Standard procedure for monosegmental anterior spondylodesis often combines anterior stabilization... more Standard procedure for monosegmental anterior spondylodesis often combines anterior stabilization with autologous iliac crest graft. Recent publications defined a minimum size of the graft as a technical specification for this procedure. The cross sectional area of the graft to be transplanted should be at least 23.9% of the cross sectional area of the vertebral bodies to be fused. We investigated whether the required minimum size of autologous graft, as identified both experimentally and clinically, is compatible with the anatomical conditions in central european patients. Computed tomography scans (n = 348) of polytraumatized patients were obtained in the course of initial diagnosis. The scans were evaluated for vertebral body size and the possible size of autologous bone graft in the region of the anterior superior iliac crest. The evaluation of 348 CT scans demonstrated that 95% of the quantified iliac crest grafts would achieve the size recommended for anterior spinal fusion be...
Аннотация Hyaline cartilage is thought to be unable to regenerate. All efforts so far-including a... more Аннотация Hyaline cartilage is thought to be unable to regenerate. All efforts so far-including autologous chondrocyte cell transplantation-to reconstruct cartilage defects in joints have not been totally convincing. However, mesenchymal cells are able to ...
Journal of orthopaedic research : official publication of the Orthopaedic Research Society, Jan 25, 2015
Cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint rest... more Cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint restoration with minimal bone loss. Good clinical results have been reported, but due to the radiopaque metal shell no data is available on the structure, osseous integration and bone stock under the implant. 14 hemi-CSRAs (4 manufacturers) with two geometries (crown (n = 7)/ stem (n = 7) fixation) were retrieved from patients undergoing revision due to glenoidal erosion. Histological sections cutting through the implant centre and bone were analysed. Quantitative histomorphometry evaluated the bone-implant-contact and compared the bone-area to native humeral retrievals (n = 7). The bone-implant-interface was further assessed by scanning-electron-microscopy (SEM) and energy-dispersive-x-ray (EDX). Qualitative histology revealed a reduced and inhomogeneous bone stock. Obvious signs of stress shielding were observed with bone predominantly visible at the stem and implant rim. Quantitative hist...
Technology and health care : official journal of the European Society for Engineering and Medicine, 2013
Anterior spondylodesis with bone grafting for fusion of spinal motion segments is a common proced... more Anterior spondylodesis with bone grafting for fusion of spinal motion segments is a common procedure in clinical routine. Bone grafts for fusion include autologous, allogenic and xenogenic grafts that are inserted in the unstable spinal motion segment. Nevertheless, biomechanical data for autologous, allogenic and xenogenic grafts are rare. The purpose of this study was to conduct biomechanical comparison of native and conserved bone grafts used in spondylodesis of the spine. Grafts examined were native ovine tricortical iliac crest grafts, bovine cancellous bone blocks and ovine, tricortical iliac crest grafts, conserved in the same way as the bovine cancellous bone blocks. The grafts were tested biomechanically to failure. Compared parameters were maximum torque, maximum rotation angle and graft stiffness at failure. The Mann-Whitney-U test with Bonferroni adjustment was used for statistical analysis. Maximum torque at failure of the bovine cancellous bone graft did not differ sig...
Technology and health care : official journal of the European Society for Engineering and Medicine, 2012
An in vivo axial loading model of the rat ulna was developed almost two decades ago. As a minimal... more An in vivo axial loading model of the rat ulna was developed almost two decades ago. As a minimally invasive model, it lends itself particularly well for the study of functional adaptation in bone and the interosseous membrane, a ligament spanning between the radius and ulna. The objective of this paper is to review computational and experimental approaches to elucidate its applicability for the study of multiscale bone and ligament mechanobiology. Specifically, this review describes approaches, including i) measurement of strains on bone tissue surfaces, ii) development of a three-dimensional finite element (FE) mesh of a skeletally mature rat ulna, iii) parametric study of the relative influence of mechanical constants and materials properties on computational model predictions, iv) comparison of experimental and computational strain distribution data, and analysis of the radius and interosseous membrane (IOM) ligament's effect on axial load distribution through the ulna of th...
