Bones of Carpus | Gross Anatomy | Anjani Mishra

  GROSS STUDY OF CARPUS/CARPAL BONE

Bones of the Manus

Written By Anjani Mishra

Manus is the fourth segment of forelimb/thoracic limb

It consists of three segments;

• Carpus- consists of carpal bones
• Metacarpus- consists of metacarpal bones
• Digit/digits- consists of phalanges and sesamoid bones

General plan for Carpus (in domestic animals and birds) 

• A group of carpal bones are known as carpus.
• Carpus is the first segment of manus.
• Carpus consists of number of bones ranging from two to eight carpal bones in domestic animals and  birds.
• These bones are arranged in two rows; i.e., proximal row and distal row.
• The proximal row consists of two to four carpal bones and are arranged from medial to lateral as radial, intermediate, ulnar, and accessory carpal.
• The distal row consists of zero to four carpal bones and are arranged in the same manner as first, second, third, and fourth carpal.
• In case of fowl, the carpus consists of two bones, the radial and ulnar in the proximal row as   mammals. During fetal life the distal row of carpus is present which exist as cartilaginous bodies that fuse with the metacarpus as carpo-metacarpus.

Carpus(ox)

• It is the first section of the manus and consists of six short bones, arranged in two  rows; proximal and distal.
• The bones of carpus are arranged between the radius-ulna above and metacarpal bones below.
• The bones of the proximal row ( from medial to lateral) are: radial carpal ( scaphoid), intermediate carpal (semilunar), ulnar carpal (cuneiform), and accessory carpal (pisiform)
• Bones of the distal row are: second & third fused carpal (os magnum) and fourth carpal (unciform).
• The first carpal bone at the distal row is absent in cattle BUT present in pig, dog, rabbit and occasionally present in horse.

Carpals of Proximal Row(ox)

RADIAL CARPAL:

Shape: It is small, and somewhat compressed transversely.

Location: It is medial bone of the proximal row.

Relation/Articulation: 
           Proximally- the radius.
           Distally- the second & third fused carpal. 

           Laterally- the intermediate carpal and. 

           Medially- free.

Composition: It presents SIX surfaces of which THREE are articular

A)   Proximal Surface: is wide and convex in front; narrow and concave behind this surface articulates with the medial facet on the distal extremity of the radius.

B)    Distal Surface: is similar but narrower in front and wider behind. It articulated with the medial facet on the proximal surface of the second and third fused carpal bone.

C)   Lateral Surface: has upper and lower elongated facets for articulation with the medial surface of the intermediate carpal. The area between these two facets in rough and excavated.

D, E & F) Anterior, Medial and Posterior Surface: are continuous, rough and non-articular. The anterior surface is convex, the medial surface is slightly depressed and the posterior surface bears tubercles on its lower aspect.

INTERMEDIATE CARPAL:

      Shape: It is somewhat wedge shaped, being constricted in the middle and wider palmarly.

Location: It is second and the central bone of the proximal row of the carpus.

Relation/Articulation: 
             Proximally- the radius. 

             Distally- the second + third fused carpal and fourth carpal. 

             Laterally- the ulnar carpal. 

             Medially- the radial carpal.

Composition: It presents SIX surfaces of which FOUR are articular

A) Proximal Surface: is convex in front; concave behind, tapering medially and articulated with the middle facet on the distal extremity of the radius.

B) Distal Surface: is convexo-concave and is crossed by a ridge, which divides the surface into two unequal halves. The medial facet articulates with the lateral facet on the proximal surface of the 2^nd & 3^rd fused carpal bone. The lateral facet is larger and articulates with the medial facet on the proximal surface of the 4^th carpal.

C) Medial Surface: has tow facets separated by a rough excavated area for the articulation with the redial carpal.

D) Lateral Surface: is larger and has facets similar to those on the medial surface; these articulate with the facets on the medial surface of the ulnar carpal.

E) Anterior Surface: is convex and rough for ligamentous attachment.

F) Posterior Surface: is narrow and bears a tubercle on its lower part.

ULNAR CARPAL:

Shape: It is large and very irregular bone.

Location: The ulnar carpal is the outermost bone, situated lateral to the intermediate carpal.

Relation/Articulation: 
          Proximally- ulnar carpal articulates with the radius and the styloid process of ulna.
          Distally- the fourth carpal.
          Medially- the intermediate carpal.
          Posteriorly- the accessory carpal.

Composition: It presents SIX surfaces of which FOUR are articular

A) Proximal Surface: has concave facet that extends over the lateral surface. It articulates with the lateral facet on the distal extremity of the radius and styloid process of the ulna.

B) Distal Surface: is small, concave and articulates with lateral facet on the proximal surface of the 4^th carpal.

C) Medial Surface: have two facets on its anterior part, which articulates with the intermediate carpal. The area between two facets is rough and excavated.

D) Posterior Surface: is oblique and has an oval facets for articulation with the accessory carpal below this facet, the bone is extend in tuberous form.

E & F) Anterior and Lateral surfaces are non-articular, continuous and rough.

ACCESSORY CARPAL

•     It is short, thick, rounded piece of bone.
•     It is placed behind the ulnar carpal.
•     Its anterior surface has an oval concave facet for articulation with ulnar carpal.
•     The medial surface is concave while lateral is convex.
•    This bone articulates with the ulnar carpal anteriorly.

Carpals of  Distal Row

The First Carpal bone is absent in cattle. The distal row consists second and third fused carpal(medially) and the fourth carpal(laterally).
 

