Peter P. Pott

Today's state of the art in surgical robotics

Objective: This paper describes the current level of development of robots for surgery. Material and Methods: This paper is based on a literature search in Pubmed, IEEExplore, CiteSeer and the abstract volumes of the MICCAI 2002, 2003 and 2004, CARS 2003 and 2004, CAOS 2003 and 2004, CURAC 2003 and 2004 and MRNV 2004 meetings. Results: Divided into different disciplines (imaging, abdominal and thoracic surgery, ENT, OMS, neurosurgery, orthopaedic surgery, radiosurgery, trauma surgery, urology), 159 robot systems are introduced. Their functionality, deployment, origin and mechanical set-up are described. Additional contacts and internet links are listed. Conclusions: The systems perform diverse tasks such as milling cavities in bone, harvesting skin, screwing pedicles or irradiating tumors. From a technical perspective the strong specialization of the systems stands out. Most of the systems are being developed in Germany, the United States, Japan or France.

Mechanical Properties of Mesh Materials Used for Hernia Repair and Soft Tissue Augmentation

Background Hernia repair is the most common surgical procedure in the world. Augmentation with synthetic meshes has gained importance in recent decades. Most of the published work about hernia meshes focuses on the surgical technique, outcome in terms of mortality and morbidity and the recurrence rate. Appropriate biomechanical and engineering terminology is frequently absent. Meshes are under continuous development but there is little knowledge in the public domain about their mechanical properties. In the presented experimental study we investigated the mechanical properties of several widely available meshes according to German Industrial Standards (DIN ISO). Methodology/Principal Findings Six different meshes were assessed considering longitudinal and transverse direction in a uni-axial tensile test. Based on the force/displacement curve, the maximum force, breaking strain, and stiffness were computed. According to the maximum force the values were assigned to the groups weak and strong to determine a base for comparison. We discovered differences in the maximum force (11.1±6.4 to 100.9±9.4 N/cm), stiffness (0.3±0.1 to 4.6±0.5 N/mm), and breaking strain (150±6% to 340±20%) considering the direction of tension. Conclusions/Significance The measured stiffness and breaking strength vary widely among available mesh materials for hernia repair, and most of the materials show significant anisotropy in their mechanical behavior. Considering the forces present in the abdominal wall, our results suggest that some meshes should be implanted in an appropriate orientation, and that information regarding the directionality of their mechanical properties should be provided by the manufacturers.

Acellular Dermal Matrix Seeded with Autologous Fibroblasts Improves Wound Breaking Strength in a Rodent Soft Tissue Damage Model in Neoadjuvant Settings

Soft tissue defects following resectional surgery or trauma often result in deadspaces and require free or pedicled flaps. A programmed formation of filling tissue with enhanced biomechanical properties could be helpful. This study examined the effects on wound healing of acellular dermal matrix (ADM) seeded with autologous fibroblasts in a standardized rodent model. As pre- or postoperative radiotherapy is standard in many treatments of malignancies, we also investigated the effects of additional radiotherapy. Fischer rats were randomised and received a standardized unilateral soft tissue defect at the buttock. The defect was filled with ADM+fibroblasts or ADM alone. Controls received no filling. Either no radiation, adjuvant (postoperative) or neoadjuvant (preoperative) radiation was applied to the defect site. Six weeks later the defect volume was measured by MR-tomography. Wound breaking strength was examined by tensiometry according to German Industrial Standards. Filling of the defect side was significantly larger in ADM and ADM+fibroblast treated groups compared to the control group in all settings. Wound breaking strength in the unimodal setting was significantly improved in the ADM+fibroblasts group compared to the ADM group. In the neoadjuvant setting there was no significant difference between control and ADM group. However, the ADM+fibroblasts groups showed a significantly increased wound breaking strength compared to the control and the ADM-alone group. Seeded or unseeded ADM is able to fill deadspace in this rodent model in all settings. Implanting non-irradiated, vital, proliferating autologous fibroblasts on ADM results in significantly increased wound breaking strength.

