Jason E. Mitchell

Preliminary Evaluations of a Self-Contained Anthropomorphic Transfemoral Prosthesis

This paper presents a self-contained powered knee and ankle prosthesis, intended to enhance the mobility of transfemoral amputees. A finite-state based impedance control approach, previously developed by the authors, is used for the control of the prosthesis during walking and standing. Experiments on an amputee subject for level treadmill and overground walking are described. Knee and ankle joint angle, torque, and power data taken during walking experiments at various speeds demonstrate the ability of the prosthesis to provide a functional gait that is representative of normal gait biomechanics. Measurements from the battery during level overground walking indicate that the self-contained device can provide more than 4500 strides, or 9 km, of walking at a speed of 5.1 km/h between battery charges.

Self-contained powered knee and ankle prosthesis: Initial evaluation on a transfemoral amputee

This paper presents an overview of the design and control of a fully self-contained prosthesis, which is intended to improve the mobility of transfemoral amputees. A finite-state based impedance control approach, previously developed by the authors, is used for the control of the prosthesis during walking and standing. The prosthesis was tested on an unilateral amputee subject for over-ground walking. Prosthesis sensor data (joint angles and torques) acquired during level ground walking experiments at a self-selected cadence demonstrates the ability of the device to provide a functional gait similar to normal gait biomechanics. Battery measurements during level ground walking experiments show that the self-contained device provides over 4,500 strides (9.0 km of walking at a speed of 5.1 km/h) between battery charges.

Design and control of an active electrical knee and ankle prosthesis

This paper presents an overview of the design and control of an electrically powered knee and ankle prosthesis. The prosthesis design incorporates two motor-driven ball screw units to drive the knee and ankle joints. A spring in parallel with the ankle motor unit is employed to decrease the power consumption and increase the torque output for a given motor size. The devicepsilas sensor package includes a custom load cell to measure the sagittal socket interface moment above the knee joint, a custom sensorized foot to measure the ground reaction force at the heel and ball of the foot, and commercial potentiometers and load cells to measure joint positions and torques. A finite-state based impedance control approach, previously developed by the authors, is used and experimental results on level treadmill walking are presented that demonstrate the potential of the device to restore normal gait. The experimental power consumption of the device projects a walking distance of 5.0 km at a speed of 2.8 km/hr with a lithium polymer battery pack.

Design and Control of an Electrically Powered Knee Prosthesis

This paper describes the design and control of a transfemoral prosthesis with an electrically powered knee joint. This paper details the design of the active-knee prototype and presents an impedance-based control approach with which to coordinate the interaction between the prosthesis and user during level walking. The control methodology is implemented on the prosthesis, and experimental results and video frame sequences are shown that demonstrate the effectiveness of the prosthesis and control approach for level walking.

Percutaneous Cochlear Implant Drilling via Customized Frames: an in vitro study

Objective: Percutaneous cochlear implantation (PCI) surgery uses patient-specific customized microstereotactic frames to achieve a single drill-pass from the lateral skull to the cochlea, avoiding vital anatomy. We demonstrate the use of a specific microstereotactic frame, called a “microtable,” to perform PCI surgery on cadaveric temporal bone specimens. Study Design: Feasibility study using cadaveric temporal bones. Subjects and Methods: PCI drilling was performed on six cadaveric temporal bone specimens. The main steps involved were 1) placing three bone-implanted markers surrounding the ear, 2) obtaining a CT scan, 3) planning a safe surgical path to the cochlea avoiding vital anatomy, 4) constructing a microstereotactic frame to constrain the drill to the planned path, and 5) affixing the frame to the markers and using it to drill to the cochlea. The specimens were CT scanned after drilling to show the achieved path. Deviation of the drilled path from the desired path was computed, and the closest distance of the mid-axis of the drilled path from critical structures was measured. Results: In all six specimens, we drilled successfully to the cochlea, preserving the facial nerve and ossicles. In four of six specimens, the chorda tympani was preserved, and in two of six specimens, it was sacrificed. The mean ± standard deviation error at the target was found to be 0.31 ± 0.10 mm. The closest distances of the mid-axis of the drilled path to structures were 1.28 ± 0.17 mm to the facial nerve, 1.31 ± 0.36 mm to the chorda tympani, and 1.59 ± 0.43 mm to the ossicles. Conclusion: In a cadaveric model, PCI drilling is safe and effective.

A Gas-Actuated Anthropomorphic Prosthesis for Transhumeral Amputees

This paper presents the design of a gas-actuated anthropomorphic arm prosthesis with 21 degrees of freedom and nine independent actuators. The prosthesis utilizes the monopropellant hydrogen peroxide as a gas generator to power nine pneumatic type actuators. Of the nine independent actuators, one provides direct- drive actuation of the elbow, three provide direct-drive actuation for the wrist, and the remaining five actuate an underactuated 17 degree of freedom hand. This paper describes the design of the prosthesis, including the design of small-scale high-performance servovalves, which enable the implementation of the monopropellant concept in a transhumeral prosthesis. Experimental results are given characterizing both the servovalve performance and the force and/or motion control of various joints under closed-loop control.

