Antonius Rohlmann

..However, walking is the exercise that plays the major role concerning pedicle screw breakage because it causes the highest bending moments of all exercises studied and it loads the fixation devices most frequently...

..The results do not support the assumption that disc loads are significantly reduced by a dynamic implant. For axial rotation, however, dynamic fixation devices do reduce the force in the facet joint...

..In a modern chair, spinal loading is no higher than with non-adjustable office chairs...

..Owing to the preload, maximum stresses were higher for the rigid bond than when contact elements were used...

..Clinical studies will be required to show whether or not there is a strong correlation of parameter combinations that cause high facet joint forces and low back pain after total disc replacement...

..The loads acting on a vertebral body replacement (VBR) were measured in vivo...

..Great care should be taken to choose the optimal implant height and to insert the implant in the best position for each individual patient...

..Among other things, such data are required for choosing the optimal rehabilitation program for a patient and for evaluating the efficacy of aids like crutches and braces...

..This study adds new information about the mechanical behavior of the lumbar spine after insertion of posterior and anterior spine-stabilizing implants. This information improves our biomechanical understanding of the spine...

..The mechanical behavior of the lumbar spine after insertion of a ProDisc prosthesis was studied using 3-dimensional nonlinear finite element models...

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..In addition, this shift leads to a stronger increase of intradiscal pressure than the augmentation of the vertebral body with bone cement...

..For axial rotation the decrease takes place in the final stage. Intradiscal pressure is lower while facet joint force and maximum von Mises stress in the annulus are higher in a degenerated compared to a healthy disc...

..Implant size and stiffness have only a minor effect on intradiscal pressure. The maximum von Mises stress in the vertebral arch is strongly increased by the implant...

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..Little is known about the stiffening effect of this fusion-bone mass on the mechanical behavior of the corresponding bone region, including the load distribution between the different parts...

..The mobile connectors moved considerably along the rod when the spine was bent. It can be expected that the connectors also move along the rod as the adolescent grows, possibly leaving the discs intact until the patient is fully grown...

..Thus, the results of this study demonstrate that a dynamic implant does not necessarily reduce axial spinal loads compared to an un-instrumented spine...

..The measuring implant described here will provide additional information on spinal loads...

..Different sizes of the contact area between implant and vertebral body have only a local effect on stress distribution...

..In our patients, flexion of the upper body was most likely a combination of hip- and lumbar spine bending...

..To estimate the muscle forces during upper-body inclination and to determine their influence on stress distribution in the annulus fibrosus of the lumbar spine discs...

..Implant loads decreased with increasing inclination of the upper body while sitting on a chair with an adjustable backrest. Implant loads were about 27% higher for standing up and sitting down than for sitting...

..Applying a follower load of 500 N is the only loading mode simulating standing for which the calculated values for intervertebral rotations and intradiscal pressures agreed well with in vivo data from literature...

..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...

..Only then will results of different studies be comparable...

..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...

..In the case of a wedge-shaped deformation of a vertebral body, the relative increase of the flexion moment is a function of the wedge angle and of the original position of the centre of gravity of the upper body...

..Implant loads were measured in 10 patients using telemeterized internal spinal fixation devices...

..In some cases the average contact pressures were higher for the small-sized VBR, in others for the large-sized one. Our results reveal that from the mechanical point of view, a small-sized VBR is not generally disadvantageous...

..Sitting is frequently assumed to cause high spinal loads because people with sedentary work often suffer from low back pain. It is assumed that the posture while sitting, as well as several seat parameters, also affects the spinal loads...

..There are several different artificial discs for the lumbar spine in clinical use. Though clinically established, little is known about the biomechanical advantages of different disc kinematics...

..The validation of these methods requires in vivo data; therefore, the purpose of this study was to provide in vivo loading data of the knee joint...

..Inductive power supply, calculation of the loads from the measured deformations and real time load display are carried out by the external equipment. The maximum error of the load components is 2% including crosstalk...

..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...

..However, the optimised values lead to the best agreement with in vivo measured values. Their consequent application would lead to a better comparability of different investigations...

..Our results suggest that the mechanical factors studied have only a minor influence on fusion rate and that other factors, such as incomplete resection of cartilage plate and poor local blood supply, are more decisive...

