Could you get away with just HALF a knee op?
DURING a knee replacement operation, the worn ends of the thigh and shin bones and any remaining cartilage are removed and replaced with titanium or cobalt-chrome components.
Almost all knee replacement operations — which take around an hour — are carried out through a 10 in incision down the front of the knee. Just 5 per cent of procedures are keyhole (through a 5 in incision).
Here, we guide you through the different types of implants on offer.
PARTIAL REPLACEMENT
IF ARTHRITIS affects only one side of the knee, it may be possible to have a partial knee replacement, where only the damaged bone is scraped out and replaced.
Most partial replacements are mobile-bearing implants, which means the plastic insert replacing the cartilage is not fixed to the metal part of the implant attached to the shin. Mobile-bearing is said to wear better in partial knee replacements, but needs support from existing tissue, so isn’t suitable if you have ligament problems.
Because the operation is less invasive than total replacement, as less bone is removed, recovery is quicker and the knee functions better afterwards.
‘it is not uncommon to be off your crutches at two weeks and walking normally by four to six, compared with a total knee replacement where you are off crutches by six to eight weeks,’ says Professor Adrian Wilson, a knee specialist at Winchester university and the Wellington Hospital in London.
A recent study in BMJ Open suggested that half of patients needing a knee replacement could be suitable for a partial replacement. the Oxford university study found that when partial replacements are carried out by surgeons who do lots of them, the outcomes are better than total knee replacements — and it’s cheaper for the NHS.
However, if the surgeon only does a small number of partial operations, the outcomes are worse than a total replacement.
researcher Professor David Murray said: ‘ this is an important finding. if surgeons use partial knees in a quarter or more of knee replacements, this will improve results, save money and more patients will benefit.’
Currently, partial replacements are only used for 20 per cent of patients — more commonly younger, slimmer, active ones — as for most patients the wear and tear in the knee is too advanced and the ligaments are not strong enough.
Although movement can be better afterwards than with a total knee replacement, figures from the national Joint registry suggest a partial replacement is also more likely to fail.
Around 10 per cent will need a second operation after ten years compared with less than 5 per cent with full replacement.
TOTAL REPLACEMENT
THIS is the most common type of knee replacement surgery, used in 75 per cent of cases. it involves replacing joint surfaces at the end of the thighbone and top of the shinbone and inserting a plastic spacer in between; this acts like cartilage, helping the joint move freely.
there are several versions of this operation and 60 different prostheses can be used.
CEMENTED OR UNCEMENTED? Most artificial knees are cemented into the ends of the thigh and shin bones for greater stability. if cement is not used, the surface of the implant facing the bone is coated to encourage bone to grow on to it, forming a natural bond.
uncemented knees are more expensive, but the surgery is quicker, and some say it fits to the bone better. But there is little difference in results.
FIXED VS MOBILE: normally, the plastic spacer in an implant is fixed to the metal plate on the end of the shin (a fixed-bearing joint) but, with a mobile-bearing joint, the spacer can rotate within a certain range on the plate, so it can ‘find its own position of comfort’, says Howard Ware, a knee surgeon at Chase farm Hospital in London. it’s thought this reduces wear and tear, but there’s no evidence yet it’s better than fixed bearing for total replacement.
LIGAMENTS: KEEP OR SACRIFICE? Ligaments are bands of fibrous tissue that connect bones to each other. they are essential for keeping the joint stable.
some knee implants retain the posterior cruciate ligament (PCL) which runs from the back of the shin to the bottom of the thigh; others involve removing it (as the implant is differently shaped) to give the knee the equivalent stability.
if the PCL is retained, it should make the knee feel more ‘normal’, but is only suitable for those with ligaments strong enough. Yet research shows keeping or removing the PCL makes little difference to the functioning of the knee.
KNEECAP: RESURFACE IT OR NOT? A total knee replacement may also involve replacing the undersurface of your kneecap with a smooth plastic dome.
surgeons are split 50:50 on whether this should be done.
those in favour say it’s an opportunity to treat arthritis in the kneecap as well as the joint itself and reduce pain afterwards, so there’s a lower risk of further surgery. those against argue that treating the arthritis in the main part of the knee is enough to treat the pain, and resurfacing the kneecap can cause problems of its own.
‘Persistent pain after a knee replacement can occur, and when it does it can be a significant problem,’ says Mark Wilkinson, a professor of orthopaedics at sheffield university who operates at Claremont Hospital in sheffield.
this is thought to be caused by the way the nervous system works in some patients. ‘Anything to reduce that risk makes sense, so i always resurface the kneecap,’ he says.