Hinge screw or no hinge stabilization provides decreased stability compared to hinge plate in a biomechanical evaluation of distal femoral derotational osteotomies.

PURPOSE: Derotational distal femoral osteotomy (DFO) is the causal treatment for patients with femoral torsional deformity. The fixation is achieved by a unilateral angle-stable plate. Delayed- or non-unions are one of the main risks of the procedure. An additional contralateral fixation may benefit the outcome. Therefore, we hypothesize that primary stability in DFO can be improved by an additional fixation with a hinge screw or an internal plate. METHODS: Derotational DFO was performed in 15 knees and fixed either with an angle-stable plate only (group 'None'), with an additional lateral screw (group 'Screw') or with an additional lateral plate (group 'Plate'). Biomechanical evaluation was carried out under axial loading of 150 N (partial weight bearing) and 800 N (full weight bearing), followed by internal and external rotation. After linear axial loading in step 1, a cyclic torsional load of 5 Nm was applied under constant axial load in step 2. In step 3, the specimens were unloaded. Micromovements between the distal and proximal parts of the osteotomy were recorded at each step for all specimens. RESULTS: In step 1, the extent of micromovements was highest in group 'None' and lowest in group 'Plate' without being significantly different. In step 2, group 'Plate' showed significantly higher stability, reflected by less rotation and lower micromovements. Increasing the axial load from 150 to 800 N at step 2 resulted in increased stability in all groups but only reached significance in group 'None'. CONCLUSION: An additional contralateral plate significantly increased stability in derotational DFO compared to the unilateral angle-stable plate only. Contrary, a contralateral hinge screw did not provide improved stability. STUDY DESIGN: Experimental study. LEVEL OF EVIDENCE: IV.

The influence of surgical technique guidance and surgeon's experience on the femoral head assembly in total hip arthroplasty.

INTRODUCTION: The importance of the assembly procedure on the taper connection strength is evident. However, existent surgical technique guides frequently lack comprehensive and precise instructions in this regard. The aim of our experimental study was to evaluate the influence of the surgical technique guide on the femoral head assembly procedure in surgeons with differing levels of experience in total hip arthroplasty. MATERIALS AND METHODS: Twenty-eight participants, divided into four groups based on their lifetime experience in total hip arthroplasty, conducted a femoral head assembly procedure in a simulated intraoperative environment before and after reviewing the surgical technique guide. Demographic information and the number of hammer blows were documented. Hammer velocity and impaction angle were recorded using an optical motion capturing system, while the impaction force was measured using a dynamic force sensor within the impactor. RESULTS: We observed a high variation in the number of hammer blows, maximum force, and impaction angle. Overall, the number of hammer blows decreased significantly from 3 to 2.2 after reviewing the surgical technique guide. The only significant intragroup difference in the number of hammer blows was observed in the group with no prior experience in total hip arthroplasty. No correlation was found between individual factors (age, weight, height) or experience and the measured parameters (velocity, maximum force and angle). CONCLUSIONS: The present study demonstrated a high variation in the parameters of the femoral head assembly procedure. Consideration of the surgical technique guide was found to be a limited factor among participants with varying levels of experience in total hip arthroplasty. These findings underline the importance of sufficient preoperative training, to standardize the assembly procedure, including impaction force, angle, and use of instruments.

Quantitative analysis of trabecular bone tissue cryosections via a fully automated neural network-based approach.

Cryosectioning is known as a common and well-established histological method, due to its easy accessibility, speed, and cost efficiency. However, the creation of bone cryosections is especially difficult. In this study, a cryosectioning protocol for trabecular bone that offers a relatively cheap and undemanding alternative to paraffin or resin embedded sectioning was developed. Sections are stainable with common histological dying methods while maintaining sufficient quality to answer a variety of scientific questions. Furthermore, this study introduces an automated protocol for analysing such sections, enabling users to rapidly access a wide range of different stainings. Therefore, an automated 'QuPath' neural network-based image analysis protocol for histochemical analysis of trabecular bone samples was established, and compared to other automated approaches as well as manual analysis regarding scattering, quality, and reliability. This highly automated protocol can handle enormous amounts of image data with no significant differences in its results when compared with a manual method. Even though this method was applied specifically for bone tissue, it works for a wide variety of different tissues and scientific questions.

Impact of Structural Compliance of a Six Degree of Freedom Joint Simulator on Virtual Ligament Force Calculation in Total Knee Endoprosthesis Testing.

