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A two-step method for investigating the stiffnesses and failure loads of vertebral bodies is presented. It is based on the representation of the spine in a global finite element model of structural elements. A detailed model of two interconnected vertebrae and an intervertebral disc was implemented. Calculations on this model are shown which illustrate the dependencies of structural stiffnesses on vertebral body properties. These structural stiffnesses can then be used to represent the spine in the global model.

In tissue engineering and regenerative medicine mesenchymal stem cells (MSC) are widely used to replace and restore the function of dysfunctional or missing tissue. Recent studies have shown significant enhancements of the in vivo healing process following dentofacial bone augmentation procedures employing stem cell-loaded xenografts. We conducted experimental and numerical investigations in perfusion flow bioreactor-xenograft-systems to identify flow conditions as well as bioreactor design features that allow for homogeneous MSC-distribution in Geistlich Bio- Oss Block xenografts. Pressure gradient - velocity characteristics and flow distributions were investigated experimentally and numerically for two bioreactor designs at steady-state flow conditions with Reynolds numbers (Re) ranging from 0.01 ≤ Re ≤ 0.32. Distilled water at 20°C with a dynamic viscosity of 1.002 mPa∙s and a density of 998 kg/m3 was used. The geometry of the xenograft utilized in three-dimensional computational fluid dynamics (CFD) simulation was obtained by means of micro-computed tomography (μCT) at an isotropic spatial resolution of 9.5 μm. The permeability values calculated from the experimental data are in good accordance with the numerical results. The investigations showed that the increase of the inflow- and outflow-area diameter, as well as the decrease of the volumetric flow rate, result in a decreasing heterogeneity of the flow distribution within the xenograft. The calculated wall shear stress rates in the three-dimensional (3D) scaffold range from 1∙10-12Pa ≤ τ ≤ 0.2 Pa. Experimentally validated CFD simulations introduced in this study provide an applicable tool to assess optimal flow conditions for homogeneous MSC distribution in bioreactor-xenograft-systems.

In dentofacial surgery, augmentation procedures employing xenografts have become a reliable treatment. Recent studies, however, have shown significant enhance-ments of the in vivo bone tissue augmentation using mesenchymal stem cells loaded into bone grafts. We conducted experimental and numerical investigations in flow perfusion systems to determine flow conditions which allow for homogenous stem cell distribution in BioOss Block (Geistlich Pharma AG, Switzerland) xenografts. Pressure gradient-velocity characteristics and flow distributions were investigated experimentally and numerically at steady state flow conditions with Reynolds numbers (Re) ranging from 0.01 ≤ Re ≤ 0.40. Distilled water at 20°C with a dynamic viscosity of 1.002 mPa.s and a density of 998 kg/m3 was used. The geometry utilized in three-dimensional computa-tional fluid dynamics (CFD) simulation was obtained by means of micro-computed tomography (μCT). Results of CFD analysis are in good accordance with experimental data. The comparison of the pressure gradient-velocity characteris-tics for experimental and numerical data yields a relative error of 3.6%. According to Darcy’s law for creeping fluid flow the experimentally determined permeability is 2.55.10-9 m2. Moreover, numerical flow distribution analysis shows an increasingly heterogenic streamline distribution for increasing Reynolds numbers. Experimentally validated CFD simulations introduced in this study provide a tool to assess optimal flow conditions for a homogenous stem cell distribution in perfusion flow systems.

The investigation of matching of endoprosthesis tibial components to the bone cross section is of interest for the manufacturer as well as for the surgeon. On the one hand, a systemic design of the prosthesis and the assortment is possible, on the other hand, a better matching implantation is enabled on the basis of experience of this study. CT sections were segmented manually using a CAD system and fitted by spline functions, then superseded with cross sections of the tibial component of a modified Hintermann H3 prosthesis. The principal moments of inertia, the direction of the principal axes and the area of the section were evaluated. Based on the relative differences of the principal moments of inertia, recommendations for application of the different prosthesis size and its selection with the surgery can be made.

