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Ulrike Mueller - One of the best experts on this subject based on the ideXlab platform.
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influence of taper angle clearance on the taper Connection Strength
Orthopaedic Proceedings, 2018Co-Authors: Ulrike Mueller, J. Philippe KretzerAbstract:IntroductionTaper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper Strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper Connection Strength.Material & MethodsFor the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group an...
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mixing of head stem components in total hip arthroplasty
Journal of Arthroplasty, 2017Co-Authors: Ulrike Mueller, Benjamin Panzram, Steffen Braun, Robert Sonntag, Philippe J KretzerAbstract:Abstract Background Implant manufacturers proclaim that the tapers of modular total hip arthroplasty are not standardized and can vary from manufacturer to manufacturer. That is why the combination of various components from different manufacturers (“Mix and Match”) is not permitted. In this study, different taper combinations were investigated experimentally to assess the effect of “Mix and Match” regarding the taper Connection Strength. Methods Torque-off tests using hip stems and metal femoral heads from 6 different implant manufacturers were performed. First the components were tested as intended and afterwards the stems were combined with metal heads from other manufacturers. Results There was no significant difference in taper Connection Strength when stems from the manufacturers Link, Smith & Nephew, and Zimmer were combined with heads from other manufacturers. The Biomet stems showed a significantly reduced taper Connection Strength if femoral heads of Aesculap, DePuy, or Smith & Nephew were used. On the contrary, the DePuy stems in combination with the originally intended femoral heads showed a significantly lower taper Connection Strength compared to the use of heads from Link, Biomet, and Zimmer. The same was observed for the Aesculap stems in combination with Zimmer heads. Conclusion The results of this study suggest that mixing components from different manufacturers may affect the taper Connection Strength and could reduce the stability. As safety should be a high priority in patient treatment, any potential risks should be avoided. Therefore, mixing and matching of heads and femoral stems from different manufacturers cannot be recommended.
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influence of taper angle clearance on the taper Connection Strength
Journal of Bone and Joint Surgery-british Volume, 2017Co-Authors: Ulrike Mueller, J. Philippe KretzerAbstract:Introduction Taper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper Strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper Connection Strength. Material & Methods For the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group and five repetitive measurements per samples were performed. All taper Connections were impacted with different forces (1 kN, 3 kN, 6 kN and 10 kN) and afterwards an increasing torque was applied until the head disconnected. The maximal torque off value was used as a measure for the taper Strength. Results A greater taper clearance leads to a higher taper Strength (Fig. 1). However, this effect is also influenced by the assembly force and becomes even stronger with higher assembly forces. When comparing a distal, full and proximal contact situation the full contact shows the lowest taper Strength, whereas the distal contact situation leads to the highest taper Strength. Discussion and conclusion The design variability in taper Connections influences its Strength. A smaller contact area leads to higher local contact pressure. It is assumed that this increases local plastic deformations of the surface structure which is beneficial for this self-locking mechanism of the junction. However, the effect of the assembly force seems to overcome the effect of the taper clearance. Therefore taper junctions should be firmly connected in total hip replacements. Furthermore, surgeons should be aware that in a clinical case of a Mix & Match the taper Strength may be reduced depending on the combined components. For figures/tables, please contact authors directly.
Lee Cossell - One of the best experts on this subject based on the ideXlab platform.
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functional organization of excitatory synaptic Strength in primary visual cortex
Nature, 2015Co-Authors: Lee Cossell, Maria Florencia Iacaruso, Dylan R Muir, Rachael Houlton, Elie Sader, Sonja B Hofer, Thomas D MrsicflogelAbstract:The Strength of synaptic Connections fundamentally determines how neurons influence each other's firing. Excitatory Connection amplitudes between pairs of cortical neurons vary over two orders of magnitude, comprising only very few strong Connections among many weaker ones. Although this highly skewed distribution of Connection Strengths is observed in diverse cortical areas, its functional significance remains unknown: it is not clear how Connection Strength relates to neuronal response properties, nor how strong and weak inputs contribute to information processing in local microcircuits. Here we reveal that the Strength of Connections between layer 2/3 (L2/3) pyramidal neurons in mouse primary visual cortex (V1) obeys a simple rule--the few strong Connections occur between neurons with most correlated responses, while only weak Connections link neurons with uncorrelated responses. Moreover, we show that strong and reciprocal Connections occur between cells with similar spatial receptive field structure. Although weak Connections far outnumber strong Connections, each neuron receives the majority of its local excitation from a small number of strong inputs provided by the few neurons with similar responses to visual features. By dominating recurrent excitation, these infrequent yet powerful inputs disproportionately contribute to feature preference and selectivity. Therefore, our results show that the apparently complex organization of excitatory Connection Strength reflects the similarity of neuronal responses, and suggest that rare, strong Connections mediate stimulus-specific response amplification in cortical microcircuits.
