The Wrist Joint

The wrist has a large, three hundred and sixty degree cone of movement facing forwards at the end of the arm, a consequence of the close arrangement of the small carpal bones. Group movements or individual ones between the bones can occur and this allows precise control of the hand, thumb and fingers. The rows are arranged irregularly but in general two of the bones line up with the end of each of the metacarpals. This allows the creation of a line of several joints leading to each finger which enables the separate and flexible movements of the hand.

The wrist itself is positioned between the forearm and the hand and consists of eight small bones known as the carpal bones which are arranged in two rows and situated in between the ends of the radius and ulna and the metacarpal bones. The metacarpals run from the furthest row of carpal bones down towards the knuckles to join the finger bones. As the metacarpals are narrow and run almost parallel to each other this gives them the ability to flatten themselves out to make the hand wide or to curl themselves up to aid grasping, a very useful ability.

The neat, close group of carpal bones allows the wrist to perform a conical range of movement facing forwards, with a full 360 degree rotation possible. The bones can move as a group or to some degree individually to permit fine control of the thumb, fingers and hand. The rows are somewhat irregular but on average there are two bones in line with each metacarpal between it and the forearm. This pattern creates a series of joints in line with each other and permits a great variety of individual movements to translate into precise and varied positioning.

The thumb is the most manoeuvrable and astonishing part of the human hand. We possess an “opposable thumb” which is absent from apes and allows us to achieve the high levels of precision movements we require. On the outside of the hand the thumb’s metacarpal is not flat in the same plane as the others in the palm but is turned inwards, giving it the function of crossing the palm to allow the thumb to meet the ends of the fingers in gripping. Much of the specialised thumb movement comes from the junction of its carpal and metacarpal bones.

The movements of the carpal bones can be in unison in small amounts as they move together to allow a movement to occur. As the hands move small amplitudes of movement occur between the individual carpal bones and the carpal rows. The metacarpals are able to rotate around their long axes which allows the palm to be curled into a cupped position. As the palm moulds round to assist gripping it also allows the fingers to align so that they can effectively grip at the correct angle. Any loss of the accessory movements of the carpals and metacarpals can reduce the ability of the hand to function adequately.

Wrist function can be adversely affected by heavy work with the hands such as grasping and pulling heavy objects, pulling ropes and using vibrating machinery. When the hand is grasping something firmly the longitudinal forces this generates are very great as the carpal bones are compressed between the metacarpals and the forearm bones. This can cause a reduction in the essential accessory movements of the carpal bones. Forced extension of the wrist may wedge one of the carpal bones, the lunate, slightly forwards which causes pain and disability.

A fall on the outstretched hand (FOOSH) is the most typical reason for the wrist to be extended forcibly and a Colles fracture is a common result where the break is located in the last inch of the radius and ulna near the wrist. Older women are most likely to suffer from this fracture and although most attention is concentrated on the fracture there is often a significant soft tissue injury of the wrist bones as well. The fracture will heal in five or six weeks but pain, weakness and functional difficulty may persist for much longer, related to some extent to the loss of individual movements between the carpal bones.

Jonathan Blood Smyth is the Superintendent of Physiotherapy at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for physiotherapists in bradford visit his website.