The Wrist
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 bones are a grouping of eight small bones called the carpal bones and which are arranged in two rows between the metacarpals and the ulna and radius of the forearm. From the end row of carpal bones the metacarpals run down the hand to the junction with the phalanges at the knuckles, making a mobile central hand area. Running virtually parallel to each other and being long and narrow the metacarpals can alter their positioning, either becoming flattened to support something large or rotated round to cup the palm for increased grasping 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.
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 carpal bones typically move in small motions which are reflected throughout the wrist, in other words they often move all together to accomplish a movement. There are small amounts of motion between all the carpal bones as the hand is moved, and with the ability of the metacarpals to rotate in regard to each other, this allows a cupping posture of the hand. Cupping the hand moulds the palm so that objects can be gripped and brings the fingers round to an appropriate angle to hold something. If the metacarpals lose the small accessory movements which occur between them this can affect the use of the wrist and so the ability of the hand.
Using the hands very heavily such as in gripping and holding heavy objects, hauling ropes or operating heavy machinery can adversely affect wrist function. The longitudinal forces which are generated across the wrist are very high as the hand grasping power is applied, compressing the carpal bones between the forearm and the metacarpals. The carpal bones can then suffer a reduction in the accessory movements possible between them. If the wrist is forcibly extended this may dislodge the lunate bone, one of the wrist bones, forwards and cause pain.
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, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in halifax. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
