Moshe Shoham

Bone-mounted miniature robot for surgical procedures: Concept and clinical applications

This paper presents a new approach to robot-assisted spine and trauma surgery in which a miniature robot is directly mounted on the patients bony structure near the surgical site. The robot is designed to operate in a semiactive mode to precisely position and orient a drill or a needle in various surgical procedures. Since the robot forms a single rigid body with the anatomy, there is no need for immobilization or motion tracking, which greatly enhances and simplifies the robots registration to the target anatomy. To demonstrate this concept, we developed the MiniAture Robot for Surgical procedures (MARS), a cylindrical 5/spl times/7 cm/sup 3/, 200-g, six-degree-of-freedom parallel manipulator. We are currently developing two clinical applications to demonstrate the concept: 1) surgical tools guiding for spinal pedicle screws placement; and 2) drill guiding for distal locking screws in intramedullary nailing. In both cases, a tool guide attached to the robot is positioned at a planned location with a few intraoperative fluoroscopic X-ray images. Preliminary in-vitro experiments demonstrate the feasibility of this concept.

Image-Guided Robotic Flexible Needle Steering

This paper presents a robotic system for steering under real-time fluoroscopic guidance a flexible needle in soft tissue. Given a target and possible obstacle locations, the computer calculates the flexible needle-tip trajectory that avoids the obstacle and hits the target. Using an inverse kinematics algorithm, the needle base maneuvers required for a tip to follow this trajectory are calculated, enabling a robot to perform controlled needle insertion. Assuming small displacements, the flexible needle is modeled as a linear beam supported by virtual springs, where the stiffness coefficients of the springs can vary along the needle. Using this simplified model, the forward and inverse kinematics of the needle are solved analytically, enabling both path planning and path correction in real time. The needle shape is detected in real time from fluoroscopic images, and the controller commands the needle base motion that minimizes the needle tip error. This approach was verified experimentally using a robot to maneuver the base of a flexible needle inserted into a muscle tissue. Along the 40-mm trajectory that avoids the obstacle and hits the target, the error stayed below the 0.5-mm level. This study demonstrates the ability to perform closed-loop control and steering of a flexible needle by maneuvering the needle base so that its tip achieves a planned trajectory.

A biomechanical model of index finger dynamics

A dynamic model of the biomechanics of the index finger for flexion-extension and abduction-adduction motion is introduced. The model takes into account all the tendons in the finger and relates to their varying moment arms during motion. A new set of moment arm coefficients and elongation equations is derived based on experimental measurements of previous studies. Constraint equations using variable coefficients are introduced and an optimization approach used to obtain the tendon forces required for any given motion and external force. The model and optimization approach are tested with data from a rapid pinch experiment as well as a hypothetical disc rotation. Good correlation is obtained with respect to electromyographic data in the literature.

Ultrasound-Guided Robot for Flexible Needle Steering

The success rate of medical procedures involving needle insertion is often directly related to needle placement accuracy. Due to inherent limitations of commonly used freehand needle placement techniques, there is a need for a system providing for controlled needle steering for procedures that demand high positional accuracy. This paper describes a robotic system developed for flexible needle steering inside soft tissues under real-time ultrasound imaging. An inverse kinematics algorithm based on a virtual spring model is applied to calculate needle base manipulations required for the tip to follow a curved trajectory while avoiding physiological obstacles. The needle tip position is derived from ultrasound images and is used in calculations to minimize the tracking error, enabling a closed-loop needle insertion. In addition, as tissue stiffness is a necessary input to the control algorithm, a novel method to classify tissue stiffness from localized tissue displacements is proposed and shown to successfully distinguish between soft and stiff tissue. The system performance was experimentally verified by robotic manipulation of the needle base inside a phantom with layers of varying stiffnesses. The closed-loop experiment with updated tissue stiffness parameters demonstrated a needle-tip tracking error of ~ 1 mm and proved to be significantly more accurate than the freehand method.

Flexible Needle Steering and Optimal Trajectory Planning for Percutaneous Therapies

Flexible needle insertion into viscoelastic tissue is modeled in this paper with a linear beam supported by virtual springs. Using this simplified model, the forward and inverse kinematics of the needle is solved analytically, providing a way for simulation and path planning in real-time. Using the inverse kinematics, the required needle basis trajectory can be computed for any desired needle tip path. It is shown that the needle base trajectory is not unique and can be optimized to minimize lateral pressure of the needle body on the tissue. Experimental results are provided of robotically assisted insertion of flexible needle while avoiding “obstacle”.

