The elbow is the central joint of the arm and divides it up into two convenient halves, looking initially merely like a backwards and forwards hinge. On closer examination the elbow shows itself to be a remarkably clever and multi-talented joint. The humerus or upper arm bone connects with the two lower arm bones, the radius and the ulna. The elbow joint itself is formed from the lower end of the humerus and the upper end of the ulna which makes up the bony point of the elbow which can be easily felt. The upper end of the ulna has a ladle like shape which carries in its bowl the end of the humerus.
At the elbow the main component of the forearm joint is made up of the ulna which is a large expanded area, narrowing down to the ulnar head at the wrist where the radius is now much larger. Rotation of the lower arm is the main job of the radial joint with the humerus at the elbow, allowing the very useful twisting action of the lower arm. Along with the highly mobile and coordinated wrist, fingers and thumb, the whole unit makes a highly functional tool of the hand-arm complex. Elbows typically show an angle of bend when they are at rest from tension in the surrounding soft tissues.
If the palm is facing upwards the radius is along the outside of the forearm and the upper part of the bone is formed into a rounded prominence resembling a cotton reel, articulating with a bony area on the lower humerus. This radial head is closely positioned next to the ulna just inside it and there is a circular structure of ligamentous material, the radial ligament, which surrounds the head and holds it in place as it rotates. The radius performs the greatest amount of movement in forearm rotation, starting in line with the ulna and ending up rotated over it so the radius is on the inner side and the hand is palm downwards.
For manipulating objects it is very important to have the abilities of joint rotation. The thumb and fingers, the most important part of human coordination and precision, are relatively restricted in their freedom of movement. In order to permit the vast number of varying positions which are required to manage hand use, rotation is a vital function. Extension and flexion of the elbow joint, when combined with rotation, allows the hand to be placed in position with precision. At times this ability can be unhelpful as its usefulness may mean we repeat the exact same action a large number of times.
When we decide to reach forward for something we extend the elbow, turn the hand over, extend the wrist and position the fingers above the object, permitting at the same time the maximum power from the fingers. If you try and grip something firmly whilst flexing the wrist downwards you will find yourself unable to exert much strength. Pronation is the name given to the action of twisting the forearm so the palm faces down, and as these muscles only do this action they are not very strong.
The pronators’ lack of strength is a bit like the calf muscles which pull our feet up as we step and are much less powerful than the calf muscles which propel us. An inability to extend the wrist or pronate the forearm makes the process of gripping and holding objects difficult and awkward, as the main muscles of gripping are unable to exert full power.
The opposite movement, that of bending the elbow and turning the palm up, is known as flexion and supination. It is a much stronger movement than pronation and performed many times during a typical day from bringing food up to the mouth to turning a screwdriver. The biceps is the main muscle which flexes the elbow and it also supinates the forearm, with a further powerful supination action coming from a small muscle near the elbow joint called the supinator. The supinator originates in the same areas as the extensor muscles of wrist, an area called the common extensor origin.
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 physiothrapists in Southampton visit his website.
