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Multifunctional materials have been described to meet the diverse requirements of implant materials for femoral components of uncemented total knee replacements. These materials aim to combine the high wear and corrosion resistance of oxide ceramics at the joint surfaces with the osteogenic potential of titanium alloys at the bone-implant interface. Our objective was to evaluate the biomechanical performance of hybrid material-based femoral components regarding mechanical stress within the implant during cementless implantation and stress shielding (evaluated by strain energy density) of the periprosthetic bone during two-legged squat motion using finite element modeling. The hybrid materials consisted of alumina-toughened zirconia (ATZ) ceramic joined with additively manufactured Ti–6Al–4V or Ti–35Nb–6Ta alloys. The titanium component was modeled with or without an open porous surface structure. Monolithic femoral components of ATZ ceramic or Co–28Cr–6Mo alloy were used as reference. The elasticity of the open porous surface structure was determined within experimental compression tests and was significantly higher for Ti–35Nb–6Ta compared to Ti–6Al–4V (5.2 ± 0.2 GPa vs. 8.8 ± 0.8 GPa, p < 0.001). During implantation, the maximum stress within the ATZ femoral component decreased from 1568.9 MPa (monolithic ATZ) to 367.6 MPa (Ti–6Al–4V/ATZ), 560.9 MPa (Ti–6Al–4V/ATZ with an open porous surface), 474.9 MPa (Ti–35Nb–6Ta/ATZ), and 648.4 MPa (Ti–35Nb–6Ta/ATZ with an open porous surface). The strain energy density increased at higher flexion angles for all models during the squat movement. At ∼90° knee flexion, the strain energy density in the anterior region of the distal femur increased by 25.7 % (Ti–6Al–4V/ATZ), 70.3 % (Ti–6Al–4V/ATZ with an open porous surface), 43.7 % (Ti–35Nb–6Ta/ATZ), and 82.5% (Ti–35Nb–6Ta/ATZ with an open porous surface) compared to monolithic ATZ. Thus, the hybrid material-based femoral component decreases the intraoperative fracture risk of the ATZ part and considerably reduces the risk of stress shielding of the periprosthetic bone. [Display omitted] • Multifunctional materials combining advantageous properties of ceramics and titanium alloys. • Evaluation of hybrid femoral components for total knee replacements using FEM during implantation and squat motion. • Hybrid femoral components reduce maximum stress in ATZ, reducing intraoperative fracture risk. • Hybrid femoral components may reduce stress shielding and periprosthetic bone resorption. [ABSTRACT FROM AUTHOR]

Background: In total hip arthroplasty, acetabular press-fit cups require a proper bone stock for sufficient primary implant fixation. The presence of acetabular bone defects compromises the primary fixation stability of acetabular press-fit cups. The aim of the present study is to determine the fixation stability of a cementless acetabular cup regarding standardized bone defects in an experimental setup.Methods: An acetabular defect model was developed and transferred to a biomechanical cup-block model. The lack of superior cup coverage was divided into 4 stages of superior rim loss (33%, 50%, 67%, and 83%) in the anterior-posterior direction and into 4 stages of mediolateral wall absence (11%, 22%, 33%, and 50%). This resulted in 11 different defect cavities, which were compared to the intact cavity in push-in and lever-out tests of one press-fit cup design (56 mm outer diameter). Thereby, push-in force, lever-out moment, lever-out angle, and interface stiffness were determined.Results: The determined lever-out moments range from 15.53 ± 1.38 Nm (intact cavity) to 1.37 ± 0.54 Nm (83%/50% defect). Smaller defects (33%/11%, 33%/22%, and 50%/11%) reduce the lever-out moments by an average of 33.9% ± 2.8%.Conclusion: The lack of mediolateral acetabular coverage of 50% was assessed as critical for cementless cup fixation, whereby the contact zone between implant and bone in the defect is lost. A lack of 20% to 30% mediolateral coverage appears to be acceptable for press-fit cup fixation in the presence of primary stability. A defect of 50%/50% was identified as the threshold for using additional fixation methods. [ABSTRACT FROM AUTHOR]

Today hip cups are used in a large variety of design variants and in increasing numbers of units. Their development is steadily progressing. In addition to conventional manufacturing methods for hip cups, additive methods, in particular, play an increasingly important role as development progresses. The present paper describes a modified cup model developed based on a commercially available press-fit cup (Allofit 54/JJ). The press-fit cup was designed in two variants and manufactured using selective laser melting (SLM). Variant 1 (Ti) was modeled on the Allofit cup using an adapted process technology. Variant 2 (Ti-S) was provided with a porous load bearing structure on its surface. In addition to the typical (complete) geometry, both variants were also manufactured and tested in a reduced shape where only the press-fit area was formed. To assess the primary stability of the press-fit cups in the artificial bone cavity, pull-out and lever-out tests were carried out. Exact fit conditions and two-millimeter press-fit were investigated. The closed-cell PU foam used as an artificial bone cavity was mechanically characterized to exclude any influence on the results of the investigation. The pull-out forces of the Ti-variant (complete-526 N, reduced-468 N) and the Ti-S variant (complete-548 N, reduced-526 N) as well as the lever-out moments of the Ti-variant (complete-10 Nm, reduced–9.8 Nm) and the Ti-S variant (complete-9 Nm, reduced–7.9 N) show no significant differences in the results between complete and reduced cups. The results show that the use of reduced cups in a press-fit design is possible within the scope of development work. [ABSTRACT FROM AUTHOR]

