Introduction

Bone is a living structure. It is continuously being broken down by osteoclasts and built up again by osteoblasts. It has a blood supply and a nerve supply, and is therefore subject to diseases and problems just like the rest of the body. Perhaps because of its relatively low rate of turnover it is unusual for a primary bone tumour to occur, but bone is a common site for secondaries. Similarly, bone infection is rare but when it does occur it is very difficult to eradicate.

Articular cartilage has no blood supply at all. It receives its nutrition from synovial fluid. Its powers of healing are therefore very limited. Once damage occurs, repair is difficult if not impossible. Further breakdown is inevitable, slowly at first, then more rapidly.