Anatomy, Recognition, and Medical Insights of Carpal Bones

 

CARPAL BONES

Eight carpal bones, organized in two rows, make up the carpus. The proximal row contains the following bones (from lateral to medial side):

• The triquetral
• The lunate
• The scaphoid
• The pisiform

2. The items in the distal row are in the same order.

• The capitate
• The trapezoid
• The trapezium
• The hamate

Recognition

1. The lateral side of the boat-shaped scaphoid has a tubercle.
2. The lunate has a crescent or half-moon form.
3. The distal portion of the palmar surface contains an isolated oval facet on the pyramid-shaped triquetral.
4. The proximal portion of the dorsal surface of the pea-shaped pisiform contains a single oval facet.
5. The trapezium has a crest and a groove anteriorly, and it has a quadrangular shape. It features a distal sellar articular surface.
6. The trapezoid is similar to a baby's shoe.
7. The largest carpal bone, the capitate, has a rounded head 8. The lunate has a hook close to its base and is wedge-shaped.

Determination of the Side

Overview

1. The proximal row has concave distally and convex proximally.
2. The distal row is flat distally and convex proximally.
3. There are six surfaces on each bone.
   i. With the exception of the triquetral and pisiform surfaces, the palmar and dorsal surfaces are non-articular.
   ii. The two lateral bones, the trapezium and the scaphoid, have non-articular lateral surfaces.
   iii. The triquetral, pisiform, and hamate, the three medial bones, have non-articular medial surfaces.
4. With the exception of lunates, where the palmar non-articular surface is greater than the dorsal, the dorsal non-articular surface is always larger.
5. For the majority of bones, the general points aid in distinguishing the proximal, distal, palmar, and dorsal surfaces. The particular points can be used to ultimately identify the side.

Particulars

• The scaphoid:
  The tubercle points forward, downward, and laterally.
• The lunate:
  a. On the lateral side is a tiny semilunar articular surface for the scaphoid.
  b. On the medial side is a quadrilateral articular surface for the triquetral.
• The distal portion of the palmar surface is home to the oval facet of the pisiform in the triquetral region.
  The dorsal and medial surfaces are non-articular and continuous.
• The pisiform:
  a. The proximal portion of the dorsal surface is home to the oval facet for the triquetral.
  b. The ulnar nerve grooves the lateral surface.
• The trapezium:
  a. The flexor carpi radialis tendon is housed in a vertical groove on the palmar surface.
  b. The trapezium's crest limits the groove laterally.
  c. A sellar concavoconvex articular surface for the base of the first metacarpal bone is present on the distal surface.
• The trapezoidal
  a. Compared to the proximal, the distal articular surface is larger.
  b. Laterally, the palmar non-articular surface is extended.
• The capitate:
  a. The furthest projection from the capitate's body is the dorsomedial angle.
  b. A tiny facet corresponds to the fourth metacarpal bone.
• The humate:
  The hook extends laterally from the distal portion of the palmar surface.

Attachments

• At each of the carpus's four corners are four bony pillars. All connections are made to these four foundations.
• The flexor retinaculum and a few abductor pollicis breves fibres make up the scaphoid tubercle.
• Pisiform, which provides
  i. Flexor carpi ulnaris (FCU) is inserted.
  ii. A sesamoid bone in the FCU tendon is called the pisiform. Its superficial slip and Flexor retinaculum
  iii. Digitor abductor minimi
  iv. The retinaculum extends
• The trapezium
  i. The flexor pollicis brevis, opponens pollicis, and abductor pollicis brevis originate from the crest.
  ii. These are the thenar eminence muscles.
  iii. The two lavers of the flexor retinaculum are attached to the groove's margins. The wrist joint's lateral ligament is attached to the lateral surface
  iv. The tendon of the flexor carpi radialis is lodged in the groove.
• The hamate
  i. The flexor retinaculum
  ii It is attached to the hook's tip. Both the flexor and opponens digiti minimi can be attached to the hook's medial side.

Articulations

1. The lunate, scaphoid, trapezium, and trapezoid capitate.
2. The lunate: triquetral, hamate, capitate, scaphoid, and radius.
3. The articular disc of the inner radioulnar joint, as well as the pisiform, lunate, hamate, and triquetral.
4. The triquetral is the only way the pisiform articulates. 
5. The trapezium First and second metacarpals, trapezoid, and scaphoid.
6. The trapezoid: capitate, second metacarpal, trapezium, and scaphoid.
7. The capitate: trapezoid, lunate, hamate, second, third, and fourth metacarpals
8. The hamate Capitate, lunate, triquetral, and the fourth and fifth metacarpals.

OSSIFICATION

The year that the carpal bone's ossification center first appeared

MEDICAL ANATOMY

Scaphoid fractures are rather common. The bone breaks at a straight angle to its long axis through the waist. A fall on the outstretched hand or on the tips of the fingers causes the fracture. This results in pain when the thumb and index finger are percussionally moved longitudinally, as well as soreness and edema in the anatomical snuffbox. Compared to the wrist joint, the midcarpal joint has a more noticeable residual impairment. The fracture is significant because it increases the risk of non-union and avascular necrosis of the bone's body, which causes pain in the anatomical snuffbox.

Two nutritive arteries normally enter the dorsal surface of the body and the palmar surface of the tubercle, respectively, through the scaphoid. Both veins can occasionally enter through the distal portion of the bone or the tubercle (13% of instances). In certain situations, a fracture may rob the blood supply to the proximal part of the bone, resulting in avascular necrosis. Treatment options are similar to those for osteoarthritis. A fall onto the sharply dorsiflexed hand with the elbow joint flexed may result in lunate dislocation. This also causes the lunate to shift anteriorly, producing symptoms akin to carpal tunnel syndrome.