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functional organization of excitatory synaptic Strength in primary visual cortex
Nature, 2015Co-Authors: Lee Cossell, Maria Florencia Iacaruso, Dylan R Muir, Rachael Houlton, Elie Sader, Ho Ko, Sonja B HoferAbstract:In complex networks of the cerebral cortex, the majority of Connections are weak and only a minority strong, but it is not known why; here the authors show that excitatory neurons in primary visual cortex follow a rule by which strong Connections are sparse and occur between neurons with correlated responses to visual stimuli, whereas only weak Connections link neurons with uncorrelated responses. The degree to which a neuron influences the activity of others is dependent on the Strength of the synaptic Connections it makes with its partners, and it is known that this Connection Strength can vary over two orders of magnitude. Using a combination of two-photon calcium imaging and simultaneous intracellular recordings from pairs of neurons, Thomas Mrsic-Flogel and colleagues show that layer 2/3 neurons in mouse primary visual cortex (V1) follow a simple rule: strong Connections are sparse and occur between neurons with correlated responses to visual stimuli, whereas only weak Connections link neurons with uncorrelated responses. This bias in functional Connection Strength may be a means by which neuronal selectivity for visual features is computed in areas downstream of V1. The Strength of synaptic Connections fundamentally determines how neurons influence each other’s firing. Excitatory Connection amplitudes between pairs of cortical neurons vary over two orders of magnitude, comprising only very few strong Connections among many weaker ones1,2,3,4,5,6,7,8,9. Although this highly skewed distribution of Connection Strengths is observed in diverse cortical areas1,2,3,4,5,6,7,8,9, its functional significance remains unknown: it is not clear how Connection Strength relates to neuronal response properties, nor how strong and weak inputs contribute to information processing in local microcircuits. Here we reveal that the Strength of Connections between layer 2/3 (L2/3) pyramidal neurons in mouse primary visual cortex (V1) obeys a simple rule—the few strong Connections occur between neurons with most correlated responses, while only weak Connections link neurons with uncorrelated responses. Moreover, we show that strong and reciprocal Connections occur between cells with similar spatial receptive field structure. Although weak Connections far outnumber strong Connections, each neuron receives the majority of its local excitation from a small number of strong inputs provided by the few neurons with similar responses to visual features. By dominating recurrent excitation, these infrequent yet powerful inputs disproportionately contribute to feature preference and selectivity. Therefore, our results show that the apparently complex organization of excitatory Connection Strength reflects the similarity of neuronal responses, and suggest that rare, strong Connections mediate stimulus-specific response amplification in cortical microcircuits.
J. Philippe Kretzer - One of the best experts on this subject based on the ideXlab platform.
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influence of taper angle clearance on the taper Connection Strength
Orthopaedic Proceedings, 2018Co-Authors: Ulrike Mueller, J. Philippe KretzerAbstract:IntroductionTaper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper Strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper Connection Strength.Material & MethodsFor the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group an...
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influence of taper angle clearance on the taper Connection Strength
Journal of Bone and Joint Surgery-british Volume, 2017Co-Authors: Ulrike Mueller, J. Philippe KretzerAbstract:Introduction Taper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper Strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper Connection Strength. Material & Methods For the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group and five repetitive measurements per samples were performed. All taper Connections were impacted with different forces (1 kN, 3 kN, 6 kN and 10 kN) and afterwards an increasing torque was applied until the head disconnected. The maximal torque off value was used as a measure for the taper Strength. Results A greater taper clearance leads to a higher taper Strength (Fig. 1). However, this effect is also influenced by the assembly force and becomes even stronger with higher assembly forces. When comparing a distal, full and proximal contact situation the full contact shows the lowest taper Strength, whereas the distal contact situation leads to the highest taper Strength. Discussion and conclusion The design variability in taper Connections influences its Strength. A smaller contact area leads to higher local contact pressure. It is assumed that this increases local plastic deformations of the surface structure which is beneficial for this self-locking mechanism of the junction. However, the effect of the assembly force seems to overcome the effect of the taper clearance. Therefore taper junctions should be firmly connected in total hip replacements. Furthermore, surgeons should be aware that in a clinical case of a Mix & Match the taper Strength may be reduced depending on the combined components. For figures/tables, please contact authors directly.
