Feasibility of Automated Mobility Assessment of Older Adults via an Instrumented Cane.

This study explored the feasibility of automated characterization of functional mobility via an Instrumented Cane System (ICS) within an older adult sample of cane users. An off-the-shelf offset cane was instrumented with inertial, force, and ultrasound sensors for noninvasive data collection. Eighteen patients from a neurological out-patient rehabilitation clinic and nine independently mobile controls participated in standard clinical evaluations of mobility using the ICS while under the care of an attending physical therapist. Feasibility of the ICS was gauged through two studies. The first demonstrated the capability of the ICS to reliably collect meaningful usage metrics, and the second provided preliminary support for the discriminability of high and low falls risk from system-reported metrics. Specifically, the cane significantly differentiated patients and controls (p < 0.05), and a measure of the variation in rotational velocity was associated with total scores on the Functional Gait Assessment (partial r = 0.61, p < 0.01). These findings may ultimately serve to complement and even extend current clinical assessment practices.

A Compact, Bone-Attached Robot for Mastoidectomy.

Otologic surgery often involves a mastoidectomy, which is the removal of a portion of the mastoid region of the temporal bone, to safely access the middle and inner ear. The surgery is challenging because many critical structures are embedded within the bone, making them difficult to see and requiring a high level of accuracy with the surgical dissection instrument, a high-speed drill. We propose to automate the mastoidectomy portion of the surgery using a compact, bone-attached robot. The system described in this paper is a milling robot with four degrees-of-freedom (DOF) that is fixed to the patient during surgery using a rigid positioning frame screwed into the surface of the bone. The target volume to be removed is manually identified by the surgeon pre-operatively in a computed tomography (CT) scan and converted to a milling path for the robot. The surgeon attaches the robot to the patient in the operating room and monitors the procedure. Several design considerations are discussed in the paper as well as the proposed surgical workflow. The mean targeting error of the system in free space was measured to be 0.5 mm or less at vital structures. Four mastoidectomies were then performed in cadaveric temporal bones, and the error at the edges of the target volume was measured by registering a postoperative computed tomography (CT) to the pre-operative CT. The mean error along the border of the milled cavity was 0.38 mm, and all critical anatomical structures were preserved.

Preliminary Testing of a Compact, Bone-Attached Robot for Otologic Surgery.

Otologic surgery often involves a mastoidectomy procedure, in which part of the temporal bone is milled away in order to visualize critical structures embedded in the bone and safely access the middle and inner ear. We propose to automate this portion of the surgery using a compact, bone-attached milling robot. A high level of accuracy is required to avoid damage to vital anatomy along the surgical path, most notably the facial nerve, making this procedure well-suited for robotic intervention. In this study, several of the design considerations are discussed and a robot design and prototype are presented. The prototype is a 4 degrees-of-freedom robot similar to a four-axis milling machine that mounts to the patient's skull. A positioning frame, containing fiducial markers and attachment points for the robot, is rigidly attached to the skull of the patient, and a CT scan is acquired. The target bone volume is manually segmented in the CT by the surgeon and automatically converted to a milling path and robot trajectory. The robot is then attached to the positioning frame and is used to drill the desired volume. The accuracy of the entire system (image processing, planning, robot) was evaluated at several critical locations within or near the target bone volume with a mean free space accuracy result of 0.50 mm or less at all points. A milling test in a phantom material was then performed to evaluate the surgical workflow. The resulting milled volume did not violate any critical structures.

An experimental evaluation of the force requirements for robotic mastoidectomy.

HYPOTHESIS: During robotic milling of the temporal bone, forces on the cutting burr may be lowered by choice of cutting parameters. BACKGROUND: Robotic bone removal systems are used in orthopedic procedures, but they are currently not accurate enough for safe use in otologic surgery. We propose the use of a bone-attached milling robot to achieve the required accuracy and speed. To design such a robot and plan its milling trajectories, it is necessary to predict the forces that the robot must exert and withstand under likely cutting conditions. MATERIALS AND METHODS: We measured forces during bone removal for several surgical burr types, drill angles, depths of cut, cutting velocities, and bone types (cortical/surface bone and mastoid) on human temporal bone specimens. RESULTS: Lower forces were observed for 5-mm diameter burrs compared with 3-mm burrs for a given bone removal rate. Higher linear cutting velocities and greater cutting depths independently resulted in higher forces. For combinations of velocities and depths that resulted in the same overall bone removal rate, lower forces were observed in parameter sets that combined higher cutting velocities and shallower depths. Lower mean forces and higher variability were observed in the mastoid compared with cortical/surface bone. CONCLUSION: Forces during robotic milling of the temporal bone can be predicted from the parameter sets tested in this study. This information can be used to guide the design of a sufficiently rigid and powerful bone-attached milling robot and to plan efficient milling trajectories. To reduce the time of the surgical intervention without creating very large forces, high linear cutting velocities may be combined with shallow depths of cut. Faster and deeper cuts may be used in mastoid bone compared with the cortical bone for a chosen force threshold.

