PubMed Health⌕ Search

Biomedical subjects

R Riener

Publications and source records attributed to R Riener.

At least 19 recordsLinked to original sources
PubMed2005

Robot-aided neurorehabilitation of the upper extremities.

Task-oriented repetitive movements can improve muscle strength and movement co-ordination in patients with impairments due to neurological lesions. The application of robotics and automation technology can serve to assist, enhance, evaluate and document the rehabilitation of movements. The paper provides an overview of existing devices that can support movement therapy of the upper extremities in subjects with neurological pathologies. The devices are critically compared with respect to technical function, clinical applicability, and, if they exist, clinical outcomes.

Arm↗
PubMed2004

In vivo kinematic measurement during laparoscopic cholecystectomy.

BACKGROUND: Despite the rapid development of computer-assisted surgery, studies on kinematic measurement for surgical innovation are rare. This study describes a system for kinematic measurement in real operating theater environments. Six laparoscopic cholecystectomies were recorded and analyzed. In addition to a demonstration of the feasibility of the method, basis data for the development of an actuated laparoscopic camera holder are evaluated. METHODS: The positions of four receivers were recorded by an electromagnetic motion acquisition system. Analysis of the data was performed postoperatively with matlab. Parameters such as coordinates, velocities, angles, angular velocities, workspaces in typical phases of an operation, and subareas of the coordinate ranges were computed. RESULTS: The workspace during the operation in situ before (II) and after (V) removal of the gallbladder at the upper camera end was as follows: (X, Y, Z; given in cm): II: 65.5 . 42.7 . 27.3 (subarea 90% = 8.3. 14.0.6.3); V: 57.4.33.3.26.2, (90% = 10.3.16.5.7.9). Workspaces at the lower camera end were smaller: II: 14.8.9.7.15.4; (90% = 3.5.3.1.4.3). During these operation phases, velocities up to 82.9 cm/s were documented. Most of the measured velocities were much smaller. The camera -tilt-angles in left/right (alphax) and head/ feet (alphay) direction were as follows: alphax: -69 degrees to +69 degrees and alphay: -74 degrees to +48 degrees. CONCLUSION: This study demonstrates the feasibility of real-time kinematic measurement in the operation environment. The information might be of future value not only as basis data for the development of camera holders, but also for further investigations on robotics, ergonomics, and simulation.

Biomechanical Phenomena↗
PubMed2004

Optimised robot-based system for the exploration of elastic joint properties.

Numerous publications provide measured biomechanical data relating to synovial joints. However, in general, they do not reflect the non-linear elastic joint properties in detail or do not consider all degrees of freedom (DOF), or the quantity of data is sparse. To perform more comprehensive, extended measurements of elastic joint properties, an optimised robot-based approach was developed. The basis was an industrial, high-precision robot that was capable of applying loads to the joint and measuring the joint displacement in 6 DOF. The system was equipped with novel, custom-made control hardware. In contrast to the commonly used sampling rates that are below 100 Hz, a rate of 4 kHz was realised for each DOF. This made it possible to implement advanced, highly dynamic, quasi-continuous closed-loop controllers. Thus oscillations of the robot were avoided, and measurements were speeded up. The stiffness of the entire system was greater than 44 kNm(-1) and 22 Nm deg(-1), and the maximum difference between two successive measurements was less than 0.5 deg. A sophisticated CT-based referencing routine facilitated the matching of kinematic data with the individual anatomy of the tested joint. The detailed detection of the elastic varus-valgus properties of a human knee joint is described, and the need for high spatial resolution is demonstrated.

Biomechanical Phenomena↗
PubMed2004

Impact of laparoscopic adjustable gastric banding on plasma ghrelin, eating behaviour and body weight.

BACKGROUND: Plasma ghrelin, an orexigenic peptide derived from the stomach and duodenum, increases following weight loss and might contribute to weight regain. The aim of the present study was to evaluate the effect of laparoscopic adjustable gastric banding (LAGB) on body weight and body composition as well as plasma ghrelin in relation to eating behaviour in morbidly obese patients. MATERIALS AND METHODS: This study was performed in 23 morbidly obese subjects who underwent standardized LAGB. Fasting plasma ghrelin was measured before and 6 months after surgery and was correlated with body weight, body composition, and eating behaviour. RESULTS: Six months after LAGB, body weight decreased significantly by -15.7 +/- 1.4 kg (mean +/- SEM, P = 0.0001) which was accompanied by an increased cognitive restraint of eating (P = 0.001), and by a decreased disinhibition of eating and susceptibility to hunger (P = 0.0001). Plasma ghrelin increased (P = 0.016) by 27.2% from 100.39 +/- 12.90 to 127.22 +/- 13.15 fmol mL(-1). The change in plasma ghrelin correlated with changes in body weight (r = -0.49, P = 0.02), BMI (r = -0.42, P = 0.048) and fat mass (r = -0.519, P = 0.013), but not with changes of fat-free mass and of the three dimensions of eating behaviour. CONCLUSION: Weight loss following LAGB leads to an increase in fasting plasma ghrelin and is accompanied by a decrease in hunger, disinhibition of eating and an increase in cognitive restraint. Thus, changes in eating behaviour, which promote reduction of food intake and not fasting ghrelin, determines weight loss achieved by LAGB.

