PubMed Health⌕ Search

Biomedical subjects

P Lugner

Publications and source records attributed to P Lugner.

10 recordsLinked to original sources
PubMed2001

Test bed with force-measuring crank for static and dynamic investigations on cycling by means of functional electrical stimulation.

Cycling by means of functional electrical stimulation (FES) is an attractive training method for individuals with paraplegia. The physiological benefits of FES are combined with the psychological incentive of independent locomotion. In addition, cycling has the advantage in that the generated muscle forces are converted into drive power with relatively high efficiency compared to other means of locomotion, e.g., walking. For the design of an appropriate cycling device and the development of optimal stimulation patterns, it has to be investigated how the geometry for FES cycling, influenced by individual parameters of the FES-generated drive torques and the magnitude of variations among subjects with paraplegia, can be optimized. This study shows the design of a freely adjustable test bed with additional motor drive which allows static and dynamic measurements of force components and drive torque at the crank. Furthermore, the influence of geometry and various individual parameters on FES pedaling can be tested for each subject individually. A pedal path realized by a three-bar linkage that was optimized according to preliminary simulations further increases leg cycling efficiency. Safety precautions avoid injuries in case of excessive forces, e.g., spasms. Test results illustrate the application of the test bed and measurement routines. A test series with four paraplegic test persons showed that the presented static and dynamic measurement routines allow to provide optimal stimulation patterns for individual paraplegic subjects. While pedaling with these optimal stimulation patterns only negligible negative active drive torques, due to active muscle forces, were applied to the crank and sufficient drive power was generated to power a cycle independently.

Adult↗
PubMed2000

Mechanical factors responsible for the obstruction of the gliding mechanism of a dynamic hip screw for stabilizing pertrochanteric femoral fractures.

BACKGROUND: In treatment of pertrochanteric femoral fractures with dynamic hip screws (DHSs) (135-degree, Synthes, Bettlach, Switzerland), damage was observed in removed lag screws, leading to the conclusion that the gliding mechanism must have been obstructed as a result of either inappropriate position of the implant or insufficient medial support in the fracture zone. METHODS: The forces and moments transmitted in the screw socket are calculated using a mathematical model to find the optimal position of the implant. RESULTS: The forces and moments depend on the position and orientation of the lag screw as well as on the position of the contact point between the two main fragments. By changing the point of contact, a better decrease of the load to the DHS can be achieved than by changing the position and orientation of the screw. For a low contact point, the model shows the lowest values for the forces in the socket. CONCLUSION: Complete agreement was found between the results of the presented calculations and our own clinical experience in removed DHSs.

Aged↗
PubMed2000

Cycling by means of functional electrical stimulation.

The goal of this paper was the development of an optimized stimulation pattern of leg muscles that would allow paraplegic subjects to perform the movement of pedaling and thereby to drive a tricycle by means of functional electrical stimulation (FES). To obtain maximum average power output with minimum muscle force, the start, duration and amplitude of the stimulation signal applied to the individual muscles had to be optimized depending on the pedaling frequency. For the basic theoretical investigations the rider-tricycle system was modeled as a rigid body system on which the muscle forces are applied as joint moments. The muscles gluteus maximus, rectus femoris, vastii, and hamstrings were stimulated and the passive forces of some other muscles were considered. The modeling and simulation approach was then used to produce maximum power pedaling and steady-state pedaling at 35 rpm. Hamstrings (41.9%) and vastii (35.8%) were the primary contributors to the optimization cost function of maximum power with minimum muscle loading. Based on these theoretical investigations an efficient stimulation pattern could be provided, taking into account the realistic possibilities of today's practical applications.

Bicycling↗
PubMed1998

Exercise tricycle for paraplegics.

The work describes a tricycle that can be used by paraplegics without assistance. Paraplegics can get on and off the tricycle independently, using hydraulic adjustment of the saddle height. The two rear wheels can be swivelled with adjustable hydraulic damping, which avoids the stability problems of a standard tricycle when riding around bends. The principal driving power is assumed to be provided by functional electrical stimulation of the femoral muscles. A hub motor is integrated in the front wheel to increase the radius of action, as additional drive for cycling up gradients and in case muscle force is not sufficient. The desired drive power is adjusted by a throttle grip on the handlebar. The percentage of motor power can also be adjusted. The force applied to the pedal, the absolute angular position of the crank, and the angular velocity of the front wheel are continuously measured by a force measurement pedal and a goniometer. Based on this information, the motor and the functional electrical stimulation of the legs are controlled.

Biomedical Engineering↗
PubMed1996

[Experimental studies of the biomechanics of scaphoid screws].

The purpose of this study was to determine the anchoring forces of four commonly used scaphoid screws in synthetic polyurethane foam. A linear relation was found between the length of the probe and the anchoring forces. The leading thread of the Herbert screw showed a anchoring force of 54 N/mm, the trailing thread 80 N/mm, and the Ulrich screw 75 N/mm. This linear relation of the shaft screws was only relevant upto a border probe length no longer that of the thread. Furthermore, it is valid for screws with continuous threads up to a probe length of 12 mm respectively. The cortical screw developed an anchoring force of 59 N/mm and the cancellous screw, 63 N/mm. With short probes of 4 and 6 mm, the trailing threads of the Herbert and Ulrich screws have the best anchoring forces, with values of 319 N/399 N and 307 N/435 N, respectively. The forces necessary for extraction of the tested scapoid bone screws placed in 8 mm polyurethane cubes were between 404 N and 527 N and were narrowly distributed. An additional conclusion of this study was that the application of screws with flat ends (Herbert and Ulrich screws) which were placed perpendicular to the dense material layer, significantly increased the anchoring forces.

Bone Screws↗
PubMed1995

Stress in the Achilles tendon during a topple-over movement in the ankle joint.

The achilles tendon is one of the strongest tendons in the human body, and a healthy tendon will only rupture under very severe conditions. Experiments and statistics show a high probability of tendon rupture in the case of a person trying to make a quick start and thereby toppling over in the ankle joint. Toppling over means a quick overturning in the lower ankle joint as it may occur when starting out of the sagittal plane. Based on a verified model of the achilles tendon, of M. Gastrocnemius and M. Soleus (Hatze, H. (1980) IEEE Trans. Automatic Control 25, 375-385; Hoy et al. (1990) J. Biomechanics 23, 1185-1198.), the stress in different tendon fibres during such a movement is investigated. The results of this simulation show that the expected extreme stresses in the lateral tendon fibres are a possible starting point for a rupture.

Achilles Tendon↗