Coating poly-ether-ether-ketone (PEEK) with rough and porous titanium plasma spray (TPS) coatings is a technique which is commonly used to enhance the osseointegrative properties of medical implants. However, the influence of the TPS coating on the PEEK mechanical properties has not been sufficiently evaluated to date. In this study, PEEK samples were coated with a thick TPS layer with grains of 90 µm and 180 µm diameter. The coating characteristics and the adhesive strength of the coatings on the samples were determined and compared to coatings on titanium samples. The influence of the coating process on the mechanical and chemical-physical properties of PEEK was also evaluated. All TPS coatings on PEEK and titanium fulfilled the manufacturer's requirements for thickness (200 ± 50 µm), porosity (30 ± 10%) and roughness (90 µm grain diameter coating: 25 ± 5 µm and 180 µm grain diameter coating: 45 ± 15 µm) and were able to meet the demands required for adhesive strength (> 22 MPa) and shear strength (> 20 MPa). However, the mechanical properties i.e. yield stress, fracture strain, flexural modulus and flexural stress, of the PEEK samples were influenced by the coating process, while the chemical-physical properties were not altered. [ABSTRACT FROM AUTHOR]

Background: Large diameter heads (LDHs) of metal-on-metal bearings in total hip arthroplasty provide increased range of motion and reduced dislocation rates. However, major concerns grew over high wear rates from the modular connection between femoral stem and head, especially in combination with adapter sleeves.Methods: A computational study on the taper connection stability of LDH (50 mm) with adapter sleeves of different lengths (S, M, L, and XL) compared with a standard femoral head (32 mm) without adapter sleeves was conducted using explicit finite element analyses. Four different impact configurations were considered resulting from varied mallet mass (0.5 vs 1.0 kg) and velocity (1.0 vs 2.0 m/s). The taper stability was evaluated by determination of the pull-off forces and micromotions due to simulated joint loads during walking (2 kN and 7.9 Nm, respectively). Moreover, the deformations of the adapter sleeves and the contact area in the taper connections were evaluated.Results: Although the pull-off forces of the LDH with different-sized adapter sleeves were comparable, contact area decreased and adapter sleeve deformations increased (up to 283%) with an increasing adapter sleeve length. Moreover, the micromotions of LDH with adapter sleeves were up to 7-times higher, as compared with the standard femoral head without an adapter sleeve.Conclusion: The present numerical study confirms that the assembly technique of LDH with adapter sleeves reveals increased micromotions compared with standard femoral head sizes. We could demonstrate that deviations of the stem trunnion geometry and improper surgical instructions led to worse mechanical stability of the taper connection. [ABSTRACT FROM AUTHOR]

In order to reduce the implant stiffness, open-porous designs in two geometrical dimensions were investigated (twisted design). Scaffolds were fabricated by an SLM process using Ti6Al4V and material properties were determined by conducting uniaxial compression testing. Furthermore, the unit cell was tested in different orientations to determine the mechanical properties. The elastic modulus of the scaffolds varied between 3.4 and 26.3 GPa and scaffolds porosity ranged from 54 to 60%. Linear relationship was found between compression strain, compressive strength and modulus of elasticity. Results show a clear influence of the unit cell orientation on elastic modulus, compressive strength and strain. Moreover, the specific yielding that characterizes the relationship between modulus of elasticity and porosity under consideration of the cell orientation could be described in functional terms. We successfully generated scaffolds with mechanical properties close to those of human cortical bone. The influence on the unit cell orientation demonstrated the necessity of considering the load direction in the evaluation of bone scaffolds. [ABSTRACT FROM AUTHOR]

Background: Degenerative hip and spine disease are known to frequently coexist. Lumbar spine disorders (LSDs), as opposed to other patient-related factors, are disregarded in the assessment of the clinical outcome after total hip replacement (THR). This prospective study investigates the influence of LSDs on the pre- and postoperative health-related quality of life and functional outcome of patients undergoing THR.Methods: According to clearly defined criteria, 42 patients scheduled for cementless THR were assigned either to the LSD (13 patients with LSDs) or non-LSD group (29 patients without LSDs). A clinical assessment was performed preoperatively as well as 12, 24 and 60 months postoperatively using the Harris hip score (HHS), the Western Ontario and McMaster University osteoarthritis index (WOMAC) and the 36-item short form health survey (SF-36).Results: The statistical analysis comparing the pre- and postoperative status within both groups showed an ongoing improvement of mean HHS and WOMAC after THR. The non-LSD group had a significantly higher postoperative HHS and WOMAC after 12, 24 and 60 months as well as SF-36 after 24 and 60 months. The LSD group improved significantly in the HHS at 24 and 60 months and the WOMAC at 12, 24 and 60 months postoperatively, whereas the SF-36 improvement was not significant. Comparison of preoperative data in both groups revealed a significantly higher SF-36 in the non-LSD group but no difference between the HHS and WOMAC. At each postoperative assessment, the HHS, WOMAC and SF-36, including its physical and mental health sum scores, were significantly higher in the non-LSD group, except for the WOMAC after 60 months.Conclusion: Owing to their crucial impact on hip function scores and health-related quality of life, it is recommended to consider LSDs preoperatively in studies dealing with the clinical outcome after THR. [ABSTRACT FROM AUTHOR]

The aim of the present wear simulator study was to assess the effect of steep acetabular cup positions on the wear propagation of highly cross-linked-PE (HX-PE) liners. Furthermore, a finite element analysis (FEA) was performed in order to calculate the stress within the HX-PE material in case of steep cup positions under physiological loadings. The higher stress in the HX-PE at a steep acetabular cup position did not result in increased wear in the present wear simulator study. The gravimetrical wear rates at normal (45°) and steep cup inclinations (75°) showed wear amounts of 3.15 ± 0.27 mg and 2.18 ± 0.31 mg per million cycles (p = 0.028), respectively. However, FEA revealed clear increase in stress at the HX-PE liners with respect to steep cup positions. [ABSTRACT FROM AUTHOR]

