Download Knee joint replacement

50 active years after 50: CASE STUDIES
Heart valve transplants
A technique of stripping cells from human and animal tissue to leave a ‘scaffold’ into
which new cells can grow was patented by the team in 2001. Since that time the
technique has been used successfully with human heart valves to overcome some of the
problems associated with traditional transplants.
Over 5,000 patients benefit from heart valve replacement in the UK each year, but none
of the current replacements are adequate for patients with life expectancies beyond 1015 years. Although donor valves remain the “gold standard”, they are subject to immune
reactions in the patient.
The patented technique may, therefore, offer a realistic alternative for many of these
patients. The scaffold enables the patients own cells to grow into it and the implanted
valve has the potential to act like natural tissue. It doesn’t provoke an immune response
and it retains flexibility, growing with the patient –a potentially major benefit in surgery on
children. Animal trials have now shown these scaffolds are repopulated by cells within
six months, though it is expected to take longer in humans.
The technique has been used successfully on human valves during clinical studies in
Brazil, with findings showing no revisions or complications related to the valve
transplant. This has led to ongoing work in the UK with NHS Blood and Transplant, with
a view to introducing the innovation into the UK in the next decade.
Low wear hip replacement
A unique hip joint which creates ten times less wear than other designs is now being
used across most of the world.
The joint’s longer lifespan means it can be used with younger patients, enabling them to
continue to lead active lives for longer.
A traditional replacement hip joint has a metal head in a polyethylene cup, which creates
a lot of wear and so has a limited lifespan. Because of this, many patients are advised to
wait as long as possible, often in considerable discomfort, before having an artificial hip
put in place.
Other options include metal-on-metal or ceramic-on-ceramic joints, which can be used
on younger patients. Both are more durable and create less wear than polyethylene,
giving the joint a longer lifespan and reducing the need for further surgery.
The new innovation mixes these two materials to create a ceramic-on-metal hip joint.
The bearing includes a new type of ceramic ball, which fits inside a metal cup. The
combination creates ten times less metal wear than the metal-on-metal joint. The
ceramic head remains smooth and undamaged, improving the movement and lubrication
of the joint.
The new design has been developed under licence by Depuy-Johnson & Johnson. It has
been used in most parts of the world since 2006 and a panel recently recommended to
the Food and Drug Administration in the USA that it also be approved for use there.
Spinal disc replacement
New methods of testing spinal disc replacements to simulate the long-term impacts of
this type of device in the human body are currently being developed.
Although still fairly new, disc replacement is being used more and more in the UK to
combat spinal disease and degeneration. Innovative mechanical techniques to test joint
replacements are being developed by the team at Leeds, together with partners at the
University of Iowa in the USA who are working on computer simulations. Although this
research builds on existing knowledge of hip and knee joint replacements it does require
some refinement, the spine is a very different and delicate environment, the proximity to
the spinal cord means any problem with a replacement disc could prove catastrophic.
The new assessment methods have already identified that wear of the replacement disc
is likely to be significant, creating particles that are of a size that could stimulate a
reaction by the body. This means that osteolysis is a potential problem, where the bone
disappears from around the implant as the body attempts to clean up the particles,
causing the disc to loosen.
Continuing development of the models will help scientists and surgeons estimate the
timescale within which such problems are likely to occur and identify ways of mitigating
their impact.
Self repair of teeth, bone and soft tissue
Teeth are constantly being attacked by acid, which creates small micropores in the
enamel, precursors to cavities. A new technique uses specifically designed peptide
molecules which are triggered by the conditions inside the micro-pores to join together in
three-dimensional scaffold-like structures within these tiny holes. Calcium ions are
attracted to the peptides, creating a natural repair to the tooth.
The peptides can be applied in a liquid, either by brush or mouth wash, and will also
prevent tooth sensitivity by strengthening areas of root exposed by receding gums.
Discussions are underway to license this technology for commercialisation, and the
potential impact is great. It could ensure people are able to retain their own teeth for
longer, reduce the need for expensive drilling, filling and other repair and so reduce the
cost of dentistry to the NHS overall.
The technology is also being investigated for use in other parts of the body for
regeneration and repair of soft and other skeletal tissues. Research is focusing
particularly on repair of blood vessels, bone and cartilage.
Knee joint replacement
Scientific analysis of how knee joints move has provided two new concepts in
engineering design, which are helping companies across the world create better, more
durable knee joint replacements.
The knee has a very complex motion, which is difficult to replicate in a replacement joint.
Although a natural knee has a number of moving surfaces, replacements tended to have
only one, with the other parts static.
When a new ‘mobile bearing knee’ with two moving surfaces was put through simulation
and analysis, an unexpected advantage was discovered. Because the movements were
linear, less wear was created than in the traditional design. Companies have now
developed designs using linear movement to create low wearing knee replacements.
Most traditional designs also tried to ensure contact between the polyethylene parts of
the joint was spread over a large surface area, as this was thought to create less wear.
Recent research has shown that in fact, the opposite is true: the less surface area in
contact, the less wear. Designers are now able to use this concept to optimise their
design to minimise surface wear and extend the predicted lifetime of knee replacements.