ORTHOPEDIC SURGERY (see Chapter 61 )

Total Hip Arthroplasty

In 1992, Paul, a veterinarian who worked in collaboration with IBM, developed a robotic system that could be used for hip replacement in dogs. The research collaboration resulted in the first surgical robot—ROBODOC. This was the first medical application, and it started with orthopedic surgery. In this procedure, the femoral implant is placed into an axial canal of the proximal shaft of the femur. The femoral component can be glued or pressed in to the femoral shaft as a tight fit. Long-term radiographs after hip replacement surgery have shown that adhesives are prone to cracking, loosening, and producing osteolysis that leads to surgical failure of the prosthetic hip. Modern femoral implants have a porous surface that allows for bone growth into the surface, promoting better hip longevity. For this reason, a tight fit of the implant into the femoral canal is essential. The formation of this femoral canal is created with higher precision by a robot than by the visual cues that are used in the manual method. The cavity it creates is 10 times more accurate than is achieved by manual methods.^[73] The robot gets its visual or coordinate cues from image-based information such as MRI or CT. The accurate registration of the femoral coordinates in three-dimensional space is essential for precise bone milling of the femoral canal so that it can accommodate the surgical implant. Titanium pins are placed in the femoral condyles and the greater trochanter. The patient's leg is then imaged by CT, and three-dimensional information about the femoral bone and registration pins is recorded in a computer.

In the operating room, the surgeon removes the native femoral head and places the acetabular cup into its place in the routine manual procedure. The femur is then rigidly clamped and secured by the robot fixator. The robot is allowed to recognize the three titanium registration pins and compares their location relative to the data obtained from CT. In this manner, the robot has a perfect sense of where the femur lies in three-dimensional space and can perform precise milling of the femoral canal. The remainder of the surgery proceeds manually.

The ROBODOC-treated patients showed fewer gaps between the prosthesis and bone, and no intraoperative femoral fractures occurred.^[74] The overall complication rate in one study was reduced to 11.6%.^[75]

Hip dislocation after hip arthroplasty is the most common postoperative complication, with a rate of 1% to 5%.^[76] To surmount this complication, the HipNav system is being developed. The system has a range-of-motion simulator, a preoperative planner, and an intraoperative tracking and guidance control. This system can optimize acetabular orientation for a "best-fit" prosthetic implant. ^[77]