Design of a bone-attached parallel robot for percutaneous cochlear implantation.

Access to the cochlea requires drilling in close proximity to bone-embedded nerves, blood vessels, and other structures, the violation of which can result in complications for the patient. It has recently been shown that microstereotactic frames can enable an image-guided percutaneous approach, removing reliance on human experience and hand-eye coordination, and reducing trauma. However, constructing current microstereotactic frames disrupts the clinical workflow, requiring multiday intrasurgical manufacturing delays, or an on-call machine shop in or near the hospital. In this paper, we describe a new kind of microsterotactic frame that obviates these delay and infrastructure issues by being repositionable. Inspired by the prior success of bone-attached parallel robots in knee and spinal procedures, we present an automated image-guided microstereotactic frame. Experiments demonstrate a mean accuracy at the cochlea of 0.20 ± 0.07 mm in phantom testing with trajectories taken from a human clinical dataset. We also describe a cadaver experiment evaluating the entire image-guided surgery pipeline, where we achieved an accuracy of 0.38 mm at the cochlea.

Robotic mastoidectomy.

HYPOTHESIS: Using image-guided surgical techniques, we propose that an industrial robot can be programmed to safely, effectively, and efficiently perform a mastoidectomy. BACKGROUND: Whereas robotics is a mature field in many surgical applications, robots have yet to be clinically used in otologic surgery despite significant advantages including reliability and precision. METHODS: We designed a robotic system that incorporates custom software with an industrial robot to manipulate a surgical drill through a complex milling profile. The software controls the movements of the robot based on real-time feedback from a commercially available optical tracking system. The desired path of the drill to remove the desired volume of mastoid bone was planned using computed tomographic scans of cadaveric specimens and then implemented using the robotic system. Bone-implanted fiducial markers were used to provide accurate registration between computed tomographic and physical space. RESULTS: A mastoid cavity was milled on 3 cadaveric specimens with a 5-mm fluted ball bit. Postmilling computed tomographic scans showed that, for the 3 specimens, 97.70%, 99.99%, and 96.05% of the target region was ablated without violation of any critical feature. CONCLUSION: To the best of our knowledge, this is the first time that a robot has been used to perform a mastoidectomy. Although significant hurdles remain to translate this technology to clinical use, we have shown that it is feasible. The prospect of reducing surgical time and enhancing patient safety by replacing human hand-eye coordination with machine precision motivates future work toward translating this technique to clinical use.

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.

Effect of varying hamstring tension on anterior cruciate ligament strain during in vitro impulsive knee flexion and compression loading.

BACKGROUND: The hamstring muscles are well positioned to limit both anterior tibial translation and anterior cruciate ligament strain during the knee flexion phase of a jump landing. We hypothesized that systematically increasing or decreasing hamstring tension during the knee flexion phase of a simulated jump landing would significantly affect peak relative strain in the anterior cruciate ligament. METHODS: Ten cadaveric knees from four male and six female donors (mean age [and standard deviation] at the time of death, 60.3 +/- 23.6 years) were mounted in a custom fixture to initially position the specimen in 25 degrees of knee flexion and simulate axial impulsive loading averaging 1700 N to cause an increase in knee flexion. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated with use of pretensioned linear springs, with the tension in the hamstrings arranged to be increased, held constant, decreased, at "baseline," or absent during knee flexion. Impulsive loading applied along the tibia and femur was monitored with use of triaxial load transducers, while uniaxial load cells monitored quadriceps and medial and lateral hamstring forces. Relative strain in the anterior cruciate ligament was measured with use of a differential variable reluctance transducer, and tibiofemoral kinematics were measured optoelectronically. For each specimen, anterior cruciate ligament strains were recorded over eighty impact trials: ten preconditioning trials, ten "baseline" trials involving decreasing hamstring tension performed before and after three sets of ten trials conducted with increasing hamstring tension, constant hamstring tension, or no hamstring tension. Peak relative strains in the anterior cruciate ligament were normalized for comparison across specimens. RESULTS: Increasing hamstring force during the knee flexion landing phase decreased the peak relative strain in the anterior cruciate ligament by >70% compared with the baseline condition (p = 0.005). Neither a constant hamstring muscle force nor the absence of a hamstring force significantly changed the peak strain in the anterior cruciate ligament relative to the baseline condition. CONCLUSIONS: Increasing hamstring muscle force during the knee flexion phase of a simulated jump landing significantly reduces the peak relative strain in the anterior cruciate ligament in vitro.