The patellofemoral joint constitutes a complex anatomical and functional entity. The tensile forc... more The patellofemoral joint constitutes a complex anatomical and functional entity. The tensile force of the quadriceps femoris muscle is transmitted through the patella and patellar ligament onto the tibial tuberosity. This particular three-dimensional arrangement increases the torsional moment acting on the knee joint. Dynamic alignment of the patella is determined by trochlear geometry and is supported by active muscular and passive connective tissue stabilizers. In addition to the retinaculum of the patella, the medial patellofemoral ligament is attracting increasing clinical attention. Multidirectional motion of the patella is closely connected to retropatellar pressure distribution which can be modulated by moving the patellar ligament insertion. Implantation of a knee endoprosthesis changes the joint surface geometry and consequently patella kinematics and retropatellar pressure distribution. Finite element analysis provides the possibility to assess retropatellar pressure distr...
A comparative study on growth of the sheep and human spine. To validate the immature sheep spine ... more A comparative study on growth of the sheep and human spine. To validate the immature sheep spine as model for the growing human spine and to yield a database for planning and interpretation of future animal experiments. With the current change of paradigm to nonfusion strategies for pediatric spine deformities, experimental surgery on spines of growing goats, sheep, and pigs has gained importance as preclinical proof-of-concept test. However, despite the proceeding use of animals, there is a lack of knowledge regarding the growth of the sheep spine and the relation to the human spine. Thoracic and lumbar cadaver spines were harvested from 50 Swiss alpine sheep. Specimens were obtained from newborn, 1, 3, 6, 9 and 12, 15 and 18 months old female sheep. Direct spondylometry yielded vertebral body heights, widths, and depths and spinal canal size, which were compared to pooled data on human spine growth retrieved from the literature. Sheep spine growth ceases at age 15 to 18 months, wh...
Zeitschrift für Orthopädie und Unfallchirurgie, 2010
Spinal injuries are common and a standard procedure for the stabilisation of spinal injuries is v... more Spinal injuries are common and a standard procedure for the stabilisation of spinal injuries is ventral spondylodesis with an autograft from the iliac crest. Because of the high incidence of harvesting complications there is a need to search for alternative materials. The aim of our study was to evaluate graft integration in the lumbar spine of bovine cancellous bone compared to autologous iliac crest material. Two groups of eight female adult sheep (median age 3 years, range 2.4-3.8 years) received surgical treatment in the form of anterior monosegmental spondylodesis. The spondylodesis was performed in all animals in the motion segment L3/4 through a lateral approach with the animals lying on their right sides. To produce serial sections, the explanted vertebral segments were implanted in methyl methacrylate. On one side the histological preparation was examined qualitatively and in addition we analysed the quantity of the bone structure with special software. The bone structure i...
Foraminal degenerative lumbar stenosis is traditionally considered a result of bony narrowing due... more Foraminal degenerative lumbar stenosis is traditionally considered a result of bony narrowing due to osteophytic appositions on the superior articular process. Clinical experience reveals that significant additional compression of the neural structures is due to degenerative hypertrophy of the adjacent ligamentum flavum. Therefore, microanatomical and neuroradiological investigations were performed to determine the microtopography of this ligament, especially with respect to its lateral extension. Lumbar spine specimens of eight mid-aged human cadavers (mean age 34.5 years) were collected, and MRI studies with T1-weighted images were performed. The specially embedded specimens were sectioned horizontally at the level of the spinal ganglion (slice thickness: 2 mm). Anatomical morphometric data were correlated with identical measurements based on neuroradiological imaging and were analyzed statistically. The distance between midline and extraforaminal extension of the ligamentum flavu...
Advances in anatomy, embryology, and cell biology, 2005
The present study pursues the hypothesis that local compressive force and the occurrence of carti... more The present study pursues the hypothesis that local compressive force and the occurrence of cartilage-specific transformation processes within the extracellular matrix of tendons and ligaments are directly correlated. We compare the pattern of certain marker molecules typical of (fibro)cartilage in select examples. Investigations are carried out of the extensor tendons of toes and fingers, the transverse ligament of the atlas, the transverse ligament of the acetabulum, and of the tendon of the superior oblique muscle and its trochlea. The marker molecules are detected with standardized immunohistochemical methods. The results show that certain molecules only occur under conditions of (relatively high) compressive stress, others being the result of tensile stress. The molecular spectrum of the molecules of the ECM allows qualifying conclusions as to the mechanical situation of a given part of the tissue. A quantifying statement about the intensity of compressive stress is not possibl...
