Alon Wolf

Highly articulated robotic probe for minimally invasive surgery

We have developed a novel highly articulated robotic probe (HARP) that can thread through tightly packed volumes without disturbing the surrounding tissues and organs. We use cardiac surgery as the focal application of this work. As such, we have designed the HARP to enter the pericardial cavity through a subxiphoid port. The surgeon can effectively reach remote intrapericardial locations on the epicardium and deliver therapeutic interventions under direct control. Reducing the overall cross-sectional diameter of the mechanism was the main challenge in the design of this device. Our device differs from others in that we use conventional actuation and still have good maneuverability. We have performed simple proof-of-concept clinical experiments to give preliminary validation of the ideas presented here

A mobile hyper redundant mechanism for search and rescue tasks

In this work we introduce a new concept of a search and rescue robotic system that is composed of an elephant trunk-like robot mounted on a mobile base. This system is capable not only of inspecting areas reachable by the mobile base but also to inspect unreachable areas such as small cracks, and pipes, using the camera mounted on its elephant trunk robot. In the report we describe the mechanical structure of the elephant trunk robot, the kinematic analysis of the structure, the robot control, and its human interface systems.

Cup alignment error model for total hip arthroplasty.

Almost all computer-assisted orthopaedic surgery systems that rely on the anterior pelvic plane definition, such as in computed tomography and magnetic resonance image-based, fluoroscopy-based, and nonimage total hip replacement approaches, are derived from identifying two pairs of pelvic bony landmarks: anterior superior iliac spines and the pubic tubercles. Although these systems strive to achieve cup alignment accuracy of approximately 1°, even a minor failure to correctly identify these anatomic landmarks can lead to higher inaccuracies in the final cup alignment. This study shows how to examine the effects of these inaccuracies on the final acetabular cup implant orientation during total hip replacement by generating a kinematic model, which then is simulated. Simulation results indicate that, for example, a total error of 4 mm in measuring the anterior superior iliac spine and the pubic tubercles would result in a final cup orientation of 47° and 27° in abduction and version respectively, resulting in a 2° abduction error and 7° error in version when targeting 45° abduction and 20° version results. These calculations can be repeated for any error values.

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.

Control of knee coronal plane moment via modulation of center of pressure: A prospective gait analysis study

OBJECTIVES Footwear-generated biomechanical manipulations (e.g., wedge insoles) have been shown to reduce the magnitude of adduction moment about the knee. The theory behind wedged insoles is that a more laterally shifted location of the center of pressure reduces the distance between the ground reaction force and the center of the knee joint, thereby reducing adduction moment during gait. However, the relationship between the center of pressure and the knee adduction moment has not been studied previously. The aim of this study was to examine the association between the location of the center of pressure and the relative magnitude of the knee adduction moment during gait in healthy men. METHODS A novel foot-worn biomechanical device which allows controlled manipulation of the center of pressure location was utilized. Twelve healthy men underwent successive gait analysis testing in a controlled setting and with the device set to convey three different para-sagittal locations of the center of pressure: neutral, medial offset and lateral offset. RESULTS The knee adduction moment during the stance phase significantly correlated with the shift of the center of pressure from the functional neutral sagittal axis in the coronal plane (i.e., from medial to lateral). The moment was reduced with the lateral sagittal axis configuration and augmented with the medial sagittal axis configuration. CONCLUSIONS The study results confirm the hypothesis of a direct correlation between the coronal location of the center of pressure and the magnitude of the knee adduction moment.

Percutaneous Intrapericardial Interventions Using a Highly Articulated Robotic Probe

In order to overcome the limitations of currently available assistive technologies for minimally invasive surgery (MIS), we have developed a novel highly articulated robotic probe (HARP) that can exploit its snake-like structure to navigate in a confined anatomical environment while minimally interacting with the environment along its path. We believe that for procedures involving epicardial interventions on the beating heart, cardiac MIS can be effectively realized with the HARP, entering the pericardial cavity through a subxiphoid port, reaching remote intrapericardial locations on the epicardium without causing hemodynamic and electrophysiologic interference and delivering therapeutic interventions under the direct control of the surgeon

Reduction in knee adduction moment via non-invasive biomechanical training: A longitudinal gait analysis study

