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Item type:Publication, Access status: with files , Effect of cavity preparation and bone mineral density on bone-interface densification and bone-implant contact during press-fit implantation of hip stems(2019-03-25); ; ; ; Implant loosening and periprosthetic fracture are two major revision causes for uncemented hip stems. The chosen method of cavity preparation could play a key role for both failure mechanisms. The aim of this study was to determine the dependence of the broach type as well as patient bone mineral density (BMD) on densification and contact conditions at the bone-implant interface. Hip stems were implanted into cadaveric femora using compaction, blunt extraction or sharp extraction broaches with computed tomography scans performed prior to broaching, after broaching and after stem implantation. Proximal periprosthetic bone densification as well as press-fit, contact area and stem seating relative to the last broach were determined. Median bone densification was higher with the compaction and blunt extraction broaches compared to sharp extraction broaches (181% and 177%, respectively, p = 0.002). The bone densification of femora prepared with compaction broaching increased with higher BMD (R2 = 0.183, p = 0.037), while stem seating decreased with higher BMD for all broach types (R2 = 0.259, p = 0.001). Incomplete seated prostheses were associated with smaller press-fit and bone-implant contact area (R2 = 0.249, p = 0.001; R2 = 0.287, p < 0.001). Clinical Significance: The results suggest that compaction broaching maximizes bone densification in patients with higher bone density. However, there appears to be an increased risk of insufficient stem seating in high-density bone that could limit the benefits for primary stability. For lower quality bone, the broach type appears to play a lesser role, but care must be taken to limit extensive stem seating which might increase periprosthetic fracture risk. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.Publicationtype: Journal ArticleScopus© Citations 15 354 352 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The influence of cavity preparation and press-fit cup implantation on restoring the hip rotation center(2019-03-20); ; ; ; Reaming of the acetabular cavity and cup implantation directly influence the hip rotation center and contact area between implant and bone. Previous studies have reported on an altered rotation center after total hip arthroplasty, but have not studied the influence of reaming and cup implantation separately. Aim of this study was therefore to analyze the individual influence of acetabular reaming and subsequent cup implantation on the rotation center and how this influences the contact conditions at the bone-implant interface.Publicationtype: Journal Article285 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A description of spinal fatigue strength(2016-04-11); ; ; ; Understanding fatigue failure of the spine is important to establish dynamic loading limits for occupational health and safety. In this study experimental data were combined with published data to develop a description of the predictive parameters for spinal fatigue failure. 41 lumbar functional spinal units (FSUs) from cadaveric spines (age 49.0±11.9 yr) where cyclically loaded. Three different levels of sinusoidal axial compression (0-3 kN, 0-2 kN or 1-3 kN) were applied for 300,000 cycles. Further, published data consisted of 70 thoracic and lumbar FSUs loaded in axial compression for 5000 cycles. Cyclic forces ranged from lower peaks (Fmin) of 0.7-1 kN to upper peaks (Fmax) of 1.2-7.1 kN. Based on Wöhler analysis, a fatigue model was developed accounting for three parameters: I) specimen-specific scaling based on the endplate area, II) specimen-specific strength dependency on age or bone mineral density, III) load-specific correction factors based on Fmax and Fmin.The most predictive model was achieved for a combination of Fmax, endplate area and bone mineral density; this model explained 61% of variation (p<0.001). A model including Fmax, endplate area and age explained only 28% of variation (p<0.001). Inclusion of a load-specific correction factor did not significantly improve model prediction of fatigue failure.This analysis presents the basis for the prediction of specimen-specific fatigue failure of the lumbar spine, provided the endplate area and bone mineral density can be derived.Publicationtype: Journal Article108 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Failure of the human lumbar motion-segments resulting from anterior shear fatigue loading(2016-01-30); ; ; ; An in-vitro experiment was designed to investigate the mode of failure following shear fatigue loading of lumbar motion-segments. Human male lumbar motion-segments (age 32-42 years, n=6) were immersed in Ringer solution at 37°C and repeatedly loaded, using a modified materials testing machine. Fatigue loading consisted of a sinusoidal shear load from 0 N to 1,500 N (750 N ± 750 N) applied to the upper vertebra of the motion-segment, at a frequency of 5 Hz. During fatigue experiments, several failure events were observed in the dynamic creep curves. Post-test x-ray, CT and dissection revealed that all specimens had delamination of the intervertebral disc. Anterior shear fatigue predominantly resulted in fracture of the apophyseal processes of the upper vertebrae (n=4). Exposure to the anterior shear fatigue loading caused motion-segment instability and resulted in vertebral slip corresponding to grade I and ‘mild’ grade II spondylolisthesis, as observed clinically.Publicationtype: Journal Article136 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the relationship between stature and anthropometric measurements of lumbar vertebraeStature estimation is important for identifying human remains. Analysis of body parts has become an important forensic tool during global operations in the context of cases in which human remains have been dismembered, mutilated or decomposed. However, unless almost the full skeleton or at least a long bone of the lower limb is available, accuracy is still limited to approximate body height. Especially with respect to single vertebral measurements, only a rough prediction is possible. Due to their complex geometry, vertebral measurements are possible at various locations. Nine locations have been considered in this study. Regression equations for stature estimation using lumbar vertebral geometry from computed tomography scans have been evaluated to identify the measurement which gives the most reliable body height estimation. The study group comprised a representative sample of a German metropolitan male population (42 autopsied individuals). Comparing the influence of various vertebral geometry measurements with body height resulted in a coefficient of correlation (R) of 0.19-0.53 and a 95% confidence interval (CI) of ±. 11.6 up to ±. 13.1 cm.The largest correlation with a single vertebral measurement was achieved with the central height of the vertebral body of L2 as predictor the standard error (SE) of the estimate was 5.9 cm. Using models from CT scans appeared superior to current invasive procedures that use direct measurements of the vertebral body, in terms of reproducibility and time efficiency. For fragmented non-skeletonized human bodies, height prediction based on an all-virtual model of the vertebrae is possible. However, the regression coefficient may be similar to classic caliper measurements that prove easier if skeletonized bones are available.Publicationtype: Journal Article120 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Estimation of shear load sharing in moderately degenerated human lumbar spine(Elsevier, 2013-01-10); ; ; ; Shear load sharing between intervertebral discs and apophyseal joints was investigated experimentally in human lumbar motion segments with moderately degenerated intervertebral discs. 'Motion-Segments' (21-42 years, n=6) and 'Disc-Segments' (22-42 years, n=6) were subjected to shear in 0° flexion, using a modified materials testing machine, while immersed in a Ringer bath at 37. °C. Initially, two cycles of anterior and posterior shear loading up to 200. N (50. N/s) were applied, to evaluate stiffnesses in both directions. Specimens were then exposed to 15. mm of anterior displacement at a rate of 0.5. mm/s. A physiological compressive load of 500. N was applied throughout. The initial 5. mm of the load-displacement curves were approximated with 6th order polynomials for evaluation of the mean behaviour in each group. 'Disc-Segments' were 66% (p=0.002) and 43% (p=0.026) less stiff than 'Motion-Segments' for anterior and posterior shear directions, respectively. 'Disc-Segments' exhibited 44% lower peak shear load (p=0.015) than 'Motion-Segments'. All specimens in the 'Disc-Segments' group showed damage either at the interface between the endplates and the disc. The intervertebral disc contributes 38% to initial anterior shear load-bearing, increasing to 66% at 5. mm displacement. Some over-estimation of disc load-bearing might have been caused by the comparison of segments from different levels. The apophyseal joints make a substantial contribution (65-55%) to anterior shear load-bearing over the initial 2. mm of shear displacement but this decreases with increasing shear displacement.Publicationtype: Journal Article132 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strain changes on the cortical shell of vertebral bodies due to spine ageing: a parametric study using a finite element model evaluated by strain measurementsThe probability