P.a. Robinson - One of the best experts on this subject based on the ideXlab platform.
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effects of physiological parameter evolution on the dynamics of tonic clonic seizures
PLOS ONE, 2020Co-Authors: Farah Deeba, Paula Sanzleon, P.a. RobinsonAbstract:The temporal and spectral characteristics of tonic-clonic seizures are investigated using a neural field model of the corticothalamic system in the presence of a temporally varying Connection Strength between the cerebral cortex and thalamus. Increasing Connection Strength drives the system into ∼ 10 Hz seizure oscillations once a threshold is passed and a subcritical Hopf bifurcation occurs. In this study, the spectral and temporal characteristics of tonic-clonic seizures are explored as functions of the relevant properties of physiological Connection Strengths, such as maximum Strength, time above threshold, and the ramp rate at which the Strength increases or decreases. Analysis shows that the seizure onset time decreases with the maximum Connection Strength and time above threshold, but increases with the ramp rate. Seizure duration and offset time increase with maximum Connection Strength, time above threshold, and rate of change. Spectral analysis reveals that the power of nonlinear harmonics and the duration of the oscillations increase as the maximum Connection Strength and the time above threshold increase. A secondary limit cycle at ∼ 18 Hz, termed a saddle-cycle, is also seen during seizure onset and becomes more prominent and robust with increasing ramp rate. If the time above the threshold is too small, the system does not reach the 10 Hz limit cycle, and only exhibits 18 Hz saddle-cycle oscillations. It is also seen that the time to reach the saturated large amplitude limit-cycle seizure oscillation from both the instability threshold and from the end of the saddle-cycle oscillations is inversely proportional to the square root of the ramp rate.
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effects of physiological parameter evolution on the dynamics of tonic clonic seizures
bioRxiv, 2019Co-Authors: Paula Sanzleon, Farah Deeba, P.a. RobinsonAbstract:The temporal and spectral characteristics of tonic-clonic seizures are investigated using a neural field model of the corticothalamic system in the presence of a temporally varying Connection Strength between the cerebral cortex and thalamus. Increasing Connection Strength drives the system into ~10 Hz seizure oscillations once a threshold is passed and a subcritical Hopf bifurcation occurs. In this study, the spectral and temporal characteristics of tonic-clonic seizures are explored as functions of the relevant properties of physiological Connection Strengths, such as maximum Strength, time above threshold, and the ramp rate at which the Strength increases or decreases. Analysis shows that the seizure onset time decreases with the maximum Connection Strength and time above threshold, but increases with the ramp rate. Seizure duration and offset time increase with maximum Connection Strength, time above threshold, and rate of change. Spectral analysis reveals that the power of nonlinear harmonics and the duration of the oscillations increase as the maximum Connection Strength and the time above threshold increase. A secondary limit cycle at ~18 Hz, termed a saddle-cycle, is also seen during seizure onset and becomes more prominent and robust with increasing ramp rate. If the time above the threshold is too small, the system does not reach the 10 Hz limit cycle, and only exhibits 18 Hz saddle-cycle oscillations. It is also seen that the times to reach the saturated large amplitude limit-cycle seizure oscillation from both the instability threshold and from the end of the saddle-cycle oscillations are inversely proportional to the square root of the ramp rate.
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dependence of absence seizure dynamics on physiological parameter evolution
Journal of Theoretical Biology, 2018Co-Authors: Farah Deeba, Paula Sanzleon, P.a. RobinsonAbstract:Abstract A neural field model of the corticothalamic system is applied to investigate the temporal and spectral characteristics of absence seizures in the presence of a temporally varying Connection Strength between the cerebral cortex and thalamus. Increasing Connection Strength drives the system into an absence seizure-like state once a threshold is passed and a supercritical Hopf bifurcation occurs. The dynamics and spectral characteristics of the resulting model seizures are explored as functions of maximum Connection Strength, time above threshold, and the rate at which the Connection Strength increases (ramp rate). Our results enable spectral and temporal characteristics of seizures to be related to changes in the underlying physiological evolution of Connections via nonlinear dynamics and neural field theory. Spectral analysis reveals that the power of the harmonics and the duration of the oscillations increase as the maximum Connection Strength and the time above threshold increase. It is also found that the time to reach the stable limit-cycle seizure oscillation from the instability threshold decreases with the square root of the ramp rate.
