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Biomedical subjects

A Rohlmann

Publications and source records attributed to A Rohlmann.

At least 37 records · Page 2Linked to original sources
PubMed1997

Loads on an internal spinal fixation device during walking.

Only little knowledge exists concerning the loads on internal spinal fixation devices during walking. In this study, forces and moments were measured in two patients using telemeterized spinal fixators. Although implant loads differed strongly before and after anterior fusion as well as between the two patients, some results were consistent. In every test series, implant loads were higher in walking than in lying, sitting or standing. Walking speed had little influence on implant loads. Staircase walking put slightly higher loads on the implants than normal level walking. Normal use of two crutches reduced implant loads only slightly, whereas a wheeled invalid walker reduced them by about 25%.

Adult↗
PubMed1997

Comparison of loads on internal spinal fixation devices measured in vitro and in vivo.

The loads on internal spinal fixation devices were measured using modified, telemeterized AO-Dick internal fixators. The implants allow measurement of the three force components and the three moments acting on the implant. The modified fixators were mounted on cadaver spines, and the implant loads were measured in the intact and postcorpectomy spines for different loading modes, including axial compression force, flexion, extension, lateral bending, and torsion. The in vitro experiment did not consider muscle forces. Modified fixators were also implanted in three patients, and the implant loads were determined before and after anterior interbody fusion with autologous iliac-crest bone grafts. The results for different in vitro loading modes were compared with those in vivo in order to demonstrate the extent to which the in vitro loads represent the real situation in patients. In several cases, the implant loads in the in vitro experiment differed strongly from those measured in patients. For flexion and lateral bending, a tensile axial force occasionally was measured in the in vitro experiment, while in the patients the axial force was always compressive. Extension was predominantly associated with extension bending moments in the in vitro study but with flexion bending moments in the patients. When muscle forces are not considered in the in vitro experiment, the loads on the fixators may differ significantly from the situation found in patients.

Adult↗
PubMed1997

Longitudinal study of neuropsychological outcome in blind extremely-low-birthweight children.

This study evaluated neurological and psychological development in 10 blind children over a 4-year period. Five of the children were born preterm with an extremely low birthweight (ELBW) and a diagnosis of retinopathy, whereas the other five were term. All children received their first neurological examination at a mean age of 10 months and then annual follow ups. In addition, the Bielefeld Developmental Test for Blind Infants and Preschoolers (BDTB) was administered every 6 months (from the ages of 18 to 48 months) to assess developmental outcome in different domains (e.g. cognition, language, gross motor abilities). Results showed a higher number of peri- and neonatal complications in blind ELBW children as well as a significantly higher number of neurological symptoms over the 4-year period. At the mean age of 4 years 10 months, blind ELBW children had a significantly lower body weight, body height, head circumference, and body-mass index compared with the term children. Findings on psychological development revealed that blind ELBW children also had significantly lower scores on all domains covered by the BDTB. Finally, the overall score on the BDTB correlated significantly with gestational age, birthweight, duration of mechanical respiration, and days spent in hospital after delivery.

Blindness↗
PubMed1997

Hip joint forces during load carrying.

In some diseases affecting only 1 hip joint, it is necessary to keep the contact force between femoral head and acetabulum (hip joint force) permanently low at the affected side. Six subjects were examined while they were walking and carrying a load in 1 or 2 hands. It was determined how the forces in both hip joints are influenced by the magnitude of the load and the manner in which it is carried. A mathematical model was used to calculate the maximum forces in the frontal plane. One subject had instrumented endoprostheses implanted in both hips. For him the measured values were slightly higher than the calculated ones, but the overall results were similar. Carrying a load on 1 side keeps the force constant at the ipsilateral hip joint or even slightly lowers it. At the same time, there is a large increase on the opposite side. Carrying 25% of body weight with 1 hand causes about 2/3 higher forces in the contralateral joint than on the loaded side. If this load is evenly distributed between the 2 sides, both hip joint forces increase by 25%. In unilateral load carrying, additional relief of the ipsilateral joint can be achieved if the upper body is held upright and the loadcarrying arm is abducted, such as when using a large shopping basket.

