For 10 years, Mrs Stockton coped. When the pain became too great, she was temporarily bedridden and forced to give up her work as a secretary. Cortisone injections in her left wrist helped to relieve the pain, but her right wrist was unresponsive to treatment. 'The inflammation had virtually solidified the joint so I couldn't bend it,' she says.
Last April, Mrs Stockton's painful wrist joint was fused using coral plucked from the warm-water reefs off New Caledonia in the south Pacific. Mrs Stockton, one of the first patients in Britain on whom coral was used, is now free of pain. Her operation was so successful that she can type with ease and is back at work: she says she has never been busier.
The standard surgical solution to Mrs Stockton's problem would have involved two operations. First, a lump of bone would have been chiselled from her pelvis. This is as painful as it sounds. The piece of hipbone would then have been inserted into her wrist during a second operation. This would make the wrist rigid but would stop the pain. It is an expensive and time-consuming procedure.
Several years previously Mrs Stockton, who is in her sixties, had undergone an operation to remove a small, diseased part of her ulna, one of the bones in the forearm, at the point where it meets the wrist bone. Following this experience, she was keen to keep surgery to a minimum.
'I had been warned by someone who had a hip-bone graft that it was terribly painful,' Mrs Stockton says. 'So when I learnt only one operation would be needed with the coral, I was delighted. All operations are painful, but it would have been far worse if I had needed two.'
In last year's operation dozens of small spheres of coral, each about 4mm across, were packed between and around the tiny carpal bones of the wrist and the radius, the second bone of the forearm. The surfaces of the wrist bones were first scraped to encourage new bone growth.
Two metal pins were inserted into Mrs Stockton's wrist, which was then set in plaster. After six weeks the pins were removed and the plaster cast replaced. When this was taken off six weeks later, the coral had dissolved and new bone growth had locked the wrist solid.
The bone forms a solid bridge across the wrist, so the joint cannot be flexed. 'My hand goes straight out from my arm now and I can't bend it, but the pain has completely gone,' Mrs Stockton says. She still has movement in her fingers, and is able to continue her secretarial career.
The decision to use coral was taken by Mr Bernard Meggitt, consultant orthopaedic surgeon at Addenbrooke's Hospital in Cambridge. For the past year he has been carrying out clinical trials to evaluate coral's medical usefulness. Mrs Stockton is one of three patients to have wrist operations using coral.
Coral is very similar in structure to bone: through a microscope it looks like a sponge full of tiny holes. When it is used to repair or replace bone, human blood vessels invade the holes and new bone begins to form. As new bone grows, the coral is absorbed and eventually disappears.
At Addenbrooke's, coral has been used successfully on 14 other patients to treat a range of conditions. Coral wedges have been used to straighten bent limbs; pieces have replaced shattered bones; and coral is going to be used next to repair damaged vertebrae. 'Coral is very strong,' explains Mr Meggitt. 'It won't collapse under load and so it's good for providing strength in spines. The advantage of coral is that bone cells dissolve away the coral and at the same time completely replace it with new, natural bone.
'Coral can also be kept in the storeroom of an operating theatre, so a bone graft is immediately available. Nor does it carry a risk of transmitting HIV or hepatitis that may exist with bone grafts from a donor. We are quite excited,' he says.
'Most bone substitutes haven't got much strength. But coral is so tough to use that you can't really shape it in the operating theatre unless you have a diamond-tipped dental drill.'
Only three out of the 2,500 species of coral are suitable for surgery. By the time it reaches the operating theatre, the coral has been sterilised with radiation to ensure that it will not cause infection or deteriorate.
On New Caledonia, a French colony, and its surrounding islands, coral is used to build everything from houses and sewer pipes to jewellery and ornaments. It is the external skeleton of a marine animal, composed mainly of calcium. Although organs from other mammals have been used in human transplants, it is rare to implant material from a group of
animals quite so unrelated.
Coral's medical potential was recognised in the early Seventies when a bio-engineer at Liverpool University discovered its structural similarity to human bone. In France more than 35,000 operations using coral have been carried out, and it is often used to rebuild severely damaged jawbones. Implants have enabled teeth to be put back into sections of human jaws that would otherwise have been lost.
In Britain, coral has been slower to catch on as a bone substitute. But surgeons in London, Blackpool, Peterborough and Cambridge have used coral with promising results in the past year.
Mr Martin Sutcliffe, consultant orthopaedic surgeon at the Edith Cavell Hospital, Peterborough, has carried out several successful operations using coral to repair major bone fractures. 'If you are trying to bridge a big gap in a bone, you need to build a scaffold along which bone cells can grow,' he explained. 'Coral has the right microscopic structure to enable bone cells to creep along so that they eventually join, closing the gap.' This gives coral a considerable advantage over the conventional metal plates and pins usually used to splint broken bones.
The technique used by Mr Sutcliffe costs about as much as a hip replacement - pounds 3,800 - and is likely to benefit those suffering severe trauma. 'Conventional orthopaedic surgery does not need coral. But people who have been badly injured and need to have big gaps grafted, for example many of those involved in motorcycle accidents, may need coral,' Mr Sutcliffe says.
For Margaret Stockton, coral has meant she can once again drive her car, work in an office and play the piano. She is considering having her left wrist fused in the same way.
Although she cannot bend her wrist, exercise has gradually returned the strength to her right hand. 'I can't carry heavy things, and occasionally ask someone in the office to help me pick up a large book or ledger, but my life has been transformed.'