by Justin Wong

The knee is a complex joint and there is a wide range of alignments (from varus to valgus) in normal knees. The behaviour of the ligaments and other soft tissue around the knee joint also varies from person to person. Before robotics, the standard approach was a one size fits all philosophy that aimed to make every knee perfectly straight. Robotics allows us to customise the positioning of the prostheses of the knee replacement to fit the anatomy and biomechanics of each patient individually.

There are two parts to robotic knee replacements – 1. Planning where to place the prostheses, and 2. Precisely cutting the bones so that the prostheses are implanted exactly where we plan to place them.

In the planning stage, the software shows us a 3D image of the bones and we can place the virtual implants on this virtual model. We can adjust the positioning of the implants by 0.5mm and 0.5 degrees at a time to fit the patient’s bones exactly. The knee is also taken through a range of movement while we stress the soft tissue on either side of the knee, including the medial and lateral collateral ligaments. The software uses this information to predict how the soft tissue will behave once the prostheses are implanted. We can adjust the positions of the prostheses to make sure that the soft tissue on either side of the knee will be perfectly “balanced”, and not too loose or too tight during the full range of movement of the knee.

Once the planned positions of the prostheses is finalised, the robot system uses this plan to control the robotic cutting tool, which is either a saw blade or a burr. The surgeon guides the robot, which cuts the bone according to the plan, and does not allow bone outside of the plan to be cut. Once the bone cuts have been completed, the knee replacement prostheses are then implanted.

Robotic total knee replacement surgery allows us to position the prostheses with a precision far greater than can be achieved through conventional surgical techniques. It allows us to customise the position of the knee replacement to fit each individual knee in a way that we couldn’t do previously.