Wrist

From ArticleWorld

The wrist is a complex joint that, in primates, connects the forearm to the hand and assists in the small motor function of the hand. Muscles around the wrist joint allow the wrist to move in 4-5 different motions. The rotation near the wrist that allows for turning the palm upward or downward is actually due to rotation of the forearm and does not involve much of the wrist movement.

Anatomy

The proximal (toward the body) aspect of the wrist joint is comprised of the distal ends of the radius and the ulna bones. The distal part of the joint is formed by 3 wrist bones, all of which are irregular in shape. The navicular (or scaphoid) bone, the lunate bone and the triquetral (or triangular) bone in the wrist itself together form the distal (the side closest to the hand) articular surface.

The remaining five bones of the wrist are the pisiform, the capitate, the hamate, the trapezoid and the trapezium bone. All of the bony parts of the wrist are tightly surrounded by a joint capsule and by several ligaments. The volar radiocarpal ligament is located on the inner aspect of the wrist and serves the dual purpose of supporting the joint and protecting important nerves and blood vessels that run under it.

The dorsal radiocarpal joint is located on the back of the wrist and is much thicker and stronger that its volar counterpart. The tendons that connect to and extend the fingers are partially fixed into place by this ligament. The ulnar collateral ligament is a cord-like ligament that splits to attach to the triquetral bone as well as the pisiform bone. The radiocarpal ligament is located on the same side as the thumb. It connects the lateral radius to the radial aspect of the navicular bone.

Function

The wrist can perform several movements. It can flex or bend forward. It can extend or tip backward. It can also abduct adduct, which are the movements that tip the wrist from side to side. The term, circumduction, refers to moving the wrist in a circular motion.

Conditions

As the wrist bones are relatively rounded, small and well protected, they rarely break, with the exception of the navicular bone which sometimes fractures in an injury. “Fractured wrists” actually involve fractures of the distal radius and ulna; however, the fracture line can extend into the joint surface.

The condition known as carpal tunnel syndrome involves the entrapment of the median nerve from swelling or thickening of the volar radiocarpal ligament underneath which the nerve travels. Symptoms include numbness and tingling of the palm of the hand, the first three digits and half of the fourth digit.