Adult↗
PubMed1996

Defective forebrain development in mice lacking gp330/megalin.

gp330/megalin, a member of the low density lipoprotein (LDL) receptor gene family, is expressed on the apical surfaces of epithelial tissues, including the neuroepithelium, where it mediates the endocytic uptake of diverse macromolecules, such as cholesterol-carrying lipoproteins, proteases, and antiproteinases. Megalin knockout mice manifest abnormalities in epithelial tissues including lung and kidney that normally express the protein and they die perinatally from respiratory insufficiency. In brain, impaired proliferation of neuroepithelium produces a holoprosencephalic syndrome, characterized by lack of olfactory bulbs, forebrain fusion, and a common ventricular system. Similar syndromes in humans and animals are caused by insufficient supply of cholesterol during development. Because megalin can bind lipoproteins, we propose that the receptor is part of the maternal-fetal lipoprotein transport system and mediates the endocytic uptake of essential nutrients in the postgastrulation stage.

Animals↗
PubMed1996

RAP, a specialized chaperone, prevents ligand-induced ER retention and degradation of LDL receptor-related endocytic receptors.

The multifunctional low density lipoprotein (LDL) receptor-related protein (LRP) forms a complex with a receptor-associated protein (RAP) within the secretory pathway. RAP inhibits ligand binding to LRP and is required for normal functional expression of LRP in vivo, suggesting a physiological function as a specialized chaperone. We have used RAP-deficient mice, generated by gene targeting, to investigate the role of RAP in the biosynthesis and biological activity of LRP and other members of the LDL receptor gene family in various organs and in embryonic fibroblasts. Our results demonstrate that RAP is required for the proper folding and export of the receptors from the endoplasmic reticulum (ER) by preventing the premature binding of co-expressed ligands. Overexpression of apolipoprotein E (apoE), a high affinity ligand for LRP, results in dramatically reduced cellular LRP expression, an effect that is prevented by co-expression of RAP. RAP thus defines a novel class of molecular chaperones that selectively protect endocytic receptors by binding to newly synthesized receptor polypeptides, thereby preventing ligand-induced aggregation and subsequent degradation in the ER.

Animals↗
PubMed1996

Patient monitoring system for load measurement with spinal fixation devices.

Fractures of the spine can be stabilized by different implants. Their stiffness varies widely and only little is known about the loads acting on these devices. In order to measure the forces and moments in the implant, the internal fixator after Dick was modified. An inductively powered telemetry unit is placed inside the fixator and is hermetically sealed against body fluids. An integrated eight channel telemetry chip was developed to measure the signals of six strain gauge sensors, the implant temperature and the power supply. Because two fixators are implanted together, two telemetry transmitters run at the same time. This paper describes the function of the instrumented implant and the external system components.

Biomechanical Phenomena↗
PubMed1996

In vitro load measurement using an instrumented spinal fixation device.

An AO spinal fixateur interne was modified to study the effects of a corpectomy on implant performance. A hermetically sealed cartridge containing strain gauges and an inductively powered telemetry unit was integrated into the threaded portion of the original implant. Five cadaveric spines were instrumented with the modified implant spanning a single lumbar vertebra. The spines were tested in axial compression, torsion, flexion, extension and lateral bending. Measurements of the three forces and moments within the implant were performed in the intact spine and repeated following a corpectomy and corpectomy plus complete posterior ligamentous injury. The bending moment, increased following corpectomy in all testing modes. The largest increase was in the flexion bending moment, which increased from 155 Nmm to 3328 Nmm following corpectomy.

Aged↗
PubMed1996

Sustained somatic gene inactivation by viral transfer of Cre recombinase.

