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Biomedical subjects

G Bergmann

Publications and source records attributed to G Bergmann.

At least 19 recordsLinked to original sources
PubMed1999

Internal spinal fixator stiffness has only a minor influence on stresses in the adjacent discs.

STUDY DESIGN: Stresses in vertebral endplates and discs were calculated using the three-dimensional nonlinear finite-element model of a lumbar spine with an internal spinal fixation device. OBJECTIVE: To determine the influence of fixator stiffness on stresses in the adjacent discs. SUMMARY OF BACKGROUND DATA: There are few computer models of the lumbar spine with a fixator. Most of these models neglect the muscle forces. Fixator stiffness is assumed to influence greatly the stresses in the adjacent discs. METHODS: Two three-dimensional nonlinear finite-element models were used to determine stresses in the lumbar spine for standing and 60 degrees flexion of the upper body. One model had an internal spinal fixator, the other did not. In a parameter study, the diameters of the longitudinal rod of the fixator were assumed to be 3, 5, 7, and 10 mm. In the computer model, the forces of the trunk muscles were simulated. RESULTS: The diameter of the longitudinal rod strongly affected the fixator loads but hardly influenced the stresses in the vertebral endplates. The stresses in the bridged discs were strongly reduced. However, the internal fixator had only a minor influence on the stresses in the anulus fibrosus and the pressure in the nucleus pulposus of the adjacent discs. CONCLUSIONS: The stiffness of an internal spinal fixation device has only a minor influence on stresses in the adjacent discs.

Elasticity↗
PubMed1999

Loads on internal spinal fixators measured in different body positions.

Telemeterized internal spinal fixation devices were implanted in ten patients. The loads acting on the fixators were compared for different body positions, including standing, sitting, and lying in a supine, prone, and lateral position. Implant loads differed considerably from patient to patient depending, for example, on the indication for surgery and the surgical procedure. They were altered by anterior interbody fusion. Mostly, only small differences in implant loads were found for the various lying positions. Flexion bending moments were significantly higher in upright than in lying body positions. Loads on the fixators were not higher for sitting than for standing. Patients who have undergone mono- or bisegmental spine stabilization should therefore be allowed to sit as soon as they can leave the bed.

Adult↗
PubMed1999

Estimation of trunk muscle forces using the finite element method and in vivo loads measured by telemeterized internal spinal fixation devices.

Direct quantitative measurement of muscle forces is not possible. Forces in the trunk muscles were estimated for standing and flexion of the upper body using three-dimensional, nonlinear finite element models of the lumbar spine with and without an internal spinal fixation device. Muscle forces assumed were two pairs dorsally and one ventrally, each representing several muscles. Muscle forces in the model with internal fixators were varied in discrete steps until the implant loads calculated closely corresponded to those measured in a patient with an instrumented implant. The calculated angles between adjacent lumbar vertebrae were compared with corresponding values measured on X-ray films of a patient as well as with literature values and served as a second criterion for predicting muscle forces. For the model without an implant, the muscle forces of the first model were slightly varied until the lumbar spine shape and the intradiscal pressure were physiological. The abdomen was shown to have a considerable supporting function for flexion.

Abdominal Muscles↗
PubMed1999

Hip joint forces in sheep.

Testing orthopaedic implants at the proximal femur of sheep requires knowledge of the contact forces acting on this joint. Telemeterized implants were used for long-term measurements of these forces in four sheep, mostly during treadmill walking. Joint forces in the same sheep varied widely from day to day and interindividual differences were also pronounced. Forces during walking were mostly higher than in previous short-term measurements. At medium walking speed, loads in the range of 65-140% of the body weight were typical. Fast walking increased the forces by only 20%, compared to slow speed. Stomping on the ground at the beginning of the stance phase and starting to run freely led to very high forces. The highest values observed were nearly four times the body weight. As in humans, the directions of high forces varied only slightly in the frontal plane throughout the whole stance phase but much more in the transverse plane. With regard to the force magnitudes and their directions, sheep seem to be a good model for testing human implant at the proximal femur.

Animals↗
PubMed1999

Hip endoprosthesis for in vivo measurement of joint force and temperature.

Friction between the prosthetic head and acetabular cup increases the temperature in hip implants during activities like walking. A hip endoprosthesis was instrumented with sensors to measure the joint contact forces and the temperature distribution along the entire length of the titanium implant. Sensors and two inductively powered telemetry units are placed inside the hip implant and hermetically sealed against body fluids. Each telemetry unit contains an integrated 8-channel telemetry chip and a radio frequency transmitter. Force, temperature and power supply data are transmitted at different frequencies by two antennas to an external twin receiver. The inductive power supply is controlled by a personal computer. Force and temperature are monitored in real time and all data are stored on a video tape together with the patient's images. This paper describes the design and accuracy of the instrumented implant and the principal function of the external system components.

Body Temperature↗
PubMed1999

Braces do not reduce loads on internal spinal fixation devices.

OBJECTIVE: To determine the effect of a brace or harness on loads on internal spinal fixation devices. DESIGN: The implant loads were measured in vivo using telemeterized internal spinal fixators. BACKGROUND: Only limited information exists regarding the load reduction due to a brace or harness. METHODS: A Boston overlap brace, a reclination brace, and a lumbotrain harness were examined to determine how they affect the loads on internal spinal fixation devices. The implant loads were measured using telemeterized fixators in six patients for several positions and activities, including sitting, standing, walking, bending forward, and lifting an extended leg in a supine position. RESULTS: None of the braces studied were able to markedly reduce the loads on the fixators. Frequently even higher fixator loads were measured when wearing a brace or harness. CONCLUSIONS: It does not seem helpful to brace patients after mono- or bisegmental stabilization of the lumbar spine.