Adolescent↗
PubMed2002

[Initial results with the Munich knee simulator].

In orthopaedics more than 50 different clinical knee joint evaluation tests exist that have to be trained in orthopaedic education. Often it is not possible to obtain sufficient practical training in a clinical environment. The training can be improved by Virtual Reality technology. In the frame of the Munich Knee Joint Simulation project an artificial leg with anatomical properties is attached by a force-torque sensor to an industrial robot. The recorded forces and torques are the input for a simple biomechanical model of the human knee joint. The robot is controlled in such way that the user gets the feeling he moves a real leg. The leg is embedded in a realistic environment with a couch and a patient on it.

Artificial Limbs↗
PubMed2001

Model-based control of FES-induced single joint movements.

A crucial issue of functional electrical stimulation (FES) is the control of motor function by the artificial activation of paralyzed muscles. Major problems that limit the success of current FES systems are the nonlinearity of the target system and the rapid change of muscle properties due to fatigue. In this study, four different strategies, including an adaptive algorithm, to control the movement of the freely swinging shank were developed on the basis of computer simulations and experimentally evaluated on two subjects with paraplegia due to a complete thoracic spinal cord injury. After developing a nonlinear, physiologically based model describing the dynamic behavior of the knee joint and muscles, an open-loop approach, a closed-loop approach, and a combination of both were tested. In order to automate the individual adjustments cited above, we further evaluated the performances of an adaptive feedforward controller. The two parameters chosen for the adaptation were the threshold pulse width and the scaling factor for adjusting the active moment produced by the stimulated muscle to the fitness of the muscle. These parameters have been chosen because of their significant time variability. The first three controllers with fixed parameters yielded satisfactory result. An additional improvement was achieved by applying the adaptive algorithm that could cope with problems due to muscle fatigue, thus permitting on-line identification of critical parameters of the plant. Although the present study is limited to a simplified experimental setup, its applicability to more complex and functional movements can be expected.

Biomechanical Phenomena↗
PubMed2001

A survey study for the development of virtual reality technologies in orthopedics.

Virtual reality (VR) technologies have the potential to support medical education and training. In order to orient the development of medical VR applications towards the actual deficiencies and demands in orthopedics, we performed a survey among 56 orthopedic physicians. They were asked to provide information about the kind of physical joint evaluation tests which they perform most often, the importance of physical joint evaluation in comparison to alternative diagnostic methods, and their opinion about current medical education system as well as the prospects of VR applications in orthopedics. The main conclusion of this survey is that VR applications have the potential to improve the lacking medical education and orthopedic training, e.g. by improving the quality of joint evaluation methods, reducing the high number of unhealthy, risky and expensive alternative diagnostic procedures.

Curriculum↗
PubMed2001

Development of a multi-modal virtual human knee joint for education and training in orthopaedics.

Due to limited simultaneous access to a greater pool of patients an effective training of medical students or young orthopedic physicians is difficult. A knee joint simulator that comprises the properties of a healthy or pathological knee can support medical education and training. In this paper a mechatronic system is presented that provides visual, acoustic, and haptic (force) feedback so that it allows a user to touch and move a virtual shank, bones or muscles within the leg, and simultaneously observe the generated movement, feel the contact force, and hear sounds. These and further features enable the user to study and assess the properties of the knee, e.g. by testing the joint laxity and end-point stiffness in six degrees-of-motion (DOF) and by grasping and pulling at muscles, rupturing ligaments or changing muscle/ligament paths. Such a tool can support training of physical knee evaluation required for diagnosis and therapeutic planning, since any kind of pathology of any subject type can be tested at any time. Furthermore, it can provide a better understanding of functional anatomy, e.g. for the education of medical students.

Computer Simulation↗
PubMed2000

Biomechanical analysis of sit-to-stand transfer in healthy and paraplegic subjects.

