Carpal Bones Anatomy

Carpus is the region between metacarpals and distal ends of radius and ulna. It corresponds to the region of wrist.

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 carpus is made up of 8 carpal bones, which are arranged in two rows.

1. The proximal row of carpal bones contains (from lateral to medial side) (i)the scaphoid, (ii)lunate, (iii) triquetral, and (iv) pisiform bones.

2. The distal row  of carpal bones contains in the same order (i) the trapezium, (ii) trapezoid, (iii) capitate, and (iv) hamate bones.

General Features of Carpal Bones

Carpal Bones and Hand

Identification of Carpal Bones

  1. The scaphoid, is boat-shaped and has a tubercle on its lateral side.
  2. The lunate, is half-moon-shaped or crescentic.
  3. The triquetral, is pyramidal in shape, and has an isolated oval facet on the distal part of the palmar surface.
  4. The pisiform, is pea-shaped, and has only one oval facet on the proximal part of its dorsal surface.
  5. The trapezium, is quadrangular in shape, and has a crest and a groove anteriorly. It has a concavoconvex articular surface distally.
  6. The trapezoid, resembles the shoe of a baby.
  7. The capitate, is the largest carpal bone, with a rounded head.
  8. The hamate, is wedge-shaped, with a hook near its base.

General Features of Carpal Bones

1. The proximal row is convex proximally, and concave distally.
2. The distal row is convex proximally and flat distally.
3. Each bone has 6 surfaces:
(i) The palmar and dorsal surfaces are non-articular except for the triquetral and pisiform.
(ii) The lateral surfaces of the two lateral bones (scaphoid and trapezium) are nonarticular.
(iii) The medial surfaces of the three medial bones (triquetral, pisiform and hamate) are nonarticular.

4. The dorsal nonarticular surface is always larger than the palmar nonarticular surface, except for the lunate, in which the palmar surface is larger than the dorsal.

The general points help in identifying the proximal, distal, palmar and dorsal surfaces in most of the bones. The side can be finally determined with the help of the specific points.

Specific Features of Different Carpal Bones

Scaphoid.

The tubercle is directed laterally, forwards and downwards.

Lunate.

  •  A small semilunar articular surface for the scaphoid is on the lateral side, and
  • A quadrilateral articular surface for the triquetral is on the medial side.

Triquetral.

  • The oval facet for the pisiform lies on the distal part of the palmar surface.
  • The medial and dorsal surfaces are continuous and nonarticular.

Pisiform

  • The oval facet for the triquetral lies on the proximal part of the dorsal surface.
  • The lateral surface is grooved by the ulnar nerve.

Trapezium

  • The palmar surface has a vertical groove for the tendon of the flexor carpi radialis
  • The groove is limited laterally by the crest of the trapezium
  • The distal surface bears a concavoconvex articular surface for the base of the first metacarpal bone.

Trapezoid.

  • The distal articular surface is bigger than the proximal.
  • The palmar nonarticular surface is prolonged laterally.

Capitate.

The dorsomedial angle is the distal-most projection from the body of the capitate. It bears a small facet for the 4th metacarpal bone.

Hamate.

The hook projects from the distal part of the palmar surface, and is directed laterally.

Individual Carpal Bones

Carpal bones are eight bones arranged in two rows, proximal and distal.

Carpal Bones – Distal and Proximal Rows Proximal: A=Scaphoid, B=Lunate, C=Triquetral, D=Pisiform Distal: E=Trapezium, F=Trapezoid, G=Capitate, H=Hamate

Proximal row has from lateral to medial side scaphoid, lunate, triquetral and pisiform.

Distal row has trapezium, trapezoid, capitate and hamate

Scaphoid

The scaphoid bone is the largest bone of the proximal row of carpal bones and is situated at the radial (radius bone) side of the carpus [See fig below].

It is approximately the size and shape of a medium sized cashew and its long axis is directed from above downward, lateralward, and forward.

Skaphe means “a boat,” and eidos means “form” in Greek. The name scaphoid is derived by combining two words signifying its shape.

Carpal Bones – Distal and Proximal Rows Proximal: A=Scaphoid, B=Lunate, C=Triquetral, D=Pisiform Distal: E=Trapezium, F=Trapezoid, G=Capitate, H=Hamate

Surfaces & Articulations

The superior surface is convex, smooth, of triangular shape, and articulates with 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 trapezium, the medial with the trapezoid.

