The Elbow

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.

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.

The upper end of the radius, which is positioned at the outside of the elbow when the palm is facing upwards, is shaped like a small cotton reel with the top against a bony protrusion on the base of the humerus. This part of the bone is called the head of the radius and is firmly attached to the ulna next to it by the radial ligament, a circular band of strong tissue encompassing the head and allowing it to rotate without slipping from its joint. When the forearm rotates it is the radius which does the vast majority of the work, starting from a position parallel to the ulna and then rotating over and inwards around it until the hand is in a palm down position.

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.

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.

Jonathan Blood Smyth is the Superintendent of Physiotherapists 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 physiotherapists in Brighton visit his website.