OBJECTIVE: An experimental study of the sit-to-stand transfer in healthy adults with/without arm-support and in paraplegic patients with/without electrical stimulation of the quadriceps muscles was performed. The study was aimed to compare the joint torques, momentum transfer hypothesis, and stability of the sit-to-stand transfer in the healthy and paraplegic subjects. METHODS: A planar 3-linkage rigid body model was used to compute the body-segmental linear momentum and the reaction forces and torques at the joints from measured data. RESULTS: In healthy subjects the arm-support enlarged the support base of the body and thus, increased the postural stability. Strong arm-assistance reduced the maximum hip and knee joint torques by more than 50%. It was observed that the healthy participants rising with arm-support used momentum transfer to facilitate the transition from sitting to standing. The paraplegic participants did not apply the momentum transfer strategy and the sit-to-stand transfer was accomplished in a quasi-static manner. Stimulating the quadriceps, the legs could participate partly in the movement dynamics. CONCLUSION: Our results indicate that some significant differences exist between the maneuver applied by the paraplegic patients to stand up and the strategies used by the healthy adults rising with arm-support. RELEVANCE: Analysis of the biomechanical factors underlying the sit-to-stand activity is essential in the design of competent closed-loop neuroprosthesis controllers which assist paraplegic patients during rising.

Adult↗
PubMed2000

Analysis of passive elastic joint moments in paraplegics.

In the functional electrical stimulation of the lower extremity of paraplegics to achieve standing and walking, a mathematical model describing the passive elastic joint moments is essential in order to implement model-based control algorithms. In a previous investigation of ten normal persons we had found significant coupling of passive, elastic joint moments between neighboring joints due to muscle groups that span both joints (biarticular muscles). Thus, we now investigated the biarticular coupling in six paraplegic patients. A comparison to the averaged results of the ten normal persons showed that while the biarticular joint moment coupling due to the gastrocnemius muscle was well preserved in all patients, the coupling due to the rectus femoris was greatly reduced and the coupling due to the hamstring muscle group was negligible. We offer pathophysiologically based explanations for these characteristic differences including the speculation that the predominantly extensor-type spasticity in our patients exercises mainly the anti-gravity muscles such as the gastrocnemius and the rectus femoris, while permitting greater atrophy of the hamstring muscle group. A previously presented double-exponential equation that predicts the joint moments under consideration of the neighboring joint angles could be fitted well to the experimental data.

Adult↗
PubMed2000

Patient-driven control of FES-supported standing up and sitting down: experimental results.

A patient-driven control strategy for standing-up and sitting-down was experimentally tested on two paraplegic patients by applying functional electrical stimulation (FES) to the quadriceps muscle. The strategy--also known as "patient-driven motion reinforcement" (PDMR)--was developed by computer simulations reported in a former study. It is based on an inverse dynamic model (IDM) that predicts the stimulation pattern required to maintain the movement as it is initiated by the patient's voluntary effort. For reasons of safety and weight relief, the movement was supported by a seesaw construction. After some practice the patients were able to influence the stimulator output and to control the movement by their voluntary effort. Consequently, no pre-programmed reference trajectory was required. As a positive side effect, upper body effort could be minimized compared to trials without FES. To achieve a satisfactory performance of the PDMR controller a careful parameter identification of the inverse dynamic model was fundamental.

Adult↗
PubMed1999

Model-based development of neuroprosthesis for paraplegic patients.

In paraplegic patients with upper motor neuron lesions the signal path from the central nervous system to the muscles is interrupted. Functional electrical stimulation applied to the lower motor neurons can replace the lacking signals. A so-called neuroprosthesis may be used to restore motor function in paraplegic patients on the basis of functional electrical stimulation. However, the control of multiple joints is difficult due to the complexity, nonlinearity, and time-variance of the system involved. Furthermore, effects such as muscle fatigue, spasticity, and limited force in the stimulated muscle further complicate the control task. Mathematical models of the human musculoskeletal system can support the development of neuroprosthesis. In this article a detailed overview of the existing work in the literature is given and two examples developed by the author are presented that give an insight into model-based development of neuroprosthesis for paraplegic patients. It is shown that modelling the musculoskeletal system can provide better understanding of muscular force production and movement coordination principles. Models can also be used to design and test stimulation patterns and feedback control strategies. Additionally, model components can be implemented in a controller to improve control performance. Eventually, the use of musculoskeletal models for neuroprosthesis design may help to avoid internal disturbances such as fatigue and optimize muscular force output. Furthermore, better controller quality can be obtained than in previous empirical approaches. In addition, the number of experimental tests to be performed with human subjects can be reduced. It is concluded that mathematical models play an increasing role in the development of reliable closed-loop controlled, lower extremity neuroprostheses.

Electric Stimulation Therapy↗
PubMed1999

Instrumented staircase for ground reaction measurement.

