Introduction Stretching of tissue stimulates angiogenesis but increased motion at a fracture site... more Introduction Stretching of tissue stimulates angiogenesis but increased motion at a fracture site hinders revascularisation. In vitro studies have indicated that mechanical stimuli promote angiogenic responses in endothelial cells, but can either inhibit or enhance responses when applied directly to angiogenesis assays. We anticipated that cyclic tension applied during endothelial network assembly would increase vascular structure formation up to a certain threshold. Methods Fibroblast/HUVEC co-cultures were subjected to cyclic equibiaxial strain (1 Hz; 6 h/day; 7 days) using the FlexerCell FX-4000T system and limiting rings for simultaneous application of multiple strain magnitudes (0–13%). Cells were labelled using anti-PECAM-1, and image analysis provided measures of endothelial network length and numbers of junctions. Results Cyclic stretching had no significant effect on the total length of endothelial networks (P > 0.2) but resulted in a strain-dependent decrease in branchi...
Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also pat... more Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also patients with secondary osteoarthritis of the hip with pathological anteversion of the femoral neck are treated increasingly using this method. Therefore an investigation was performed to analyze the resulting hip contact force and femoral loading in the proximal femur at the solid model of the "standardized femur". Two different situations of femoral component anteversion were simulated. Increased hip contact forces and an increase of medial and lateral cortex loads result in the anteverted model. With present level of knowledge about the influence of the hip contact force the use of short-stemmed implants is not uncritically in patients with degenerative osteoarthritis of the hip combined with rotational disorders of the proximal femur. The selection of the tribological pairing is to be considered more strongly regarding the wear behavior.
Introduction Minimally invasive total hip arthroplasty has been successfully introduced in the pa... more Introduction Minimally invasive total hip arthroplasty has been successfully introduced in the past decade. Never-theless, standard approaches such as the direct lateral approach are still commonly used in orthopaedic surgery due to easy handling, good intra-operative overview and low complication rates. However, a frequent occurrence of fatty atrophy within the anterior third of the gluteus medius muscle has been demonstrated when using the modiWed direct-lateral approach (mDL), which may be associated with a reduction in function, limitation of internal leg rota-tion, gait disorders and pain. The question addressed in this study is whether mDL-approach leads to unfavourable changes in foot progression angle (FPA), gait and to more postoperative pain compared with a minimally invasive anterolateral approach (ALMI). Methods Thirty patients with primary osteoarthritis of the hip were recruited for this study. All subjects received an uncemented THA (Alloclassic ® -Zweymüller stem, Al...
The tough bulk of dentin in teeth supports enamel, creating cutting and grinding biostructures wi... more The tough bulk of dentin in teeth supports enamel, creating cutting and grinding biostructures with superior failure resistance that is not fully understood. Synchrotron-based diffraction methods, utilizing micro- and nanofocused X-ray beams, reveal that the nm-sized mineral particles aligned with collagen are precompressed and that the residual strains vanish upon mild annealing. We show the link between the mineral nanoparticles and known damage propagation trajectories in dentin, suggesting a previously overlooked compression-mediated toughening mechanism.
Journal of biomedical materials research. Part A, Jan 8, 2015
Interactions between cells and the extracellular matrix (ECM) are known to play critical roles in... more Interactions between cells and the extracellular matrix (ECM) are known to play critical roles in regulating cell phenotype. The identity of ECM ligands presented to mesenchymal stem cells (MSCs) has previously been shown to direct the cell fate commitment of these cells. To enhance osteogenic differentiation of MSCs, alginate hydrogels were prepared that present the DGEA ligand derived from collagen I. When presented from hydrogel surfaces in 2D, the DGEA ligand did not facilitate cell adhesion, while hydrogels presenting the RGD ligand derived from fibronectin did encourage cell adhesion and spreading. However, the osteogenic differentiation of MSCs encapsulated within alginate hydrogels presenting the DGEA ligand was enhanced when compared with unmodified alginate hydrogels and hydrogels presenting the RGD ligand. MSCs cultured in DGEA-presenting gels exhibited increased levels of osteocalcin production and mineral deposition. These data suggest that the presentation of the colla...