Test bed for assessment of the kinematical determination of navigation systems for total knee arthroplasty. Does a limited range of motion of the hip joint influence the accuracy of the determination

Objective: To locate the rotational center of the hip joint, CT-less navigation systems for artificial knee-joint replacement use movements of the femur with a rigid body attached. It cannot be assumed that the hip joint provides free mobility at all times. The purpose of the present study was: 1) To build a mechanical model to assess the systems accuracy in locating the rotational center of the hip by simulating a step-wise reduction of the range of motion (ROM) of the hip joint. 2) To determine the systems resolution by assessing a critical distance between two positions of the same femoral rigid body during the process of locating the rotational center of the hip. 3) To determine the sensitivity of the navigation system to the rotation of a femoral rigid body relative to the femoral bone while locating the rotational center of the hip joint. Material and Methods: To assess the impact that a limited ROM of the hip joint has on the accuracy of determination of the hip joints rotational center, a test bed was built. This enables validation of the algorithm used by a CT-less navigation system. Results: In the first part of the study, it was shown that a reduction of the ROM of the hip joint to 30% of its initial value had no evident influence on the accuracy of locating the rotational center of the joint. In the second part of the study, it was determined that the limit of resolution between two spatial points of the pivoting process is between 4.4 and 8.7 cm. The third part of the study showed that the examined system rejected the determination of the hip center even when the rigid body was only rotated through 22.5°. Conclusions: The results show that osteoarthritis of the hip with a limited ROM, for example, cannot be taken as a contraindication for the use of the evaluated CT-less navigation system. However, the surgeon should ensure that the pivoting of the femur is performed without hindrance within the free range of motion of the hip joint. In accordance with the vendors recommendation, a minimum distance of 10 cm should be maintained between two spatial points. To ensure safe and unconstrained operation, the rigid body must be firmly attached to the bone and must not be dislocated.

Flow-aided path following of an underwater robot

This paper describes an underwater robot navigation strategy in flow. Our aim is to demonstrate that knowing the relative flow speed is advantageous because it permits using more energy efficient and stable control for trajectory following. We use a biomimetic robot that moves in uniform flow using a side-slipping maneuver. Side-slipping permits the robot to move laterally with respect to the incoming flow by exploiting its passive dynamics. The side-slipping maneuver is controlled by adjusting the heading of the robot with respect to the flow. We implement simple PID controllers for controlling the motion of the side-slipping robot laterally and transversely. Also, we compare the performance of the robot in the case where the robot does not know the flow speed. In this latter case the robots heading towards the waypoint is controlled and the flow effect is considered as a disturbance compensated by the control algorithm. Comparative experiments demonstrate that it is advantageous for a robot to know not just its speed and orientation with respect to the worlds frame of reference but also its local flow-relative speed. It permits the robot to follow trajectories more stable and using less energy. In the discussion section we propose possible future directions for implementing the on board flow-relative control.

Tribologische Messungen am Gelenkknorpel

Values for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.ZusammenfassungMit geeigneten tribologischen Prüfsystemen kann die Reibungszahl von Knorpelgewebe ermittelt werden, für die eine Größenordnung im Prozent- bis Promillebereich anzusetzen ist. Die Reibungszahl wird aus der Reibkraft und der senkrecht darauf stehenden Belastungskraft errechnet. Ihr Betrag wird durch verschiedene Prüfparameter beeinflusst. Zur Ermittlung der Reibungszahl wurde ein geeignetes Prüfsystem entwickelt, mit dem Reibungszahlen für Knorpelgewebe unter verschiedenen Fragestellungen bestimmt wurden. Dabei wurde nachgewiesen, dass sich die Reibungszahl für den Knorpel aus dem medialen und dem lateralen Kompartiment von Kniegelenken von Schlachthofschweinen nicht unterscheidet. Gefroren gelagerter Knorpel unterscheidet sich in seiner Reibungszahl nicht von frischem Knorpelgewebe. In einem Ansatz mit geschädigtem Knorpel und in einem Pilotversuch mit In-vitro-Tissue-Engineering(TE)-Konstrukten wurden Unterschiede zu einer nativen Kontrollgruppe gesehen. Die Ergebnisse zeigen, dass mit dem tribologischen Prüfstand die biomechanische Kompetenz von Gelenkknorpel, Regeneraten aus In-vivo-Studien und von In-vitro-TE-Konstrukten zur Qualitätssicherung ermittelt werden kann.AbstractValues for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.

A new single-port robotic system based on a parallel kinematic structure

In this paper we present a new single port robotic system particularly designed for single port access surgery in the field of colon cancer. In contrast to most state of the art systems the two intracorporeal manipulator arms are set up using a parallel kinematic structure with 5DOF, which are integrated into a shaft of 38mm in diameter. The parallel kinematic structure and its workspace are discussed in detail. As a unique feature, the kinematics uses the translation and rotation of three rods per manipulation arm. Using a parallel kinematic approach enables dynamic, stiff and precise movements which are needed to generate a realistic haptic feedback. The results of several performed circle tests are presented showing the ability of performing precise and dynamic movements with speeds of up to 327 mm/s and under load condition of 4 N.

