduction<br>'''Right''': Radial abduction]]
[[File:Braus 1921 214.png|thumb|'''Left''': Dorsiflexion<br>'''Right''': Palmar flexion]]
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.
<ref name="Platzer-132" />
Radial abduction is produced by (in order of importance) [[Extensor carpi radialis longus muscle|extensor carpi radialis longus]], [[Abductor pollicis longus muscle|abductor pollicis longus]], [[Extensor pollicis longus muscle|extensor pollicis longus]], [[Flexor carpi radialis muscle|flexor carpi radialis]], and [[Flexor pollicis longus muscle|flexor pollicis longus]].
<ref name="Platzer-172">Platzer 2004, p 172</ref>

'''Ulnar adduction''' causes a tilting or dorsal shifting of the proximal row of carpal bones.<ref name="Platzer-132" />
It is produced by [[Extensor carpi ulnaris muscle|extensor carpi ulnaris]], [[Flexor carpi ulnaris muscle|flexor carpi ulnaris]], [[Extensor digitorum muscle|extensor digitorum]], and [[Extensor digiti minimi muscle|extensor digiti minimi]].<ref name="Platzer-172" />

Both radial abduction and ulnar adduction occurs around a dorsopalmar axis running through the head of the capitate bone.
<ref name="Platzer-132" />

==== 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 &mdash; passing through the lunate bone for the proximal row and through the capitate bone for the distal row &mdash; palmar flexion occurs mainly in the [[radiocarpal joint]] and dorsiflexion in the [[midcarpal joint]].
<ref name="Platzer-134" />

Dorsiflexion is produced by (in order of importance) [[Extensor digitorum muscle|extensor digitorum]], [[Extensor carpi radialis longus muscle|extensor carpi radialis longus]], [[Extensor carpi radialis brevis muscle|extensor carpi radialis brevis]], [[Extensor indicis muscle|extensor indicis]], [[Extensor pollicis longus muscle|extensor pollicis longus]], and [[Extensor digiti minimi muscle|extensor digiti minimi]]. Palmar flexion is produced by (in order of importance) [[Flexor digitorum superficialis muscle|flexor digitorum superficialis]], [[Flexor digitorum profundus muscle|flexor digitorum profundus]], [[Flexor carpi ulnaris muscle|flexor carpi ulnaris]], [[Flexor pollicis longus muscle|flexor pollicis longus]], [[Flexor carpi radialis muscle|flexor carpi radialis]], and [[Abductor pollicis longus muscle|abductor pollicis longus]].
<ref name="Platzer-172" />

==== 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.<ref name="Platzer-134" />

==== Accessory movements ====
[[Anatomical terms of location#Anterior and posterior 2|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).
<ref name="Palastanga-184">Palastanga 2006, p 184</ref>

== Other animals==
{{See also|Carpus and tarsus of land vertebrates}}
The structure of the carpus varies widely between different groups of [[tetrapod]]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''', '''intermedium''', and '''ulnare''', after their proximal articulations, and are [[homology (biology)|homologous]] with the scaphoid, lunate, and triquetral 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 [[vertebrate]]s, including modern [[amphibian]]s, have undergone varying degrees of loss and fusion of these primitive bones, resulting in a smaller number of carpals. Almost all [[mammal]]s and [[reptile]]s, 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 fewer 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.<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 200–202|isbn= 0-03-910284-X}}</ref>

The carpus and tarsus are both described as podial elements or (clusters of) podial bones.<ref>{{Cite journal|last1=Galateanu|first1=Gabriela|last2=Hildebrandt|first2=Thomas B.|last3=Maillot|first3=Alexis|last4=Etienne|first4=Pascal|last5=Potier|first5=Romain|last6=Mulot|first6=Baptiste|last7=Saragusty|first7=Joseph|last8=Hermes|first8=Robert|date=2013-07-09|title=One Small Step for Rhinos, One Giant Leap for Wildlife Management- Imaging Diagnosis of Bone Pathology in Distal Limb|journal=PLOS ONE|language=en|volume=8|issue=7|pages=e68493|doi=10.1371/journal.pone.0068493|issn=1932-6203|pmc=3706412|pmid=23874643|bibcode=2013PLoSO...868493G|doi-access=free}}</ref>

In some [[Macropodidae|macropod]]s, the scaphoid and lunar bones are fused into the scapholunar bone.<ref>[http://home.brisnet.org.au/~mccready/Swamp%20Wallaby.htm Swamp Wallaby (''Wallabia bicolor'') carpals<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20070930015714/http://home.brisnet.org.au/~mccready/Swamp%20Wallaby.htm |date=2007-09-30 }}</ref>

In [[crustacean]]s, "carpus" is the scientific term for the claws or "pincers" present on some legs. (See [[Decapod anatomy]])

== Etymology ==
The Latin word "carpus" is derived from Greek {{lang|el|καρπὁς}} meaning "wrist". The root "carp-" translates to "[[wikt:pluck|pluck]]", an action performed by the wrist.<ref name="Diab-48">Diab 1999, p 48</ref>

== See also ==
{{Anatomy-terms}}
* [[Carpal tunnel]]
* [[Carpal tunnel syndrome]]
* [[List of mnemonics]]

== Notes ==
{{Reflist|2}}

==References==
* {{cite book
 | title = Lexicon of Orthopaedic Etymology
 | url = https://books.google.com/books?id=fstFQVnw8-wC&pg=PA49
 | first = Mohammad | last = Diab
 | publisher = Taylor & Francis | year = 1999
 | isbn = 90-5702-597-3
}}
* {{cite book
 | url = https://books.google.com/books?id=6DH97qvthj4C
 | title = Understanding joints: a practical guide to their structure and function
 | first = Bernard | last = Kingston
 | publisher = Nelson Thornes | year = 2000
 | isbn = 0-7487-5399-0
}}
* {{cite book
 | title = Anatomy and human movement: structure and function
 | url = https://books.google.com/books?id=rRtPExr9Hz8C&pg=PA178
 | first = Nigel | last = Palastanga |author2=Field, Derek |author3=Soames, Roger
 | publisher = Elsevier Health Sciences | year = 2006 | isbn = 0-7506-8814-9
}}
* {{cite book
 | first = Werner | last = Platzer
 | title = Color Atlas of Human Anatomy, Vol. 1: Locomotor System
 | publisher = [[Thieme Medical Publishers|Thieme]] | isbn = 3-13-533305-1<!---US: 1-58890-159-9--->
 | year = 2004 | edition = 5th
}}
* {{cite book
 | title = Surgical anatomy of the hand
 | url = https://books.google.com/books?id=L7a1tkBU8eMC&pg=PA29
 | first1 = Hans-Martin | last1 = Schmidt | first2 = Ulrich | last2 = Lanz
 | publisher = Thieme | year = 2003
 | isbn = 1-58890-007-X
}}
* {{cite book
 | title = Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System
 | publisher = Thieme | year = 2006 | isbn = 1-58890-419-9
}}

==External links==
{{Commons category}}
{{wiktionary}}
* {{SUNYAnatomyLabs|08|os|01|01}}—"Palm of the Hand: [https://www.knowyourbody.net/carpal-bones.html Carpal bones]"
* {{KansasHandKinesiology|bone/wrist.html}}

{{Bones of upper extremity}}
{{Authority control}}

[[Category:Carpal bones| ]]
[[Category:Bones of the hand]]
[[Category:Short bones]]
[[Category:Wrist]]