Dr. Andre Bauer, MD
Founder and Medical Director
Marbella High Care, Traumatology and Orthopaedic Hospital
Marbella, SPAIN
Introduction
Since 1992 the active robot system Robodoc is assisting surgeons in the preparation of the femoral cavity during total hip replacement. Although with the currently available two active robot systems (Robodoc and Caspar) worldwide more than 8.000 surgeries have been performed, passive navigational systems are now developed and are entering the market. This gives reason to study the different concepts of the systems and review clinical experience.
Materials and Methods
Active Robots are modified industrial robots that perform certain tasks of the surgery autonomously according to a preoperative established plan. The planning process is based on images that currently are processed from CT data. These images are displayed on a workstation, where the surgeon selects the implant from a library and determines size and orientation of the implant in the three-dimensional space. Data of this plan are transferred to the robot. Before starting his actual task, the robot has to perform the process of registration, which means matching real world and virtual world. Registration can be based on preoperatively inserted fixed markers (pins) or selected surface points at the proximal and distal femur. Following successful registration the robot reams the cavity with a high-speed drum cutter under constant irrigation. This active robot technique is currently available for primary stem placement during THR, revision hip surgery (Robodoc only) and TKR.
Passive navigation can also be based on preoperative acquired images or on images derived intraoperatively from fluoroscope. With preoperative images a plan can be established, intraoperative images serve orientation purposes only. Patient and instruments are equipped with optical markers, allowing the determination of the relative position in the three-dimensional space. Hand-held standard instruments during THR or TKR are navigated during surgery. The surgeon receives information on the position by a screen and manually corrects position of the instruments.
Results
Active robot assisted surgery overlooks a period of now eight years, counting from the first surgery of Dr. Bargar in 1992. Results are available from this randomized trial, conducted in three centers in the United States with a total of 140 patients. The Frankfurt group has published results on 4000 patients in their series, which started in 1994. Other published results regard cadaver studies (Paul, von Hasselbach), animal experiment (Bauer) and the accuracy of the surgery regarding position of the implant (Lahmer). These studies prove feasibility and safeness of the system. They show that the established plans are transformed with highest precision. Those studies dealing with the interface suggest a smoother preparation of the bone, preserving the cancellous structure and avoiding micro fractures.
Currently the passive navigator systems are either in pre-clinical or early clinical testing. Accuracy regarding the placement of the acetabular component was proven by DiGioia. Accuracy regarding the position of the stem has not been published. The preparation of the cavity and the interface should not differ from the conventional method.
Discussion
Although historically older, the active robotic systems represent the more advanced technical solution, and reflect a broader laboratory and clinical experience. Beside the exact transformation of the plan the application of robot specific instruments enable safe and sparing preparation of the interface. Striking advantage of the navigational systems is the fact, that the surgeon remains actively involved in the procedure. Navigated surgery on the other hand is thus restricted to the use of conventional instruments. The future certainly will bring a combination of robotic and navigational features, allowing the surgeon to decide which degree of assistance is desirable during a certain step in a surgical procedure.
Short CV of Dr. Andre Bauer