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Biomedical subjects

G Bergmann

Publications and source records attributed to G Bergmann.

At least 37 records · Page 2Linked to original sources
PubMed2000

2000 Volvo Award winner in biomechanical studies: Monitoring in vivo implant loads with a telemeterized internal spinal fixation device.

STUDY DESIGN: Implant loads were measured in 10 patients using telemeterized internal spinal fixation devices. OBJECTIVE: To determine the postoperative temporal course of implant loads. SUMMARY OF BACKGROUND DATA: Little information exists regarding the temporal course of loads on internal spinal fixation devices. METHODS: The telemeterized internal spinal fixator allows the measurement of three force components and three moments acting in the fixator. Implant loads were determined in up to 20 measuring sessions for different activities, including walking, standing, sitting, lying in the supine position, and lifting an extended leg while in the supine position. RESULTS: Implant loads often increased shortly after anterior interbody fusion was performed. Several patients retained the same high level even after fusion had taken place. This explains the reason why screw breakage sometimes occurs more than half a year after implantation. The time of fusion could not be pinpointed from the loading curves. CONCLUSIONS: The results show that fixators may be highly loaded even after fusion has occurred. A flexion bending moment acts on the implant even with the body in a relaxed lying position. This means that already shortly after the anterior procedure, the shape of the spine is not neutral and unloaded, but slightly deformed, which loads the fixators. Pedicle screw breakage more than half a year after insertion does not prove that anterior interbody fusion has not occurred.

Adult↗
PubMed2000

Influence of load carrying on loads in internal spinal fixators.

After spinal stabilization with an implant, patients want to know whether carrying loads will endanger their spine and their implant. Therefore, the effect of carrying a weight on the loading of internal spinal fixation devices was determined in 10 patients using instrumented, telemeterized internal fixators. Patients carried a 5kg dumbbell in one hand as well as up to 20kg in both hands. Compared to normal standing carrying a weight caused only a slight increase of the fixator loads in all patients. The maximum flexion bending moment in the fixators was then lower than during walking. Carrying a weight even decreased the axial compression force in the fixators of the patients with the T11 or T12 vertebra bridged. Patients also raised their arms in anteversion while holding weights of up to 5kg with both hands. This increased the flexion bending moment in the fixators. Only a small part of a carried weight is taken over by internal fixators. Carrying a shopping bag only slightly increases the risk of pedicle screw breakage, however, since the spine has to support most of the additional weight, it represents a risk with regard to correction loss and bone sintering.

Adult↗
PubMed2000

Interfacial conditions between a press-fit acetabular cup and bone during daily activities: implications for achieving bone in-growth.

Interfacial gaps and relative micromotions during activities are widely believed to restrict the boney in-growth process of non-cemented acetabular cups. Using finite element modeling of the cup-bone system, relative micromotions and interfacial gaps are calculated for walking slow, normal and fast and for climbing upstairs, downstairs and standing up from a chair. A 2mm press-fit is simulated and interfacial conditions in the immediate postoperative period (i.e. prior to boney in-growth) calculated between paired nodes covering the whole of the interface. In regions of 'safe' micromotions and 'allowable' gaps, boney in-growth is simulated by specifying zero relative displacement between nodal pairs. The modified model is then resubjected to the loads associated with climbing upstairs, which was shown to be the worst activity. Interfacial conditions are recalculated for subsequent iterations. The procedure is repeated until no further in-growth is predicted. The final pattern of in-growth calculated with the model compares reasonably well with histological evidence from explanted canine cups (Cha et al., 1998. Transactions of the Orthopaedic Research Society, 23, p. 373). Bridging between adjacent regions of in-growth is observed. Notably, in-growth occurs at most of the periphery but not in the polar region. The lack of polar in-growth is caused by the interfacial gap assumed to exist after cup implantation. It is suggested that increasing/decreasing hip-joint loads would have little effect on this lack of polar in-growth. However, excessive micromotions as a result of high hip-joint loads cause a lack of in-growth in the anterior region of the periphery in the model. Although such results were not found in the canine study, if relevant to the general human population, the avoidance of harsh weight-bearing activities may encourage complete peripheral in-growth but is speculated to do little for polar in-growth.

Acetabulum↗
PubMed2000

Family perception of interpersonal behavior as a predictor in eating disorders: a prospective, six-year followup study.

This study assessed family perception patterns of interpersonal behavior in families with a daughter diagnosed with an eating disorder 6 years after treatment that used a prospective design. Family perception patterns of patients found to have a poor outcome at followup (n = 15) were compared with patients with a good outcome (n = 23), as well as a control group (n = 36). Using the system of multiple level observation of groups (SYMLOG), all 238 family members evaluated themselves and each other. The index patients with a poor outcome perceived themselves as friendlier and more positive than they were perceived by their families. In comparison to parents of daughters with a good outcome and the control group, parents of daughters in the poor outcome group perceived themselves to be less friendly than their partners perceived them to be. A rigid polarization of the perception of the index patient by family members and a discrepancy in this perception between the index patient and the rest of the family were found to be indicative of a poor prognosis. Implications for treatment based on family perception patterns of interpersonal behavior are discussed.

Adolescent↗
PubMed2000

Changes in the loads on an internal spinal fixator after iliac-crest autograft.

Spines are often stabilised posteriorly by internal fixation and anteriorly by a bone graft. The effect of an autologous bone graft from the iliac crest on implant loads is unknown. We used an internal spinal fixation device with telemetry to measure implant loads for several body positions and activities in nine patients before and after anterior interbody fusion. With the body upright, implant loads were often higher after than before fusion using a bone graft. Distraction of the bridged region led to high implant loads in patients with a fractured vertebra and to marked changes in load in those with degenerative instability. Leaving the lower of the bridged intervertebral discs intact led to only small changes in fixator load after anterior interbody fusion. A bone graft alone does not guarantee a reduction of implant loads.

Adult↗
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↗