The skeleton is a bony frame linked together by joints which enables the human to carry out all its sophisticated movements, while at the same time providing protection for vulnerable organs, such as the brain, heart and lungs. Groups of muscles are attached to the bones and are arranged in opposition to each other around a joint so that as one group contracts the other relaxes.

As a result of this synchronised action joints move easily and smoothly, and while the person is still young, and hasn’t been subjected to heavy wear or abnormal stresses or strains, it moves without any difficulty, such as pain or stiffness. In time appreciable wear erodes the once healthy joint surface. In the well functioning joint any possible friction between the ends of the bones in the joints is reduced by cartilage. Cartilage is a glistening, slippery tissue, which covers the surfaces of the bones within the joint and act as a cushion and washer between the bone ends.

Once the cartilage has been worn away as happens once there is osteoarthritis, every movement becomes increasingly painful and the movements more stiff so that eventually they become agonising. The cartilage is assisted in its friction-reducing role by the synovial fluid in the joint. This clear fluid has the same role as lubricating oil in a machine allows repeated movements of the joint, and the articulated limbs to bear someone’s weight without any resulting damage. The joints are held together, and kept correctly aligned by strong ligaments, tough bands of fibrous material, which add to the strength of the joint capsule.