Propulsion Method for Swimming Microrobots

This paper presents a novel swimming method mediated by traveling waves in elastic tails. The propulsion method is potentially appropriate for maneuvering microrobots inside the human body. The swimming action relies on the creation of a traveling wave along a piezoelectric layered beam divided into several segments. This requires that a voltage with the same frequency, but different phases and amplitudes, be applied to each segment. The swimming pattern was analyzed theoretically by solving the coupled electric-elastic-fluidic problem, and was optimized to attain reasonable thrust. It was found that despite extreme size limitations, a tail manufactured by current microelectromechanical-devices technology, using piezoelectric material, is able to swim in water at a speed of several centimeters per second. The swimming theory was verified experimentally using an upscaled model that produced propulsion of 0.04 mN, which matches closely the theoretically predicted propulsion

Investigation of Parallel Manipulators Using Linear Complex Approximation

This investigation deals with singularity analysis of parallel manipulators and their instantaneous behavior while in or close to a singular configuration. The method presented utilizes line geometry tools and screw theory to describe a manipulator in a given position. Then, this description is used to obtain the closest linear complex, presented by its screw coordinates, to the set of governing lines of the manipulator. The linear complex axis and pitch provide additional information and a better physical understanding of the type of singularity and the motion the manipulator tends to perform in a singular point and in its neighborhood. Examples of Hunts, Fichters and 3-UPU singularities, along with a few selected examples taken from Merlets work [1], are presented and analyzed using this method.

Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: part 2--Evaluation of system accuracy.

OBJECTIVE To evaluate the accuracy of a novel bone-mounted miniature robotic system for percutaneous placement of pedicle and translaminar facet screws. METHODS Thirty-five spinal levels in 10 cadavers were instrumented. Each cadavers entire torso was scanned before the procedure. Surgeons planned optimal entry points and trajectories for screws on reconstructed three-dimensional virtual x-rays of each vertebra. Either a clamp or a minimally invasive external frame was attached to the bony anatomy. Anteroposterior and lateral fluoroscopic images using targeting devices were obtained and automatically registered with the virtual x-rays of each vertebra generated from the computed tomographic scan obtained before the procedure. A miniature robot was mounted onto the clamp and external frame and the system controlled the robots motions to align the cannulated drill guide along the planned trajectory. A drill bit was introduced through the cannulated guide and a hole was drilled through the cortex. Then, K-wires were introduced and advanced through the same cannulated guide and left inside the cadaver. The cadavers were scanned with computed tomography after the procedure and the systems accuracy was evaluated in three planes, comparing K-wire positions with the preoperative plan. A total of fifty-five procedures were evaluated. RESULTS Twenty-nine of 32 K-wires and all four screws were placed with less than 1.5 mm of deviation; average deviation was 0.87 ± 0.63 mm (range, 0–1.7 mm) from the preoperative plan in this group. Sixteen of 19 K-wires were placed with less than 1.5 mm of deviation. There was one broken and one bent K-wire. Another K-wire was misplaced because of collision with the previously placed wire on the contralateral side of the same vertebra because of a mistake in planning, resulting in a 6.5-mm deviation. When this case was excluded, average deviation was 0.82 ± 0.65 mm (range, 0–1.5 mm). CONCLUSION These results verify the systems accuracy and support its use for minimally invasive spine surgery in selected patients.

Robotic assisted spinal surgery - from concept to clinical practice

After several years of product development, animal trials and human cadaver testing, the SpineAssist®–a miniature bone-mounted robotic system–has recently entered clinical use. To the best of the authors’ knowledge, this is the only available image-based mechanical guidance system that enables pedicle screw insertion with an overall accuracy in the range of 1 mm in both open and minimally invasive procedures. In this paper, we describe the development and clinical trial process that has brought the SpineAssist to its current state, with an emphasis on the various difficulties encountered along the way and the corresponding solutions. All aspects of product development are discussed, including mechanical design, CT-to-fluoroscopy image registration, and surgical techniques. Finally, we describe a series of preclinical trials with human cadavers, as well as clinical use, which verify the systems accuracy and efficacy.

Application of Grassmann-Cayley Algebra to Geometrical Interpretation of Parallel Robot Singularities

The aim of this paper is two—fold: first, it provides an overview of the implementation of Grassmann—Cayley algebra to the study of singularities of parallel robots1 and, second, this algebra is utilized to solve the singularity of a general class of Gough—Stewart platforms (GSPs). The Grassmann—Cayley algebra has an intuitive way of representing geometric entities and writing them and their incidence algebraically. The singularity analysis is performed using the bracket representation of the Jacobian matrix determinant associated with this algebra. This representation is a coordinate-free one, and for all cases treated and addressed in this paper, it enables the translation of the algebraic expression into a geometrically meaningful statement. The class of GSPs having two pairs of collocated joints, whose singularity is treated in this paper, is one of the more general classes. Their singularity analysis and geometrical interpretation, is presented here, to the best of our knowledge, for the first time.