By Jane Elliott
Health reporter, BBC News
Susan is now pain free
Within hours of her hip surgery Susan Scott knew there was something wrong.
And as she started walking, the pain grew gradually.
Within months her new joint was so painful that she could not walk at all, but her doctors were baffled.
All the usual tests and X-rays came back negative and the medics could see no obvious reason to show why the 42-year-old's hip resurfacing had not been a success.
The treatment involves replacing diseased or damaged surfaces in the hip joint with metal and is usually carried out successfully on younger patients, like Susan.
But because of her young age and the natural wear and tear on the joint she will probably need another operation in the next two or three decades.
Resurfacing rather than replacing the joint enables surgeons to conserve much more bone.
Each year there are 60,000 hip replacements in England and Wales.
About 6,000 of these involve resurfacing both the ball and socket parts of the joint with metal, and of these about 2.5% fail within three years - many like Susan's are for unexplained reasons.
"I felt it was not right after I had it done in December 2006 as I was in a lot of pain," said Susan.
"I gave it time to recover, but I still could not walk properly and needed to stay on the painkillers.
"I went back again and again and they could not find anything. Then in September 2007 I just could not walk at all.
"They examined it to see whether there was fluid on it but there wasn't.
"I just carried on for over a year - but was in constant pain.
"In bed I could only lie on my right hand side and could not straighten my leg and had to try and position myself where I was comfortable."
Months later doctors found that Susan, from Doncaster, had developed a blood clot in her leg and that her leg was badly swollen.
So they sent her to the London Implant Retrieval Centre (LIRC), at Charing Cross Hospital, part of the Imperial College NHS Trust.
This new centre is the first of its kind to systematically evaluate metal on metal partial hip replacements.
It examines why they fail, assesses who they benefit most, and using 3D computer technology to work out how best to position them to get the most effective results.
Medics examined Susan and within hours had established what had gone wrong.
Pieces of metal had come away from the new surface covering her bone.
These had triggered an inflammatory response within her tissue, which had eaten away part of her pelvic bone.
Dr Alister Hart helped set up the new centre
"That's why I was in so much pain," said Susan.
"Every time I was putting pressure on the pelvis to walk and it was agony."
Doctors took away the damaged joint, repaired Susan's pelvis and gave her a complete hip replacement.
"I was out of bed the next day," she said.
"And I managed to walk, it was only a few steps, but my pain had gone and I knew it was different."
Alister Hart, consultant orthopaedic surgeon at Imperial College Healthcare and senior lecturer at Imperial College London, is the principal investigator of the LIRC, which he co-founded with John Skinner, consultant orthopaedic surgeon at the Royal National Orthopaedic Hospital Trust.
He said they had so far received 190 failed implants from patients like Susan.
They perform a series of sophisticated tests on the joints, including MRI and CT scanning to look at positioning, and investigations on blood and tissue samples to determine metal levels worn from the hip surface.
The also put tissue into the Diamond light particle accelerator - a super microscope based in Oxford - to carry out minute analysis of the problem.
Examination of some removed hip implants has shown wear at a rate 70 times greater than that predicted by engineers in the laboratory.
"Susan is a good example of the cases we get - of unexplained inflammatory pain," said Dr Hart.
"We are trying to get some answers as to why it happens - basically it is a biocompatibility problem."
In essence the body's immune system reacts adversely to the metal particles from the implant, and tries to attack them, triggering inflammation.
"But in the meantime we can put people like Susan right by removing it and replacing the hip with a type of hip that does not produce metal," Dr Hart said.
Dr Hart said that most people with a hip resurfacing do well and thrive - but that there is currently no way of establishing whose will fail.
They hope their research will one day predict this, eliminating the need for costly extra surgery.
"What this centre aims to do is to bring clinicians, industry and basic scientists together to discover exactly why this is happening, by taking research from the bedside back to the bench and beyond."
"Small numbers fail, but the full economic cost to the country for revision is up to £30,000 for more surgery and loss of work.
"And the type of disability can be quite severe because it can dissolve away the bone and the tendons."
The LIRC is a research collaboration between Imperial College London, The Royal National Orthopaedic Hospital Trust, the British Orthopaedic Association, the Association of British Healthcare Industries and nine orthopaedic companies who are helping to fund the project.