Carpal bones

From Ganfyd

Jump to: navigation, search

ΕΤΥΜΟΛΟΓΙΑ

Greek, karpos meaning 'wrist' or earlier 'to rotate'

The carpal bones (carpals, carpus) are the eight small bones that sit between the distal ends of the radius and ulna and the five metacarpals. They vary in size considerably, from the small pisiform and trapezoid to the larger capitate and scaphoid.

Carpal bones
Carpal.PNG
System: Skeletal system
Function: Support structure wrist and articulate with radius and ulnar proximally, metacarpals distally
Origin:
Branches:
Insertion:
Arterial supply:
Venous drainage:
Lymphatic drainage:
Innervation:
Vertebral levels:
Search for Carpal bones in Gray's.

Contents

Surface Anatomy

The capitate can be felt by identifying the middle metacarpal and then sliding proximally until reaching a slight depression. This is the location of the capitate, which becomes more prominent on flexion of the wrist.

All other bones can be identified from the capitate by their relative positions. The pisiform, scaphoid and hamate may be identified separately as detailed in their individual sections.

Shape

The bones are arranged in two carpal rows with four bones in each row. From radial to ulnar sides, the bones are:

Proximal row

Distal row

The pisiform articulates only with the triquetral, lying anteriorly. The other bones of the proximal row form an arch which is convex proximally, allowing articulation at the wrist. The distal row bulges proximally into this arch to fit tightly when the carpus is extended.

The dorsal surface of the carpal bones is convex, whilst the palmar surface is concave with a central groove, the borders being accentuated by the anterior position of pisiform and the anteriorly projecting hook of hamate medially, and the anterior tubercles of scaphoid and trapezium medially.

Ligaments

Flexor Retinaculum

The flexor retinaculum is an accessory ligament, formed from a thickening of the deep fascia on the palmar surface of the wrist, that bridges the carpal bones. It is attached medially to the to the pisiform and hook of the hamate. Laterally it attaches to the scaphoid and trapezium. It forms the roof of the carpal tunnel.

Proximal Row

  • A dorsal ligament connects scaphoid to lunate and lunate to triquetral
  • A palmar ligament connects scaphoid to lunate and lunate to triquetral
  • Interosseous ligaments connect scaphoid to lunate and lunate to triquetral
  • A capsular ligament covers the pisotriquetral joint
  • In addition the pisohamate and pisometacarpal ligaments, neither true ligaments, connect the pisiform to the hamate and little metacarpal respectively.

Distal Row

  • A dorsal ligament connects trapezium to trapezoid, trapezoid to capitate, and capitate to hamate
  • A palmar ligament connects trapezium to trapezoid, trapezoid to capitate, and capitate to hamate
  • Interosseous ligaments connect trapezium to trapezoid, trapezoid to capitate, and capitate to hamate. The ligament connecting capitate to hamate is strong, one or both of the other two may be absent.

Collateral Ligaments

  • The ulnar collateral carpal ligament attaches the tip of the ulna styloid to the triquetral and pisiform
  • The radial collateral carpal ligament attaches the tip of the radial styloid to the scaphoid and occasionally trapezium
  • A radial collateral ligament connects the scaphoid and trapezium at the midcarpal joint
  • An ulnar collateral ligament connects the triquetral and hamate at the midcarpal joint

Wrist ligaments

Muscles

Joints

  • The wrist is an articulation between the triangular articular disc attached to the ulnar styloid process, the distal radius and the proximal articular surfaces of the scaphoid, lunate and triquetral.
  • The midcarpal joint between the two rows articulates the scaphoid, lunate and triquetral proximally with the trapezium, trapezoid, capitate and hamate distally
  • The small pisotriquetral joint between pisiform and triquetral
  • The other intercarpal joints have a very limited degree of movement due to the strong ligaments binding the rows together
  • The carpometacarpal joint of the thumb is an articulation between the trapezium and the metacarpal bone of the thumb.
  • The other carpometacarpal joints:
    • Between the trapezium, trapezoid and the index metacarpal
    • Between the capitate and the middle metacarpal
    • Between the capitate, hamate and ring metacarpal
    • Between the hamate and little metacarpal.

Direct Relations

Ossification

Each carpal bone is ossified from a single centre, starting with the largest (capitate and hamate) in the first few months and continuing until the smallest (pisiform) which starts to ossify in the ninth to twelfth years.

Variations

An os centrale may occur between scaphoid, trapezoid and capitate; this usually fuses with the scaphoid during the second prenatal month.

See also

Individual carpal bones

Personal tools