A staircase was developed to record ground reactions during stair climbing at different slopes (inclinations). Each step is instrumented with six strain-gauge-based force transducers which allow the measurement of three-dimensional ground reaction force and moment as well as the centre of pressure (COP) location. A specific sensor arrangement permits accurate recording, especially of the COP location. The overall design of the staircase and details of a single instrumented step are presented. Static and dynamic characteristics have been evaluated by different experimental procedures. Preliminary results of ground reaction forces are shown.

Biomechanical Phenomena↗
PubMed1999

Identification of passive elastic joint moments in the lower extremities.

Musculotendon actuators produce active and passive moments at the joints they span. Due to the existence of bi-articular muscles, the passive elastic joint moments are influenced by the angular positions of adjacent joints. To obtain quantitative information about this passive elastic coupling between lower limb joints, we examined the passive elastic joint properties of the hip, knee, and ankle joint of ten healthy subjects. Passive elastic joint moments were found to considerably depend on the adjacent joint angles. We present a simple mathematical model that describes these properties on the basis of a double-exponential expression. The model can be implemented in biomechanical models of the lower extremities, which are generally used for the simulation of multi-joint movements such as standing-up, walking, running, or jumping.

Adult↗
PubMed1998

Patient-driven control of FES-supported standing up: a simulation study.

To control movements aided by functional electrical stimulation (FES) in paraplegic patients, stimulation of the paralyzed lower limbs might be adjusted in response to voluntary upper body effort. Recently, Donaldson and Yu proposed a theoretical approach, called "control by handle reactions of leg muscle stimulation" (CHRELMS), in which stimulation of the lower limbs depends on upper body effort, i.e., body posture and recorded hand reactions, and is aimed to minimize arm forces during standing up and standing. An alternative strategy is presented in this paper, which accounts for voluntary upper body effort as well, but does not require estimation of hand reactions. The objective of this study is to test both strategies by applying them to a generic two-dimensional (2-D) neuromusculoskeletal model. The model takes into account the major properties of muscle and segmental dynamics during FES-supported standing-up movements of a paraplegic patient. In comparison to standing up without FES-support, both closed-loop strategies yield satisfying standing-up movements although no reference information (e.g., a desired trajectory) is required. Arm forces can be significantly reduced. Using the model to optimize the controller, time-consuming and strenuous trial-and-error experimentation could be avoided. However, final experimental studies are planned to verify the presented strategies.

Arm↗
PubMed1997

Inverse dynamics as a tool for motion analysis: arm tracking movements in cerebellar patients.

Kinematic analysis of limb movements can be used to evaluate motion of patients with movement disorders. Those with clinically mild to moderate impairment, however, often show only small, insignificant deviations in the measured trajectories compared to those of healthy controls. Furthermore, kinematic data alone do not give sufficient information about internal quantities such as muscle activation or joint moments. In order to improve the sensitivity of motion analysis of limb movements, we propose the use of inverse dynamics, since it allows biomechanical quantities to be determined without restricting movement. We developed an inverse dynamic model of the upper limb with 9 degrees of freedom. Spatial positions (Cartesian coordinates) of anatomical landmarks, which were recorded by an infrared video-based three-dimensional motion analysis system, are transformed into body-related Cardan angles. The model determines joint moments and powers at the shoulder, elbow, and wrist. Arm tracking movements in a patient with a mild cerebellar ataxia and a healthy control demonstrate that the model allows a clear differentiation between normal and abnormal limb movements, even if no significant differences are noted in the recorded trajectories. We conlude that inverse dynamic modeling can be an effective tool for motion analysis in patients with cerebellar disorders. It also gives further insight into the parameters that may be controlled by the central nervous system.

Arm↗
PubMed1997

Comparison of simulation and experiments of different closed-loop strategies for functional electrical stimulation: experiments in paraplegics.

Open-loop and closed-loop stimulation of the knee extensors for the control of the knee joint angle and torque were tested as a potential basis for more complex functional electrical stimulation (FES) systems to be used in human locomotion. The output of the biomechanical simulation model described previously was compared with stimulation experiments in patients with complete thoracic spinal cord injury. Good correspondence between simulation and experiments was obtained under both isometric conditions and conditions with a freely swinging shank. For closed-loop control, a simple proportional integral derivative (PID) controller yielded sufficient performance only under isometric conditions, especially if combined with (linear) feedforward. Because of additional nonlinearities of musculotendon and body segmental dynamics, more complex strategies have to be applied to the control of unconstrained movements. To compensate for these nonlinearities, an inverse model was derived from the direct biomechanical model. This inverse model had satisfactory agreement between the measured knee angle and the desired trajectory already under open-loop conditions. A combination of the inverse model in the feedforward part of the control loop and a PID controller provided robust and precise control of the knee angle. Further improvement may be achieved by including elements of spasticity into the simulation model and by controlling both agonistic and antagonistic muscles.

Biomechanical Phenomena↗