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Biomedical subjects

U Boenick

Publications and source records attributed to U Boenick.

At least 19 recordsLinked to original sources
PubMed1996

[Development of a measuring set-up for determination of light distribution of scattered light applicators for interstitial laser treatment].

In the medical setting, scattering dome applicators are used in various therapeutic and diagnostic procedures, e.g. laser-induced interstitial thermotherapy. The present study reports on the development of an automatic measuring system for determining the light distribution along the active end of scattering dome applicators. Using a stepper motor, the applicator is gradually moved into an integrating sphere, in which the light intensity is measured with a photodetector. It was shown the light distribution is determined mainly by the conditions under which the laser beam is coupled to the transmission fiber. The results made it possible to optimize the production of applicators, and showed that the set-up was suitable for quality control use.

Equipment Design↗
PubMed1996

[Modeling vestibulo-ocular reflexes in everyday activities].

Fundamental data for the establishment of a new clinical testing procedure for patients suffering from equilibrium disorders were developed. A mathematical model that predicts vestibulo-ocular reflex responses (eye velocities) to three-dimensional head movements was investigated. An experimental set-up permitting the simultaneous recording of the head and eye movements was developed to investigate the vestibulo-ocular reflex (VOR) during everyday activities. The test results show that computer simulation of the VOR occurring during complex movements is indeed possible. The model was able to predict the trend of the experimentally determined eye velocities. It was ascertained that for the further development of the model, the influence of the cervico-ocular reflex (COR) on the resulting eye velocities also has to be taken into account. The proposed method for investigating patients with equilibrium disorders appears suitable enough to make further development to the clinical stage worthwhile. An adaptation of the feedback amplification parameters of the model to take account of the nature of the stimulus and the influence of COR is needed to improve the agreement between the amplitudes of measured and predicted eye velocities. To reliably quantify the feedback amplification parameters, tests need to be carried out in a large number of subjects.

Activities of Daily Living↗
PubMed1996

[Biomechanics of the pubic symphysis. Which forces lead to mobility of the symphysis in physiological conditions?].

For estimation of the loads of fixation devices, physiological movements and acting forces at the symphysis pubis are examined. Experimentally, Walheim determined the movements of the pubic symphysis under physiological conditions (one-leg stance, walking): there is no effective mobility in the horizontal direction. During the one-leg stance he observed symphyseal mobility of up to 2.6 mm (Phi 1.2 mm) in the vertical direction and 1.3 mm (Phi 0.6 mm) in the sagittal direction. During walking he found symphyseal mobility of up to 2.2 mm (Phi 0.9 mm) in the vertical direction and 1.3 mm (Phi 0.6 mm) in the sagittal direction. Until now the forces leading to symphyseal mobility have not been estimated either experimentally or mathematically. In our experimental study we examined ten fresh cadaver anterior pelvic rings by means of a multidirectional force-mobility measurement. Maximal physiological movements, as determined by Walheim, were increasingly induced in ten equal steps, and the forces required were measured for every single step. Out of the resulting force-mobility curves for the ten cadaver specimens the mean force required (with standard deviation) was calculated for each of the ten measure points, separately for the vertical (y-) direction and sagittal (z-) direction. The values were graphically transferred, and a regression curve was created. This curve allows the acting force to be estimated for every movement of the pubic symphysis: During the one-leg stance the mean force to induce mean mobility is 169 N in vertical direction and 148 N in sagittal direction; for maximal mobility a force of 398 N in the vertical direction and 148 N in the sagittal direction is necessary. During walking, the force required to induce mean movement of the symphysis pubis is 120 N in the vertical direction and 68 N in the sagittal direction; for maximal mobility 333 N is required in the vertical direction and 136 N in the sagittal direction. For mobilization of patients with a symphyseal rupture (type Tile B 1) with partial weight-bearing, neutralization of the mean acting forces during the one-leg stance (169 N in the vertical direction, 68 N in the sagittal direction) must be achieved by an adequate fixation device. In cases where full weight bearing is desirable, such as in patients with limited compliance, stability can only be reached by neutralization of the maximal acting forces during walking (333 N in the vertical direction, 136 N in the sagittal direction).