Left Scaphoid Bone

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 has a 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 articulates with the lunate bone the inferior for the head of the capitate bone.

The distal convex surface articulates with trapezium and trapezoid.

Vascular Supply of Scaphoid

Scaphoid receives majority of its blood supply via dorsal vessels at or just distal to waist area, perfusing proximal pole in a retrograde fashion. Mojor blood supply of the scaphoid is through vascular branches of radial artery entering scaphoid through foramina along its dorsal ridge. It supplies 70-80% of bone, including entire proximal pole.

Second group arise from palmar & superficial palmar branches of radial artery & enter carpal scaphoid in region of its distal tubercle perfusing distal 20-30 % of bone, including tuberosity.

Because of its unusual retrograde vascular supply, the scaphoid has a high risk of nonunion and osteonecrosis after fracture.

Lunate

The lunate bone or semilunar bone is a carpal bone situated in the center of the proximal row of the carpus (wrist). {See diagram below}

Lunate is situated between the lateral scaphoid bone and medial triquetral bone. .

The name derives from the Latin luna which means “moon”, the lunate bone looks semi-similar to a crescent moon.

The superior surface, convex and smooth, articulates with the radius.

The inferior surface is deeply concave and articulates with the head of the capitate, and, by a long, narrow facet with the hamate.

 

Left Lunate Bone

The dorsal and palmar surfaces are rough, for the attachment of ligaments.

The lateral surface articulates with the scaphoid.

The medial surface is marked by a smooth, quadrilateral facet, for articulation with the triangular bone (triquetral).

Triquetral

The triquetral bone (also called triquetrum bone, pyramidal bone, three-cornered bone, and triangular bone) is located in the wrist on the medial side of the proximal row of the carpal bones between the lunate and pisiform bones. [See below]

It is on the ulnar side of the hand and articulates connects with the pisiform, hamate, and lunatebones.

It is the 3rd most commonly fractured bone out of all carpal bones fractures.

Left Triquetral Bone

The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone.

In Latin triquetrus which means “three-cornered.”

The superior surface presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist.

The inferior surface, directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments.

The volar surface presents, on its medial part, an oval facet, for articulation with the pisiform; its lateral part is rough for ligamentous attachment.

The lateral surface, the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate.

The medial surface, the summit of the pyramid, is pointed and roughened, for the attachment of the ulnar collateral ligament of the wrist.

Pisiform

The pisiform bone (also called pisiform or lentiform bone) is a small, pea-shaped carpal bone found in the proximal row of the carpal bones. It is located where the ulna joins the carpus (wrist). It articulates only with the triquetral.

It is a sesamoid bone.

Its dorsal surface presents a smooth, oval facet, for articulation with the triquetral.

The palmar surface is rounded and rough, and gives attachment to the transverse carpal ligament, flexor carpi ulnaris, abductor digiti quinti.

The lateral and medial surfaces are also rough, the former being concave, the latter usually convex.

Trapezium

The trapezium bone or greater multangular bone is a carpal bone situated at distal row on the radial side of the carpus, between the scaphoid and the first metacarpal bone.

Surfaces and Articulations

The inferior surface is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base of the first metacarpal bone.

The dorsal surface is rough.

Left Trapezium Bone, Lesser Multangular means Trapezoid and navicular is another name for scaphoid

The palmar surface is narrow and rough. At its upper part is a deep groove, it transmits the tendon of the Flexor carpi radialis.

The lateral surface is broad and rough, for the attachment of ligaments.

The medial surface presents two facets; the upper, large and concave, articulates with the trapezoid; the lower, small and oval, with the base of the second metacarpal.

Trapezoid

The trapezoid bone or lesser multangular bone is smallest bone in the distal row. [See fig].

It is s wedge-shaped and has having four articular facets touching each other, and separated by sharp edges.

Surfaces and Articulations

The superior surface, quadrilateral, smooth, and slightly concave, articulates with the scaphoid.

Left Trapezoid Bone, Greater Multangular is another name for trapezium. Navicular is another name for Scaphoid

The inferior surface articulates with the proximal end of the second metacarpal bone.

The dorsal and palmar surfaces are rough for the attachment of ligaments, the former being the larger of the two.

The lateral surface articulates with the trapezium.

