 
Artificial joint replacements must be installed accurately to ensure proper biomechanics. Proper installation requires cutting precise shapes out of bone. The Precision Freehand Sculptor (PFS) is a handheld tool to assist the surgeon in accurately cutting these shapes. Its rotating cutter only allows the surgeon to remove waste bone; the cutter turns off when it hits good bone. Thus the surgeon can use the PFS freehand while it automatically restricts the cut to the proper shape. Prior to surgery, the Precision Freehand Sculptor (PFS) is programmed with the target shape for the bone. In surgery, the PFS cutter turns on and off to allow the surgeon to cut the target shape automatically. The cutter turns on when it is touching waste bone, and turns off when it hits the target shape.The PFS is a handheld tool connected by wires to a computer system (fig 1). The PFS uses flashing infrared markers on the tool and bone to sense the position of the tool and the bone at all times. A camera system locates the markers and communicates the position of the markers to the PFS computer system. Knowing the positions of the tool and the bone, the PFS computer system can calculate what part of the bone the cutter is touching and turn the cutter off before it cuts into the target shape. 
In the OR the surgeon interfaces with the PFS system through 2 footpedals and a monitor. The monitor displays the tool's position with respect to the target surface as well as menus for controlling the PFS. The footpedals allow the surgeon to access the menus. The interface is discussed further here . 
The clutch tool, shown above, was developed to test
the PFS idea. It simply has a clutch wich starts and stops the rotating
cutter. One disadvantage is that when the cutter stops or starts cutting it
tends to bite into the surface and kick. Another disadvantage is that
the cut surface is covered with spherical divots so that it looks like a
golf ball.
The retractable blade tool, shown above, is the next generation of the PFS. It is currently under construction. The retractable blade will prevent the kicking-out problem of the clutch tool. The flat blade will give a smoother surface than the "golf ball" surface generated by the clutch tool. The cutterhead (grey part at left) is removable so that different shaped cutters can be used. 
|