The Human Elbow Joint

The arm is a long lever and the elbow breaks it up into two manageable halves, appearing at first like a straightforward hinge with back and forth movement. However the elbow can do much more than this and performs complex and useful motions. The two bones of the forearm , the radius and the ulna, connect with the humerus to form the elbow. The elbow consists of the junction between the upper expansion of the ulna and the lower expansion of the humerus, and the ulna is easily palpated as the obvious bony prominence behind the elbow. The humeral part of the joint is a cylinder like shape and the ulnar part mirrors it.

The major part of the elbow joint is composed of the the humerus and the enlarged upper end of the ulna, which gradually gets smaller as it travels down towards the wrist where the much larger bone is the radius. Up at the elbow the radial head performs the rotational movements of the forearm which are functionally so useful. This added dimension to the mobile joints of the fingers, thumb and wrist allows the high level of mobility and co-ordination available to the hand. The soft tissues around the elbow are usually dominant in a flexing direction, giving a degree of natural elbow bend at rest.

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.

Rotation of many body joints is a vital movement to possess to aid the manipulation of things with the hands. The thumbs and fingers are very mobile but possess movement mostly in one direction of forwards and back, so the ability to rotate the limb to position the direction of movement correctly for the fingers to be effective is essential. Along with rotation, bending and straightening the elbow joint allows the wrist and hand to be placed precisely in space for complex activities. This function can have a downside as it is so useful we repeatedly perform quite narrow actions and risk overuse problems.

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.

Elbow supination and flexion, the opposite of pronation and extension, occurs when the elbow is actively bent and the palm brought to face up. Typical functions involving this movement are taking food to the mouth with a fork and screwing in screws, so this is both a very common action indeed and one with much more strength than pronation. Supination and flexion of the elbow is primarily performed by the biceps muscle with a contribution from a smaller but strong muscle termed supinator. The common extensor origin is the area on the outer part of the elbow which has the origin of the extensor muscles of the wrist and supinator.