Inverse Dynamic Model and a Control Application of a Novel 6-DOF Hybrid Kinematics Manipulator

Kinematics with six degrees of freedom can be of several types. This paper describes the inverse dynamic model of a novel hybrid kinematics manipulator. The so-called Epizactor consists of two planar disk systems that together move a connecting element in 6 DOF. To do so each of the disk systems has a linkage point equipped with a homokinetic joint. Each disk system can be described as a serial 3-link planar manipulator with unlimited angles of rotation. To compensate singularities, a kinematic redundancy is introduced via a fourth link. The kinematic concept leads to several technical advantages for compact 6-DOF-manipulators when compared to established parallel kinematics: The ratio of workspace volume and installation space is beneficial, the number of kinematic elements is smaller, and rotating drives are used exclusively. For a singularity-robust control-approach, the inverse dynamic model is derived using the iterative Newton–Euler-method. Feasibility is shown by the application of the model to an example where excessive actuator velocities and torques are avoided.

[Tribological assessment of articular cartilage. A system for the analysis of the friction coefficient of cartilage, regenerates and tissue engineering constructs; initial results].

Values for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.ZusammenfassungMit geeigneten tribologischen Prüfsystemen kann die Reibungszahl von Knorpelgewebe ermittelt werden, für die eine Größenordnung im Prozent- bis Promillebereich anzusetzen ist. Die Reibungszahl wird aus der Reibkraft und der senkrecht darauf stehenden Belastungskraft errechnet. Ihr Betrag wird durch verschiedene Prüfparameter beeinflusst. Zur Ermittlung der Reibungszahl wurde ein geeignetes Prüfsystem entwickelt, mit dem Reibungszahlen für Knorpelgewebe unter verschiedenen Fragestellungen bestimmt wurden. Dabei wurde nachgewiesen, dass sich die Reibungszahl für den Knorpel aus dem medialen und dem lateralen Kompartiment von Kniegelenken von Schlachthofschweinen nicht unterscheidet. Gefroren gelagerter Knorpel unterscheidet sich in seiner Reibungszahl nicht von frischem Knorpelgewebe. In einem Ansatz mit geschädigtem Knorpel und in einem Pilotversuch mit In-vitro-Tissue-Engineering(TE)-Konstrukten wurden Unterschiede zu einer nativen Kontrollgruppe gesehen. Die Ergebnisse zeigen, dass mit dem tribologischen Prüfstand die biomechanische Kompetenz von Gelenkknorpel, Regeneraten aus In-vivo-Studien und von In-vitro-TE-Konstrukten zur Qualitätssicherung ermittelt werden kann.AbstractValues for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.

Development of a Low-Cost Polymethylmethacrylate Stand-Alone Cervical Cage: Technical Note

BACKGROUND AND STUDY AIMS Stand-alone cervical cages aim to provide primary stability, yield solid fusion in the long-term course, and maintain physiologic alignment. However, many implants designed for these purposes fail in achieving these goals. Following implantation, relatively high rates of cage subsidence and failure of disc height maintenance may lead to cervical kyphosis and poor alignment of the cervical spine. At the same time, costs for cage implantation are relatively high compared with their unfavorable radiologic performance. Thus the aim of the study was to develop and test mechanically a low-cost polymethylmethacrylate (PMMA) cage with similar mechanical and procedural properties compared with a commercial polyetheretherketone (PEEK) cage. MATERIAL AND METHODS Following determination of the cage design, a casting mold was developed for the production of PMMA cages. Nine cages were produced and compared with nine PEEK cages using static compression tests for 0 and 45 degrees according to the recommendations of the American Society for Testing and Materials. Mean compressive yield strength, mean yield displacement, mean tensile strength, and mean stiffness were determined. RESULTS At 0 degrees axial compression, the mean compressive yield strength, mean displacement, and mean tensile strength of the PMMA cage was significantly higher compared with the PEEK cage (p < 0.001). Stiffness of both implants did not differ significantly (p = 0.903). At 45 degrees axial compression, PEEK cages could not be investigated because slipping of the holding fixture occurred. Under these conditions, PMMA cages showed a mean compressive yield strength of 804.9 ± 60.5 N, a mean displacement of 0.66 mm ± 0.05 mm, a mean tensile strength of 7.92 ± 0.6 N/mm(2), and a mean stiffness of 1,228 ± 79.4 N/mm. CONCLUSIONS The newly developed PMMA cage seems to show similar to superior mechanical properties compared with the commercial PEEK cage. Considering a preparation time of only 10 minutes and the low price for the PMMA material, the cost-benefit ratio clearly points to the use of the PMMA cage. However, clinical effectiveness has to be proven in a separate study.