Tissue engineering opens up new ways for therapy of bone defects. Therefore, the aim of this stud... more Tissue engineering opens up new ways for therapy of bone defects. Therefore, the aim of this study was to establish a mouse model to investigate local cell growth of human mesenchymal stem cells (hMSC) on the scaffold in vivo. Moreover, migration of cells to other organs should be excluded.hMSC (Cambrex, USA) were cultivated according to supplier's recommendations. After inoculation on cylindric scaffolds, one matrix cell construct and one scaffold without hMSC were implanted subcutaneously left and right paravertebrally in athymic nude mice. After 2, 4, 8, and 12 weeks constructs and organs were harvested for immunohistological evaluation and PCR. In conclusion, we found integration of scaffolds loaded with hMSC implanted ectopically. HMSC seeded on 3D scaffolds survived for a period of up to 12 weeks. In addition, we could not detect hMSC in any other organ of the host.
The purpose of this study was to test the hypothesis that shock waves can induce new bone formati... more The purpose of this study was to test the hypothesis that shock waves can induce new bone formation even without cortical fractures and periosteal detachment as suggested in the literature. Extracorporeal shock waves with energy flux densities between 0 mJ/mm(2) (sham treatment) and 1.2 mJ/mm(2) were applied in vivo to the distal femoral region of rabbits (1500 pulses at 1 Hz frequency each). Oxytetracycline was injected on days 5-9 and the animals were sacrificed on day 10. Sections of both femora of all animals were investigated with broadband fluorescence microscopy and contact microradiography for new periosteal and endosteal bone, periosteal detachment, cortical fractures, and trabecular bone with callus. Shock waves with energy flux densities of 0.9 mJ/mm(2) and 1.2 mJ/mm(2) resulted in new periosteal bone formation in the presence of cortical fractures and periosteal detachment. After application of shock waves with energy flux density of 0.5 mJ/mm(2), clearly detectable sign...
Standard procedure for monosegmental anterior spondylodesis often combines anterior stabilization... more Standard procedure for monosegmental anterior spondylodesis often combines anterior stabilization with autologous iliac crest graft. Recent publications defined a minimum size of the graft as a technical specification for this procedure. The cross sectional area of the graft to be transplanted should be at least 23.9% of the cross sectional area of the vertebral bodies to be fused. We investigated whether the required minimum size of autologous graft, as identified both experimentally and clinically, is compatible with the anatomical conditions in central european patients. Computed tomography scans (n = 348) of polytraumatized patients were obtained in the course of initial diagnosis. The scans were evaluated for vertebral body size and the possible size of autologous bone graft in the region of the anterior superior iliac crest. The evaluation of 348 CT scans demonstrated that 95% of the quantified iliac crest grafts would achieve the size recommended for anterior spinal fusion be...
Аннотация Hyaline cartilage is thought to be unable to regenerate. All efforts so far-including a... more Аннотация Hyaline cartilage is thought to be unable to regenerate. All efforts so far-including autologous chondrocyte cell transplantation-to reconstruct cartilage defects in joints have not been totally convincing. However, mesenchymal cells are able to ...
Journal of orthopaedic research : official publication of the Orthopaedic Research Society, Jan 25, 2015
Cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint rest... more Cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint restoration with minimal bone loss. Good clinical results have been reported, but due to the radiopaque metal shell no data is available on the structure, osseous integration and bone stock under the implant. 14 hemi-CSRAs (4 manufacturers) with two geometries (crown (n = 7)/ stem (n = 7) fixation) were retrieved from patients undergoing revision due to glenoidal erosion. Histological sections cutting through the implant centre and bone were analysed. Quantitative histomorphometry evaluated the bone-implant-contact and compared the bone-area to native humeral retrievals (n = 7). The bone-implant-interface was further assessed by scanning-electron-microscopy (SEM) and energy-dispersive-x-ray (EDX). Qualitative histology revealed a reduced and inhomogeneous bone stock. Obvious signs of stress shielding were observed with bone predominantly visible at the stem and implant rim. Quantitative hist...