Transgenic and knockout mice have proven invaluable tools for analyzing physiologically relavant functions of numerous genes. In some cases, however, pleiotropic effects that result from a variable requirement for a particular gene in different tissues, cell types, or stages of embryonic development may complicate the analysis due to a complex phenotype or embryonic lethality. The loxP/Cre-mediated recombination system, which allows tissue-specific gene targeting in the mouse, can be used to overcome these problems. A limitation of current methods is that a mouse carrying a loxP-tagged gene must be crossed with a transgenic mouse expressing the Cre recombinase in an appropriate tissue to obtain the desired gene rearrangement. We have used recombinant adenovirus carrying the Cre recombinase to induce virtually quantitative somatic cell gene disruption in the liver. The targeted gene was the multifunctional low-density lipoprotein receptor-related protein (LRP), a cell surface receptor for alpha 2-macroglobulin and other ligands. Transient expression of Cre following adenoviral infection produced the predicted gene rearrangement, functionally inactivating LRP in the liver. Rearrangement occurred within 6 days after infection and remained stable for at least 28 days. The results demonstrate the suitability of adenoviral Cre gene transfer to induce long-term, quantitative, and temporally controlled gene disruption in the mouse.

Adenoviridae↗
PubMed1996

Clamping stiffness and its influence on load distribution between paired internal spinal fixation devices.

The load distribution between two internal spinal fixation devices depends, besides other factors, on their stiffness. The stiffness ranges were determined experimentally for the clamps of the AO internal fixator with lateral nut and with posterior nut as well as for the clamps of the SOCON fixator. The stiffness of eight devices each differed by a factor of 3.1 for the clamp with lateral nut, by a factor of 1.5 for the clamp with posterior nut, and by a factor of 1.4 for the clamp of the SOCON fixator. For the AO clamp with lateral nut, the influence of the nut-tightening torque on the stiffness was determined. Using instrumented internal spinal fixation devices mounted to plastic vertebrae and simulating a corpectomy, the load distribution between the implants was measured for different tightening torques. It could be shown that, for the AO internal fixator whose clamps have a lateral nut, a nut-tightening torque > 5 Nm has only a negligible influence on load-sharing between the implants. Tooth damage occurs when the teeth of the clamp body and clamping jaw of the clamp with lateral nut do not gear together exactly, which leads to changes in the clamping stiffness and load-sharing between the two implants.

Humans↗
PubMed1995

Telemeterized load measurement using instrumented spinal internal fixators in a patient with degenerative instability.

STUDY DESIGN: In the present study, the loads in an internal spinal fixation device were measured in vivo. OBJECTIVES: To determine the implant loads for different activities before and after additional anterior stabilization of the spine. SUMMARY OF BACKGROUND DATA: Mathematical models exist for predicting spinal loads. The intradiscal pressure has been measured for many body positions and activities. The loads on internal spinal fixation devices have not been measured before in vivo. METHODS: Telemeterized AO spinal internal fixators were implanted in a patient with degenerative instability. The implants allow the in vivo measurement of three force components and three moments acting in the implant. RESULTS: When the patient was lying in relaxed positions, the implant loads were small. Before additional anterior stabilization, the loads were also small for sitting, standing, and walking. The bending moment in the sagittal plane was less than 3 Nm for these activities. The highest loads within the first 4 weeks after implantation were measured while the patient turned from a supine to a lateral position against the advice of the physiotherapist. After anterior stabilization, the maximum loads for the relaxed lying positions were altered only slightly. Much higher axial forces and bending moments were measured for sitting, standing, and walking. The maximum bending moment increased to 5-8 Nm for these activities. The implant loads for sitting were not higher than for standing. CONCLUSION: Flexion and lateral bending of the upper body and weight-carrying during sitting, standing, or walking should be avoided in the first few months after anterior stabilization.

Bone Screws↗
PubMed1995

In vivo measurement of implant loads in a patient with a fractured vertebral body.

It is not known what loads act on an internal spinal fixation device in patients with a fractured vertebral body. To measure the implant loads in vivo, telemeterized internal spinal fixators were implanted in a patient, and the implant loads measured for numerous body positions and activities before and after anterior fusion. The highest implant loads were found while the patient lifted both extended legs in a supine position. High implant loads were also measured for lateral bending during standing as well as for walking and carrying a load in one hand. The implant loads were small in recumbent positions. In contrast to findings in another patient, who was treated for degenerative instability, implant loads were smaller in the first months after anterior fusion than before. The indication for stabilization and surgical procedure strongly influence implant loads.

Adult↗
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↗