The wrist-hand complex is a highly complicated tool which allows for the precise use of the hand and its very important role in human function, with the wrist a vital link in this process. The shoulder and scapula allow crude arm positioning, the elbow allows the distance from the body to be varied, the forearm sets the angle at which the wrist will be positioned and the wrist finishes off the last detail of hand positioning. As the joints get closer to the hand the smaller and more precise their movements.
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.
Human hand function is a highly complex process as the thumb, fingers and hand are placed in a precise posture to suit the task being performed, with the wrist performing a pivotal role. The major, less precise, arm positioning is provided by the shoulder and shoulder blade, the body to hand distance is controlled by the elbow, the wrist angle is set by the forearm and the last adjustments of hand position are performed by the wrist. The movements become more precise the closer the joint becomes to the wrist.
In the human hand the most specialised and most useful part is the thumb. Apes do not have the “opposable thumb” which humans possess and which allows us to perform the highly controlled manual activities we need to. Unlike the metacarpals of the palm, which all lie in one plane, the metacarpal of the thumb lies away from this plane and is rotatable across the palm of the hand, allowing the thumb to grip against the fingers. The joint between the thumb metacarpal and its carpal bone is unusual in structure and confers much specialised movement.
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.
The heavy use of the hands in manual work such as lifting and moving large objects, manipulating heavy machines and pulling ropes can damage the function of the wrist. High mechanical forces are generated when the hand grips something hard, squeezing the wrist bones between the metacarpal bones and the radius and ulna of the forearm. This can allow a reduction of the accessory movements between the individual wrist bones. The lunate bone can be moved from its position with painful consequences if the wrist is extended with force.
The commonest reason for the wrist to be extended forcibly is a FOOSH or a fall on the outstretched hand, which can result in a Colles fracture which involves the last inch of the radius and ulna near the wrist. The fracture, commonest in older females, is the most obvious part of the overall injury which results also in wrist sprain and soft tissue injury. Five to six weeks will be enough to heal the fracture but there may be weakness, pain and difficulty with use in the hand for a longer period, partly related to a upset in the inter carpal movements.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, Physiotherapists in Bournemouth, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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