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GMS Current Topics in Computer and Robot Assisted Surgery

Deutsche Gesellschaft für Computer- und Roboterassistierte Chirurgie (CURAC)

ISSN 1863-3153

Integration of a robotic system in the neurosurgical operation theatre

Research Article

  • corresponding author Martin Engelhardt - Department of Neurosurgery, Ruhr University Bochum, Bochum, Germany
  • author Aleksandra Popovic - Helmholtz-Institute for Biomedical Engineering, Aachen University, Aachen, Germany
  • author Pierre Bast - Helmholtz-Institute for Biomedical Engineering, Aachen University, Aachen, Germany
  • author Wolfgang Lauer - Helmholtz-Institute for Biomedical Engineering, Aachen University, Aachen, Germany
  • author Martin Scholz - Department of Neurosurgery, Ruhr University Bochum, Bochum, Germany
  • author Klaus Radermacher - Helmholtz-Institute for Biomedical Engineering, Aachen University, Aachen, Germany
  • author Kirsten Schmieder - Department of Neurosurgery, Ruhr University Bochum, Bochum, Germany

GMS CURAC 2006;1:Doc11

Die elektronische Version dieses Artikels ist vollständig und ist verfügbar unter:

Veröffentlicht: 9. Oktober 2006

© 2006 Engelhardt et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen ( Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


To integrate a robot assisted trepanation system into the neurosurgical operation theatre, requirements of the system have to be addressed. To perform a craniectomy with removal of the pathological calvaria and to insert a prefabricated implant in one surgical procedure, the results of a study concerning the entities, the location and the histological findings of calvarial tumors had to be considered. Furthermore, the small space around the patients´ head during surgery, the work angles in surgical procedures as well as the possible positioning of the robotic system and its design have been analyzed. Sterile and ergonomic aspects have been adjusted and proven to fulfill the requirements of the workflow during surgery.

The result is a small hexapod robotic system, which is placed beneath the patients´ head on a replaceable stage, able to reach the majority of calvarial tumors that are typically located around the forehead. The handling of the hardware as well as the software user-interface is appropriate to be integrated into the operation theatre.

Keywords: neurosurgery, robotic assisted surgery, craniotomy, workflow


Integration of a robotic system into surgical procedures is an important goal of research efforts for man-machine interlinked systems [1], [2], [3], [4], [5]. An interdisciplinary work group, consisting of engineers and clinicians, supported by the German Research Foundation (Deutsche Forschungsgemeinschaft SPP1124 „Medizinische Navigation und Robotik“, RA548/2-1), has developed a small robotic system capable of drilling bone [6], [7], [8], proven in laboratory surrounding. The aim of this study was to analyze the integration of the robotic system in the operation theatre fulfilling the different criteria of accurate and sufficient bone milling, sterile workflow, limited workspace, and handling of instruments to perform the craniectomy. The system should be able to accurately remove pathologic calvaria and create a graft for prefabricated titanium implant for coverage. Some other robotic systems which have been evaluated in surgical environments, are more bulky, and space occupying [5], [9], [10], causing difficult integration into surgical workflow. Other obstacles are high costs and the high weight and dimensions of other robotic systems could alter the current workflow or require changes in the operation theatre concerning architecture or general surgical planning [11]. Thus, the developed system should be mobile in the operation theatre and must not interfere with standard procedures, if possible.

The main objective of CRANIO project was to development of a small and mobile system, removable in case of emergency and not altering surgical procedures if possible. Comparison with other medical robotics systems was not feasible, due to the differences in application field and system architecture.


Firstly, the required workspace for the robotic system had to be defined, analyzing surgically treated calvarial tumors within a ten-year period. Therefore, ten years were analyzed retrospectively to characterize calvarial tumors (Figure 1 [Fig. 1]) concerning their locations, sizes and histological findings [12], [13].

Furthermore, most frequent used trepanations in neurosurgery were defined. Their dimensions and topography on the surface of the skull were marked (Figure 2 [Fig. 2]) to determine the robot’s work area needed for craniectomies for the actual phase of the project and for craniotomies in further development. Therefore, commonly used surgical tools were digitalized and an analysis was done, concerning their range of motion and the resulting drill zone while resection of pathological calvaria (Figure 3 [Fig. 3]).

In the next step the setting in the neurosurgical theatre was analyzed to define the optimal location of the robotic system. The analysis was done using digital documentation and measurements of patients positioning and dimensions around the patient’s head during surgery (Figure 4 [Fig. 4]). In this virtual reality the optimal location of the robotic system was simulated and resulting requirements for the robotic system including all criteria for positioning, handling and sterile workflow were addressed. The possible working area of the hexapod robotic system was analyzed (Figure 4 [Fig. 4]) and correlated to the main calvarial tumor’s location.