Treatment of large segmental bone defects, especially in load bearing areas, is a complex procedure in orthopedic surgery. The usage of additive manufacturing processes enables the creation of customized bone implants with arbitrary open-porous structure satisfying both the mechanical and the biological requirements for a sufficient bone ingrowth. Aim of the present numerical study was to optimize the geometrical parameters of open-porous titanium scaffolds to match the elastic properties of human cortical bone with respect to an adequate pore size. Three different scaffold designs (cubic, diagonal and pyramidal) were numerically investigated by using an optimization approach. Beam elements were used to create the lattice structures of the scaffolds. The design parameters strut diameter and pore size ranged from 0.2 to 1.5 mm and from 0 to 3.0 mm, respectively. In a first optimization step, the geometrical parameters were varied under uniaxial compression to obtain a structural modulus of 15 GPa (Young's modulus of cortical bone) and a pore size of 800 µm was aimed to enable cell ingrowth. Furthermore, the mechanical behavior of the optimized structures under bending and torsion was investigated. Results for bending modulus were between 9.0 and 14.5 GPa. In contrast, shear modulus was lowest for cubic and pyramidal design of approximately 1 GPa. Here, the diagonal design revealed a modulus of nearly 20 GPa. In a second step, large-sized bone scaffolds were created and placed in a biomechanical loading situation within a 30 mm segmental femoral defect, stabilized with an osteosynthesis plate and loaded with physiological muscle forces. Strut diameter for the 17 sections of each scaffold was optimized independently in order to match the biomechanical stability of intact bone. For each design, highest strut diameter was found at the dorsal/medial site of the defect and smallest strut diameter in the center. In conclusion, we demonstrated the possibility of providing optimized open-porous scaffolds for bone regeneration by considering both mechanical and biological aspects. Furthermore, the results revealed the need of the investigation and comparison of different load scenarios (compression, bending and torsion) as well as complex biomechanical loading for a profound characterization of different scaffold designs. The usage of a numerical optimization process was proven to be a feasible tool to reduce the amount of the required titanium material without influencing the biomechanical performance of the scaffold negatively. By using fully parameterized models, the optimization approach is adaptable to other scaffold designs and bone defect situations. [ABSTRACT FROM AUTHOR]

Abstract: Due to the prevalence of problems caused by wear particles, the reduced durability of total joint replacements is well documented. The characterization of wear debris enables the size and morphology of these wear particles to be measured and provides an assessment of the biological response in vivo. However, the impact of different methodologies of particle analysis is not yet clear. Hence, the aim of this investigation was to analyze the influence of different particle characterization methods performed by three research centers within the scope of a “round robin test”. To obtain knowledge about possible pitfalls, single steps of the particle characterization process (storage, pore size of the filter, coating durations by gold sputtering and scanning electron microscopy (SEM) magnification) were analyzed. The round robin test showed significant differences between the research groups, especially for the morphology of the particles. The SEM magnification was identified as having the greatest influence on the size and shape of the particles, followed by the storage conditions of the wear particle containing lubricant. Gold sputter coating and filter pore size also exhibit significant effects. However, even though they are statistically significant, it should be emphasized that the differences are small. In conclusion, particle characterization is a complex analytical method with a multiplicity of influencing factors. It becomes apparent that a comparison of wear particle results between different research groups is challenging. [Copyright &y& Elsevier]

Total knee replacement (TKR) is a successful procedure in orthopedic surgery. In order to further improve survival rates and obtain optimal clinical outcome with higher range of motion, improvements in fixation and wear couples as well as specific designs have been made. The worldwide circulation of ceramics in total hip replacement is justified through its extreme wear and corrosion resistance because of the excellent tribological properties and the absence of electrochemical reactions. Using these advantages, as well as finding a solution in cases of hypersensitivity against metallic implant materials, led to the development of total knee replacement systems with ceramic components. However, ceramic materials are brittle and less resistant especially to impact load in comparison to metallic implants. This requires components with sufficient thickness on the tibial side, which can lead to increased bone loss. In particular, this may lead to inadequate stability and dislocation of the joint line. Furthermore, the tribological behavior of an all-ceramic total knee, i.e. the femoral and tibial component as well as the insert, is not clearly investigated so far. Therefore, all-ceramic knee endoprostheses are not feasible at the moment. There is still a need for further development and adequate preclinical testing of all-ceramic implants. Major prerequisite should be the optimization of existing designs of the femoral ceramic component. [Copyright &y& Elsevier]

Total knee arthroplasty (TKA) has been developed into a safe and reliable procedure in orthopedic surgery. Nevertheless, in some cases, wear particles trigger the well-known cascade of osteolysis-inducing aseptic implant loosening. Furthermore, hypersensitivity to allergens such as chromium, cobalt, and nickel can lead to implant failure. These facts have led to a rising interest in research for solutions of alternative implant materials in TKA. The use of ceramics in total hip arthroplasty is based on excellent wear resistance and corrosion durability. These advantages have led to the development of a TKA system with a Biolox delta composite ceramic femoral component. In the present article, the clinical experience and radiological results of a 2-year follow-up in some standard and specific indications are presented. Furthermore, special features on intraoperative handling, advantages, as well as limitations in clinical application are demonstrated. [ABSTRACT FROM AUTHOR]

Ceramics have increasingly been used since the 1970s in total joint arthroplasty, providing constant improvements in material properties. Nowadays, different ceramics (alumina, zirconia, and new composite materials) are available as bearing surfaces. Ceramic materials offer reduced wear rates at articulating surfaces because of their excellent friction properties, which support longevity of endoprosthetic implants. In total hip arthroplasty, long-term clinical studies confirm the advantageous properties of ceramic materials providing low risk of implant failure. In total knee arthroplasty, ceramics revealed superior experimental data concerning low wear rates as well as promising results of the first clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: Invited international experts participated in a 2-day workshop organized by the European Society of Toxicologic Pathology (ESTP) to evaluate and discuss spontaneous and induced laryngeal lesions in rodents. The main purpose of the workshop was to agree upon the terminology and relevance of a range of laryngeal changes that varied from very subtle epithelial alterations up to severe metaplastic or neoplastic lesions. The workshop experts concluded that minimal, focal epithelial changes of the laryngeal epithelium, predominantly occurring at the base of the epiglottis, should be given the descriptive term of “epithelial alteration” and assessed as “non-adverse”. Although observed as induced effects they may also occur in non-treated animals and were not considered to have a potential for a laryngeal dysfunction. Also, cases of minimal to slight laryngeal squamous metaplasia that are not observed diffusely could occur spontaneously or as treatment-induced lesions and should be assessed as “non-adverse”. Cases of moderate to severe laryngeal squamous metaplasia observed diffusely in multiple levels should be regarded as “adverse”, as there is a potential for dysfunction of the larynx. The occurrence of dysplasia or cellular atypia linked to laryngeal squamous metaplasia should always be reported separately and described in detail. In the evaluation of treatment-related effects of the larynx in studies utilizing aged animals, it has to be considered that moderate or even severe cases of focal laryngeal squamous metaplasia may occasionally be found as age-related, spontaneous lesions. Although inhalation exposure of rodents to non-genotoxic compounds may cause laryngeal squamous metaplasia, none of the workshop experts were aware of any reported cases of tumor induction in the larynx with a non-genotoxic compound. Therefore, for non-genotoxic compounds, the workshop experts did not regard laryngeal squamous metaplasia by itself as a precancerous lesion. [Copyright &y& Elsevier]

