Notes on Carpal Bones (Identification, Side Determination, Attachments & Articulations)

Notes on Carpal Bones (Identification, Side Determination, Attachments & Articulations)

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

1. The proximal row contains (from lateral to medial side):

(i) The scaphoid,

(ii) The lunate,

(iii) The triquetral, and

(iv) The pisiform bones.

2. The distal row contains in the same order:

(i) The trapezium,

(ii) The trapezoid,

(iii) The capitate, and

(iv) The hamate bones.

Identification:

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.

Side Determination :

General Points :

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 Points :

1. The scaphoid

The tubercle is directed laterally, forward and downwards.

2. The lunate

(i) A small semilunar articular surface for the scaphoid is on the lateral side.

(ii) A quadrilateral articular surface for the triquetral is on the medial side.

3. The triquetral

(i) The oval facet for the pisiform lies on the distal part of the palmar surface.

(ii) The medial and dorsal surfaces are continuous and nonarticular.

4. The pisiform

(i) The oval facet for the triquetral lies on the proximal part of the dorsal surface.

(ii) The lateral surface is grooved by the ulnar nerve.

5. The trapezium

(i) The palmar surface has a vertical groove for the tendon of the flexor carpi radialis.

(ii) The groove is limited laterally by the crest of the trapezium.

(iii) The distal surface bears a convexoconcave articular surface for the base of the first metacarpal bone.

6. The trapezoid

(i) The distal articular surface is bigger than the proximal.

(ii) The palmar nonarticular surface is prolonged laterally.

7. The 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.

8. The hamate

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

Attachments:

There are four bony pillars at the four corners of the carpus. All attachments are to these four pillars.

1. The tubercle of the scaphoid gives attachment to:

(i) The flexor retinaculum,

(ii) A few fibres of the abductor pollicis brevis.

2. The pisiform gives attachment to:

(i) Flexor carpi ulnaris,

(ii) Flexor retinaculum and its superficial slip,

(iii) Abductor digiti minimi,

(iv) Extensor retinaculum.

3. The trapezium has the following attachments:

(i) The crest gives origin to the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. These constitute muscles of thenar eminence. The distribution of median and superficial branch of ulnar nerves in the palm.

(ii) The edges of the groove give attachment to the two layers of the flexor retinaculum.

(iii) The lateral surface gives attachment to the lateral ligament of the wrist joint.

(iv) The groove lodges the tendon of the flexor carpi radialis.

4. Hamate.

(i) The tip of the hook gives attachment to the flexor retinaculum.

(ii) The medial side of the hook gives attachment to the flexor digiti minimi and the opponens digiti minimi.

Articulations:

1. The scaphoid articulates with the following bones: Radius, lunate, capitate, trapezium and trapezoid.

2. The lunate articulates with the following bones: Radius, scaphoid, capitate, hamate and triquetral.

3. The triquetral articulates with the following bones: Pisiform, lunate, hamate and articular disc of the inferior radioulnar joint.

4. The pisiform articulates only with the triquetral.

5. The trapezium articulates with the following bones: Scaphoid, 1st and 2nd metacarpals and capitate.

6. The trapezoid articulates with the following bones: Scaphoid, trapezium, 2nd metacarpal and capitate.

7. The capitate articulates with the following bones: Scaphoid, lunate, hamate, 2nd, 3rd and 4th metacarpals and trapezoid.

8. The hamate articulates with the following bones: Lunate, triquetral, capitate, and 4th and 5th metacarpals.

Ossification:

The year of appearance of centre of ossification in the carpal bones.