A process orientated risk analysis was done for the complete robotic system using CARAD risk-analysis software (SurgiTAIX, Aachen) combining FMEA (Failure Management and Effect Analysis) and FTA (Failure Tree Analysis) (Figure 5 [Fig. 5]).

In the final step the handling of the robotic system was tested (Figure 6 [Fig. 6], Figure 7 [Fig. 7]) several times concerning practicability of hardware integration and appreciation of software instructions. Important ergonomic aspects were determined and added to optimize the design of the robotic system and the user guidance software.


As the retrospective study demonstrated, 87% of 83 surgically treated osseous tumors in a ten year time period were located in the frontal, the temporal and the anterior parietal region of the skull (Table 1 [Tab. 1]), shown in examples (Figure 1 [Fig. 1]). This vizor-like workspace has to be reached using trepanation tools (Figure 3 [Fig. 3]). Additionally, most of the standard trepanations are located in similar shaped areas (Figure 2 [Fig. 2]). Since the Stewart platform based parallel robots’ workspace has a shape that resembles an opened umbrella (Figure 4 [Fig. 4]) craniotomy geometries shown in Figure 2 [Fig. 2] are suitable for the resection with the robot.

In order to evaluate the robots’ workspace and determine the optimal position of the platform in relation to the patient placed in supine position, fixed with the Mayfield clamp, a virtual model of the skull was used. The skull was simulated using a sphere with a 200 mm diameter, milling area with angle of 70° to reflection axis with the maximum tool angle of 25°. Following the virtual simulation (Figure 4 [Fig. 4]) the optimal position of the patient and the robotic system due to its working area was found to be beneath the operation table directly under the patients´ head (Figure 6 [Fig. 6]). An alternative fixation of the patients’ head has to be constructed in further progress of the project, taking a collision of the Mayfield clamp and the robotic system into account, using the measurement of the real surgical environment in the operation theatre (Figure 4 [Fig. 4]). The system was divided into the lower part containing the electrics with the control unit and the leg motors (Figure 6 [Fig. 6]). The mechanical upper part consists of a strong removable C-shaped arm. The upper part of the arm can be sterilized before the procedure. The surgical instruments are fixed to the C-shaped arm to realize high accuracy during the milling procedure (Figure 6 [Fig. 6]). The entire system is placed on a replaceable stage to allow easier handling and prepositioning. The usability was proved in simulated surgical surroundings by several surgeons and engineers and an easy workflow was used to achieve a sterile management during surgery. Furthermore, the instructing user-interface has been evaluated during simulation and was revised with some additional hints and pictograms.

As a result of the risk analysis a need for a redundant hardware for enhancement of the system safety emerged (Figure 5 [Fig. 5]). This safety unit was designed as a stand-alone system, connected between the control unit and manipulator. Safety hardware continuously inspects various values and signals, e.g. motor and amplifier signals. If an error is detected, the safety unit will execute an emergency stop, e.g. by turning the motor brakes.

Ending the adaptation of this new robotic system within a simulated surgical setting, test courses were done (Figure 6 [Fig. 6] and 7 [Fig. 7]), including positioning of the virtual patient and the robotic system and installation of the neuronavigation.


Compared to other robotic systems [2], [3], [5], [9], which are available for medical requirements, the actual system of this group is smaller and easier to be moved in the operation theatre and removed in case of emergency, which could be important within the surgical procedure and workflow. After fulfilling its task the presence of the lower part of the system doesn’t neither obstruct the surgeon to continue surgery, nor hinders the workflow of the ongoing surgical process. During surgery the small dimension of the system is well matched with the small surgical area around the patients´ head. The system is self-explaining with a user-guided software and the ergonomic aspects fulfill the criteria for a necessary sterile workflow, achieved with the systems composition in two divided parts, one of them fully autoclavable. Motion, one factor for infections, takes place beneath the table, outside the surgical field.

The primary task, drilling calvarial pathologies, is possible and the system fulfils every criteria which has been postulated before construction; even achieving the most occurring locations of calvarial tumors using common surgical tools with high accuracy.

The evaluation in a real surgical procedure and a comparison with different systems has to be proven in the future.


The robotic system constructed, based on a hexapod robot, is able to perform a craniectomy in all requested regions including the stated locations of calvarial tumors. Furthermore, it is suitable for the neurosurgical operation theatre since sterile and not sterile components do not interfere with the current workflow.

Regarding the ergonomic aspects the handling of the arm and the fixation device of the drill have to be optimized. Actual performing craniectomies using a drill is possible, fulfilling a craniotomy using a craniotome, additional degrees of freedom concerning the motion of the surgical tool are required. Currently a new robotic arm with three additional degrees of freedom to hold the trepanation tool and to cover the different surface angles of the calvaria during craniotomy is ready to be integrated.


Authors 1 and 2 contribute equally to the authorship of this paper.


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