The objective of this work was to design a compact, accurate, safe, and ease-to-use surgical robot for total knee arthroplasty. The goal of the bone-mounted robot, named Praxiteles, is to precisely position a surgical bone-cutting guide in the appropriate planes surrounding the knee, so that the surgeon can perform the cuts manually using the guide. The robot architecture is comprised of 2 motorized degrees of freedom (DOF) whose axes of rotation are arranged in parallel, and are precisely aligned to the implant cutting planes with a 2 DOF serial adjustment mechanism. An initial prototype was first developed and tested on saw bones and cadavers, and construction of a new, refined version is now well underway. A backdrivable system, with high-stiffness, high-precision static positioning capabilities and safe low-force dynamic movement is achieved using a quick-release, spring-loaded mechanical braking system integrated in a gear transmission unit at the level of the motor outputs. This paper discusses the technical challenges encountered during the development, design, and construction of the system.

The CRIGOS (compact robot for image-guided orthopedic surgery) project was set up for the development of a compact surgical robot system for image-guided orthopedic surgery based on user requirements. The modular system comprises a compact parallel robot and a software system for planning of the surgical interventions and for supervision of the robotic device. Because it is not sufficient to consider only technical aspects in order to improve in clinical routine the therapeutic outcome of conventional interventions, a user-centered and task-oriented design process has been developed which also takes human factors into account. The design process for the CRIGOS system was started from requirement analysis of various orthopedic interventions using information gathered from literature, questionnaires, and workshops with domain experts. This resulted in identification of conventional interventions for which the robotic system would improve the medical and procedural quality. A system design concept has been elaborated which includes definitions of components, functionalities, and interfaces. Approaches to the acquisition of calibrated X-rays will be presented in the paper together with design and evaluation of a first human-computer interface. Finally, the first labtype parallel robot based on low-cost standard components is presented together with the first evaluation results concerning positioning accuracy.

The accurate matching of 3D anatomical surfaces with sensory data such as 2D X-ray projections is a basic problem in computer and robot assisted surgery, In model-based vision, this problem can be formulated as the estimation of the spatial pose (position and orientation) of a 3D smooth object from 2D video images. The authors present a new method for determining the rigid body transformation that describes this match. The authors' method performs a least squares minimization of the energy necessary to bring the set of the camera-contour projection lines tangent to the surface. To correctly deal with projection lines that penetrate the surface, the authors consider the minimum signed distance to the surface along each line (i.e., distances inside the object are negative). To quickly and accurately compute distances to the surface, the authors introduce a precomputed distance map represented using an octree spline whose resolution increases near the surface. This octree structure allows the authors to quickly find the minimum distance along each line using best-first search. Experimental results for 3D surface to 2D projection matching are presented for both simulated and real data. The combination of the authors' problem formulation in 3D, their computation of line to surface distances with the octree-spline distance map, and their simple minimization technique based on the Levenberg-Marquardt algorithm results in a method that solves the 3D/2D matching problem for arbitrary smooth shapes accurately and quickly.>

The registration of multiple 3D data sets obtained with a laser range finder is examined. A sensor calibration technique based on the conjunction of a mathematical camera model, the N-planes B-spline (NPBS), with an accurate mechanical calibration setup, is proposed. An algorithm for recovering the rigid transformation (rotation and translation) between the two sets of 3D coordinates obtained by the calibrated imaging range sensor is developed. Its input is sets of points lying on the surface of the object. This input is converted into an octree-spline that allows point-to-surface distances to be computed quickly. A robust nonlinear least-squares minimization technique then finds the optimal pose by minimizing the sum of square distances between the two sets of 3D coordinates. The algorithm has been applied to matching human faces with highly accurate results.>

A method is presented for modeling and calibration of sensors, to reach an accuracy similar in magnitude to the resolution of the sensors. The authors focus on camera and range image calibration. They show the limitations of existing methods, and present an approach and camera calibration using mathematical B-Spline functions. This method is abbreviated as NPBS (N-Planes B-Spline). It is an extension of the two-planes method, but relies on pure mathematical modeling based on spline approximation theory. The mathematical modeling is combined with a calibration device that enables accurate data acquisition to calibrate a camera and a light plane independently. Experimental results are presented showing accuracy on the determination of a scattered plane.>

Describes a system based on the combined use of medical imaging and robot positioning used in stereotactic neurosurgery. The types of interventions performed with the help of this system require a high precision (less than 1 millimeter) of positioning with respect to the patients brain with no direct visibility of the target; they are executed through a hole in the skull of 2.3 millimeters. A typical example is the placement of a stimulating electrode in a particular nucleus of the thalamus for patients suffering from Parkinson's disease. These interventions rely on the intensive use of medical imaging to define the operative strategy. The target is defined with respect to the images. A six-axis robot whose end-effector is a linear guide automatically reaches a configuration generated such that if the surgical instrument (needle, electrode, etc.) is introduced in the guide, the surgeon reaches the target using a linear displacement of the instrument. This system is operational and is in routine clinical use.>