Femoral bone loss due to stress and strain shielding is a common problem in hip resurfacing arthroplasty (HRA), which arises from the different stiffness of implant materials and the adjacent bone. Usually, the implants used in HRA are made of cobalt-chromium alloy (CoCr). As a novel concept, implants may also be made of ceramics, whose stiffness exceeds that of the adjacent bone by a multiple. Therefore, this computational study aimed to evaluate whether poly (ether-ether-ketone) (PEEK) or a hybrid material with a PEEK body and ceramic surface made of alumina toughened zirconia (ATZ) might be more suitable implant alternatives for HRA, as they can avoid stress and strain shielding. A reconstructed model of a human femur with an HRA implant was simulated, whereby the material of the HRA was varied between CoCr, ATZ, zirconia toughened alumina (ZTA), PEEK, and a hybrid PEEK-ATZ material. The implant fixation method also varied (cemented or cementless). The simulated models were compared with an intact model to analyze stress and strain distribution in the femoral head and neck. The strain distribution was evaluated at a total of 30,344 (cemented HRA) and 63,531 (uncemented HRA) nodes in the femoral head and neck region and divided into different strain regions (<400 µm/m: atrophy; 400–3000 μm/m: bone preserving and building; 3000–20,000 μm/m: yielding and >20,000 μm/m fracture). In addition, the mechanical stability of the implants was evaluated. When the material of the HRA implant was simulated as metal or ceramic while evaluating the strains, it was seen that around 22–26% of the analyzed nodes in the femoral head and neck were in an atrophic region, 47–51% were in a preserving or building region, and 27–28% were in a yielding region. In the case of PEEK implant, less than 0.5% of the analyzed nodes were in an atrophic region, 66–69% in a preserving or building region, and 31–34% in a yielding region. The fixation technique also had a small influence. When a hybrid HRA was simulated, the strains at the analyzed nodes depended on the thickness of the ceramic material. In conclusion, the material of the HRA implant was crucial in terms of stress and strain distribution in the adjacent bone. HRA made of PEEK or a hybrid material leads to decisively reduced stress and strain alteration compared to stiffer materials such as CoCr, ATZ, and ZTA. This confirms the potential for reduction in stress and strain shielding in the femoral head with the use of a hybrid material with a PEEK body for HRA. [ABSTRACT FROM AUTHOR]

For preclinical wear testing of total knee endoprostheses bovine serum as lubricant is recommended. Recent studies address the suitability of bovine serum as a lubricant due to its different properties compared to human synovial fluid. Therefore, wear tests according to ISO 14243 with synthetic synovial fluid vs. bovine serum as lubricants were performed in present study. The polyethylene inserts showed similar and typical wear patterns and products with both lubricants. However, higher wear rates were measured with synthetic synovial fluid as lubricant. In general, synthetic synovial fluid seems suitable for preclinical wear testing of total knee endoprostheses. • The wear rates of the polyethylene inserts were higher with synthetic synovial fluid as lubricant compared to bovine serum. • With synthetic synovial fluid, similar wear patterns and wear products were observed in comparison to retrievals. • The used synthetic synovial fluid showed biochemical stability over 500,000 load cycles. [ABSTRACT FROM AUTHOR]

Background: Stress shielding and nonphysiological load transfer after primary or revision total hip replacement (THR) prepare the ground for resorptive bone remodeling. The quality of the bone stock influences the risk of periprosthetic fractures and the severity of future revision surgeries. The question of whether or not bending stiffness and distal screw interlocking influence load transfer of a modular revision hip stem with a solid, hollow, and hollow-slotted stem extension led to the conception of this experimental study. The results were compared with a standard hip stem for primary THR. Methods: Revision stems were implanted in photoelastically coated composite femora. Cortical strain mapping was conducted before and after insertion of the implants under standardized loading conditions, considering the relevant muscle forces. Statistical analysis was based on a 95% confidence interval and a variance analysis for repeated measurements. Results: Significant stress shielding was observed after insertion of all types of hip stems compared with the intact femora. There was also a marked difference between strain alterations induced by standard and revision hip stems. With revision stems, the most distinct stress shielding effects were registered with the solid stem extension, particularly in the femoral diaphysis. Distal interlocking screws only had a local action on strain pattern and tended to enhance stress shielding at the midstem area when using the more flexible components. Conclusion: More flexible revision stems provide a cortical strain pattern of the femur closer to the preoperative status. This may reduce resorptive bone remodeling in the long term. However, any type of revision stem tested in this study caused higher stress shielding than the hip stem for primary THR, especially in the diaphyseal region medially and laterally. With sufficient proximal anchorage, the influence of distal interlocking screws on the femoral strain pattern was localized. [ABSTRACT FROM AUTHOR]

