The Elbow Joint

The elbow makes up the middle joint of the arm and makes two reasonable length and useful levers of the arm. At first glance the elbow looks like a simple forwards and backwards hinge but on looking more closely it is capable of a lot more. The upper arm bone (humerus) connects in the elbow with the two forearm bones, the ulna and the radius. The upper part of the ulna and the lower part of the humerus form the elbow joint, with the easily felt bony point of the ulna at the back of the joint. The end of the humerus has a rounded cylinder shape which is surrounded partially by the ulnar part of the joint.

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.

A bony protrusion on the cylindrical end of the humerus articulates with the upper part of the radius which is on the outer side of the elbow when the hand is facing upwards. The radial head is the other part of that articulation, a rounded part somewhat like a cotton reel, placed close to the ulna and held in place during rotatory movements by the radial ligament, a band of ligament surrounding the head. Forearm rotation is predominantly performed by the radius, beginning with it lying in parallel with the ulna and then turning and crossing over that bone to achieve the full pronation movement with the palm down.

The ability to rotate the forearm is a vital ability in the manipulation of objects. Much human activity and dexterity involves the thumb and fingers which are relatively restricted to forward and back movement. This means other movements are necessary to allow the endlessly varied positions we need to access with our hands. Elbow function combines flexing and extending the joint in combination with rotation, allowing smooth and coordinated movement of the hand. This precision and adaptability can have a negative side because it is so useful it can be repeated many times and to excess.

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.