The Elbow Joint
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.
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.
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 wrist naturally extends when we reach out for something, bringing the fingers above the object to be grasped and allowing the fingers to exert their power best. Try and flex your wrist downwards, hold it there and grip something powerfully, it just doesn’t work. Turning the forearm over so the palm is down is called pronation, and this activity only ever works against the weight of the arm to position the hand for light activities such as grasping small objects or writing.
This means that the pronators are not powerful muscles as the only job they have to do is position the arm, a bit like the muscles which pull our feet up when walking. A lack of pronation or the ability to extend the wrist back when reaching makes gripping objects a clumsy procedure, with the primary power muscles of gripping inhibited in use.
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, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, physiotherapists in London, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