Technology and health care : official journal of the European Society for Engineering and Medicine, 2013
Anterior spondylodesis with bone grafting for fusion of spinal motion segments is a common proced... more Anterior spondylodesis with bone grafting for fusion of spinal motion segments is a common procedure in clinical routine. Bone grafts for fusion include autologous, allogenic and xenogenic grafts that are inserted in the unstable spinal motion segment. Nevertheless, biomechanical data for autologous, allogenic and xenogenic grafts are rare. The purpose of this study was to conduct biomechanical comparison of native and conserved bone grafts used in spondylodesis of the spine. Grafts examined were native ovine tricortical iliac crest grafts, bovine cancellous bone blocks and ovine, tricortical iliac crest grafts, conserved in the same way as the bovine cancellous bone blocks. The grafts were tested biomechanically to failure. Compared parameters were maximum torque, maximum rotation angle and graft stiffness at failure. The Mann-Whitney-U test with Bonferroni adjustment was used for statistical analysis. Maximum torque at failure of the bovine cancellous bone graft did not differ sig...
Technology and health care : official journal of the European Society for Engineering and Medicine, 2012
An in vivo axial loading model of the rat ulna was developed almost two decades ago. As a minimal... more An in vivo axial loading model of the rat ulna was developed almost two decades ago. As a minimally invasive model, it lends itself particularly well for the study of functional adaptation in bone and the interosseous membrane, a ligament spanning between the radius and ulna. The objective of this paper is to review computational and experimental approaches to elucidate its applicability for the study of multiscale bone and ligament mechanobiology. Specifically, this review describes approaches, including i) measurement of strains on bone tissue surfaces, ii) development of a three-dimensional finite element (FE) mesh of a skeletally mature rat ulna, iii) parametric study of the relative influence of mechanical constants and materials properties on computational model predictions, iv) comparison of experimental and computational strain distribution data, and analysis of the radius and interosseous membrane (IOM) ligament's effect on axial load distribution through the ulna of th...
The patellofemoral joint constitutes a complex anatomical and functional entity. The tensile forc... more The patellofemoral joint constitutes a complex anatomical and functional entity. The tensile force of the quadriceps femoris muscle is transmitted through the patella and patellar ligament onto the tibial tuberosity. This particular three-dimensional arrangement increases the torsional moment acting on the knee joint. Dynamic alignment of the patella is determined by trochlear geometry and is supported by active muscular and passive connective tissue stabilizers. In addition to the retinaculum of the patella, the medial patellofemoral ligament is attracting increasing clinical attention. Multidirectional motion of the patella is closely connected to retropatellar pressure distribution which can be modulated by moving the patellar ligament insertion. Implantation of a knee endoprosthesis changes the joint surface geometry and consequently patella kinematics and retropatellar pressure distribution. Finite element analysis provides the possibility to assess retropatellar pressure distr...
A comparative study on growth of the sheep and human spine. To validate the immature sheep spine ... more A comparative study on growth of the sheep and human spine. To validate the immature sheep spine as model for the growing human spine and to yield a database for planning and interpretation of future animal experiments. With the current change of paradigm to nonfusion strategies for pediatric spine deformities, experimental surgery on spines of growing goats, sheep, and pigs has gained importance as preclinical proof-of-concept test. However, despite the proceeding use of animals, there is a lack of knowledge regarding the growth of the sheep spine and the relation to the human spine. Thoracic and lumbar cadaver spines were harvested from 50 Swiss alpine sheep. Specimens were obtained from newborn, 1, 3, 6, 9 and 12, 15 and 18 months old female sheep. Direct spondylometry yielded vertebral body heights, widths, and depths and spinal canal size, which were compared to pooled data on human spine growth retrieved from the literature. Sheep spine growth ceases at age 15 to 18 months, wh...
