Touching Lives - November 2007
Cartilage is a structural material used throughout the body and can be thought of as like bone but without the mineral content. One kind gives rigidity to the external ear; there it behaves like a stiff rubbery substance composed largely of strands of a protein called collagen (incidentally, collagen, when it is boiled, becomes old-fashioned glue, and when purified, gelatine). If the ear is frequently damaged, for example in boxing, the cartilage is robbed of its blood supply and so deteriorates and curls up, resulting in ‘cauliflower ear’.
A more important site for cartilage is the inside of joints, such as the hip, where the ball-shaped end of the femur moves within a spherical cup in the pelvis.The surfaces in contact are both covered with a shining white incredibly smooth layer of articular cartilage, with very low friction, lubricated with synovial fluid.
Cartilage behaves like a very tough sponge containing water, cushioning the load (even ordinary walking imposes an impact load equivalent to three times the body weight at every step). It is perhaps not surprising therefore that cartilage wears and cracks after long use giving rise to a very painful joint, which may have to be replaced by an artificial one.This now relatively common hip operation was pioneered in the 1960s by Sir John Charnley, who was supported by Action Medical Research.
Another site where cartilage can prove troublesome is between the vertebrae of the spine.The spine is made up of bony segments, with the spinal cord going up a channel through the middle, and nerves sprouting out sideways at every junction to connect the brain to muscles and organs. Between every vertebra there is a disk made largely from cartilage, to prevent bone grinding on bone, to promote flexibility and to protect against shocks. A ‘slipped disk’, has not actually slipped out of place, but the softer centre can be displaced and pressure is exerted on the nerves or the spinal cord, causing pain.
Bearing in mind how much battering our cartilage has to take in a lifetime of walking and bending, it is a very remarkable substance. TL