An orthopaedic surgical robot is a robot arm, guided by tracking cameras, that helps a surgeon cut bone exactly where the operation plan says. As a result, an artificial knee or hip goes in at the planned position and angle. It is also called a robotic-arm-assisted system or a navigation robot. It differs from a soft-tissue surgical robot, where the surgeon sits at a console. Here, the surgeon stands at the table and holds the arm, and the robot limits where the saw or drill can go.
The system has three parts. The first is the plan. It is made before the operation from a CT scan, on software that builds a 3D model of the bones. The second is the tracking camera, which stands near the table. It sends out infrared light and sees small reflective balls on markers that the surgeon fixes to the bones. It measures their position many times a second, so the system always knows where the bones are, even when the leg moves. The third is the robot arm, which holds the saw. Its software draws a virtual boundary around the bone that the plan says to remove. If the blade reaches the boundary, the arm resists, or the saw stops.
Here is a typical case. A surgeon at a hospital in Chandigarh is replacing a 70-year-old man's knee. The plan says to remove 9 mm of bone from the end of his thigh bone, at an angle of 3 degrees. First, the surgeon touches about 40 points on the bone with a pointed probe. The software matches these points to the 3D model, so that it knows exactly how the real bone lines up with the plan. This step is called registration. The surgeon then moves the saw across the bone. The arm lets the blade cut only inside the 9 mm boundary. After each cut, the software measures the result. The actual cuts are within 1 mm and 1 degree of the plan. Then the orthopaedic implant is fitted.
The arm is built much like an industrial robot, with motors, joint sensors and force sensors. But it works next to an open wound, so it is held to medical rules. Its makers must test it against every way in which it could fail. For example, it must stop safely if the camera loses sight of a marker. This is the kind of proof described in safety certification.
The robot does not decide anything about the operation. The surgeon approves the plan, holds the saw, and can change the plan during the operation.