The Bauschinger effect is a phenomenon metals show as a result of plastic deformation. After a primary plastic deformation the yield strength in the opposite loading direction decreases. The aim of this study is to investigate if there is a phenomenon similar to Bauschinger effect in thermoplastic polymers for stent application that would influence the mechanical properties of these biodegradable implants. Combined uniaxial tensile with subsequent compression tests as well as conventional compression tests without prior tensile loading were performed using biodegradable polymers for stent application (PLLA and a PLLA based blend). Comparing the results of compression tests with prior tensile loading to the compression-only tests a decrease in compressive strength can be observed for both of the tested materials. The conclusion of the performed experiments is that there is a phenomenon similar to Bauschinger effect not only in metallic materials but also in the examined thermoplastic polymers. The observed reduction of compressive strength as a consequence of prior tensile loading can influence the mechanical behaviour, e.g. the radial strength, of polymeric stents after sustaining a complex load history due to crimping and expansion.

For the investigation of reaction moments of wrist joint with external fixator, a test device was developed that allows a well-defined investigation of the joint loads during hand flexion movements. The reaction moments are considered as a measure for the joint loads due to the constraint forces, which occur with differences of the rotation axis of the fixator device from the physiological rotation axis of the wrist joint. The developed test device allows a dynamic momentum load application into the wrist by a servohydraulic testing machine. This testing device converts the force to a moment by a constant lever arm and allows thereby the measurement of the reaction moments by the force load cell of the testing machine. Measurements on cadaveric wrist joints with external fixator can be thereby performed under reproducible conditions. The cadaveric wrist joints can be integrally casted into bone cement and thereby clamped to the testing device. Preliminary experiments with artificial bones showed that forces within the measuring range of the load cell of the testing machine can be measured. The design of the test device is presented. Hence, the requirements for measurements of the reaction moments with wrists with external fixator for distal radius fractures under dynamic loads are created.

Theoretical and experimental investigations were carried out for development of human lens implants made from hydrogel material. The material properties were measured and implemented in a Finite element model. Though the material is still too stiff for accommodative lenses, the theoretical and experimental foundations for the implant development were established.

Hydrogels were introduced as suitable materials for applications in, e.g., medical, agriculture, or daily life areas. Swelling characteristics of a hydrogel are important and must be precisely known for various fields of application. In medicine, where hydrogels are used as implants or drug delivery systems, precise knowledge of the swelling behavior is essential. Especially in ophthalmology as part of cataract surgery, the visco‐elastic properties of the hydrogels could even allow for the restoration of accommodation. The easiest way to describe the swelling is by measuring the swelling ratio, generally done by scaling. Besides that, it can also be done by volume investigations. The similarities and differences are studied on five hydrogel samples made of methyl methacrylate and N‐vinyl pyrrolidone. Additionally, a first camera‐based approach, potentially providing an automated, quasi‐continuous non‐contact method for swelling kinetics investigations, is described. [ABSTRACT FROM AUTHOR]

Abstract Background It is often suggested that sagittal instability at the first tarso-metatarsal joint level is a primary factor for hallux valgus and that sagittal instability increases with the progression of the deformity. The assessment of the degree of vertical instability is usually made by clinical evaluation while any measurements mostly refer to a static assessment of medial ray mobility (i.e. the plantar/dorsal flexion in the sagittal plane). Testing methods currently available cannot attribute the degree of mobility to the corresponding anatomical joints making up the medial column of the foot. The aim of this study was to develop a technique which allows for a quantification of the in-vivo sagittal mobility of the joints of the medial foot column during the roll-over process under full weight bearing. Methods Mobility of first ray bones was investigated by dynamic distortion-free fluoroscopy (25 frames/s) of 14 healthy volunteers and 8 patients with manifested clinical instability of the first ray. A CAD-based evaluation method allowed the determination of mobility and relative displacements and rotations of the first ray bones within the sagittal plane during the stance phase of gait. Results Total flexion of the first ray was found to be 13.63 (SD 6.14) mm with the healthy volunteers and 13.06 (SD 8.01) mm with the patients (resolution: 0.245 mm/pixel). The dorsiflexion angle was 5.27 (SD 2.34) degrees in the healthy volunteers and increased to 5.56 (SD 3.37) degrees in the patients. Maximum rotations were found at the naviculo-cuneiform joints and least at the first tarso-metatarsal joint level in both groups. Conclusions Dynamic fluoroscopic assessment has been shown to be a valuable tool for characterisation of the kinematics of the joints of the medial foot column during gait. A significant difference in first ray flexion and angular rotation between the patients and healthy volunteers however could not be found.