Adult↗
PubMed1995

[Materials for hip endoprostheses--alternatives to standard materials].

A review of current clinically applied biomaterials for the femoral heads and acetabular cups of total hip prostheses (UHMWPE, CoCrMo alloys, alumina and zirkonium) in terms of their resistance to wear is presented. Further developments in metallic and ceramic materials over the last few years have now left UHMWPE as the weakest link in the prosthesis material chain. Alternative materials aimed at improving the tribological properties of the femoral head/acetabular head system are presented. New surface hardening and coating techniques for titanium alloys, polymer coatings, optimized UHMWPE, as well as various carbon-fibre-reinforced synthetic materials are described. The advantages, disadvantages and prospects of these materials are compared with those of standard materials and documented in experimental and clinical studies.

Biocompatible Materials↗
PubMed1995

[Integrated gait analysis: a complex expert system approach to detailed data evaluation].

Integrated Gait Analysis is still not accepted as an important tool in a routine clinical environment because of its lack of assessment procedures closely based on the raw data measurements. Furthermore, an adequate treatment of the complex process of human movement is missing. This contribution is intended to successively describe the scheme of a dedicated approach for gait analysis data assessment. Therein, different technologies already discussed in the literature have been used. Some examples are given for the purpose of illustration. To provide in advance sufficiently different and well-known measurement conditions, extreme manipulations in the alignment of below-knee prostheses have been carried out. It is shown that some specific data formats consisting of subgroups of gait patterns have turned out to be important for further partial processing and for interfacing the different subsystems. However, due to data characteristics of the raw data and the lack of a well-founded a priori knowledge, some principal questions have to be left open. Therefore, on the basis of the different results presented below and their discussion, a more detailed model of the process is proposed for further research following this concept.

Artificial Limbs↗
PubMed1995

[In vitro studies of the specifications for methodological and technical equipment requirements of endoscopic infrared diaphanoscopy].

Endoscopic infrared diaphanoscopy is a method of improving orientation in the nasal cavity during endoscopy-controlled endonasal surgery. The transillumination is expected to facilitate the localisation of the natural passageways between the paranasal sinuses and the nasal cavity during endoscopic procedures. The present study specifies the necessary conditions on the basis of in vitro examinations using an animal model (sheep) and an anatomical preparation of half of the human head. The questions as to what paranasal sinus is at all accessible to diaphanoscopy, whether the method actually enables the connecting pathways between an individual sinus and the nasal cavity to be identified, and what technical demands need to be met, are considered and answered.

Animals↗
PubMed1994

[Effect of hardness and surface quality of metal cones on fracture load of ceramic ball heads of hip endoprostheses].

The safety of ceramic ball heads attached to hip endoprostheses by means of a conical fitting requires that the connection be designed with the ceramic material in mind. The ISO 7206-5 standard describes a static testing protocol to measure the maximal loading limit of the conical connection. In order to achieve high fracture loads in this test, it is necessary to optimize the load-bearing parts of the connection to prevent stress concentrations, to which the ceramic ball is sensitive. For this reason, manufacturers of ceramic balls give their customers specifications for the design of the metal taper, specifying tolerances for angle, roughness, roundness and straightness. In order to investigate which parameters of the metal taper have an influence on the fracture load achievable according to ISO 7206-5, fracture load tests were conducted with zircon oxide (ZIOLOX) heads in combination with test tapers from various manufacturers. The test tapers were made of Ti- or CoCr-based alloys. Before the tests the tapers were completely measured and characterized according to geometric parameters of roughness, roundness, straightness, profile and angle, and physical parameters such as hardness and elastic modulus. Subsequent measurements after the fracture tests characterized changes that occurred in the metal tapers. The fracture loads achieved depended on the potential for deformation of the taper surface. This potential can be described by a factor computed as hardness/roughness. A dependence of the fracture load on elastic modulus, form deviations or taper angle could not be established within the Cerasiv specifications.