Biomechanical non-invasive interventions have been previously reported to reduce pain and facilitate superior levels of function in patients with medial knee osteoarthritis [OA]. One such treatment is the AposTherapy, a customized program utilizing a foot-worn biomechanical device allowing center of pressure modification and continuous perturbation during gait. The influence of this intervention on objective gait metrics has yet to be determined. The aim of the current study was to prospectively examine changes in kinetic and kinematic parameters in patients enrolled in this treatment program. Twenty-five females with symptomatic bilateral medial compartment knee OA were enrolled in the customized daily treatment program. All patients underwent barefoot gait analysis testing and completed subjective questionnaires prior to treatment initiation and on two follow-up visits. Significantly reduced knee adduction moment (KAM) magnitude was noted during barefoot walking after three and nine months of treatment. On average, the knee adduction impulse and the 1st and 2nd KAM peaks were reduced by 13%, 8.4%, and 12.7%, respectively. Furthermore, moment reduction was accompanied by elevated walking velocity, significant pain reduction, and increased functional activity. In addition to symptomatic improvement, our results suggest that this treatment program can alter kinetic gait parameters in this population. We speculate that these adaptations account for the symptomatic and functional improvement reported for this intervention.

Morphometric study of the human lumbar spine for operation-workspace specifications.

Study Design. The anatomy of the lumbar vertebrae of 55 patients was measured by use of data provided by computed tomography. On the basis of these measurements, the location of puncture points and the orientation of the surgical instruments for pedicle, vertebral body, and disc entry points were calculated for open as well as percutaneous surgery. Objective. Normal anatomic variations of the lumbar spine were investigated to define the workspace for several spinal procedures and to define the workspace of a robot designed to guide the physician during those procedures. Summary of Background. Several comprehensive studies of vertebrae dimensions have been conducted in the past, but they lack several dimensions that are needed to determine the exact location of the entry point and orientation of the tool, in particular when a computerized guidance system is used. Methods. Fifty-five spinal columns (L1–L5, total 250 vertebrae) were measured by computed tomography. These data provide geometric relations that determine entry points and tool orientations for different spinal interventions. Results. The workspace for spinal operations was defined on the basis of anatomic data taken from computed tomography scans. The data included 15 measurements for each vertebra that defined its shape. The processed data provided puncture points for several spinal procedures in both open and percutaneous surgery. Conclusions. This study provides additional information on vertebral structure needed to calculate accurately the entry point and tool orientation in various spinal procedures. These statistical data are also valuable for model and implant designs and for workspace specifications for a robot-assisted surgery system.

The influence of sagittal center of pressure offset on gait kinematics and kinetics

OBJECTIVES Kinetic patterns of the lower extremity joints have been shown to be influenced by modification of the location of the center of pressure (CoP) of the foot. The accepted theory is that a shifted location of the CoP alters the distance between the ground reaction force and the center of the joint, thereby modifying torques during gait. Various footwear designs have been reported to significantly alter the magnitude of sagittal joint torques during gait. However, the relationship between the CoP and the kinetic patterns in the sagittal plane has not been examined. The aim of this study was to evaluate the association between the sagittal location of the CoP and gait patterns during gait in healthy men. METHODS A foot-worn biomechanical device which allows controlled manipulation of the CoP location was utilized. Fourteen healthy men underwent successive gait analysis with the device set to convey three different sagittal locations of the CoP: neutral, anterior offset and posterior offset. RESULTS CoP translation in the sagittal plane (i.e., from posterior to anterior) significantly related with an ankle dorsiflexion torque and a knee extension torque shift throughout the stance phase. Likewise, an anterior translation of the CoP significantly reduced the extension torque at the hip during pre-swing. CONCLUSIONS The study results confirm a direct correlation between sagittal offset of the CoP and the magnitude of joint torques throughout the lower extremity.

New joint design for three-dimensional hyper redundant robots

This paper presents a novel compact design for a two degrees of freedom (DOF) joint mechanism. The joint is optimized for compactness, strength and range of motion which makes it ideal for constructing spatial or three-dimensional hyper redundant robots. We also identify and classify various prior joint designs that led to the development of this new concept. Finally, we present the joint forward kinematics, and force and torque calculations to verify the joints range of motion and mechanical advantage.