Background: In connection with technological advances in the manufacturing of medical ceramics, a newly developed ceramic femoral component was introduced in total knee arthroplasty. We generated an explicit finite-element-model to calculate the stresses developed under the highly dynamic intraoperative impaction with regard to cobalt–chromium and ceramic implant material as well as application of a silicone cover in order to reduce stress. Methods: The impaction was calculated with the hammer hitting the backside of the impactor at previously measured initial velocities. Subsequently the impactor, consisting of a steel handhold and a polyoxymethylene head, hit the femoral component. Instead of modelling femoral bone, the implant was mounted on four spring elements with spring constants previously determined in an experimental impaction model. The maximum principal stresses in the implants were evaluated at 8000 increments during the first 4ms of impact. Findings: The ceramic implant showed principal stresses 10% to 48% higher than the cobalt chromium femoral component. The simulation of a 5mm thick silicone layer between the impactor and the femoral component showed a strong decrease of vibration resulting in a reduction of 54% to 68% of the maximum stress amounts. The calculated amounts of principal stress were beneath the ultimate bending strengths of each material. Interpretation: Based on the results, intraoperative fracture of femoral components in total knee replacement may not be caused solely by impaction, but also by contributing geometrical factors such as inadequate preparation of the distal femur. In order to minimize the influence of impaction related stress peaks we recommend limiting the velocity as well as the weight of the impaction hammer when inserting femoral components. The silicone cover seems to deliver a strong decrease of implant stress and should be considered in surgery technique in the future. [Copyright &y& Elsevier]

[Display omitted] • Beta-tricalcium phosphate (β-TCP) and zirconia (ZrO 2) were used to produce biocompatible and force-stable bone scaffolds. • For the fabrication of bioceramic scaffolds, 3D printing was combined with Freeze Foaming to achieve sufficient porosity, mimicking cancellous bone. • Good cell viability was demonstrated for β-TCP foams and hybrid scaffolds made of β-TCP foam with β-TCP/ZrO 2 support structures. • Functionalization of the β-TCP foam with bone morphogenic protein 2 had no superior effect on the differentiation capacity of bone precursor cells in vitro. This study deals with synthetic biomaterials that are biocompatible and mechanically stable to serve as a potential bone graft for improved mandibular reconstruction. To fabricate novel hybrid scaffolds containing beta-tricalcium phosphate (β-TCP) and zirconia (ZrO 2), 3D printing was combined with Freeze Foaming to achieve a certain porosity, mimicking cancellous bone. The aim was to characterize the differentiation capacity of human pre-osteoblasts on the hybrid scaffolds. Although a good biocompatibility was demonstrated for the tested components of the hybrid scaffold, pure β-TCP foams showed the best results regarding osteogenic differentiation and pro-inflammatory processes. To enhance the osteoinductive properties of the β-TCP foam, the structures were also biofunctionalized with bone morphogenic protein 2 (BMP–2) and its effect was analyzed either on single cell cultures of pre-osteoblasts or pre-osteoblasts directly co-cultured with human peripheral blood mononuclear cells (PBMCs). The latter served to analyze the induction of bone remodelling processes. The immobilization of BMP-2 on scaffolds and its biological accessibility could be demonstrated, however, the biofunctionalization did not result in an enhanced differentiation capacity and bone remodeling processes of either pre-osteoblasts or directly co-cultured pre-osteoblasts and PBMCs. [ABSTRACT FROM AUTHOR]

Computational simulation of electrical bone stimulation of the electrical and dielectric parameters of osteoarthritic bone tissue is useful for an exact patient-individual adaptation of the bone models. Therefore, we investigated electrical and dielectric parameters at a frequency of 20 Hz of cancellous and subchondral human femoral head bone samples. Furthermore, the mechanical properties and the bone mineral density (BMD) were determined. Finally, these data were compared with the electrical and dielectric parameters. The bone samples were taken from patients with hip osteoarthritis. Electrical conductivity and dielectric permittivity of cancellous bone amounted to 0.043 S/m and 8.1⋅10 6 . BMD of the bone samples determined by dual-x-ray-absorptiometry (DXA) and ashing resulted in 193 ± 70 mg/cm² and 286 ± 59 mg/cm³ respectively. Structural modulus ( E S ) and ultimate compression strength ( σ max ) were measured with 227 ± 94 N/mm² and 6.5 ± 3.4 N/mm². No linear correlation of the electrical and dielectric parameters compared with BMD and mechanical properties of cancellous bone samples was found. Electrical conductivity and dielectric permittivity of subchondral bone resulted in 0.029 S/m and 8.97 × 10 6 . [ABSTRACT FROM AUTHOR]

[Display omitted] • This research focuses on the high hydrostatic pressure (HHP) technology which can be used for processing bone allografts. • The HHP treated bone alone mediates the differentiation of osteoclast progenitors to active osteoclasts. • The choice of the applied pressure influences the resorption rate in vitro although HHP does not damage bone microscopically. • The release of immunologically reactive species due to high HHP applications promotes the resorption. • For a conceivable clinical application , bone should be processed with pressures von 250 MPa. The present study focused on the investigation of the resorption behavior of high hydrostatic pressure (HHP) treated bone allografts in vitro by analyzing the differentiation and activity of osteoclast precursors. HHP is known to be an efficient method for devitalization of bone grafts and a gentle alternative compared to conventional processing. While bone resorption is part of the physiological fracture healing, highly processed allografts are prone to excessive degradation, which ultimately leads to graft failure. The influence of HHP treatment on the extent of resorption was analyzed in bone blocks cultivated with peripheral blood mononuclear cells (PBMCs). Data on gene and protein expression as well as histological alterations were obtained. The present study showed that an application of 500 MPa led to significant osteoclastic differentiation and activity which was observed already after 8 h of incubation. Whereas a treatment of 250 MPa resulted also in the differentiation of PBMCs, osteoclastic activity was similar to the untreated control. Thus, the pressure level of HHP is crucial for the extent of degradation processes. Based on our results a treatment with 500 MPa might not be suitable for allografts intended for subsequent clinical applications. This study provides a basis for further experiments including in vivo studies which should focus on the equilibrium of bone formation and bone resorption. [ABSTRACT FROM AUTHOR]