The vertebral trabecular bone has a complex three-dimensional microstructure with an inhomogeneous morphology. Correct identification and assessment of the weakest segments of the cancellous bone may lead to better prediction of fracture risk. The aim of this study was to compare cancellous bone from 240 vertebrae of the cervical, thoracic and lumbar spine of ten body donors with osteoporosis in regard to bone volume fraction (BVF), trabecular thickness, separation, trabecular number and degree of anisotropy, to ascertain why cervical vertebrae rarely fracture, even with severe osteoporosis. Samples were obtained from all vertebrae with a Jamshidi needle (8 Gauge). The investigations were performed with a micro-computed tomography (micro-CT) device (SKYSCAN 1172, RJL Micro & Analytic GmbH, Karlsdorf-Neuthard, Germany). Existing vertebral fractures and the bone mineral density of the lumbar spine were assessed with quantitative CT. Regarding the micro-CT parameters, statistically significant differences were observed between the various sections of the spine. We found a higher BVF, trabecular number and trabecular thickness, as well as a lower trabecular separation of the cervical vertebrae compared to other vertebrae. In addition, the degree of anisotropy in the cervical spine is lower than in the other spinal column sections. These results are age and sex dependent. Thus, the cervical spine has special structural features, whose causes must be determined in further investigations. [ABSTRACT FROM AUTHOR]

Background: Open reduction and internal fixation with a plate is deemed to represent the gold standard of surgical treatment for displaced intra-articular calcaneal fractures. Standard plate fixation is usually placed through an extended lateral approach with high risk for wound complications. Minimally invasive techniques might avoid wound complications but provide limited construct stability. Therefore, 2 different types of locking nails were developed to allow for minimally invasive technique with sufficient stability. The aim of this study was to quantify primary stability of minimally invasive calcaneal interlocking nail systems in comparison to a variable-angle interlocking plate. Material and Methods: After quantitative CT analysis, a standardized Sanders type IIB fracture model was created in 21 fresh-frozen cadavers. For osteosynthesis, 2 different interlocking nail systems (C-Nail; Medin, Nov. Město n. Moravě, Czech Republic; Calcanail; FH Orthopedics SAS; Heimsbrunn, France) as well as a polyaxial interlocking plate (Rimbus; Intercus GmbH; Rudolstadt, Germany) were used. Biomechanical testing consisted of a dynamic load sequence (preload 20 N, 1000 N up to 2500 N, stepwise increase of 100 N every 100 cycles, 0.5 mm/s) and a load to failure sequence (max. load 5000 N, 0.5 mm/s). Interfragmentary movement was detected via a 3-D optical measurement system. Boehler angle was measured after osteosynthesis and after failure occurred. Results: No significant difference regarding load to failure, stiffness, Boehler angle, or interfragmentary motion was found between the different fixation systems. A significant difference was found with the dynamic failure testing sequence where 87.5% of the Calcanail implants failed in contrast to 14% of the C-Nail group (P < .01) and 66% of the Rimbus plate. The highest load to failure was observed for the C-Nail. Boehler angle showed physiologic range with all implants before and after the biomechanical tests. Conclusion: Both minimally invasive interlocking nail systems displayed a high primary stability that was not inferior to an interlocking plate. Clinical relevance: Based on our results, both interlocking nails appear to represent a viable option for treating displaced intra-articular calcaneal fractures. [ABSTRACT FROM AUTHOR]

