Search PubMed⌕ Search

Biomedical subjects

A Rohlmann

Publications and source records attributed to A Rohlmann.

At least 19 recordsLinked to original sources
PubMed1995

Is staircase walking a risk for the fixation of hip implants?

Considerable forces and moments act at hip prostheses during most kinds of physical activities. High torque around the stem axis may contribute to implant loosening. With instrumented hip prostheses the joint force and its direction, the bending moment in the frontal plane and the torque were measured in two patients during upstairs, downstairs and level walking. The data give information on whether or not stairclimbing causes a more severe loading situation for the implants than walking. While going upstairs at normal speed the joint force is 10% higher than during walking at 3 km h-1. Downstairs it increases by 20%. The bending moments change by nearly the same amounts. Upstairs the torsional moment is about twice as high as during slow walking. But walking at 5 km h-1 or slow jogging causes forces and moments of similar magnitudes. Even higher loads were observed when the patients stumbled without falling. Although torque during staircase walking is high, extreme values exclusively during stairclimbing are not confirmed by our data. The torsional moments now observed in vivo are close to or even exceed the experimentally determined limits of the torsional strength of implant fixations, found in the literature. Obviously, torsional moments play an important role for the potential loosening of hip prostheses.

Aged↗
PubMed1995

Influence of shoes and heel strike on the loading of the hip joint.

The forces and moments acting at the hip joint influence the long-term stability of the fixation of endoprostheses and the course of coxarthrosis. These loads may depend on the kind of footwear and the walking or running style. These factors were investigated in a patient with instrumented hip implants. He wore different sports shoes, normal leather shoes, hiking boots and clogs and walked barefoot with soft, normal and hard heel strikes. The loads were lowest while walking and jogging without shoes. All shoes increased the joint force and the bending moment at the implant slightly but the torsional moment rose by up to 50%. No relation was found between the different type of shoes and the load increase, only shoes with very hard soles were clearly disadvantageous. Soft heels, soles or insoles did not offer advantages. Gait stability seems to play the most important role in increasing the joint loading and should be the criterion for the choice of footwear. Smooth gait patterns with soft heel strikes are the only means to reduce joint loading during slow jogging.

Aged↗
PubMed1995

Structure--function relationships in gap junctions.

Gap junctions are metabolic and electrotonic pathways between cells and provide direct cooperation within and between cellular nets. They are among the cellular structures most frequently investigated. This chapter primarily addresses aspects of the assembly of the gap junction channel, considering the insertion of the protein into the membrane, the importance of phosphorylation of the gap junction proteins for coupling modulation, and the formation of whole channels from two hemichannels. Interactions of gap junctions with the subplasmalemmal cytoplasm on the one side and with tight junctions on the other side are closely considered. Furthermore, reviewing the significance and alterations of gap junctions during development and oncogenesis, respectively, including the role of adhesion molecules, takes up a major part of the chapter. Finally, the literature on gap junctions in the central nervous system, especially between astrocytes in the brain cortex and horizontal cells in the retina, is summarized and new aspects on their structure-function relationship included.

Animals↗
PubMed1994

Astrocytes as rapid sensors of peripheral axotomy in the facial nucleus of rats.

Facial nerve transection leads to functional and structural reactions in lesioned motor neurones and surrounding glial cells. Data from this study provide evidence that the most rapid reaction described so far consists of an increase in immunoreactivity of connexin-43 (cx-43), the predominant gap junction protein in astrocytes. The ipsilateral facial nucleus is selectively marked as early as 0.75 to 1.5 hours after axotomy, while the unlesioned side as well as the unoperated controls remain faintly stained. Thus, enhanced coupling capacity of astrocytes by gap junctions appears to be a sensitive indicator of modified neuronal-glial interaction in the CNS.

Animals↗
PubMed1994

A spinal fixation device for in vivo load measurement.

An instrumented spinal fixation device has been developed that allows in vivo measurement of the forces and moments acting on the implant. The telemetry is inductively powered, hermetically sealed by electron beam welding and is active only during the measurements. The instrumented fixateur interne is similar in size to the original Dick internal fixator implant and has the strength of the original implant. Laboratory tests with paired implants mounted in plastic vertebrae show that small changes in the position of the implants have a strong influence on the distribution of the loads on the implants.