Ceramics↗
PubMed1993

[Integrated gait analysis for future routine clinical use].

To describe the phenomenon of human movement by means of kinematic and kinetic measurements in a more objective manner, so-called integrated gait analysis systems have been developed. Although the commercially available equipment has already reached high technical levels, it does not play an important role in routine clinical applications. Due to this fact, the main arguments of the practitioners still address the practicability of the devices as well as the lack of meaningful software support for data assessment. The former concern has led to the integration of two KISTLER platforms beneath a treadmill belt in order to continuously capture 3D ground reaction force data. The latter one has prompted the development of an additional software kit, which statistically preprocesses the raw data set for further computations and which should prospectively allow a detailed analysis with artificial intelligence techniques. This new software becomes even more meaningful from the practitioner's point of view, because it may also be used as a stand alone unit for a preliminary assessment of gait patterns. The first part deals with the design of integrating two KISTLER platforms beneath the treadmill belt. A description of the analysis software follows, which removes noise, especially the influence of friction, from the raw data set. Thereby the 3D ground reaction force, which is originally caused by the patient while walking, is reconstructed. Preliminary results are presented. In the second part methods of automatically preprocessing the kinematic data set are focused upon.

Electromyography↗
PubMed1993

[Possibilities for recognizing and suppressing artifacts in EMG signals].

Two methods are introduced to suppress artifacts in the EMG signal, as can occur with EMG detection. These methods are based upon an adaptive threshold, which depends on the muscle activity measured just before. Even small artifacts are identified and suppressed in a small EMG, so if they are not too long in duration they do not noticeably falsify the muscle activity detection. These methods are quite effective, simple and thus easily realizable.

Artifacts↗
PubMed1993

[Possibilities for optimizing prosthetic management of leg amputees using quantitative movement analysis].

First, the differences between natural and artificial lower extremities are discussed from a biomechanical perspective. Their effects on the motion can be quantified with the help of optoelectronic gait analysis. The differences in motion between natural gait and walking with an above-knee prosthesis are illustrated with an example. Based on this, design possibilities for the improvement of the gait of prosthesis wearers are considered, and the effects of these designs are documented with the help of gait analysis. Finally, the advantages of the simultaneous measurement of forces and motion are discussed, and with this, a new development direction of integrated gait analysis is described which could be of major significance.

Amputation Stumps↗
PubMed1991

[Removal of bone cement with laser].

In operations requiring replacement of cemented endoprothesis, the removal of both the prosthesis and the cement is often difficult as the cement adheres strongly to the bone. Mechanical removal frequently results in fenestration or traumatisation of the bone. The aim of non-contact removal of polymethylmethacrylate (PMMA) with the laser, is to access normally inaccessible regions while inflicting a minimum amount of damage to the bone substance. The much cited cw or superpulsed CO2-laser cannot be used clinically, due to the thermal stressing of the bone. The paper shows spectra of PMMA with and without dopants, e.g. Tinuvin as UV absorber, optical staining with a high-pressure mercury lamp at lambda = 275 +/- 25 nm, lambda = 350 +/- 25 nm and various radiation times, as well as with an excimer laser lambda = 248 nm, FWHM 20 ns, and ablation measurements were made with the following lasers: excimer laser, Lambda Physics, EMG 102, FWHM 25 ns, lambda = 351 nm, excimer laser, Technolas, MAX 10, FWHM 60 ns, lambda = 308 nm, and a pulsed CO2 laser from PSI, lambda = 9.2 and 10.6 microns, FWHM 130 and 65 microseconds, pulse peak power 3.8 and 7.7 kW. The excimer laser, pulse length less than 100 ns, is unsuitable for clinical use because the required removal rate cannot be achieved either with doped PMMA or with pure PMMA. More promising results have been obtained with the pulsed (microseconds range) CO2 laser which has a removal rate of up to 30 times that of the above-mentioned excimer laser, with significantly lower thermal stressing of the bone than with the cw or super pulsed CO2 laser.

Bone Cements↗