Open-porous titanium scaffolds for large segmental bone defects offer advantages like early weight-bearing and limited risk of implant failure. The objective of this experimental study was to determine the biomechanical behavior of novel open-porous titanium scaffolds with mechanical-adapted properties in vivo . Two types of the custom-made, open-porous scaffolds made of Ti6Al4V (Young's modulus: 6–8 GPa and different pore sizes) were implanted into a 20 mm segmental defect in the mid-diaphysis of the metatarsus of sheep, and were stabilized with an osteosynthesis plate. After 12 and 24 weeks postoperatively, torsional testing was performed on the implanted bone and compared to the contralateral non-treated side. Maximum torque, maximum angle, torsional stiffness, fracture energy, shear modulus and shear stress were investigated. Furthermore, bone mineral density (BMD) of the newly formed bone was determined. Mechanical loading capabilities for both scaffolds were similar and about 50% after 12 weeks (e.g., max. torque of approximately 20 Nm). A further increase after 24 weeks was found for most of the investigated parameters. Results for torsional stiffness and shear modulus as well as bone formation depended on the type of scaffold. Increased BMD after 24 weeks was found for one scaffold type but remained constant for the other one. The present data showed the capability of mechanically adapted open-porous titanium scaffolds to function as bone scaffolds for large segmental defects and the influence of the scaffold's stiffness. A further increase in the biomechanical stability can be assumed for longer observation periods of greater than six months. [ABSTRACT FROM AUTHOR]

Abstract: Tripolar systems have been implanted to reduce the risk of recurrent dislocation. However, there is little known about the dynamic behavior of tripolar hip endoprostheses under daily life conditions and achieved joint stability. Hence, the objective of this biomechanical study was to examine the in vivo dynamics and dislocation behavior of two types of tripolar systems compared to a standard total hip replacement (THR) with the same outer head diameter. Several load cases of daily life activities were applied to an eccentric and a concentric tripolar system by an industrial robot. During testing, the motion of the intermediate component was measured using a stereo camera system. Additionally, their behavior under different dislocation scenarios was investigated in comparison to a standard THR. For the eccentric tripolar system, the intermediate component demonstrated the shifting into moderate valgus-positions, regardless of the type of movement. This implant showed the highest resisting torque against dislocation in combination with a large range of motion. In contrast, the concentric tripolar system tended to remain in varus-positions and was primarily moved after stem contact. According to the results, eccentric tripolar systems can work well under in vivo conditions and increase hip joint stability in comparison to standard THRs. [Copyright &y& Elsevier]

Abstract: Precise diagnosis of loosening of endoprosthetic implants plays an important role in timely, adequate treatment. However, today's diagnostic tools, mainly radiological evaluation, do not yield satisfactory results. Therefore, a new approach based on the transmission of an internally generated combined acoustic and vibration signal, was investigated. For signal generation, a magnetic oscillator which impinges inside an implant component, can be used. The signal can be detected by an external accelerometer being positioned on the skin surface. Differences in the signal generated result from varying degrees of implant fixation. This principle was tested in seven porcine foreleg specimens with a custom implant. Influence of the measurement location at the porcine skin and different levels of fixation were investigated (pressfit, slight loosening, advanced loosening), with regard to the pull-out strength. Evaluation of different parameters, especially the frequency spectrum resulted in differences of up to 12% for the comparison between pressfit and slight loosening, and 30% between pressfit and advanced loosening. A significant correlation between the measured frequency and the pull-out strength for different levels of fixation was found. Thus, the novel diagnostic method shows potential for the precise detection of implant loosening. Further work is required to determine the sensitivity and specificity of the proposed system in animal experiments. [Copyright &y& Elsevier]

Abstract: Wear debris from endoprostheses leads to osteolysis and causes aseptic loosening. Cellular interactions with ultra-high-molecular-weight polyethylene (UHMW-PE) particles are rarely described because of the difficulty of incubation of adherent cells with floating polyethylene particles in vitro. The aim of this study was to develop a technique for analysing interactions of adherent cells with UHMW-PE particles in vitro. Therefore, different volumes of a wear particle suspension, generated in a standard hip wear simulator, were digested and filtered through polycarbonate filters. The filters were applied to cell culture inserts cultivated with human osteoblasts. Particle analysis resulted in a significant reduction of particle numbers in different suspension volumes. Exposure to the highest particle density resulted in a significant decrease of collagen 1 synthesis as well as a tendency for increasing matrix metalloproteinase-1 (MMP-1) production. Therefore, involvement of osteoblasts in matrix degradation due to wear debris can be assumed. [Copyright &y& Elsevier]

Abstract: Substantial evidence exists for the age-related decline in maximal strength and strength development. Despite the importance of knee extensor strength for physical function and mobility in the elderly, studies focusing on the underlying neuromuscular mechanisms of the quadriceps muscle weakness are limited. The aim of this study was to investigate the contributions of age-related neural and muscular changes in the quadriceps muscle to decreases in isometric maximal voluntary torque (iMVT) and explosive voluntary strength. The interpolated twitch technique and normalized surface electromyography (EMG) signal during iMVT were analyzed to assess changes in neural drive to the muscles of 15 young and 15 elderly volunteers. The maximal rate of torque development as well as rate of torque development, impulse and neuromuscular activation in the early phase of contraction were determined. Spinal excitability was estimated using the H reflex technique. Changes at the muscle level were evaluated by analyzing the contractile properties and lean mass. The age-related decrease in iMVT was accompanied by a decline in voluntary activation and normalized surface EMG amplitude. Mechanical parameters of explosive voluntary strength were reduced while the corresponding muscle activation remained primarily unchanged. The spinal excitability of the vastus medialis was not different while M wave latency was longer. Contractile properties and lean mass were reduced. In conclusion, the age-related decline in iMVT of the quadriceps muscle might be due to a reduced neural drive and changes in skeletal muscle properties. The decrease in explosive voluntary strength seemed to be more affected by muscular than by neural changes. [Copyright &y& Elsevier]