Activities of Daily Living↗
PubMed1994

[Telemetric transmission system for in vivo measurement of the stress load of an internal spinal fixator].

For stabilizing fractures of the spine, a number of implantable devices are available. However, not much is known about the loads acting on these devices. In order to measure the forces and moments within the implant, the Dick internal fixation device was modified and fitted out with a hermetically sealed inductively powered telemetry unit. An integrated 8-channel telemetry chip was specially developed to measure the signals of six strain gauge sensors, the temperature of the implant and the supply voltage. Since the internal fixation devices are always implanted in pairs, two telemetry units are operated at the same time. This article details the function of the implanted electronic circuit and the external system components.

Adult↗
PubMed1994

[Effect of clamping tensile strength on load distribution in paired mounted spinal internal fixators].

Paired internal spinal fixation devices are not necessarily loaded symmetrically when the vertebrae are unable to support one another directly. A finite element model has been developed to predict the influence of clamping rigidity on the load distribution. If the stiffness of one clamping element is significantly reduced, the corresponding implant will bear only about 30 percent of the outer bending moment. The theoretical results were confirmed experimentally with sensor-loaded internal spinal fixation devices.

Biomechanical Phenomena↗
PubMed1993

Facial nerve lesions lead to increased immunostaining of the astrocytic gap junction protein (connexin 43) in the corresponding facial nucleus of rats.

After peripheral transection of the facial nerve, immunostaining of astrocytic gap junction protein changed in the corresponding brainstem nucleus of the rat. Enhanced connexin-43 immunoreactivity was restricted to the ipsilateral facial nucleus and to astrocytes surrounding lesioned motoneurons. This reaction is focally distinct, and marks only a part of the astrocytic network indicating a local plasticity of intercellular coupling. These results suggest that astrocytes work as sensors of signals which either depend on the integrity of neighboring neurons or inform about neuronal disorders.

Animals↗
PubMed1993

Hip joint loading during walking and running, measured in two patients.

The resultant hip joint force, its orientation and the moments were measured in two patients during walking and running using telemetering total hip prostheses. One patient underwent bilateral joint replacement and a second patient, additionally suffering from a neuropathic disease and atactic gait patterns, received one instrumented hip implant. The joint loading was observed over the first 30 and 18 months, respectively, following implantation. In the first patient the median peak forces increased with the walking speed from about 280% of the patient's body weight (BW) at 1 km h-1 to approximately 480% BW at 5 km h-1. Jogging and very fast walking both raised the forces to about 550% BW; stumbling on one occasion caused magnitudes of 720% BW. In the second patient median forces at 3 km h-1 were about 410% BW and a force of 870% BW was observed during stumbling. During all types of activities, the direction of the peak force in the frontal plane changed only slightly when the force magnitude was high. Perpendicular to the long femoral axis, the peak force acted predominantly from medial to lateral. The component from ventral to dorsal increased at higher force magnitudes. In one hip in the first patient and in the second patient the direction of large forces approximated the average anteversion of the natural femur. The torsional moments around the stem of the implant were 40.3 N m in the first patient and 24 N m in the second.

Aged↗
PubMed1993

[Stress measurements with an instrumented internal spinal fixator].

Little is known about the loads acting on internal spinal fixation devices. The effective forces and moments associated with different external loads have now been measured using instrumented implants. Measurements were obtained in intact cadaver spines and following vertebrectomy. The influence of the implant itself on the distribution of the loads was also investigated. It was found that the implants are not loaded symmetrically. Following vertebrectomy, the forces acting on the fixation device are significantly higher than in the case of an intact spine.

Biomechanical Phenomena↗
PubMed1992

Reactive astrocytes in myelin-deficient rat optic nerve reveal an altered distribution of orthogonal arrays of particles (OAP).

