G Bergmann

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

..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 procedure is well suited for averaging hip contact forces and other varying signals as long as their complexity and variation is not extremely large...

..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...

..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...

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

..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...

..Large moments in the joint indicate that friction in shoulder implants is high if the glenoid is not replaced. A friction coefficient of 0.1-0.2 seems to be realistic in these cases...

..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...

..For complex movements of everyday living or wheelchair propulsion, the reported loads vary considerably...

..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...

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

..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...

..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...

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

..The other parameters usually explain less than 10% of the variance. The novel lumbosacral fusion system allows good stabilization of the segment, especially when additional fixation via facet screws or fixators is performed...

..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...

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

..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...

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

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

..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...

..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...

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

..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...

..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...

..Some of the observed load components were much higher than those currently applied when testing knee implants...

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

..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...

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

..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...

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..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...

..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...

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

..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...

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

..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...

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

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

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

..There was general agreement between the calculated and measured forces in both pattern and magnitude. There were, however, discrepancies. Reasons for these differences in results are discussed and possible model developments suggested...

..It requires an extension of the fusion length or at least reduces the outcome of the correction...

..Disc pressure and fixator load were measured in an in vitro setup and compared to in vivo measurements with the identical transducers from the two groups participating in this study...

..RELEVANCE: Detailed musculo-skeletal modelling may allow pre-surgical, patient specific optimisation of loading on implant, bone and soft tissues...

..In addition, knowledge of the correction forces improves our biomechanical understanding of the spine, especially during correction of scoliosis. Intraoperative force measurement is in no way detrimental to the patient...

..It should therefore form the basis for further standardisation of pre-clinical testing by providing a more realistic approximation of physiological loading conditions...

..We propose that optimizing the biomechanical conditions through using these approaches will allow the long-term function of the replaced joint to be significantly enhanced...