PubMed Health⌕ Search

Biomedical subjects

A Rohlmann

Publications and source records attributed to A Rohlmann.

At least 55 records · Page 3Linked to original sources
PubMed1998

Influence of muscle forces on loads in internal spinal fixation devices.

STUDY DESIGN: The loads acting on an internal spinal fixation device were measured in vivo. OBJECTIVES: To determine the influence of muscle forces on implant loads. SUMMARY OF BACKGROUND DATA: Only limited information exists regarding the loads acting on spinal implants in vivo. Though the muscles greatly influence spinal load, they have been neglected in most studies. METHODS: Telemeterized internal spinal fixation devices were used to study the influence of muscle forces on the implant loads in three patients before and after anterior interbody fusion. RESULTS: Contracting abdominal or back muscles in a lying position was found to significantly increase implant loads. Hanging by the hands from wall bars as well as balancing with the hands on parallel bars reduced the implant loads compared with standing; however, hanging by the feet with the head upside down did not reduce implant loads compared with lying in a supine position. When lying on an operating table with only the foot end lowered so that the hips were bent, the patient had different load measurements in the conscious and anesthetized state before anterior interbody fusion. The anesthetized patient evidenced predominately extension moments in both fixators, whereas flexion moments were observed in the right fixator of the conscious patient. After anterior interbody fusion had occurred, the differences in implant loads resulting from anesthesia were small. CONCLUSIONS: The muscles greatly influence implant loads. They prevent an axial tensile load on the spine when part of the body weight is pulling, e.g., when the patient is hanging by his hands or feet. The implant loads may be strongly altered when the patient is under anesthesia.

Abdominal Muscles↗
PubMed1998

Inducible inactivation of hepatic LRP gene by cre-mediated recombination confirms role of LRP in clearance of chylomicron remnants.

The multifunctional low density lipoprotein (LDL) receptor-related protein (LRP) has been postulated to participate in a number of diverse physiological and pathological processes ranging from the homeostasis of plasma lipoproteins, atherosclerosis, and fibrinolysis to neuronal regeneration and survival. It has not been possible to demonstrate in vivo the physiological significance of LRP for each of these complex processes by a conventional gene knockout approach because LRP is essential for embryonic development. Here we have used the Cre/loxP recombination system to achieve inducible, tissue-specific and quantitative disruption of the LRP gene in adult mice. Inactivation of LRP in the livers of LDL receptor-deficient mice resulted in the accumulation of cholesterol-rich remnant lipoproteins in the circulation. In normal animals, this caused a compensatory upregulation of the LDL receptor in the liver. Conditional gene targeting has thus allowed us to isolate a specific physiological function of LRP for in vivo analysis and has provided unequivocal evidence for another LDL receptor-independent cholesterol clearance pathway in liver.

Animals↗
PubMed1998

Autocellular coupling by gap junctions in cultured astrocytes: a new view on cellular autoregulation during process formation.

Neocortical astrocytes make two types of gap junctions, intercellular ones create a functional syncytium, while reflexive gap junctions mediate autocellular coupling and serve unknown functions (Rohlmann and Wolff, 1996). Here, the question is addressed whether solitary astrocytes in vitro express connexin43 (Cx43) and establish gap junctions in the absence of intercellular contacts. In all media conditions tested, immunocytochemistry visualized Cx43-expression and gap junctions irrespective of the presence or absence of intercellular contacts. Reflexive gap junctions were associated with mechanical junctions (adherent spots and fascia adherens) connecting surface membranes and cytoskelal components, respectively. Both were characteristically located along incompletely separated borders between developing processes and/or branches. In addition, Cx43-immunoreactivity was found on some non-junctional membranes: i) intracellular vesicle clusters sited to forming processes and at the basis of filopodia; ii) the surface membrane of filopodial subpopulations usually appearing in bunches. Results suggest changes in the resumptive role of Cx43 in cultivated astrocytes: 1) Cx43 is not confined to intercellular gap junctions, it may even selectively compose reflexive ones; 2) from intracellular stores (vesicle aggregates), Cx43 may be incorporated into the surface membrane of filopodia; 3) by contacting other parts of the same cell surface (or neighboring cells), filopodia and membrane patches carrying Cx43-half channels may be essential in initial steps of gap junction formation; 4) the distribution of reflexive gap junctions is compatible with the hypothesis that autocellular coupling serves reorganization of cytoskeleton during the formation of cell processes and branches; 5) in general, gap junctions may be important for coordinating the cytoskeleton across intercellular contacts and within cells with complex shape.

Animals↗
PubMed1998

[Free vascularized bone transplantation in the extremities].

There is a growing trend today which calls for reconstructing the loss of bigger bone parts in the area of extremities in a suitable manner. The microvascular bone transplantation for bridging bone defects is--admist other procedures--a distinct enrichment to preserve the extremities. This method of transplantation has the capability of surviving within a weakened transplant bed. Because of this capability one inevitably wants to know the criteria which determine the biological behaviour of the transplants. Furthermore, it is essential to known how this criteria can be best managed, considering the different indications and locations. The bone healing and bone hypertrophy of 81 patients who received vascularised bone transplantations have been examined with respect to different parameters. As the positive capacities of the vital transplants are almost exclusively dependent on the actual supply with blood, angiography have been undertaken during three months after surgery. 71 patients with a patent anastomosis after surgery have been evaluated. Differences in bone healing of the vascularised transplants have been observed in regard to the following parameter:--The tumor group showed a better rate of bone healing than those patients with trauma and congenital tibiapseudarthrosis.--The bone healing results of the group of younger patients were better than those of the group of older patients. Moreover the transplants without a history of infection were better compared with transplants with a history of infection. Clear differences of the fibula hypertrophy behaviour have been observed with respect to the following parameters: upper extremities < lower extremities, thigh < lower leg, longer transplants < shorter transplants, group of older patients (35-60 years) < group of younger patients (1-18 years), plates < screws.

Blood Circulation↗
PubMed1998

Placing a bone graft more posteriorly may reduce the risk of pedicle screw breakage: analysis of an unexpected case of pedicle screw breakage.

Telemeterized internal spinal fixation devices were implanted in a patient with degenerative instability and a narrow spinal canal in order to measure the fixator loads during daily activities. Anterior interbody fusion was performed three weeks later. During walking, the typical maximum flexion bending moments were 10 N m in the left and 5 N m in the right fixator. On removal of the implants three months later, a fatigue fracture was found not on the high loaded left side but in the upper right pedicle screw. The crack started on the caudal side of the cross-sectional area and progressed cranially. Upper vertebral tilting in the sagittal plane must have caused the screw breakage. This would probably have been prevented by a more posteriorly placed bone graft.

Activities of Daily Living↗
PubMed1997

Rapid astroglial reactions in the motor cortex of adult rats following peripheral facial nerve lesions.

We report on changes in the motor cortex of adult rats that rapidly and transiently followed various types of facial nerve lesions. These reactions led to enhanced immunoreactivities of various astroglial markers: S-100 protein (a Ca2+- and Zn2+-binding protein predominantly located in the cytosol of astrocytes), glial fibrillary acidic protein (a cytoskeletal protein) and connexin 43 (the astroglial gap junction protein). Reactions could be visualized 1 h after the facial nerve lesion and disappeared within about 5 days after surgery. Combined lesions of the facial and trigeminal nerves modified the spatial pattern of the astroglial reaction, similar to intramuscular injections of botulinum toxin, which inhibits the release of acetylcholine in motor endplates. Data presented suggest that peripheral interference with muscular functions rapidly induces modifications in the motor cortex.

Acetylcholine↗
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↗