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 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.

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 manoeuvrability of the thumb is one of the most amazing parts of the function of the hand. The “opposable thumb” that humans possess and which apes do not is one of the defining characteristics of precision movement and control. The metacarpal of the thumb on the outside of the hand is not inline with all the others but rotated inwards, having the ability to rotate further inwards to allow the end of the thumb to participate in grasping with one of the fingers. The thumb has a very specialised joint at the junction of the metacarpal and carpal, allowing the specialised movement.

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.

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, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Oxford. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.