Zeitschrift für Orthopädie und Unfallchirurgie, 2010
Spinal injuries are common and a standard procedure for the stabilisation of spinal injuries is v... more Spinal injuries are common and a standard procedure for the stabilisation of spinal injuries is ventral spondylodesis with an autograft from the iliac crest. Because of the high incidence of harvesting complications there is a need to search for alternative materials. The aim of our study was to evaluate graft integration in the lumbar spine of bovine cancellous bone compared to autologous iliac crest material. Two groups of eight female adult sheep (median age 3 years, range 2.4-3.8 years) received surgical treatment in the form of anterior monosegmental spondylodesis. The spondylodesis was performed in all animals in the motion segment L3/4 through a lateral approach with the animals lying on their right sides. To produce serial sections, the explanted vertebral segments were implanted in methyl methacrylate. On one side the histological preparation was examined qualitatively and in addition we analysed the quantity of the bone structure with special software. The bone structure i...
Foraminal degenerative lumbar stenosis is traditionally considered a result of bony narrowing due... more Foraminal degenerative lumbar stenosis is traditionally considered a result of bony narrowing due to osteophytic appositions on the superior articular process. Clinical experience reveals that significant additional compression of the neural structures is due to degenerative hypertrophy of the adjacent ligamentum flavum. Therefore, microanatomical and neuroradiological investigations were performed to determine the microtopography of this ligament, especially with respect to its lateral extension. Lumbar spine specimens of eight mid-aged human cadavers (mean age 34.5 years) were collected, and MRI studies with T1-weighted images were performed. The specially embedded specimens were sectioned horizontally at the level of the spinal ganglion (slice thickness: 2 mm). Anatomical morphometric data were correlated with identical measurements based on neuroradiological imaging and were analyzed statistically. The distance between midline and extraforaminal extension of the ligamentum flavu...
Advances in anatomy, embryology, and cell biology, 2005
The present study pursues the hypothesis that local compressive force and the occurrence of carti... more The present study pursues the hypothesis that local compressive force and the occurrence of cartilage-specific transformation processes within the extracellular matrix of tendons and ligaments are directly correlated. We compare the pattern of certain marker molecules typical of (fibro)cartilage in select examples. Investigations are carried out of the extensor tendons of toes and fingers, the transverse ligament of the atlas, the transverse ligament of the acetabulum, and of the tendon of the superior oblique muscle and its trochlea. The marker molecules are detected with standardized immunohistochemical methods. The results show that certain molecules only occur under conditions of (relatively high) compressive stress, others being the result of tensile stress. The molecular spectrum of the molecules of the ECM allows qualifying conclusions as to the mechanical situation of a given part of the tissue. A quantifying statement about the intensity of compressive stress is not possibl...
Tissue engineering opens up new ways for therapy of bone defects. Therefore, the aim of this stud... more Tissue engineering opens up new ways for therapy of bone defects. Therefore, the aim of this study was to establish a mouse model to investigate local cell growth of human mesenchymal stem cells (hMSC) on the scaffold in vivo. Moreover, migration of cells to other organs should be excluded.hMSC (Cambrex, USA) were cultivated according to supplier's recommendations. After inoculation on cylindric scaffolds, one matrix cell construct and one scaffold without hMSC were implanted subcutaneously left and right paravertebrally in athymic nude mice. After 2, 4, 8, and 12 weeks constructs and organs were harvested for immunohistological evaluation and PCR. In conclusion, we found integration of scaffolds loaded with hMSC implanted ectopically. HMSC seeded on 3D scaffolds survived for a period of up to 12 weeks. In addition, we could not detect hMSC in any other organ of the host.
The purpose of this study was to test the hypothesis that shock waves can induce new bone formati... more The purpose of this study was to test the hypothesis that shock waves can induce new bone formation even without cortical fractures and periosteal detachment as suggested in the literature. Extracorporeal shock waves with energy flux densities between 0 mJ/mm(2) (sham treatment) and 1.2 mJ/mm(2) were applied in vivo to the distal femoral region of rabbits (1500 pulses at 1 Hz frequency each). Oxytetracycline was injected on days 5-9 and the animals were sacrificed on day 10. Sections of both femora of all animals were investigated with broadband fluorescence microscopy and contact microradiography for new periosteal and endosteal bone, periosteal detachment, cortical fractures, and trabecular bone with callus. Shock waves with energy flux densities of 0.9 mJ/mm(2) and 1.2 mJ/mm(2) resulted in new periosteal bone formation in the presence of cortical fractures and periosteal detachment. After application of shock waves with energy flux density of 0.5 mJ/mm(2), clearly detectable sign...
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Papers by Stefan Milz