Timothy N. Judkins

Measurement of Human Ankle Stiffness Using the Anklebot

In this paper we present initial results using a novel ankle robot to estimate human ankle stiffness. This lower-extremity robotic therapy module was developed at MIT to aid recovery of ankle function. Given the importance of the ankle during locomotion, an accurate estimate of ankle stiffness would be a valuable asset for locomotor rehabilitation, potentially providing a measure of recovery and a quantitative basis to design treatment protocols. We show that the ankle robot provides accurate measurement of ankle configuration and present a simple protocol to estimate ankle stiffness. Our initial ankle stiffness estimates compare favorably with previously published work, indicating that this method may serve as an efficient clinical measurement tool.

ERGONOMIC LAPAROSCOPIC TOOL HANDLE DESIGN

Twenty-two subjects were tested and categorized according to hand size (small, medium, or large). Each subject selected the best location for a trackball and a trigger on a handle. Each subject specified the optimum diameter/size of the handle that he or she preferred. Additionally, subjects selected their preferred pivot range for opening and closing the handle. Finally, each subject exerted his or her preferred force for the trackball and trigger controls in the selected positions. Based on the data collected in this experiment, the recommended handle diameter is in the range of 4.3 to 5.7 cm. The recommended handle pivot is the range of 8.1 to 17.3 degrees for the open and closed positions. The recommended trackball actuation force is 3.0 lbs and the recommended ratchet actuation force is 0.6 lbs, on average.

Rapid plasticity of motor corticospinal system with robotic reach training.

Goal-directed reaching is important for the activities of daily living. Populations of neurons in the primary motor cortex that project to spinal motor circuits are known to represent the kinematics of reaching movements. We investigated whether repetitive practice of goal-directed reaching movements induces use-dependent plasticity of those kinematic characteristics, in a manner similar to finger movements, as had been shown previously. Transcranial magnetic stimulation (TMS) was used to evoke upper extremity movements while the forearm was resting in a robotic cradle. Plasticity was measured by the change in kinematics of these evoked movements following goal-directed reaching practice. Baseline direction of TMS-evoked arm movements was determined for each subject. Subjects then practiced three blocks of 160 goal-directed reaching movements in a direction opposite to the baseline direction (14 cm reach 180° from baseline direction) against a 75-Nm spring field. Changes in TMS-evoked whole arm movements were assessed after each practice block and after 5 min following the end of practice. Direction and the position of the point of peak velocity of TMS-evoked movements were significantly altered following training and at a 5-min interval following training, while amplitude did not show significant changes. This was accompanied by changes in the motor-evoked potentials (MEPs) of the shoulder and elbow agonist muscles that partly explained the change in direction, mainly by increase in agonist MEP, without significant changes in antagonists. These findings demonstrate that the arm representation accessible by motor cortical stimulation under goes rapid plasticity induced by goal-directed robotic reach training in healthy subjects.

Arm movement maps evoked by cortical magnetic stimulation in a robotic environment

Many neurological diseases result in a severe inability to reach for which there is no proven therapy. Promising new interventions to address reaching rehabilitation using robotic training devices are currently under investigation in clinical trials but the neural mechanisms that underlie these interventions are not understood. Transcranial magnetic stimulation (TMS) may be used to probe such mechanisms quickly and non-invasively, by mapping muscle and movement representations in the primary motor cortex (M1). Here we investigate movement maps in healthy young subjects at rest using TMS in the robotic environment, with the goal of determining the range of TMS accessible movements, as a starting point for the study of cortical plasticity in combination with robotic therapy. We systematically stimulated the left motor cortex of 14 normal volunteers while the right hand and forearm rested in the cradle of a two degree-of-freedom planar rehabilitation robot (IMT). Maps were created by applying 10 stimuli at each of nine locations (3x3 cm(2) grid) centered on the M1 movement hotspot for each subject, defined as the stimulation location that elicited robot cradle movements of the greatest distance. TMS-evoked movement kinematics were measured by the robotic encoders and ranged in magnitude from 0 to 3 cm. Movement maps varied by subject and by location within a subject. However, movements were very consistent within a single stimulation location for a given subject. Movement vectors remained relatively constant (limited to <90 degrees section of the planar field) within some subjects across the entire map, while others covered a wider range of directions. This may be due to individual differences in cortical physiology or anatomy, resulting in a practical limit to the areas that are TMS-accessible. This study provides a baseline inventory of possible TMS-evoked arm movements in the robotic reaching trainer, and thus may provide a real-time, non-invasive platform for neurophysiology based evaluation and therapy in motor rehabilitation settings.

Enhanced Robotic Surgical Training Using Augmented Visual Feedback

The goal of this study was to enhance robotic surgical training via real-time augmented visual feedback. Thirty novices (medical students) were divided into 5 feedback groups (speed, relative phase, grip force, video, and control) and trained during 1 session in 3 inanimate surgical tasks with the da Vinci Surgical System. Task completion time, distance traveled, speed, curvature, relative phase, and grip force were measured immediately before and after training and during a retention test 2 weeks after training. All performance measures except relative phase improved after training and were retained after 2 weeks. Feedback-specific effects showed that the speed group was faster than other groups after training, and the grip force group applied less grip force. This study showed that the real-time augmented feedback during training can enhance the surgical performance and can potentially be beneficial for both training and surgery.

