A knee implant just for you
Rather than an off-the-shelf knee implant that requires the surgeon to shape the knee to fit the implant, this implant is custom-made to fit the patient.
The next step forward for knee replacement implants is here, and it offers customised implants built specifically to the measurements of each patient.
“IT’S a new revolution in knee replacement surgery,” says consultant orthopaedic surgeon Dr Tai Cheh Chin.
The “revolution” he’s speaking of is the ConforMIS knee replacement system, which offers unique advantages over traditional, off-the-shelf implants in knee replacement surgery.
“Traditionally, with knee replacement implants, we try to shape and cut the knee so that it fits the implant,” says Dr Tai.
“The patient can be male, female, bigger or smaller in size, it makes no difference – we cut the knee in the same pattern because the implant shape and size is always fixed.
“Traditional implants do not take into account the differences in knee anatomy between man, woman, Asian, Causcasian, African... You fit the knee to the implant,” he adds.
“Everybody’s knee is different,” Dr Tai goes on. “All the data’s there. A simple example – an Asian knee vs a Western knee. We cut the knee depending on data from Western populations, and that’s a problem as our sizes are different, our shapes are different; so if size, shape and alignment are different, then how can we have an implant that can fit nicely?
“So you find that in knee replacement surgeries, no matter how good a surgeon you are, for about every five knees that you operate on, one patient – even though the implant looks perfect on x-rays – will not be vey happy with the results.
“The first modern knee implant was carried out in the 1970s in the United States; the shape has not changed that much, though improvements have been made over the last 10-20 years.
“We have computer navigation to put in the implant better; to cut the knee better, we have PSI – patient specific instrumentation – where we make it more patient specific, but in the end, we still have to use that standard implant. We have focused the tech on how to cut the knee better, but the implant basically remained unchanged,” says Dr Tai.
The new system allows for patient-specific fitting of the implant, which means no implant is alike because it has been made to fit only one particular patient.
“With the system, you first CT the knee. This information is then sent to the United States, where 3D modelling of the implant is carried out according to the specifications measured from the knee CT scan.
“During this time, the surgeon will be kept informed of developments to make sure everything required is being carried out.
“Once both parties agree to the specifications, the 3D implant is made. The implant will then be delivered to the surgeon a few days before the date of surgery.
“The whole process, on average, takes between four and six weeks,” says Dr Tai.
An analogy, says Dr Tai, can be made with buying shoes. Rather then getting general sizes, such as 7, 8 or 9, you get the shoe custom-made for you, which naturally makes it a better fit and it will be much more comfortable than off-the-shelf shoes.
This system has been available in the United States for more than 10 years.
“In the US, the first such implant was carried out in 2004, so it has been more than 10 years. We have more than 10 years’ worth of data now, and it reflects the many advantag- es of this ‘new’ system,” notes Dr Tai.
One advantage of the system is that you can replace whatever portion (of the knee) that you want to.
“Unlike the traditional knee replacement, where you only have the option of partial, half-knee or total replacement, this system allows you to replace any part that is damaged. You get to keep the good parts of the knee,” explains Dr Tai.
This advantage has far-reaching implications. People getting knee replacement surgery are getting younger, so the possibility of a revision of the implant is higher. So when it’s time for a revision, such patients may still have functional parts that don’t have to be replaced.
Another plus for the system is instrumentation, which makes the surgery itself faster and easier.
“This system makes the whole knee replacement operation easier. With traditional implants, there are about eight trays of instruments in the op theatre because we don’t know what size implant to use. We need to cut open the knee and then assess the size of the implant.
“With the new system, it’s just one box,” says Dr Tai.
According to Dr Tai, studies have shown that with the new system, knee alignment accuracy is a lot better. The resulting knee kinematics is almost like normal, hence 90% of patients say their knee feels like normal (because it’s shape is good, it fits well and the kinematics are very good), compared to traditional knee replacement implants where 60-70% say their knees feel quite normal.
“Outcomes are good – shorter hospital stay; less blood loss as operating time is shorter; reduced complication rates. So although this implant is more expensive, in the short term, with shorter hospital stay, less complications, less blood loss, less revisions, you save a bit more,” notes Dr Tai.
Today, on average, US surgeons carry out approximately 4,000 to 6,000 knee replacement surgeries using this system.
“With this, we expect patients to be happier with the results. Finally, we get an implant that fits the patient, rather than requiring the patient to fit the implant; that’s the biggest change,” says Dr Tai.
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