Translation in an academic environment requires a support system-people, goals, models, partnersh... more Translation in an academic environment requires a support system-people, goals, models, partnerships, and infrastructures-that will push promising basic science and technology projects forward into the clinic.
High resolution 3D laboratory x-ray tomography data of femora from young, 1-14 day old C57BL/6 mi... more High resolution 3D laboratory x-ray tomography data of femora from young, 1-14 day old C57BL/6 mice, Data in Brief, http://dx.
During mammalian growth, long bones undergo extensive structural reorganization, transforming fro... more During mammalian growth, long bones undergo extensive structural reorganization, transforming from primitive shapes in the limb buds into mature bones. Here we shed light on the steps involved in structural formation of the mineralized tissue in midshafts of C57BL/6 femurs, shortly after birth. By combining 3D micrometer-resolution X-ray microtomography with 2D histology, we study the transformation of the tissue from a partially-mineralized scaffold into a compact bone structure. We identify three growth phases that take place during murine long bone maturation: During a patterning phase (I) mineralized struts form a loosely connected foam-like cortical network. During a transitioning phase (II), the extensive non-mineralized tracts vanish, transforming the foam into a fully continuous mass, by 14days of age. Concomitantly, closed porosity increases to about ∼1.4%, and stays at this level, also found in maturity. During a shaping phase (III), the bones gradually attain their charac...
It is commonly accepted that bone marrow-derived stem cells (BMSCs) have to be expanded in vitro,... more It is commonly accepted that bone marrow-derived stem cells (BMSCs) have to be expanded in vitro, but a prolonged time in culture decreases their multilineage potential. Mechanical and biological stimuli have been used to improve their osteogenic potential. While long-term stimulation has been shown to improve osteogenic differentiation, it remains to be seen whether short-term stimulation is also sufficient.We investigated the influence of 24 hours' cyclic loading (0.05Hz, 4kPa) on gene expression of human BMSCs in three-dimensional fibrin-DMEM constructs (n=7) in a compression bioreactor using DNA-array technology. Expression of the following genes showed a significant increase after mechanical stimulation: 2.6-fold osteopontin (OPN) and integrin-β1 (ITGB1), 2.2-fold transforming growth factor-β-receptor 1 (TGF-β-R1) and 2.4-fold SMAD5 expression, compared to controls without mechanical stimulation (p<0.05 each). Platelet-derived growth factor-α (PDGF-α ) and annexin-V were...
Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also pat... more Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also patients with secondary osteoarthritis of the hip with pathological anteversion of the femoral neck are treated increasingly using this method. Therefore an investigation was performed to analyze the resulting hip contact force and femoral loading in the proximal femur at the solid model of the "standardized femur". Two different situations of femoral component anteversion were simulated. Increased hip contact forces and an increase of medial and lateral cortex loads result in the anteverted model. With present level of knowledge about the influence of the hip contact force the use of short-stemmed implants is not uncritically in patients with degenerative osteoarthritis of the hip combined with rotational disorders of the proximal femur. The selection of the tribological pairing is to be considered more strongly regarding the wear behavior.
Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To... more Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To evaluate the potential benefits of different resorbable candidate materials for use in prophylactic kyphoplasty compared with the behavior of polymethylmethacrylate cement. Kyphoplasty using PMMA bone cement for the stabilization of fractured osteoporotic vertebrae has been established as a useful clinical tool. In several studies, consecutive compression fractures have been reported in vertebrae caudal or cranial to those augmented with bone cement. Consequently, some physicians have begun to treat adjacent vertebrae by means of prophylactic augmentation. Biomechanical in vitro testing was performed on 40 human osteoporotic nonfractured lumbar vertebrae. Three types of bone cement (PMMA, 2 different calcium phosphate cements) and one silicon derivative were assessed during compressive and cyclic sinusoidal testing. Each candidate material was applied bipedicularly under fluoroscopic co...