The effect of an impulsive knee valgus moment on in vitro relative ACL strain during a simulated jump landing.

BACKGROUND: We tested the hypothesis that impulsive compression, flexion and valgus knee moment loading during a simulated one-footed jump landing will significantly increase the peak relative strain in the anteromedial region of the anterior cruciate ligament compared with loading without the valgus moment. METHODS: Ten cadaveric knees [mean (SD) age: 67.9 (7.6) years; 5 males; 5 females] were mounted into a custom fixture to simulate a lower extremity impact loading of approximately 1600 N. Triaxial load cells monitored the 3D tibial and femoral impulsive force and moments at 2000 Hz, while 3D tibiofemoral kinematics were measured at 400 Hz. Pre-impact quadriceps, hamstring and gastrocnemius muscle forces were simulated using pretensioned steel cables. A differential variable reluctance transducer measured the relative strain in the anteromedial aspect of the anterior cruciate ligament. With the knee initially in 25 degrees flexion, 10 trials were conducted with the impulsive force directed 4 cm posterior to the knee joint center in the sagittal plane ("neutral" loading) to cause a flexion moment, 10 trials were conducted under a similar loading, but with the force directed 15 degrees lateral to the knee sagittal plane ("valgus" loading), and the 10 neutral loading trials were then repeated. A non-parametric Wilcoxon signed rank test was used to test the hypothesis using a P<0.05 significance level. FINDINGS: The peak normalized anterior cruciate ligament strain was 30% larger for the impulsive compression loading in valgus and flexion compared with an impulsive compression loading in isolated flexion (P<0.05). INTERPRETATION: Minimizing the abduction loading of the knee during a jump landing should help reduce anterior cruciate ligament strain during that maneuver.

The relationship between quadriceps muscle force, knee flexion, and anterior cruciate ligament strain in an in vitro simulated jump landing.

BACKGROUND: An instrumented cadaveric knee construct was used to quantify the association between impact force, quadriceps force, knee flexion angle, and anterior cruciate ligament relative strain in simulated unipedal jump landings. HYPOTHESIS: Anterior cruciate ligament strain will correlate with impact force, quadriceps force, and knee flexion angle. STUDY DESIGN: Descriptive laboratory study. METHODS: Eleven cadaveric knees (age, 70.8 [19.3] years; 5 male; 6 female) were mounted in a custom fixture with the tibia and femur secured to a triaxial load cell. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated using pretensioned steel cables (stiffness, 7 kN/cm), and the quadriceps tendon force was measured using a load cell. Mean strain on the anteromedial bundle of the anterior cruciate ligament was measured using a DVRT. With the knee in 25 degrees of flexion, the construct was vertically loaded by an impact force initially directed 4 cm posterior to the knee joint center. Tibiofemoral kinematics was measured using a 3D optoelectronic tracking system. RESULTS: The increase in anterior cruciate ligament relative strain was proportional to the increase in quadriceps force (r(2) = 0.74; P < .00001) and knee flexion angle (r(2) = 0.88; P < .00001) but was not correlated with the impact force (r(2) = 0.009; P = .08). CONCLUSION: The increase in knee flexion and quadriceps force during this simulated 1-footed landing strongly influenced the relative strain on the anteromedial bundle of the anterior cruciate ligament. CLINICAL RELEVANCE: These results suggest that even in the presence of knee flexor muscle forces, the increase in quadriceps force required to prevent the knee from flexing during landing can place the anterior cruciate ligament at risk for large strains.

Liquid-fueled actuation for an anthropomorphic upper extremity prosthesis.

This paper describes the design of a 21 degree-of-freedom, nine degree-of-actuation, gas-actuated arm prosthesis for transhumeral amputees. The arm incorporates a direct-drive elbow and three degree-of-freedom wrist, in addition to a 17 degree-of-freedom underactuated hand effected by five actuators. The anthropomorphic device includes full position and force sensing capability for each actuated degree of freedom and integrates a monopropellant-powered gas generator to provide on-board power for untethered operation. Design considerations addressed in this paper include the sizing of pneumatic actuators based on the requisite output energy at each joint; the development of small low-power servovalves for use with hot/cold gases; the design of compact joints with integrated position sensing; and the packaging of the actuators, on-board power, and skeletal structure within the volumetric envelope of a normal human forearm and elbow. The resulting arm prototype approaches the dexterous manipulation capabilities of its anatomical counterpart while delivering approximately 50% of the force and power output of an average human arm.