Reactive astrocytes are a common feature of various pathological conditions within the CNS. Morphological changes of reactive astrocytes include an altered nucleus-cytoplasm relationship, nuclear indentations, an increased amount of intermediate filaments, and an immunologically immature phenotype. Additionally, the number of orthogonal arrays of particles (OAP) was found to be increased within parenchymal membranes of reactive astrocytes. This observation prompted us to investigate the distribution of astroglial OAP in the amyelinated CNS of the myelin-deficient (md) rat in which reactive astrocytes prevail. In the present freeze-fracture study, astroglial OAP were determined within endfoot and nonendfoot (parenchymal) membranes in the developing optic nerve of md rats and normal littermates at the age of 12, 23, 40, and 64 days postnatally (dpn). The endfoot OAP density in md astrocytes remained constant during the entire period of investigation. In myelinated littermates, OAP densities continuously increased up to adult values. In contrast, the parenchymal OAP density in md astrocytes increased during the entire period of investigation. In normal littermates, OAP densities remained constant during the first 40 dpn and thereafter increased rapidly. These observations suggest that the absence of myelinogenesis in the md mutant may be a stimulus for parenchymal membranes of reactive astrocytes to insert OAP or to assemble OAP subunits into complete arrays.

Aging↗
PubMed1989

Aimed movements to visual targets in hemiplegic and normal children: is the "good" hand of children with infantile hemiplegia also normal?

The accuracy, reaction and movement time of pointing movements to visual targets were examined in children aged 3-13 yr with infantile hemiplegia and compared to those of comparably aged normal children. Hemiplegic children pointed with the "good" hand (i.e. ipsilateral to the lesion). Half the normal children used the preferred hand, half the non-preferred hand. Movements were made with unrestricted/restricted visual feedback, when movement distance was short/medium/long, and when number of target alternatives were 2/4/8. Normal children using the preferred hand were more accurate but reacted more slowly than children using the non-preferred hand. The performance of most of the hemiplegic children with bilateral and/or unilateral lesions was impaired; degree of accuracy was related to the extent of the brain lesion; and reaction time was related to the level of intelligence. It was concluded that unilateral lesions in children can result in bilateral visuomotor impairment.

Adolescent↗
PubMed1988

Multichannel strain gauge telemetry for orthopaedic implants.

In vivo measurements of the loads and deformations occurring in orthopaedic implants will allow future improvements to be made. This paper describes an extremely small telemetry for long term measurements with three strain gauges and methods for an absolutely safe implant design. Developed for measuring the load at hip prostheses, the telemetry can also be used for other implants. Its size makes feasible instrumentation of devices with only slight mechanical modifications. In addition to the description of our own measuring system, the paper gives a survey on the problems of telemetrized implants, on methods for measuring spatial loads, and on the investigations of other authors. Future publications will present in vivo measurements with this telemetry, among others on hip endoprostheses.

Equipment Design↗
PubMed1988

A nonlinear finite element analysis of interface conditions in porous coated hip endoprostheses.

We used a geometrically simplified finite element model to investigate load transfer between a porous coated hip endoprosthesis and a femur. Assuming both rigidly bonded and nonlinear interfaces, we analyzed fully and partially coated stems that had coatings of different elastic moduli. Our results indicate that maximum values for relative motion in the interface between bone and implant occur for implants with the same elastic modulus as compact bone. By comparison, interface motion is reduced by about half for Co-Cr-Mo alloy stems. We also showed that the elastic modulus of the porous coating had only a small influence on bone stresses.

Biomechanical Phenomena↗
PubMed1987

Effects of stem design and material properties on stresses in hip endoprostheses.

With the aid of a three-dimensional finite element stress analysis a parameteric study of the essential aspects of the femoral component of hip endoprostheses was carried out. Various designs were investigated; these included the prosthetic stem length, the existence or non-existence of the prosthetic collar and the elastic modulus of stem and cement. Variations in the stem length have only minor effects on the stress distribution for a stem length greater than 100 mm, but the elastic modulus of the prosthetic stem has a considerable influence on the stresses. A high elastic modulus of the stem increases the stresses in the stem but it decreases stresses in the cement. The cement stresses increase with an increase in the modulus of elasticity of the cement.

Bone Cements↗