Knee Replacement Techniques — What's New

Conventional Method (Instrumented)

In the traditional method, once the knee is opened, a surgeon drills a hole in the femur (thigh bone) and tibia (leg bone) and inserts a long rod (approximately 30cm) into the bone. This is used to approximate the shaft of each bone, which relates to how much the first cuts are angled. This relies on an accurate X-ray from the hip to the ankle — taken with perfect alignment — to ensure pre-operative calculations are transferred to the operating table. This has been shown to be an accurate way of performing total knee replacements in general, though there is some bleeding from the drill holes.

Navigation

During surgery, the surgeon inserts pins through the bone, away from the surgical site. This is then sensed by a computer looking over the surgeon's shoulder. The surgeon maps out the bone using a probe and sends this information to the computer. Once calculations are performed, the computer helps make accurate cuts for the final implant. This can be extremely accurate, but is dependent on the method of mapping and relies on correct information being inputted prior to cutting.

Robotic Surgery

A pre-operative scan of the knee allows the robot to determine where the cuts will finish. Guided by the surgeon, the robotic arm burrs away the bone rather than cutting it. The surgeon moves the robotic arm, which limits false moves. This technique uses similar mapping to navigation but also incorporates the pre-operative scan to improve alignment further. It is different to the Da Vinci robot — in total knee replacement surgery, the surgeon is always present and guiding the arm throughout the procedure.

Patient Specific Technology

Every knee is different. Patient specific technology relies upon a detailed 3-dimensional scan of the hip, knee and ankle to obtain a true picture of where the knee sits, its overall alignment, and any detailed abnormalities with the joint itself. Custom-made cutting blocks are created, which are used during surgery as cutting guides. This does not rely on any pins or rods drilled into the bone — it is a fast, accurate and reproducible way to provide a customised solution. The surgery is effectively performed in virtual space long before the patient is due for their operation, allowing Dr Liew to determine the best alignment without needing to make those decisions on the day.

Current research suggests that accurate implantation is critical — the hip, knee and ankle should align as close to a straight line as possible. Any deviation more than 3 degrees from this line usually results in more problems. Dr Liew uses only Patient Specific Technology as he believes it provides the most customised solution for each patient, since every knee is different.