Adult↗
PubMed1999

[Loading on internal spinal fixation devices].

The loads acting on internal spinal fixation devices were measured for different activities in ten patients using telemeterized bisegmental implants. The highest loads were found for walking and lateral bending of the upper body while standing. When bending forwards the upper body, the fixator loads were only slightly altered. The forces and moments were not higher during sitting than during standing. Therefore, sitting should be allowed for patients with instrumented spines as soon as getting up is allowed. The forces and moments in the fixators were often altered due to anterior interbody fusion. Especially in patients with degenerative instability, the implant loads were higher after anterior interbody fusion than before. Braces were not able to markedly reduce the fixator loads. Therefore, it does not seem helpful to brace patients after mono- or bisegmental stabilization of the thoracic or lumbar spine.

Braces↗
PubMed1999

[Quality of life, depression and coping behavior in patients awaiting heart transplant].

From a medical perspective, heart transplantation is now an established procedure for the treatment of patients with terminal heart failure. For the patient involved, it presents itself as a situation of great psychological distress, particularly during the waiting period. In the last few years, this situation has grown worse due to the decline in the number of donor organs and the resulting longer waiting period. The aim of this study was to systematically evaluate this phase of the transplantation procedure in a follow-up study. 52 patients could be assessed in follow-up. Although the patients had already differed from the healthy control group in the areas of depression, quality of life, and physical complaints (p < 0.001) at the beginning of the study, there was a significant increase of depression and a further decline in the reported quality of life in the course of the study. The patients presented themselves as having a low internal and a significantly increased external and fatalistic locus of control. The study stresses the necessity for supportive psychotherapeutic therapy in these patients.

Adaptation, Psychological↗
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

[Emotional status of patients on the waiting list for heart transplantation].

Although heart transplantation is by now considered an established procedure in patients with terminal heart failure, there has been a stagnation or even a decline in the number of transplantations performed due to the decreased willingness of the public to provide organs. As a consequence of this development patients have to wait for a donor organ for a much larger time. The aim of this study was to examine patients especially during this very stressful period. From July 1995 to February 1997, 62 patients who had been continuously added to the waiting list were examined regarding their quality of life and emotional state. Completely assessed were 53 patients (participation rate: 85%). As compared to a healthy control group, patients with terminal heart failure on the waiting list reported their quality of life in the physical as well as the psychological area as significantly lower (p < 0.001). The areas of depression (p < 0.001) and anxiety (p < 0.001) also showed a significant difference. There was an obvious correlation (p < 0.01) between the key symptom of terminal heart failure-- dyspnoea--and the measured level of depression. This served to support the notion that there is a connection between the psychological and the somatic state in these severely ill patients. These results point to the necessity of supportive psychotherapeutic treatment during this very stressful time.

Adult↗
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↗
PubMed1998

Psychological distress in patients awaiting heart transplantation.

Heart transplantation has become an established procedure for the treatment of terminal heart failure. However, due to a shortage of donor organs, the waiting period for a donor organ is increasing. Cross-sectional and retrospective studies have indicated that there is tremendous psychological distress during this waiting period. The aim of this study was to assess this phase systematically and longitudinally. At the beginning of their waiting period, 62 patients at the Heidelberg Transplantation Centre were examined with regard to their physical complaints, quality of life, and level of depression. Four months later the remaining 42 patients were re-examined. The sample showed a significant increase (p<0.001) in subjective physical symptoms and an impairment in social activities (p<0.05) and everyday life (p<0.05), and a significant increase in depression (p<0.001), despite the relatively short time period. These results show the necessity of supportive psychotherapy for patients undergoing heart transplantation.

Adult↗
PubMed1997

DNA ploidy and protein synthesis in squamous cell carcinoma cell lines of the head and neck.

Aneuploidy as abnormal nuclear DNA content, is considered almost positive evidence of malignancy. In this study three diploid and three aneuploid squamous cell carcinoma (SCC) cell lines were examined for DNA content by flow cytometry. The DNA indices of the SCC cell lines were found to range from 1.0 to 2.1. The mitotic activity of the diploid cell lines was 1.6 times higher and the cells were smaller than aneuploid cells. To find a molecular basis for these differences, the pattern of the de-novo synthesized proteins was analyzed by means of [35S]methionine incorporation, electrophoresis, and autoradiography. In all aneuploid SCC cell lines tested in this experiment, the increase of nuclear DNA content is associated with the synthesis of a novel protein with a molecular mass of approximate 55 kDa as well as with altered synthesis rates of two preexisting proteins (50 kDa and 100 kDa). For determination of the amino acid uptake in diploid and aneuploid cells, the accumulation of [35S]methionine was measured as a function of time by liquid scintillation counting. No significant difference was found in the uptake rate between diploid and aneuploid cells with the same protein content. However, discrepancies were revealed when equal numbers of cells with different DNA index were used, suggesting, that protein turnover is different in diploid and aneuploid SCC cells.

Aneuploidy↗
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

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

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↗