Introduction. Current treatment strategies for osteoporotic vertebral compression fractures (VCFs) focus on cement-associated solutions. Complications associated with cement application are leakage, embolism, adjacent fractures, and compromise in bony healing. This study comprises a validated VCF model in osteoporotic sheep in order to (1) evaluate a new cementless fracture fixation technique using titanium mesh implants (TMIs) and (2) demonstrate the healing capabilities in osteoporotic VCFs. Methods. Twelve 5-year-old Merino sheep received ovariectomy, corticosteroid injections, and a calcium/phosphorus/vitamin D-deficient diet for osteoporosis induction. Standardized VCFs (type AO A3.1) were created, reduced, and fixed using intravertebral TMIs. Randomly additional autologous spongiosa grafting (G1) or no augmentation was performed (G2, n=6 each). Two months postoperatively, macroscopic, micro-CT and biomechanical evaluation assessed bony consolidation. Results. Fracture reduction succeeded in all cases without intraoperative complications. Bony consolidation was proven for all cases with increased amounts of callus development for G2 (58.3%). Micro-CT revealed cage integration. Neither group showed improved results with biomechanical testing. Conclusions. Fracture reduction/fixation using TMIs without cement in osteoporotic sheep lumbar VCF resulted in bony fracture healing. Intravertebral application of autologous spongiosa showed no beneficial effects. The technique is now available for clinical use; thus, it offers an opportunity to abandon cement-associated complications. [ABSTRACT FROM AUTHOR]

This study analyses the effect of eptotermin α application into fractured vertebrae. It is hypothesized that eptotermin α is capable to enhance bony healing of the osteoporotic spine. In 10 Merino sheep osteoporosis induction was performed by ovariectomy, corticosteroid therapy and calcium/phosphorus/vitamin D-deficient diet; followed by standardized creation of lumbar vertebral compression fractures (VCFs) type A3.1 and consecutive fracture reduction/fixation using expandable mesh cages. Randomly, intravertebral eptotermin α (G1) or no augmentation was added (G2). Macroscopic, micro-CT, and biomechanical evaluation assessed bony consolidation two months postoperatively: Micro-CT data revealed bony consolidation for all cases with significant increased callus development for G2 (60%) and BV/TV (bone volume/total volume 73.45%, osteoporotic vertebrae 35.76%). Neither group showed improved biomechanical stability. Eptotermin α enhanced mineralisation in VCFs in an experimental setup with use of cementless augmentation via an expandable cage. However, higher bone mineral density did not lead to superior biomechanical properties. [ABSTRACT FROM AUTHOR]

Due to improved tissue regeneration and the enabling of post-operative minimally invasive interventions in the same vessel segment, biodegradable polymeric scaffolds represent a competitive approach to permanent metallic stents in vascular applications. Despite these advantages some challenges, such as the improvement of the scaffold mechanics and enhancement of scaffold visibility during the implantation procedure, are persisting. Therefore, the scope of our studies was to investigate the potential of gold, silver and magnetite nanoparticles incorporated in a polymeric blend of poly(L-lactide)/poly(4-hydroxybutyrate) for image enhancement in X-ray, magnetic resonance or near-infrared imaging. Their impact on mechanical properties of such modified scaffold materials was also evaluated. [ABSTRACT FROM AUTHOR]

The article reports on research which was conducted to perform a radiokinematic and pedobarographic analysis of first ray instability in hallux valgus deformity. Researchers evaluated eight patients. They found that an enlarged intermetatarsal angle was associated with increased maximum dorsiflexion of the first ray during gait in hallux valgus patients.