Minimally invasive image-guided cochlear implantation surgery: First report of clinical implementation

Minimally invasive image‐guided approach to cochlear implantation (CI) involves drilling a narrow, linear tunnel to the cochlea. Reported herein is the first clinical implementation of this approach.

Proximity Queries Between Convex Objects: An Interior Point Approach for Implicit Surfaces

This paper presents a general method for exact distance computation between convex objects represented as intersections of implicit surfaces. Exact distance computation algorithms are particularly important for applications involving objects that make intermittent contact, such as in dynamic simulations and in haptic interactions. They can also be used in the narrow phase of hierarchical collision detection. In contrast to geometric approaches developed for polyhedral objects, we formulate the distance computation problem as a convex optimization problem. We use an interior point method to solve the optimization problem and demonstrate that, for general convex objects represented as implicit surfaces, interior point approaches are globally convergent, and fast in practice. Further, they provide polynomial-time guarantees for implicit surface objects when the implicit surfaces have self-concordant barrier functions. We use a primal-dual interior point algorithm that solves the Karush-Kuhn-Tucker (KKT) conditions obtained from the convex programming formulation. For the case of polyhedra and quadrics, we establish a theoretical time complexity of O(n1.5), where n is the number of constraints. We present implementation results for example implicit surface objects, including polyhedra, quadrics, and generalizations of quadrics such as superquadrics and hyperquadrics, as well as intersections of these surfaces. We demonstrate that in practice, the algorithm takes time linear in the number of constraints, and that distance computation rates of about 1 kHz can be achieved. We also extend the approach to proximity queries between deforming convex objects. Finally, we show that continuous collision detection for linearly translating objects can be performed by solving two related convex optimization problems. For polyhedra and quadrics, we establish that the computational complexity of this problem is also O(n1.5).

Accuracy Evaluation of microTargeting Platforms for Deep-Brain Stimulation Using Virtual Targets

Deep-brain-stimulation (DBS) surgery requires implanting stimulators at target positions with sub millimetric accuracy. Traditional stereotactic frames can provide such accuracy, but a recent innovation called the micro Targeting Platform (FHC, Inc.) replaces this large, universal frame with a single-use, miniature, and custom-designed platform. Both single-target and dual-target platforms are available for unilateral and bilateral procedures, respectively. In this paper, their targeting accuracies are evaluated in vitro. Our approach employs ldquovirtual targets,rdquo which eliminates the problem of collision of the implant with the target. We implement virtual targets by mounting fiducial markers, which are not used in platform targeting, on an artificial skull and defining targets relative to the skull via that fiducial system. The fiducial system is designed to surround the targets, thereby reducing the overall effect of fiducial localization inaccuracies on the evaluation. It also provides the geometrical transformation from image to physical space. Target selection is based on an atlas of stimulation targets from a set of 31 DBS patients. The measured targeting error is the displacement between the phantom implant and the virtual target. Our results show that the micro Targeting Platform exhibits sub millimetric in vitro accuracy with a mean of 0.42 mm and a 99.9% level of 0.90 mm.

Percutaneous access to the petrous apex in vitro using customized micro-stereotactic frames based on image-guided surgical technology

Abstract Conclusion. Our study demonstrates (in cadavers) the ability to obtain a minimally invasive approach to access the petrous apex using patient-customized micro-stereotactic frames based on pre-intervention radiographic studies. Objective. To conduct in vitro studies to demonstrate the feasibility of percutaneous petrous apex access using customized, bone-mounted, micro-stereotactic frames. Methods. Cadaveric temporal bone specimens (n = 10) were affixed with three bone-implanted fiducial markers. CT scans were obtained and used in planning, in reference to the fiducial markers, a straight transmastoid infralabyrinthine trajectory from the mastoid surface to the petrous apex without violating the basal turn of the cochlea or the carotid artery. A drill press was mounted on the customized frame and used to guide a 2 mm drill bit on the desired trajectory. The course of the drill bit and its relationship to surrounding vital anatomy (cochlea, carotid artery, facial nerve, and internal jugular vein) were determined by repeat CT scanning. Results. In 10 of 10 specimens, the drill bit trajectory was accurate with clearance (mean ± standard deviation in mm) from the cochlea, facial nerve, carotid artery, and jugular vein of 3.43 ± 1.57, 3.14 ± 1.15, 4.57 ± 1.52, and 6.05 ± 2.98, respectively.