Different fixation systems are used for fracture and defect treatment. A prerequisite for complic... more Different fixation systems are used for fracture and defect treatment. A prerequisite for complication free healing is sufficient mechanical stability of the osteosynthesis. In vitro investigations offer the possibility of both analysing and assessing the pre-clinical fixation stability. Due to the complex loading environment in vivo, stiffness analysis should include a complete determination of the stiffness under standardised conditions. Based on a mathematical procedure to calculate the 3-D stiffness, a mechanical testing device for the 3-D loading of fixation systems was designed and integrated in the existing test set-up. The set-up consisted of a material testing machine to produce the necessary loads and an optical measurement device to detect the resulting inter-fragmentary movements. To validate the testing device, the 3-D stiffness matrices of different Ilizarov fixator configurations were determined and compared. The good reproducibility of the test was reflected in the s...
Using a mechanical testing procedure, various fixator constructs were tested in vitro. In additio... more Using a mechanical testing procedure, various fixator constructs were tested in vitro. In addition, the influence of the passive soft tissue structures on the fixation stiffness was determined. An increased number of Schanz' screws or Kirschner wires led to a comparable increase in stiffness than that observed with an increasing screw or wire diameter. In consequence, larger diameters should be preferred over an additional screw or wire where clinically applicable. With diaphyseal telescoping rods only the axial stiffness decreased. As expected, large ring diameters as well as titanium wires reduced stiffness components. Bracing the outer rings caused a reduction of the overall stiffness. Asymmetric pre-tensioning of the K-wires resulted in a significant reduction of tension in the neighboring wire. Removal of the soft tissues reduced stiffness to a similar extend as experienced in a fibula defect situation. The study demonstrates the correlation between design parameters, passi...
Objective. To investigate both the age and gender related distributions of bone mineral density i... more Objective. To investigate both the age and gender related distributions of bone mineral density in the proximal tibia, specifically in aged patients.
Hyaline joint cartilage has only a limited potential for self-repair. Some of the published techn... more Hyaline joint cartilage has only a limited potential for self-repair. Some of the published techniques for osteochondral defect therapy try to improve that potential. In this study, it was hypothesised that one of those surgical techniques, the crushed transplanted bone graft together with a collagen membrane, accelerates significantly the reconstruction of the subchondral bone plate and improves the mechanical and histological quality of repaired cartilage in osteochondral defects compared to an empty control defect. In order to test this hypothesis, defects were created in the left knee of 12 sheep and filled either with autologous crushed bone graft or left empty. The animals were sacrificed after 3 (n ¼ 6) and 6 (n ¼ 6) months. No differences were found either macroscopically or histomorphometrically between the bone graft and empty control defects. The biomechanical as well as the histological results of the bone graft defects were inferior to the control defects with inflammatory processes caused either by bone graft or membrane remnants. Based on the results in this sheep model, the filling of subchondral bone defects with compacted cancellous bone should be carefully reconsidered. r
Surgical intervention of the knee joint routinely endeavors to recreate a physiologically normal ... more Surgical intervention of the knee joint routinely endeavors to recreate a physiologically normal joint loading environment. The loading conditions resulting from osteotomies, fracture treatment, ligament replacements, and arthroplasties of the knee are considered to have an impact on the long term clinical outcome; however, knowledge regarding in vivo loading conditions is limited. Using a previously validated musculoskeletal lower limb model, we predicted the tibio-femoral joint contact forces that occur in the human knee during the common daily activities of walking and stair climbing. The average resultant peak force during walking was 3.1 times body weight (BW) across four total hip arthroplasty patients. Inter-individual variations proved larger than the variation of forces for each patient repeating the same task. Forces through the knee were considerably larger during stair climbing than during walking: the average resultant peak force during stair climbing was 5.4 BW although peaks of up to 6.2 BW were calculated for one particular patient. Average anteroposterior peak shear components of 0.6 BW were determined during walking and 1.3 BW during stair climbing. These results confirm both the joint contact forces reported in the literature and the importance of muscular activity in creating high forces across the joint. The magnitudes of these forces, specifically in shear, have implications for all forms of surgical intervention in the knee. The data demonstrate that high contact and shear forces are generated during weight bearing combined with knee flexion angles greater than approximately 15". Clinically, the conditions that produce these larger contact forces should be avoided during post-operative rehabilitation.
Participants at the recent Translate! 2014 meeting in Berlin, Germany, reached a consensus on the... more Participants at the recent Translate! 2014 meeting in Berlin, Germany, reached a consensus on the rate-limiting factor for advancing translational medicine.