Abstract: Repairing large segmental defects in long bones caused by fracture, tumour or infection is still a challenging problem in orthopaedic surgery. Artificial materials, i.e. titanium and its alloys performed well in clinical applications, are plenary available, and can be manufactured in a wide range of scaffold designs. Although the mechanical properties are determined, studies about the biomechanical behaviour under physiological loading conditions are rare. The goal of our numerical study was to determine the suitability of open-porous titanium scaffolds to act as bone scaffolds. Hence, the mechanical stability of fourteen different scaffold designs was characterized under both axial compression and biomechanical loading within a large segmental distal femoral defect of 30mm. This defect was stabilized with an osteosynthesis plate and physiological hip reaction forces as well as additional muscle forces were implemented to the femoral bone. Material properties of titanium scaffolds were evaluated from experimental testing. Scaffold porosity was varied between 64 and 80%. Furthermore, the amount of material was reduced up to 50%. Uniaxial compression testing revealed a structural modulus for the scaffolds between 3.5GPa and 19.1GPa depending on porosity and material consumption. The biomechanical testing showed defect gap alterations between 0.03mm and 0.22mm for the applied scaffolds and 0.09mm for the intact bone. Our results revealed that minimizing the amount of material of the inner core has a smaller influence than increasing the porosity when the scaffolds are loaded under biomechanical loading. Furthermore, an advanced scaffold design was found acting similar as the intact bone. [Copyright &y& Elsevier]

Background: To increase the range of motion of total hip endoprostheses, prosthetic heads need to be enlarged, which implies that the cup and/or liner thickness must decrease. This may have negative effects on the wear rate, because the acetabular cups and liners could deform during press-fit implantation and hip joint loading. We compared the metal cup and polyethylene liner deformations that occurred when different wall thicknesses were used in order to evaluate the resulting changes in the clearance of the articulating region. Methods: A parametric finite element model utilized three cup and liner wall thicknesses to analyze cup and liner deformations after press-fit implantation into the pelvic bone. The resultant hip joint force during heel strike was applied while the femur was fixed, accounting for physiological muscle forces. The deformation behavior of the liner under joint loading was therefore assessed as a function of the head diameter and the resulting clearance. Results: Press-fit implantation showed diametral cup deformations of 0.096, 0.034, and 0.014 mm for cup wall thicknesses of 3, 5, and 7 mm, respectively. The largest deformations (average 0.084 ± 0.003 mm) of liners with thicknesses of 4, 6, and 8 mm occurred with the smallest cup wall thickness (3 mm). The smallest liner deformation (0.011 mm) was obtained with largest cup and liner wall thicknesses. Under joint loading, liner deformations in thin-walled acetabular cups (3 mm) reduced the initial clearance by about 50 %. Conclusion: Acetabular press-fit cups with wall thicknesses of ≤5 mm should only be used in combination with polyethylene liners >6 mm thick in order to minimize the reduction in clearance. [ABSTRACT FROM AUTHOR]

Abstract: At present, wear investigations of total hip replacements are performed in accordance with the ISO standard 14242, which is based on simplified kinematic and force data of the gait cycle. The aim of this analytical study was to generate parameter sets of daily life activities in order to replicate more realistic joint load situations in wear testing. Hence, published in vivo motion and force data of daily life activities were evaluated and adjusted using analytical techniques. The created kinematically and dynamically consistent parameter sets comprised time trajectories of three Cardan angles to describe the motion of the femur with respect to the pelvis and time trajectories of three force components, representing the hip joint contact force. The parameter sets include the activities of walking, knee bending, stair climbing and a combined load case of sitting down and standing up. Additionally, a motion sequence following the frequency of daily life activities was presented. Differences of the evaluated angular motions and joint contact forces in comparison to the ISO standard 14242-1 were pointed out. The results of this study offer the possibility to extend the kinematics and dynamics of the ISO standard test protocol and to support the loading conditions of hip wear simulators with a comprehensive set of motions and loads close to reality. [Copyright &y& Elsevier]

Abstract: Background: Abduction splints for the treatment of hip dysplasia normally operate on curbing the legs at the hip flexion and abduction. The forces are absorbed in different designs of shoulder straps and thus diverted to the shoulder and the spine. The present study is the first comparing these undesired forces of two spread orthoses and subsequently the transmitted forces to the infant''s spine. Methods: Between March 2009 and October 2009 the hips of 290 infants were investigated by ultrasound within the first 3days after birth. Thereof 20 infants with a hip dysplasia Graf type IIc, D or IIIa met our inclusion criteria and were investigated with a Tübinger and a Superior abduction splint. Biomechanical evaluation was performed by using a high-sensitive strain gauge sensor applied to the infant''s orthoses between pelvic harness and shoulder straps. Findings: The transmitted forces to the infant''s shoulders correlated significantly with their body mass (P <0.05). Maximal forces on the shoulder of the infants and subsequently transmitted forces on the spine were significantly higher (P <0.05) with the Tübinger splint (range 7.6N to 32.3N; arithmetic mean M: 13.7N) in comparison to the Superior orthosis (range 0.0N to 3.5N; M: 0.7N). Interpretation: The Superior orthosis works with primary load transmission to the pelvic bone. Using the Tübinger splint the shoulders of the newborn infants are loaded with a maximum of 93.9% of their body mass. This may influence the development of the growing infant''s spine. [Copyright &y& Elsevier]

Abstract: Instability of artificial joints is still one of the most prevalent reasons for revision surgery caused by various influencing factors. In order to investigate instability mechanisms such as dislocation under reproducible, physiologically realistic boundary conditions, a novel test approach is introduced by means of a hardware-in-the-loop (HiL) simulation involving a highly flexible mechatronic test system. In this work, the underlying concept and implementation of all required units is presented enabling comparable investigations of different total hip and knee replacements, respectively. The HiL joint simulator consists of two units: a physical setup composed of a six-axes industrial robot and a numerical multibody model running in real-time. Within the multibody model, the anatomical environment of the considered joint is represented such that the soft tissue response is accounted for during an instability event. Hence, the robot loads and moves the real implant components according to the information provided by the multibody model while transferring back the position and resisting moment recorded. Functionality of the simulator is proved by testing the underlying control principles, and verified by reproducing the dislocation process of a standard total hip replacement. HiL simulations provide a new biomechanical testing tool for analyzing different joint replacement systems with respect to their instability behavior under realistic movements and physiological load conditions. [Copyright &y& Elsevier]

