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New technology helps surgeons align the new joint more accurately
Knee replacement surgery could become more accurate and less painful, thanks to the use of movement sensors.
The new technology, called iASSIST, has just been introduced in the NHS and helps surgeons align the new joint more accurately.
If
a new knee is not properly in line with the hip and ankle it can cause
discomfort and will also quickly wear out on one side. This happens in
10 to 15 per cent of cases, meaning patients need further surgery.
About
80,000 knee replacements are performed annually in the UK, mainly as a
result of osteoarthritis – where the cushioning cartilage wears away so
bone grinds on bone, causing pain.
‘Around 85-90 per cent of patients
have an excellent result and are free from pain afterwards,’ says
Nikhil Pradhan, consultant orthopaedic surgeon at Warrington and Halton
Hospitals NHS Foundation Trust.
‘But some patients have ongoing pain,
and the most common reason is that the knee replacement is not in a
straight line between the hip and ankle.
‘This means the load is on one side of the replacement knee, which can wear out more quickly and cause pain.’
Until
now the standard way to keep the hip, replacement knee and ankle in a
straight line is for surgeons to insert rods into the bone during the
operation.
With the knee joint, they insert a rod up to 30cm up
inside the thigh bone. The rods are removed once the replacement knee
joint is judged to be in place.
However there are drawbacks.
Inserting the rod means drilling into the cavity known as the medullary
canal in the thigh bone, which means the patient loses blood and bone
marrow.
And when the rod is pushed into the meduallary canal, it
displaces bubbles of fat and air, which are then pushed into the
bloodstream.
When these reach the heart and lungs, they can make the
patient feel unwell and breathless for a few weeks, because the bubbles
can block small blood vessels and reduce the oxygen reaching the lungs.
Some elderly and unwell patients need to be admitted to intensive care
as a result and in some rare cases it can even prove fatal.
Alternatively,
surgeons can take CT or MRI scans of the joints and send them to a
laboratory so technicians can make special ‘cutting’ blocks – these are
like patterns or guides specially tailored to each patient, which tells
the surgeon exactly where to make the cuts across the thigh and shin
bone.
However, these cannot be done quickly. But the iASSIST knee
system, introduced to the UK in March, means that surgeons can create a
straight joint without using rods, or waiting for scans to make the
cutting blocks.
Instead the surgeon simply puts a tiny 1cm spike into the bottom of the thigh bone, and attaches a 2-3cm square pod to it.
The
pod contains a sensor that responds to movement, like the sensors in a
smartphone which turn the text the right way up when you turn the phone
on its side.
About 80,000 knee replacements are performed annually in the UK
The pod transmits information via bluetooth – wire-free
technology which communicates to a computer – to help surgeons pinpoint
exactly where to position the new joint.
The surgeon moves the patient’s knee through 12 positions, and the computer calculates when the joint is correctly centred.
‘Studies
from the U.S. have shown that iASSIST gives a straight joint in 95 per
cent of patients, and can work for any patient,’ says Mr Pradhan, who
also works at Spire Cheshire Hospital and has pioneered the use of the
techonology in the UK.
‘We know that knee replacements placed in the correct alignment last longer and function better.
‘Now
we hope to run an NHS study at Warrington Hospital from July to test
these results, and see whether they could work for all patients.’
46
The number of years since the first knee replacement surgery was performed
Commenting
on the technology, Professor Simon Donell, consultant orthopaedic
surgeon at Norfolk and Norwich University Hospital and president of the
British Association for Surgery of the Knee, says: ‘Drilling rods into
the shaft of the bones can force bone fat into the circulation, and
affect the heart and brain.
‘The iASSIST represents a further step in surgical guidance.’
MEANWHILE, scientists are looking at whether worn-out knees could
benefit from treatment with a device normally used to help heal
fractured bones.
The handheld device, which looks like a mobile
phone, pulses low-level ultrasound on to a break via a cable and small
patch strapped on to the skin.
For reasons that aren’t yet fully understood, this stimulates the body’s natural healing process that creates new bone.
Volunteers
with knee osteoarthritis taking part in the new trail at McMaster
University, in Canada, will place the device, known as Exogen, next to
the knee joint for 20 minutes a day for three months.
Half the
patients will have a sham therapy, with the results then compared.
Researchers believe that the stimulation will improve pain and movement.
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