Loading can increase bone mass and size and this response is reduced with aging. It is unclear, h... more Loading can increase bone mass and size and this response is reduced with aging. It is unclear, however how loading affects bone mineral and matrix properties. Fourier transform infrared imaging and high resolution synchrotron scanning small angle X-ray scattering were used to study how bone&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s microscale and nanoscale compositional properties were altered in the tibial midshaft of young, adult, and elderly female C57Bl/6J mice after two weeks of controlled in vivo compressive loading in comparison to physiological loading. The effect of controlled loading on bone composition varied with animal age, since it predominantly influenced the bone composition of elderly mice. Interestingly, controlled loading led to enhanced collagen maturity in elderly mice. In addition, although the rate of bone formation was increased by controlled loading based on histomorphometry, the newly formed tissue had similar material quality to the new bone tissue formed during physiological loading. Similar to previous studies, our data showed that bone composition was animal age- and tissue age-dependent during physiological loading. The findings that the new tissue formed in response to controlled loading and physiological loading had similar bone composition and that controlled loading enhanced bone composition in elderly mice further support the use of physical activity as a noninvasive treatment to enhance bone quality as well as maintain bone mass in individuals suffering from age-related bone loss.
Introduction Stretching of tissue stimulates angiogenesis but increased motion at a fracture site... more Introduction Stretching of tissue stimulates angiogenesis but increased motion at a fracture site hinders revascularisation. In vitro studies have indicated that mechanical stimuli promote angiogenic responses in endothelial cells, but can either inhibit or enhance responses when applied directly to angiogenesis assays. We anticipated that cyclic tension applied during endothelial network assembly would increase vascular structure formation up to a certain threshold. Methods Fibroblast/HUVEC co-cultures were subjected to cyclic equibiaxial strain (1 Hz; 6 h/day; 7 days) using the FlexerCell FX-4000T system and limiting rings for simultaneous application of multiple strain magnitudes (0–13%). Cells were labelled using anti-PECAM-1, and image analysis provided measures of endothelial network length and numbers of junctions. Results Cyclic stretching had no significant effect on the total length of endothelial networks (P > 0.2) but resulted in a strain-dependent decrease in branchi...
Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also pat... more Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also patients with secondary osteoarthritis of the hip with pathological anteversion of the femoral neck are treated increasingly using this method. Therefore an investigation was performed to analyze the resulting hip contact force and femoral loading in the proximal femur at the solid model of the "standardized femur". Two different situations of femoral component anteversion were simulated. Increased hip contact forces and an increase of medial and lateral cortex loads result in the anteverted model. With present level of knowledge about the influence of the hip contact force the use of short-stemmed implants is not uncritically in patients with degenerative osteoarthritis of the hip combined with rotational disorders of the proximal femur. The selection of the tribological pairing is to be considered more strongly regarding the wear behavior.
Introduction Minimally invasive total hip arthroplasty has been successfully introduced in the pa... more Introduction Minimally invasive total hip arthroplasty has been successfully introduced in the past decade. Never-theless, standard approaches such as the direct lateral approach are still commonly used in orthopaedic surgery due to easy handling, good intra-operative overview and low complication rates. However, a frequent occurrence of fatty atrophy within the anterior third of the gluteus medius muscle has been demonstrated when using the modiWed direct-lateral approach (mDL), which may be associated with a reduction in function, limitation of internal leg rota-tion, gait disorders and pain. The question addressed in this study is whether mDL-approach leads to unfavourable changes in foot progression angle (FPA), gait and to more postoperative pain compared with a minimally invasive anterolateral approach (ALMI). Methods Thirty patients with primary osteoarthritis of the hip were recruited for this study. All subjects received an uncemented THA (Alloclassic ® -Zweymüller stem, Al...
The tough bulk of dentin in teeth supports enamel, creating cutting and grinding biostructures wi... more The tough bulk of dentin in teeth supports enamel, creating cutting and grinding biostructures with superior failure resistance that is not fully understood. Synchrotron-based diffraction methods, utilizing micro- and nanofocused X-ray beams, reveal that the nm-sized mineral particles aligned with collagen are precompressed and that the residual strains vanish upon mild annealing. We show the link between the mineral nanoparticles and known damage propagation trajectories in dentin, suggesting a previously overlooked compression-mediated toughening mechanism.