Abstract: With regard to the growing potential of finite-element-analysis (FEA) in the field of orthopaedic biomechanics, we present an approach helping in the development of appropriate models of the implant-bone compound. The algorithm is based on computed-tomography data of the bone and accordant computer-aided-design (CAD) data of the implant and aims at predicting the bone strains and interface mechanics of the included parts. The developed algorithm was validated exemplary using an acetabular cup in combination with a left and a right fresh-frozen human hemipelvis. The strains under maximum loads during the gait cycle as well as the micromotion in the bone–implant interface were measured and compared to results from equivalent finite-element-analyses. Thereby, we found strong correlation between the calculated and measured principal strains with correlation coefficients of r 2 =0.94 (left side) and r 2 =0.86 (right side). A validation of micromotion was not possible due to limited accuracy of the motion tracking system. [Copyright &y& Elsevier]

The periprosthetic femoral fracture is one of the most severe complications after total hip arthroplasty and is associated with an increased mortality. The underlying causes and the patient- and implant-specific risk factors of periprosthetic femoral fractures remain insufficiently understood. The aim of this study was to gain a more profound understanding of the underlying fracture mechanisms and to provide experimental datasets for validation of computational models. Six cadaveric femurs were implanted with straight hip stems (Zweymueller design) and loaded until fracture reproducing the clinically relevant load cases stumbling and sideways fall. Displacements and the strain distribution on the surface of the femurs and implants, as well as the fracture load and implant subsidence were measured. For the load case stumbling the mean fracture load was 6743 N and two different mechanisms leading to fracture could be identified: high subsidence with low femoral bending and small subsidence with high femoral bending. For the load case sideways fall the mean fracture load was 1757 N and both tested femurs fractured due to a rotation of the hip stem around its own axis. The detailed datasets provided by this study can be used in future computational models. We demonstrated that the underlying fracture mechanisms of periprosthetic femoral fractures can be fundamentally different in the load case stumbling. The seating and exact position of the hip stem in the femur may correlate with implant subsidence and therefore lead to different types of fracture mechanisms resulting in different patient-specific fracture risks. • Early periprosthetic femoral fractures were experimentally reproduced. • Measurement of displacements, strains, stresses, fracture loads and subsidence. • Two fundamentally different fracture mechanisms could be observed during stumbling. [ABSTRACT FROM AUTHOR]

Abstract: Dislocation remains a serious complication of total hip replacement. An insufficient range of motion can lead to impingement of the prosthetic neck on the acetabular cup. Together with the initiation of subluxation and dislocation, recurrent impingement can cause material failure in the liner. The objective of this study was to generate a validated finite element (FE) model capable of predicting the dislocation stability of different femoral head sizes with regard to impingement in different implant positions as well as the corresponding stress distribution in the liner. In order to cover posterior and anterior dislocation, two total hip dislocation associated manoeuvres were simulated using a three-dimensional nonlinear finite element model. The dislocation stability of two head sizes was determined numerically and experimentally. After validation, the FE model was used to analyse the dislocation stability of four different head sizes in variable implant positions. Range of motion (ROM) until impingement, the resisting moment that was developed and ROM until dislocation were evaluated. Additionally, stress distribution within the polyethylene liner during impingement and subluxation was determined. For both dislocation modes, a cup position of 45° lateral abduction and 15° up to 30° anteversion resulted in appropriate ROM and dislocation stability. In general, larger head diameters revealed an increase in ROM and higher resisting moments. Stress analysis showed decreased contact pressures at the egress site of the liners with the larger inner diameters during subluxation. The analysis shows that an optimal implant position and a larger head diameter can reduce the risk of dislocation induced by impingement. The finite element model that was developed enables simplification of design variations compared to experimental studies since prototyping and assembling are replaced by prompt numerical simulation. [Copyright &y& Elsevier]

Cementless modular endoprostheses with tapered fluted stems cover a wide spectrum of femoral defects in reconstructive surgery of the hip. Nevertheless, for these hip stems the recommendations concerning the minimum diaphyseal anchorage distance differ widely. The present experimental study investigated the primary stability of a conical fluted revision stem depending on different types of femoral bone defects. Using six fresh frozen human femora, the relative movement of a bi-modular revision stem within the implant-bone interface was examined under cyclic loading conditions. Implant subsidence as well as micromotions at the bone-implant interface were captured with linear variable differential transformers for the intact femora and three different defects ranging from Paprosky type II to type IIIB. Compared to the intact femur, the infliction of a Paprosky type IIIB defect (3 cm of intact diaphysis) notably increased mean stem subsidence (13–389 μm per 500 load cycles; P = 0.116) but the mean interface micromotion vector sum remained unchanged (50 μm vs. 53 μm). In Paprosky IIIB defects the subsidence component resulting from rotation (horizontal plane) was significantly higher than with the intact femur and a Paprosky II defect (P ≤ 0.041). With optimal bone quality and ideal femur preparation a 3 cm conical fixation was sufficient to meet the set criteria of bony ingrowth in vitro. A conical fixation of 7 cm should be recommended to limit rotational subsidence, especially in case of impaired diaphyseal bone quality or expected difficulties with partial weight-bearing. • Relative bone-implant interface were recorded under dynamic loading conditions. • Progressive femoral defects were simulated to investigate the minimum anchorage. • Cementless fluted revision hip stems provided a high primary stability. • 3 cm of conical stem fixation could be sufficient only under optimum conditions • Combined axial and torsional loading is recommended for such in-vitro tests. [ABSTRACT FROM AUTHOR]