The 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.

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.

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.

The action of reaching out for something in front of us demands that we stretch out the elbow, turn the hand palm down and lift the fingers above the object to be gripped, a position which also allows the optimum hand power to be exerted. Trying to grip something strongly when the wrist is bent down is very ineffective and the force available is weak. Turning the forearm over so the palm faces down is known as pronation, and these muscles are weak as they have little more to do than turn the  weight of the arm.

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.

In contrast, the action of flexing the elbow and rotating the palm upwards is known as elbow flexion and forearm supination. This movement is very commonly done throughout our day and is a much more powerful action than pronation, with examples including using a screwdriver to bring a fork to the mouth to eat. The main flexor and supinator of the elbow is the biceps muscle with assistance from another, smaller but strong muscle known as supinator. On the outer side of the elbow is the common extensor origin where both the supinator and the muscles extending the wrist originate.