Background The etiology of subchondral bone cysts in arthrotic joints is unclear. Materials and methods We used two-dimensional finite element analysis to evaluate the hypothesis that subchondral bone cysts in the osteoarthrotic hip joint may be the result of microfractures caused by localized cartilage defects or a thinned layer of cartilage. We evaluated the equivalent bone stress (von Mises (VM) stress) in the cancellous bone as an indicator of potential microfractures and further development of cystic lesions. Results Cartilage defects induced stress peaks in the subchondral bone. This peak stress distribution corresponded to the clinical observation of development of acetabular and femoral subchondral cysts in a "kissing" position. A femoral subchondral bone cyst induced a stress peak at the corresponding acetabular site, whereas subchondral acetabular cysts did not increase stress in the femoral head. Acetabular cysts showed an increased level of stress at the lateral and medial border of the lesion which was much higher than the stress levels in the femoral head, indicating a tendency to faster growth. Interpretation Our study supports the theory that stress-induced bone resorption may cause development of subchondral bone cysts in osteoarthrosis. [ABSTRACT FROM AUTHOR]

To utilize the Icare tonometer TAO1 for intraocular pressure (IOP) determination in experimental animals. To calculate true IOP calibration functions for rabbit and porcine eyes. Enucleated eyes of 3-year-old healthy experimental rabbits (New Zealand white), and healthy 1 year old experimental pigs (Deutsche Landrasse) were used for the determination of IOP. Manometric (Geuder GmbH, Heidelberg/Germany) and rebound tonometry (Icare tonometer TAO1, Icare, Helsinki/Finland) were used to record IOP in enucleated animal eyes (rabbit n = 2, pig n = 3). The Icare tonometer TAO1 measurements underestimated true IOP by 37-60% in rabbit eyes and 17-63% in porcine eyes. IOP values obtained by both rebound and manometric tonometry for rabbit and porcine eyes followed a linear regression curve. Linear functions were calculated to correct the Icare tonometer TAO1 measurements to true IOP for both rabbit ( p = 1.4244 p + 4.2421) and porcine eyes ( p = 1.0799 p + 5.8557). The Icare tonometer TAO1 can be utilized for IOP determination in rabbit and porcine eyes when measured values are corrected with the appropriate linear function. [ABSTRACT FROM AUTHOR]

Competing Interests: Die Autorinnen/Autoren geben an, dass kein Interessenkonflikt besteht.

Introduction: The human bone structure changes with an increase in age. Both material and structural properties affect bone strength. Despite the ageing of society, however, hardly any data are available on these parameters for elderly individuals. Therefore, in the present study, cancellous bone cylinders were taken from the center of each vertebral body (C3 to L5) and examined with regard to bone volume fraction, trabecular thickness, separation, number of trabeculae, cross-linking, connectivity density and degree of anisotropy., Material and Methods: Samples were obtained from 440 body donors using a Jamshidi needle and analysed using microcomputed tomography. Existing deformities, fractures and bone mineral density of each vertebra were recorded by quantitative computed tomography., Results: With regard to the microcomputed tomography parameters, statistically significant differences were found between the different sections of the vertebrae: the trabeculae of the cervical vertebrae were significantly thicker and more closely spaced than in the thoracic and lumbar vertebrae. The bone volume fraction was significantly higher in this spinal segment, as was the connection density and the number of trabeculae and cross-links. In addition, the degree of anisotropy was significantly lower in the cervical vertebrae than in the other spinal segments. With regard to quantitative computed tomography, there was a significantly higher bone mineral density in the cervical vertebrae., Conclusion: Even with osteoporosis, cervical vertebrae fracture significantly later than thoracic and lumbar vertebrae due to their unique microarchitecture and higher density. Thus, the cervical vertebrae has specific properties., Competing Interests: Die Autorinnen/Autoren geben an, dass kein Interessenkonflikt besteht., (Thieme. All rights reserved.)

