Wrist Joint - Enabling Condyloid Articulation
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Wrist Joint : Enabling Condyloid Articulation

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 23 Apr 2014 - 14:06.

The wrist or the carpus joint is made of eight bones arranged in two rows of four each which helps in articulation with an ability to perform wide range of movements.

The lower end of the radius (one of the two long bones in the forearm) in the proximal row are made of  the navicular, lunate, triangular and pisiform bones below and the distal row is made of greater multangular, lesser multangular, capitate and hamate.

The articular surface of the radius and the under surface of the articular disc, together form a transversely elliptical concave surface. This concave surface is known as the receiving cavity which is meant to receive the convex surface called the condyle formed by the superior articular surfaces of the navicular, lunate, and triangular surface. It is this condyle which gives the wrist joint name as condyloid articulation.

The wrist joint is surrounded by a capsule, strengthened by four ligaments called the volar radiocarpal, the dorsal radiocarpal, the ulnar collateral and the radial collateral.

The capsule enables the small bones in the wrist called the carpal bones to glide easily during movements of the wrist.

The wrist joint has wide range of movements namely flexion (bending the hand over the wrist forwards), extension (bending the hand over the wrist backwards), abduction (moving the hand away from the midline), adduction (moving the hand toward the midline and circumduction (circular movements of the hand over the wrist joint)

These movements of the wrist joint need to be studied along with the carpus with which they are combined.

These articulations of the wrist joint are subdivided into three sets.

  • The articulations of the proximal row of carpal bones
  • The articulation of the distal row of carpal bones
  • The articulations of the two rows with each other.

Mention must be made about the carpal bones. There are eight carpal bones with different shapes and functions which play an important role in the formation of the wrist joint and its movements. They are divided into two rows namely those which are placed proximally meaning upwards when the hand is hanging down and those which are placed distally, that is downwards when the hand is hanging down.

The upper row of bones help certain movements over the wrist, the lower row articulate with those of the row above for certain movements as well as with movements of the metacarpals (bones for the fingers).Those of the proximal row, from the radial to the ulnar side, are named the navicular, lunate, triangular, and pisiform; those of the distal row, in the same order, are named the greater multangular, lesser multangular, capitate, and hamate.

The wrist joint therefore has intricate mechanism in performing various movements with the help of several bones in the forearm, the wrist and the hand.

All the carpal bones are extensively covered by the synovial membrane. It covers every carpal bone dividing itself according the shape of the bone. As it covers the carpals it sends prolongations to cover those who are placed far away. There is a separate synovial membrane between two carpal bones namely the pisiform and the triangular.

Of all the joints in the body the wrist joint is most vulnerable for fractures and dislocations which might affect any of the carpal bones (small bones) or the long bones of the fore arm, the radius and ulna. Besides a fracture, the ligaments over the bones may also get torn.

The carpal bones have common characteristics. Each bone with the exception of the pisiform has six surfaces. Of these, the anterior (front) and posterior (back) surfaces are rough and meant for attachments of the ligaments to keep them in place without any displacements during active movements. The dorsal surfaces of each bone are broader except in the case of the navicular and lunate.The superior (upper) and inferior (lower) surfaces of each bone are articular.

The one which is superior is generally convex and the inferior surface is concave to enable articulation with each other. The medial (towards midline) and the lateral (away from the midline) surfaces are also articular when in contact with contiguous bones and rough otherwise.

The structure of each carpal is similar to every other carpal with cancellous tissue and a layer of compact bone. Of the eight carpals, the navicular bone is the largest in the proximal row. It derives its name due to its resemblance to a boat.

Conditions of the wrist bone joint will be carried in a different article' called 'Writst Joint Conidtions.'

 

*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.