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The Wrist Joint Explained
The ability to position the fingers and thumb in precise postures is vital for the highly coordinated use of the hand and the wrist has a significant role to play in this function. The shoulder blade and the shoulder perform the gross positioning of the arm, the elbow places the hand at varying distances from the body, the forearm dictates the angle of the wrist and the wrist performs the final positioning of the hand. The closer to the hand the body parts come the more precise and fine the movement becomes.
The wrist joint is placed between the hand and the forearm bones and is made up of a group of eight small bones which occur in two rows with articulations on one side with the radius and ulna and on the other side with the metacarpals. The metacarpals, the long bones in the palm of the hand, run from the further row of carpal bones down to the knuckles where they join the fingers. The metacarpals are arranged in an almost parallel pattern and are long and slim bones, giving them the ability to rotate around each other to some degree and improve grip.The Human Wrist Joint
This tight grouping of carpal bones endows the wrist with a large range of movement of 360 degrees in a conical shape facing forward. They are able to make individual and group movements to improve the precise positioning of the hand, fingers and thumb. Even though the arrangement is a little untidy the two rows of bones do line up with more or less two bones at the end of each metacarpal separating this from the forearm. The large number of in-line joints created with this arrangement allows a high degree of adaptability and precision of movement.
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.
As an overall movement of the wrist occurs to achieve a specific objective, the carpal bones move both separately and together to facilitate this. The carpal bones exhibit small levels of movement in between each other and between the rows of bones. To achieve the very functional cupping position of the hand there is a rotational ability of the metacarpals in respect of each other. The curving of the palm which assists grasping also brings the fingers round with the rotation of the metacarpals and allows the fingers to operate at functional angles. The hand can lose some of its functional ability if the accessory movements of the bones are lost.
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.
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, editor of the Physiotherapy Site, writes articles about physiotherapy, physiotherapy, physiotherapists in Manchester, 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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Filed under back pain by on Jan 23rd, 2010. 
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