Aggregatibacter actinomycetemcomitans is a Gram-negative commensal bacterium of the oral cavity which has been associated with the pathogenesis of periodontitis with severe alveolar bone destruction. The role of host factors such as reactive oxygen and nitrogen intermediates in periodontal A. actinomycetemcomitans infection and progression to periodontitis is still ill-defined. Therefore, this study aimed to analyze the role of NADPH oxidase and inducible nitric oxide synthase (iNOS) in a murine model of A. actinomycetemcomitans-induced periodontitis. NADPH oxidase-deficient (gp91 phox knockout [KO]), iNOS-deficient (iNOS KO), and C57BL/6 wild-type mice were orally infected with A. actinomycetemcomitans and analyzed for bacterial colonization at various time points. Alveolar bone mineral density and alveolar bone volume were quantified by three-dimensional micro-computed tomography, and the degree of tissue inflammation was calculated by histological analyses. At 5 weeks after infection, A. actinomycetemcomitans persisted at significantly higher levels in the murine oral cavities of infected gp91 phox KO mice than in those of iNOS KO and C57BL/6 mice. Concomitantly, alveolar bone mineral density was significantly lower in all three infected groups than in uninfected controls, but with the highest loss of bone density in infected gp91 phox KO mice. Only infected gp91 phox KO mice revealed significant loss of alveolar bone volume and enhanced inflammatory cell infiltration, as well as an increased number of osteoclasts. Our results indicate that NADPH oxidase is important to control A. actinomycetemcomitans infection in the murine oral cavity and to prevent subsequent alveolar bone destruction and osteoclastogenesis., (Copyright © 2017 American Society for Microbiology.)

Hypothesis: The prosthesis length in malleostapedotomy for otosclerosis revision surgery can be calculated if the prosthesis length of previous conventional incus stapedotomy is known., Background: Malleostapedotomy is used in revision surgery for otosclerosis in case of severe incus erosion and malleus or incus fixation., Methods: Fifteen cadaveric human temporal bone specimens were investigated by means of micro-CT followed by 3D analysis. The distance between the incus and the stapes footplate as well as distances between the malleus and the footplate were measured and compared., Results: The required length of virtually bent prostheses corresponded approximately to the 1.5-fold of virtual stapes prostheses in 93%. The addition of 2 mm predicted the required prostheses length almost correctly in 80%., Conclusion: The clinical practice will show whether a preoperative calculation of expected prosthesis length in MS based on the length of the formerly used stapes prosthesis is possible and helpful.

Purpose: Visualization of the anterior segment and biometric evaluation of the entire crystalline lens pose significant challenges for imaging techniques because of tissue-induced distortion artifacts. The present study was conducted to demonstrate the advantages of high-resolution magnetic resonance imaging (micro-MRI) for visualizing the anterior segment., Methods: High-resolution MR ocular images were acquired on an ultra-high-field MR unit using a two-channel coil with four coil elements and T(2)-weighted turbo spin echo sequences ex vivo in pig, rabbit, monkey, and human donor eyes and in vivo in rabbits. Tissue heating, reproducibility, and signal-to-noise ratio were investigated in vivo. Monkey eye lens thickness (LT) was also measured using A-scan ultrasonography (US)., Results: Anterior segment details of phakic eyes were obtained ex vivo (pig, rabbit, monkey, and human donor eyes) with pixel matrix size 512 × 512 (in-plane resolution 80 × 80 μm) and in vivo (rabbit eyes) with pixel matrix size 320 × 320 (in-plane resolution 125 × 125 μm). Complete quantification of lens dimensions as they correlate with the sulcus-sulcus and angle-angle plane can be performed. In LT determinations in monkey eyes, no significant difference was detected between micro-MRI and A-scan US (P > 0.05, Mann-Whitney U test). Biometric analysis of one pseudophakic monkey eye confirmed the absence of relevant distortion artifacts., Conclusions: Micro-MRI allows ex vivo and in vivo visualization and quantification of the spatial arrangement of the anterior eye segment. Imaging of the retroiridian region, including the entire crystalline lens, overcomes a number of major limitations in the quantitative evaluation of the anterior segment.

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.