..The designated functions of a motion preservation system can best be achieved when the longitudinal rod has a low stiffness, and when the connection between rod and pedicle screws is rigid...

..A larger graft with low stiffness should be favored from a mechanical point of view. Patients should avoid lateral bending of the upper body shortly after surgery...

..With increasing stiffness of the dynamic implant, the CoR moved towards the longitudinal rod. This posterior shift of the CoR led to a compression of the entire intervertebral disc during flexion and thus to an increase of disc bulging...

..A preceding optimization of the location of the FL path would increase the comparability of different studies...

..Eight instrumented vertebral body replacements are ready for implantation, and an instrumented tibial tray is being submitted to laboratory tests...

..The model predicts, especially for lateral eccentricities, strongly increased lumbar loads. Therefore, great care should be taken in placing the implant in an optimal position...

..For axial rotation, spinal stability is decreased even after a hemifacetectomy. Patients should therefore avoid excessive axial rotation after such a treatment...

..Loads acting in vivo on a vertebral body replacement (VBR) and the shape of the back were measured...

..At least for heavyweight and very active subjects, the real load conditions are more critical than those defined by the ISO standards for fatigue tests...

..This study should help to elucidate the role of the various ligaments...

..Driving a car or using public transportation systems-when the patient leans towards the backrest-leads to lower implant loads than walking, and can therefore be allowed already shortly after surgery...

..Elastic moduli of cement, fracture region and cancellous bone as well as cement volume have sometimes a moderate effect while number and symmetry of cement plugs have virtually no effect on the maximum stresses...

..The measured values will enhance the quality of future pre-clinical testing, numerical modeling in knee biomechanics and the patients' physiotherapy and rehabilitation...

..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...

..With regard to the force magnitudes and their directions, sheep seem to be a good model for testing human implant at the proximal femur...

..In addition, such a model is suitable for determining the effects of lumbar spine implants on spinal balance...

..Our results suggest that disc degeneration, which is sometimes found at the level directly above and below the fixators, is not caused by mechanical factors...

..Predicted facet joint forces may be used for the designing and pre-clinical testing of artificial facet joint replacements...

..CONCLUSIONS: A superimposed follower load renders spinal loading with pure moments more physiologic...

..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...

..This indicates that finite element models of spinal segments have to be validated and that a realistic quantitative prediction of ligament forces is extremely difficult...

..Because the potential risk for an individual patient cannot be foreseen, the use and improvement of low friction implant materials is important...

..Because the hip joint loading during all other common activities of most hip patients are comparably small (except during stumbling), implants should mainly be tested with loading conditions that mimic walking and stair climbing...

..3mm. These first worldwide in vivo measurements of glenohumeral contact forces are being continued in more patients and for longer postoperative times...

..Under unfavourable conditions such a risk exists, however. General improvements of implant materials and clinical studies on the possibility of implant loosening due to high temperatures are therefore required...

..To determine whether load directions for stumbling are similar to those for common activities and whether stumbling can be realistically simulated under laboratory conditions without endangering the patients...

..Using this data, many practical conclusions are drawn. Due to the huge amount of data obtained from the hip, most practical advise can be provided to patients with replacement or disorders involving this joint...

..This paper describes the design and accuracy of the instrumented implant and the principal function of the external system components...

..The aim of the study was to determine the as yet unknown optimal stiffness value of the longitudinal rods that fulfils best these opposing tasks...

..g. lifting or holding a weight with an outstretched arm. Some energy-related optimization criteria used in the literature for analytical musculoskeletal shoulder models must now be reconsidered...

..Additional errors caused by noise of the transmitted signals can be reduced by filtering if this is permitted by the sampling rate and the required frequency content of the loads...

..Up to now, plain radiographs are not well suited to assess spinal fusion. Radiostereometric analysis performed for two postures may deliver more reliable results. However, it is unknown, which postures are most suitable for this procedure...

..This study showed that SpineDMS(©) could be deployed as a reliable diagnostic tool for back posture, as well as movements in the sagittal plane...

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..The aim of this finite element study was to find load combinations that would lead to the highest internal stresses in a healthy and in degenerated discs...

..INTERPRETATION: This calibration method was performed on range of motion data; however, the procedure could also be applied to other loading scenarios and measurement parameters like disc bulge, translation and intradiscal pressure...