Journal of biomedical materials research. Part A, Jan 8, 2015
Interactions between cells and the extracellular matrix (ECM) are known to play critical roles in... more Interactions between cells and the extracellular matrix (ECM) are known to play critical roles in regulating cell phenotype. The identity of ECM ligands presented to mesenchymal stem cells (MSCs) has previously been shown to direct the cell fate commitment of these cells. To enhance osteogenic differentiation of MSCs, alginate hydrogels were prepared that present the DGEA ligand derived from collagen I. When presented from hydrogel surfaces in 2D, the DGEA ligand did not facilitate cell adhesion, while hydrogels presenting the RGD ligand derived from fibronectin did encourage cell adhesion and spreading. However, the osteogenic differentiation of MSCs encapsulated within alginate hydrogels presenting the DGEA ligand was enhanced when compared with unmodified alginate hydrogels and hydrogels presenting the RGD ligand. MSCs cultured in DGEA-presenting gels exhibited increased levels of osteocalcin production and mineral deposition. These data suggest that the presentation of the colla...
Translation in an academic environment requires a support system-people, goals, models, partnersh... more Translation in an academic environment requires a support system-people, goals, models, partnerships, and infrastructures-that will push promising basic science and technology projects forward into the clinic.
High resolution 3D laboratory x-ray tomography data of femora from young, 1-14 day old C57BL/6 mi... more High resolution 3D laboratory x-ray tomography data of femora from young, 1-14 day old C57BL/6 mice, Data in Brief, http://dx.
During mammalian growth, long bones undergo extensive structural reorganization, transforming fro... more During mammalian growth, long bones undergo extensive structural reorganization, transforming from primitive shapes in the limb buds into mature bones. Here we shed light on the steps involved in structural formation of the mineralized tissue in midshafts of C57BL/6 femurs, shortly after birth. By combining 3D micrometer-resolution X-ray microtomography with 2D histology, we study the transformation of the tissue from a partially-mineralized scaffold into a compact bone structure. We identify three growth phases that take place during murine long bone maturation: During a patterning phase (I) mineralized struts form a loosely connected foam-like cortical network. During a transitioning phase (II), the extensive non-mineralized tracts vanish, transforming the foam into a fully continuous mass, by 14days of age. Concomitantly, closed porosity increases to about ∼1.4%, and stays at this level, also found in maturity. During a shaping phase (III), the bones gradually attain their charac...
It is commonly accepted that bone marrow-derived stem cells (BMSCs) have to be expanded in vitro,... more It is commonly accepted that bone marrow-derived stem cells (BMSCs) have to be expanded in vitro, but a prolonged time in culture decreases their multilineage potential. Mechanical and biological stimuli have been used to improve their osteogenic potential. While long-term stimulation has been shown to improve osteogenic differentiation, it remains to be seen whether short-term stimulation is also sufficient.We investigated the influence of 24 hours' cyclic loading (0.05Hz, 4kPa) on gene expression of human BMSCs in three-dimensional fibrin-DMEM constructs (n=7) in a compression bioreactor using DNA-array technology. Expression of the following genes showed a significant increase after mechanical stimulation: 2.6-fold osteopontin (OPN) and integrin-β1 (ITGB1), 2.2-fold transforming growth factor-β-receptor 1 (TGF-β-R1) and 2.4-fold SMAD5 expression, compared to controls without mechanical stimulation (p<0.05 each). Platelet-derived growth factor-α (PDGF-α ) and annexin-V were...
Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also pat... more Short-stemmed hip implants were established in total hip arthroplasty in the last years. Also patients with secondary osteoarthritis of the hip with pathological anteversion of the femoral neck are treated increasingly using this method. Therefore an investigation was performed to analyze the resulting hip contact force and femoral loading in the proximal femur at the solid model of the "standardized femur". Two different situations of femoral component anteversion were simulated. Increased hip contact forces and an increase of medial and lateral cortex loads result in the anteverted model. With present level of knowledge about the influence of the hip contact force the use of short-stemmed implants is not uncritically in patients with degenerative osteoarthritis of the hip combined with rotational disorders of the proximal femur. The selection of the tribological pairing is to be considered more strongly regarding the wear behavior.
Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To... more Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To evaluate the potential benefits of different resorbable candidate materials for use in prophylactic kyphoplasty compared with the behavior of polymethylmethacrylate cement. Kyphoplasty using PMMA bone cement for the stabilization of fractured osteoporotic vertebrae has been established as a useful clinical tool. In several studies, consecutive compression fractures have been reported in vertebrae caudal or cranial to those augmented with bone cement. Consequently, some physicians have begun to treat adjacent vertebrae by means of prophylactic augmentation. Biomechanical in vitro testing was performed on 40 human osteoporotic nonfractured lumbar vertebrae. Three types of bone cement (PMMA, 2 different calcium phosphate cements) and one silicon derivative were assessed during compressive and cyclic sinusoidal testing. Each candidate material was applied bipedicularly under fluoroscopic co...
Different fixation systems are used for fracture and defect treatment. A prerequisite for complic... more Different fixation systems are used for fracture and defect treatment. A prerequisite for complication free healing is sufficient mechanical stability of the osteosynthesis. In vitro investigations offer the possibility of both analysing and assessing the pre-clinical fixation stability. Due to the complex loading environment in vivo, stiffness analysis should include a complete determination of the stiffness under standardised conditions. Based on a mathematical procedure to calculate the 3-D stiffness, a mechanical testing device for the 3-D loading of fixation systems was designed and integrated in the existing test set-up. The set-up consisted of a material testing machine to produce the necessary loads and an optical measurement device to detect the resulting inter-fragmentary movements. To validate the testing device, the 3-D stiffness matrices of different Ilizarov fixator configurations were determined and compared. The good reproducibility of the test was reflected in the s...
Using a mechanical testing procedure, various fixator constructs were tested in vitro. In additio... more Using a mechanical testing procedure, various fixator constructs were tested in vitro. In addition, the influence of the passive soft tissue structures on the fixation stiffness was determined. An increased number of Schanz' screws or Kirschner wires led to a comparable increase in stiffness than that observed with an increasing screw or wire diameter. In consequence, larger diameters should be preferred over an additional screw or wire where clinically applicable. With diaphyseal telescoping rods only the axial stiffness decreased. As expected, large ring diameters as well as titanium wires reduced stiffness components. Bracing the outer rings caused a reduction of the overall stiffness. Asymmetric pre-tensioning of the K-wires resulted in a significant reduction of tension in the neighboring wire. Removal of the soft tissues reduced stiffness to a similar extend as experienced in a fibula defect situation. The study demonstrates the correlation between design parameters, passi...
Objective. To investigate both the age and gender related distributions of bone mineral density i... more Objective. To investigate both the age and gender related distributions of bone mineral density in the proximal tibia, specifically in aged patients.