Electromyographic response is altered during robotic surgical training with augmented feedback

There is a growing prevalence of robotic systems for surgical laparoscopy. We previously developed quantitative measures to assess robotic surgical proficiency, and used augmented feedback to enhance training to reduce applied grip force and increase speed. However, there is also a need to understand the physiological demands of the surgeon during robotic surgery, and if training can reduce these demands. Therefore, the goal of this study was to use clinical biomechanical techniques via electromyography (EMG) to investigate the effects of real-time augmented visual feedback during short-term training on muscular activation and fatigue. Twenty novices were trained in three inanimate surgical tasks with the da Vinci Surgical System. Subjects were divided into five feedback groups (speed, relative phase, grip force, video, and control). Time- and frequency-domain EMG measures were obtained before and after training. Surgical training decreased muscle work as found from mean EMG and EMG envelopes. Grip force feedback further reduced average and total muscle work, while speed feedback increased average muscle work and decreased total muscle work. Training also increased the median frequency response as a result of increased speed and/or reduced fatigue during each task. More diverse motor units were recruited as revealed by increases in the frequency bandwidth post-training. We demonstrated that clinical biomechanics using EMG analysis can help to better understand the effects of training for robotic surgery. Real-time augmented feedback during training can further reduce physiological demands. Future studies will investigate other means of feedback such as biofeedback of EMG during robotic surgery training.

Effect of Grip Force on Wrist Range of Motion

This study investigated the effect of a constant grip exertion on wrist range-of-motion (ROM). Seven different levels of grip force were investigated, including two levels of zero exertion, 25%, 50%, 75%, 90%, and 100% MVC. Both hands were tested for each of three forearm positions (pronation, halfway between pronation and supination (neutral), and supination). Twenty student subjects (10 males and 10 females) were tested. Subjects held a particular grip force level constant while simultaneously moving their wrist. The maximum angles of flexion and extension were recorded to measure range-of-motion (ROM). ANOVA analysis was performed for the dependent variables of flexion angle, extension angle, and total ROM. Independent variables were gender, hand, forearm position, and exertion level. Exertion level was a significant factor for extension, flexion, and ROM. Forearm posture was a significant factor for extension and ROM. Tukey-Kramer analysis revealed similar groupings of exertion levels and forearm positions for flexion, extension, and ROM. The data show a significant decrement in wrist ROM as grip force exertion level increased.

Skills Learning in Robot-Assisted Surgery Is Benefited by Task-Specific Augmented Feedback

Background: Providing augmented visual feedback is one way to enhance robot-assisted surgery (RAS) training. However, it is unclear whether task specificity should be considered when applying augmented visual feedback. Methods: Twenty-two novice users of the da Vinci Surgical System underwent testing and training in 3 tasks: simple task, bimanual carrying (BC); intermediate task, needle passing (NP); and complex task, suture tying (ST). Pretraining (PRE), training, and posttraining (POST) trials were performed during the first session. Retention trials were performed 2 weeks later (RET). Participants were randomly assigned to 1 of 4 feedback training groups: relative phase (RP), speed, grip force, and video feedback groups. Performance measures were time to task completion (TTC), total distance traveled (D), speed (S), curvature, relative phase, and grip force (F). Results: Significant interaction for TTC and curvature showed that the RP feedback training improved temporal measures of complex ST task compared to simple BC task. Speed feedback training significantly improved the performance in simple BC task in terms of TTC, D, S, curvature, and F even after retention. There was also a lesser long-term effect of speed feedback training on complex ST task. Grip force feedback training resulted in significantly greater improvements in TTC and curvature for complex ST task. For the video feedback training group, the improvements in most of the outcome measures were evident only after RET. Conclusions: Task-specific augmented feedback is beneficial to RAS skills learning. Particularly, the RP and grip force feedback could be useful for training complex tasks.

Electromyographic frequency response of robotic laparoscopic training

Robotic laparoscopic surgery has been shown to decrease task completion time, reduce errors, and decrease training time when compared to manual laparoscopic surgery. However, current literature has not addressed physiological effects, in particular muscle responses, to training with a robotic surgical system. We seek to determine the frequency response of electromyographic (EMG) signals of specific arm and hand muscles with training using the da Vinci Surgical System (dVSS). Eight right-handed medical students were trained in three tasks with dVSS over four weeks. These subjects, along with eight controls, were tested before and after training. EMG signals were collected from four arm and hand muscles during the testing sessions and the median EMG frequency and bandwidth were computed. Median frequency decreased, while frequency bandwidth increased, post-training for two of the three tasks. The results suggested that training reduces muscle fatigue as a result of faster and more deliberate movements. These changes occurred predominantly in muscles that were the dominant muscles for each task. An evaluation of the physiological demands of robotic laparoscopic surgery using electromyography can provide us with a meaningful quantitative way to examine performance and skill acquisition.