The medial surface is concave and smooth in front, for articulation with the capitate rough behind, for the attachment of an interosseous ligament.

Capitate

Capitate bone is the largest of the carpal bones, and occupies the distal row in the center of the wrist.

It has

  • A rounded portion or head, which is received into the concavity formed by the scaphoid and lunatebones
  • A constricted portion or neck
  • The body. The bone is also found in many other mammals, and is homologous with the “third distal carpal” of reptiles and amphibians.

Capitatus in Latin means having a head.

Left Capitate Bone

Surfaces & Articulations

The superior surface is round, smooth, and articulates with the lunate bone.

The inferior surface is divided by two ridges into three facets, for articulation with the second, third, and fourth metacarpal bones, that for the third being the largest.

The dorsal surface is broad and rough.

The volar surface is narrow, rounded, and rough, for the attachment of ligaments and a part of the Adductor pollicis muscle.

The lateral surface articulates with the trapezoid by a small facet at its anterior inferior angle.

The medial surface articulates with the hamate nt.

The capitate articulates with seven bones

  • Scaphoid and lunate proximally
  • Second, third and fourth metacarpal distally
  • Trapezoid on the radial side, and hamate on the ulnar side.

Hamate

The hamate bone (unciform bone) is a wedge-shaped bone and has a hook-like process which projects from its volar surface. It is situated at the medial most side of distal row of carpal bones. It has a downward base that rests on the 4thand 5th metacarpal bones, and apex is directed upward and lateralward.

In Latin hamatus means hooked.

The superior surface, the apex of the wedge, is narrow, convex, smooth, and articulates with the lunate.

The inferior surface articulates with the fourth and fifth metacarpal bones, by concave facets which are separated by a ridge.

The dorsal surface is triangular and rough for ligamentous attachment.

The volar surface presents, at its lower and ulnar side, a curved, hook-like process, the hamulus, directed forward and lateralward.

The medial surface articulates with the triquetral bone by an oblong facet, cut obliquely from above, downward and medialward.

The lateral surface articulates with the capitate by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments

Hamate bone fracture is a common injury in baseball players. Radiological identification of hamate is used to do estimation of age.

Blood supply to the carpal bones can be divided in two

  • Extraosseous
  • Intraosseous

Extraosseous
There are six transeverse arches formed around the carpal bones with radial and ulnar artery forming longitudinal medial & lateral borders of these arches

These transverse arches are

  • Dorsal Intercarpal
  • Palmar Intercarpal
  • Dorsal Radiocarpal
  • Palmar Radiocarpal
  • Dorsal Basal Metacarpal
  • Deep Palmar

Dorsal intercarpal, palmar radiocarpal and deep palmar arches are dominant suppliers.

Scaphoid, pisiform & trapezium have direct branches off the Radial & Ulnar arteries

Intraosseous

There are three types of blood supplies in carpal bones and varies with bone

  • Scaphoid, capitate and lunate in 20% cases in few have only a single  vessels entering one surface.  In these large areas of bone is  dependent on single vessel
  • Hamate and trapezoid have more than one sites of vessel entry but lack significant anastomosis
  • Trapezium, 80% lunates, triquetrum and pisiform have got numerous anastomoses and rich internal network

The blood supply to most carpal bones enters the distal half, leaving the proximal half at risk

Text adapted from: Human Anatomy by BD Chaurasia, Wikipedia

Image Credit: Wikipedia

 

 

Incoming search terms:

  • carpal bones anatomy (62)
  • carpal (24)
  • carpal bone anatomy (24)
  • carpal anatomy (19)
  • carpal bones (15)
  • yhs-lavasoft (10)
  • 8 carpal bones (9)
  • diagram of carpal bones (6)
  • alternate name for carpals (5)
  • hand bone anatomy (4)

Comments

  1. says

    Dear Dr. Singh:

    Thank you for your page

    I just wanted to confirm with you the following:

    is the CREST of the Trapezium the same as the TUBERCLE of the Trapezium?

    Sincerely yours

    JD

  2. Dr Arun Pal Singh says

    @J D Carmo, MD,

    Sorry for such a long delay in my reply.

    Yes! They are same and in modern anatomy both terms have been replaced by TRAPEZIAL RIDGE.*

    Its good to have you here.

    Source: Human Osteology
    By Tim D. White, Michael T. Black, Pieter A. Folkens

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>