Sonja B Hofer - One of the best experts on this subject based on the ideXlab platform.
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functional organization of excitatory synaptic Strength in primary visual cortex
Nature, 2015Co-Authors: Lee Cossell, Maria Florencia Iacaruso, Dylan R Muir, Rachael Houlton, Elie Sader, Sonja B Hofer, Thomas D MrsicflogelAbstract:The Strength of synaptic Connections fundamentally determines how neurons influence each other's firing. Excitatory Connection amplitudes between pairs of cortical neurons vary over two orders of magnitude, comprising only very few strong Connections among many weaker ones. Although this highly skewed distribution of Connection Strengths is observed in diverse cortical areas, its functional significance remains unknown: it is not clear how Connection Strength relates to neuronal response properties, nor how strong and weak inputs contribute to information processing in local microcircuits. Here we reveal that the Strength of Connections between layer 2/3 (L2/3) pyramidal neurons in mouse primary visual cortex (V1) obeys a simple rule--the few strong Connections occur between neurons with most correlated responses, while only weak Connections link neurons with uncorrelated responses. Moreover, we show that strong and reciprocal Connections occur between cells with similar spatial receptive field structure. Although weak Connections far outnumber strong Connections, each neuron receives the majority of its local excitation from a small number of strong inputs provided by the few neurons with similar responses to visual features. By dominating recurrent excitation, these infrequent yet powerful inputs disproportionately contribute to feature preference and selectivity. Therefore, our results show that the apparently complex organization of excitatory Connection Strength reflects the similarity of neuronal responses, and suggest that rare, strong Connections mediate stimulus-specific response amplification in cortical microcircuits.
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functional organization of excitatory synaptic Strength in primary visual cortex
Nature, 2015Co-Authors: Lee Cossell, Maria Florencia Iacaruso, Dylan R Muir, Rachael Houlton, Elie Sader, Ho Ko, Sonja B HoferAbstract:In complex networks of the cerebral cortex, the majority of Connections are weak and only a minority strong, but it is not known why; here the authors show that excitatory neurons in primary visual cortex follow a rule by which strong Connections are sparse and occur between neurons with correlated responses to visual stimuli, whereas only weak Connections link neurons with uncorrelated responses. The degree to which a neuron influences the activity of others is dependent on the Strength of the synaptic Connections it makes with its partners, and it is known that this Connection Strength can vary over two orders of magnitude. Using a combination of two-photon calcium imaging and simultaneous intracellular recordings from pairs of neurons, Thomas Mrsic-Flogel and colleagues show that layer 2/3 neurons in mouse primary visual cortex (V1) follow a simple rule: strong Connections are sparse and occur between neurons with correlated responses to visual stimuli, whereas only weak Connections link neurons with uncorrelated responses. This bias in functional Connection Strength may be a means by which neuronal selectivity for visual features is computed in areas downstream of V1. The Strength of synaptic Connections fundamentally determines how neurons influence each other’s firing. Excitatory Connection amplitudes between pairs of cortical neurons vary over two orders of magnitude, comprising only very few strong Connections among many weaker ones1,2,3,4,5,6,7,8,9. Although this highly skewed distribution of Connection Strengths is observed in diverse cortical areas1,2,3,4,5,6,7,8,9, its functional significance remains unknown: it is not clear how Connection Strength relates to neuronal response properties, nor how strong and weak inputs contribute to information processing in local microcircuits. Here we reveal that the Strength of Connections between layer 2/3 (L2/3) pyramidal neurons in mouse primary visual cortex (V1) obeys a simple rule—the few strong Connections occur between neurons with most correlated responses, while only weak Connections link neurons with uncorrelated responses. Moreover, we show that strong and reciprocal Connections occur between cells with similar spatial receptive field structure. Although weak Connections far outnumber strong Connections, each neuron receives the majority of its local excitation from a small number of strong inputs provided by the few neurons with similar responses to visual features. By dominating recurrent excitation, these infrequent yet powerful inputs disproportionately contribute to feature preference and selectivity. Therefore, our results show that the apparently complex organization of excitatory Connection Strength reflects the similarity of neuronal responses, and suggest that rare, strong Connections mediate stimulus-specific response amplification in cortical microcircuits.