of fractures of the cortical shell of vertebral bodies increases as ageing progresses. Ageing involves all the spinal component changes. However, the effect of the spinal component ageing on the fracture risk of the cortical shell remains poorly understood. In this study, the influence of the ageing of the spinal components on cortical shell strain was investigated. A lumbar spinal specimen (L3-L5) was mechanically tested under a quasi-static axial compressive load. Clinical computed tomography images of the same specimen were used to create a corresponding finite element model. The material properties were determined by calibrating the finite element model using the L4 cortical shell strains of the anterior centre measurement site. The remaining experiment data (axial displacement, the intra-discal pressures, L4 cortical shell strain on the lateral measurement site) were used to evaluate the model. The individual ageing process of the six spinal components (cortical shell, cancellous bone, bony endplate, posterior elements, nucleus pulposus and annulus matrix) was simulated by changing their Young's moduli and Poisson's ratios, and the effect on cortical shell strain was investigated. Results show that the cortical shell strain is more sensitive to the ageing of the cortical shell and the cancellous bone than to the ageing of the nucleus pulposus, the annulus matrix, and the bony endplates and of the posterior elements. The results can help the clinicians focus on the aspects that mainly influence the vertebral cortex fracture risk factor.Publicationtype: Journal ArticleScopus© Citations 14 393 890 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dependence of spinal segment mechanics on load direction, age and gender : Research project F 2059 ; final report of the project(Bundesanstalt für Arbeitsschutz und Arbeitsmedizin, 2013); ; ; ; Publicationtype: Book4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Shear strength of the human lumbar spine(Elsevier, 2012-08-01); ; ; ; Background: Shear loading is recognised as a risk factor for lower back pain. Previous studies of shear loading have either not addressed the influence of age, bone mineral density, axial height loss due to creep or were performed on animal specimens. Methods: Intact human lumbar motion segments (L2-3) were tested in shear using a modified materials testing machine, while immersed in a Ringer bath at 37 °C. Vertebrae were rigidly embedded in neutral posture (0° flexion) and subjected to a constant axial compression load of 500 N. Shear was applied to three groups: 'Young-No-Creep' (20-42 years), 'Young-Creep' (22-38 years, creep 1000 N for 1 h) and 'Old-No-Creep' (44-64 years). Failure was induced by up to 15 mm of anterior shear displacement at a rate of 0.5 mm/s. The trabecular and apophyseal joint bone mineral densities were evaluated from computed tomography images of the intact lumbar spines. Findings: Peak shear force correlated positively with trabecular bone mineral density for specimens tested without axial creep. No significant differences were observed with respect to age. During shear overload specimens increased in height in the axial direction. Interpretation: Trabecular bone mineral density can be used to predict the peak force of lumbar spine in shear in neutral posture.Publicationtype: Journal Article12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High cycle fatigue behaviour of functional spinal units(National Institute of Occupational Safety and Health, 2010-11-29); ; ; ; Vibrations have been shown to be an important risk factor for spinal pathologies. The underlying mechanisms are poorly understood and in vivo data scarce and difficult to obtain. Consequently numerical models are used to estimate spinal loading; requiring fatigue strength information, which was obtained in this study for spinal specimens from young and old male donors of working age in vitro. Bone mineral density (BMD) and endplate area were determined using CT scans. Three groups were investigated: young specimens in neutral posture, young in flexed posture, and old in neutral posture. The loading consisted of 300,000 sinusoidal compression cycles of 2 kN, inducing a nucleus pressure peek of approximately 1.4 MPa. No failure of the young specimens in neutral posture was observed, but four specimens from older donors with low BMD failed. The product between endplate area and BMD was shown to be useful to predict fatigue strength for old donors and should therefore be considered with regard to whole body vibration injuries. In flexed posture, two specimens from young donors failed. One failure can be attributed to low BMD following the trend for the old specimens; the other failure could not be explained, leaving the influence of flexion yet unclear.Publicationtype: Journal Article5