Hyaline joint cartilage has only a limited potential for self-repair. Some of the published techn... more Hyaline joint cartilage has only a limited potential for self-repair. Some of the published techniques for osteochondral defect therapy try to improve that potential. In this study, it was hypothesised that one of those surgical techniques, the crushed transplanted bone graft together with a collagen membrane, accelerates significantly the reconstruction of the subchondral bone plate and improves the mechanical and histological quality of repaired cartilage in osteochondral defects compared to an empty control defect. In order to test this hypothesis, defects were created in the left knee of 12 sheep and filled either with autologous crushed bone graft or left empty. The animals were sacrificed after 3 (n ¼ 6) and 6 (n ¼ 6) months. No differences were found either macroscopically or histomorphometrically between the bone graft and empty control defects. The biomechanical as well as the histological results of the bone graft defects were inferior to the control defects with inflammatory processes caused either by bone graft or membrane remnants. Based on the results in this sheep model, the filling of subchondral bone defects with compacted cancellous bone should be carefully reconsidered. r
Surgical intervention of the knee joint routinely endeavors to recreate a physiologically normal ... more Surgical intervention of the knee joint routinely endeavors to recreate a physiologically normal joint loading environment. The loading conditions resulting from osteotomies, fracture treatment, ligament replacements, and arthroplasties of the knee are considered to have an impact on the long term clinical outcome; however, knowledge regarding in vivo loading conditions is limited. Using a previously validated musculoskeletal lower limb model, we predicted the tibio-femoral joint contact forces that occur in the human knee during the common daily activities of walking and stair climbing. The average resultant peak force during walking was 3.1 times body weight (BW) across four total hip arthroplasty patients. Inter-individual variations proved larger than the variation of forces for each patient repeating the same task. Forces through the knee were considerably larger during stair climbing than during walking: the average resultant peak force during stair climbing was 5.4 BW although peaks of up to 6.2 BW were calculated for one particular patient. Average anteroposterior peak shear components of 0.6 BW were determined during walking and 1.3 BW during stair climbing. These results confirm both the joint contact forces reported in the literature and the importance of muscular activity in creating high forces across the joint. The magnitudes of these forces, specifically in shear, have implications for all forms of surgical intervention in the knee. The data demonstrate that high contact and shear forces are generated during weight bearing combined with knee flexion angles greater than approximately 15". Clinically, the conditions that produce these larger contact forces should be avoided during post-operative rehabilitation.
Participants at the recent Translate! 2014 meeting in Berlin, Germany, reached a consensus on the... more Participants at the recent Translate! 2014 meeting in Berlin, Germany, reached a consensus on the rate-limiting factor for advancing translational medicine.
Loading can increase bone mass and size and this response is reduced with aging. It is unclear, h... more Loading can increase bone mass and size and this response is reduced with aging. It is unclear, however how loading affects bone mineral and matrix properties. Fourier transform infrared imaging and high resolution synchrotron scanning small angle X-ray scattering were used to study how bone&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s microscale and nanoscale compositional properties were altered in the tibial midshaft of young, adult, and elderly female C57Bl/6J mice after two weeks of controlled in vivo compressive loading in comparison to physiological loading. The effect of controlled loading on bone composition varied with animal age, since it predominantly influenced the bone composition of elderly mice. Interestingly, controlled loading led to enhanced collagen maturity in elderly mice. In addition, although the rate of bone formation was increased by controlled loading based on histomorphometry, the newly formed tissue had similar material quality to the new bone tissue formed during physiological loading. Similar to previous studies, our data showed that bone composition was animal age- and tissue age-dependent during physiological loading. The findings that the new tissue formed in response to controlled loading and physiological loading had similar bone composition and that controlled loading enhanced bone composition in elderly mice further support the use of physical activity as a noninvasive treatment to enhance bone quality as well as maintain bone mass in individuals suffering from age-related bone loss.
School of Chemistry Physics Mechanical Engineering Institute of Health and Biomedical Innovation Science Engineering Faculty, 2012
ABSTRACT Introduction Stretching of tissue stimulates angiogenesis but increased motion at a frac... more ABSTRACT Introduction Stretching of tissue stimulates angiogenesis but increased motion at a fracture site hinders revascularisation. In vitro studies have indicated that mechanical stimuli promote angiogenic responses in endothelial cells, but can either inhibit or enhance responses when applied directly to angiogenesis assays. We anticipated that cyclic tension applied during endothelial network assembly would increase vascular structure formation up to a certain threshold. Methods Fibroblast/HUVEC co-cultures were subjected to cyclic equibiaxial strain (1 Hz; 6 h/day; 7 days) using the FlexerCell FX-4000T system and limiting rings for simultaneous application of multiple strain magnitudes (0–13%). Cells were labelled using anti-PECAM-1, and image analysis provided measures of endothelial network length and numbers of junctions. Results Cyclic stretching had no significant effect on the total length of endothelial networks (P &gt; 0.2) but resulted in a strain-dependent decrease in branching and localised alignments of endothelial structures, which were in turn aligned with the supporting fibroblastic construct. Conclusion The organisation of endothelial networks under cyclic strain is dominated by structural adaptation to the supporting construct. It may be that, in fracture healing, the formation and integrity of the granulation tissue and callus is ultimately critical in revascularisation and its failure under severe strain conditions.
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Papers by Georg Duda