Second and Third Fused Carpal

Shape: The second and third carpal bones are fused to form a large quadrilateral bone. It is larger than fourth carpal.

Location: Situated medially at the distal row.

Relation/Articulation:

            Proximally- Articulates with the radial and intermediate carpal.

            Distally- Articulates with large metacarpal

            Laterally- Articulates with fourth carpal bone.

            Medially- free.

Composition: It has SIX surfaces of which THREE are articular

• The proximal surface: is wide and bears a concavo- convex articular surface divided by a ridge into two unequal halves. The medial facet of this surface is larger and articulates with the distal surface of the radial carpal. The lateral facet, is similar but narrower, and articulates with the medial facet on the distal surface of the intermediate carpal bone.
• The lateral surface: bears two facets for articulation with medial surface of the 4^th carpal bone. The area between these facets is rough and excavated.
• The distal surface: is flat and undulating (wavy outline), and articulates with the large metacarpal bone.
• The anterior and medial surfaces: are non-articular, continuous and convex, and rough for ligamentous attachment.
• The posterior surface: is narrow and non-articular.

Fourth Carpal

Shape: It is smaller quadrilateral  bone of distal row. It is thicker in front than behind.

Location: It is located laterally at the distal row.

Relation/Articulation:

 Proximally- Articulates with ulnar carpal and intermediate carpal.

            Distally- Large metacarpal.

            Medially- Second and third fused carpal bone.

            Laterally- Free.

Composition: It has SIX surfaces of which THREE are articular

           

Proximal surface: Articulates with intermediate carpal and ulnar carpal and is divided by an anterior-posterior ridge into two oblique areas. The medial facet is concavo-convex and articulates with the lateral facet on the distal surface of the intermediate carpal. The lateral facet is divided into two concave areas.

Medial surface: Presents two facets for articulation with the 2^nd and 3^rd fused carpal bone. The area between these facets is rough and excavated.

Lateral surface: It is encroached ( gradually intrude on others area), by the proximal surface and therefore, is very narrow, non- articular.

Anterior surface: It is convex, rough and continuous with the lateral surface, non articular.

Posterior surface: It is rough and tuberous and is non-articular.

Distal surface: It articulates with smaller articular area on the lateral side of the proximal extremity of the large metacarpal bone.

Comparison with:

A. Carpal bones of Horse:

• -        Consists of 7 bones, 4 in the proximal row and 3 in the distal row. Sometimes eight bones are present, when the first carpal is added.
• -         Bones in the proximal row are larger, more regular and shape resembles with the bones of ox.
• -         The radial carpal is the largest of the proximal row which is somewhat compressed and clearly six sided.
• -         The intermediate carpal is somewhat wedge shaped which bears a concave facet proximally for articulation with the radius.
• -         The ulnar carpal is smallest and most irregular bone of proximal row.
• -         The accessory carpal is flat, discoid and has a regular circumference. The lateral surface is grooved for the passage of the tendon of the ulnaris lateralis m/s.
• -         The first carpal bone is nodular when present and is placed behind the second carpal.
• -         The second carpal bone is the medial bone of the distal row and is irregularly hemispherical. It articulates distally with the 2^nd and 3^rd metacarpal bones.
• -         The third carpal  is the largest of the distal row, and is placed centrally. It is flattened proximodistally. It articulates distally with 3^rd metacarpal bone.
• -         The fourth carpal bone is larger than second carpal bone and bears a tubercle posteriorly. It is somewhat wedge shaped. It is the lateral bone of the distal row and articulates with 3^rd and 4^th metacarpal bones.

B. Carpal bones of pig:

• The carpus comprises eight bones, four in each row.
• The bones of the proximal row resemble those of the ox, with exception of the accessory, which is more like that of the horse, but has no lateral groove.
• The 1^st carpal is small, elongated from before backward, rounded and articulates in front with second carpal.
• The 2^nd carpal is high and narrow, and articulates with 2^nd & 3^rd metacarpal bones distally.
• The 3^rd carpal articulates with the radial and intermediate above, the third metacarpal bone below.
• The 4^th carpal is the largest bone of the row; articulates with the intermediate and ulnar above, the 4^th & 5^th metacarpals below, and bears a tuberosity.

C. Carpal bones of Dog:

• Carpus consists of 7 bones, 3 in the proximal row and 4 in the distal row.
• The radial and intermediate carpal bones are fused to form a single bone, and articulate distally with 1^st, 2^nd, and 3^rd carpal bones of distal row.
• The ulnar carpal bone is small and distally articulates with the 4^th carpal and extends downwards to articulate with the 5^th metacarpal.
• The accessory carpal bone is cylindrical, being constricted in the middle and has two facets on its anterior extremity, one for the ulna and other for ulnar carpal.
• The first carpal bone is smallest and articulates distally with the first metacarpal bone.
•  The 2^nd carpal bone is wedge shaped and articulates distally with the second metacarpal bone.
• The 3^rd carpal bone is similar to the 2^nd, but larger, and articulates distally with the 3^rd metacarpal.
• The 4^th carpal bone is the largest and articulates with 4^th and 5^th metacarpal bones.

D. Carpal bones of Goat:

• The carpal bones resemble those of the ox except in size.
• The accessory is long and less tuberous.

E) Carpal bones of fowl:

• There are 2 bones: – Radial and Ulnar carpal at the proximal row. 
• The bones the distal row are fused with the metacarpal bones.

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