The AMTI VIVO™ six degree of freedom joint simulator allows reproducible preclinical testing of joint endoprostheses under specific kinematic and loading conditions. When testing total knee endoprosthesis, the articulating femoral and tibial components are each mounted on an actuator with two and four degrees of freedom, respectively. To approximate realistic physiological conditions with respect to soft tissues, the joint simulator features an integrated virtual ligament model that calculates the restoring forces of the ligament apparatus to be applied by the actuators. During joint motion, the locations of the ligament insertion points are calculated depending on both actuators' coordinates. In the present study, we demonstrate that unintended elastic deformations of the actuators due to the specifically high contact forces in the artificial knee joint have a considerable impact on the calculated ligament forces. This study aims to investigate the effect of this structural compliance on experimental results. While the built-in algorithm for calculating the ligament forces cannot be altered by the user, a reduction of the ligament force deviations due to the elastic deformations could be achieved by preloading the articulating implant components in the reference configuration. As a proof of concept, a knee flexion motion with varying ligament conditions was simulated on the VIVO simulator and compared to data derived from a musculoskeletal multibody model of a total knee endoprosthesis.

Multifunctional Hybrid Material for Endoprosthetic Implants Based on Alumina-Toughened Zirconia Ceramics and Additively Manufactured TiNbTa Alloys.

Aseptic implant loosening after a total joint replacement is partially influenced by material-specific factors when cobalt-chromium alloys are used, including osteolysis induced by wear and corrosion products and stress shielding. Here, we aim to characterize a hybrid material consisting of alumina-toughened zirconia (ATZ) ceramics and additively manufactured Ti-35Nb-6Ta (TiNbTa) alloys, which are joined by a glass solder. The structure of the joint, the static and fatigue shear strength, the influence of accelerated aging, and the cytotoxicity with human osteoblasts are characterized. Furthermore, the biomechanical properties of the functional demonstrators of a femoral component for total knee replacements are evaluated. The TiNbTa-ATZ specimens showed a homogenous joint with statistically distributed micro-pores and a slight accumulation of Al-rich compounds at the glass solder-TiNbTa interface. Shear strengths of 26.4 ± 4.2 MPa and 38.2 ± 14.4 MPa were achieved for the TiNbTa-ATZ and Ti-ATZ specimens, respectively, and they were not significantly affected by the titanium material used, nor by accelerated aging (p = 0.07). All of the specimens survived 107 cycles of shear loading to 10 MPa. Furthermore, the TiNbTa-ATZ did not impair the proliferation and metabolic activity of the human osteoblasts. Functional demonstrators made of TiNbTa-ATZ provided a maximum bearable extension-flexion moment of 40.7 ± 2.2 Nm. The biomechanical and biological properties of TiNbTa-ATZ demonstrate potential applications for endoprosthetic implants.

Influence of posterior cruciate ligament tension on tibiofemoral and patellofemoral joint contact mechanics in cruciate-retaining total knee replacement: a combined musculoskeletal multibody and finite-element simulation.

The influence of posterior cruciate ligament (PCL) tension on the clinical outcome of cruciate-retaining total knee replacement (CR-TKR) remains controversial. Various numerical approaches have been used to study this influence systematically, but the models used are limited by certain assumptions and simplifications. Therefore, the objective of this computational study was to develop a combined musculoskeletal multibody and finite-element simulation during a squat motion to 90° knee flexion with a CR-TKR design to overcome previous limitations regarding model inputs. In addition, different PCL tensions (tight, lax, resected) were modeled and the influence on tibiofemoral and resurfaced patellofemoral joint dynamics and contact stresses was evaluated. The effect of the PCL on knee joint dynamics and contact stresses was more pronounced at higher flexion angles. Tibiofemoral joint dynamics were influenced and a tight PCL induced increased posterior femoral translation during flexion. The maximum contact stress in the tibial insert increased from 20.6 MPa to 22.5 MPa for the resected and tightest PCL at 90° knee flexion. Patellofemoral joint dynamics were only slightly affected by PCL tension. However, the maximum contact stress in the patellar component decreased from 58.0 MPa to 53.7 MPa for the resected and tightest PCL at 90° knee flexion. The combination of musculoskeletal multibody and finite-element simulation is a sufficient method to comprehensively investigate knee joint dynamics and contact stresses in CR-TKR. The PCL tension after CR-TKR affects joint dynamics and contact stresses at the articulating implant surfaces.

Refixation of the anterior cruciate ligament: A biomechanical analysis of suture techniques in a porcine model.

Purpose: Refixation of acute anterior cruciate ligament (ACL) tears represents an increasingly popular treatment option. Systematic evaluations of various suture technique parameters are still pending. We therefore aimed to evaluate the mechanical pull-out outcomes of various suture methods for optimization of ACL refixation. Methods: Sixty fresh knees from mature domestic pigs were dissected and the femoral attachment of the ACL was peeled off. The 60 knees were divided in 10 groups and sutured as follows: (A) one suture (1, 2, 4 and 6 passes), (B) two sutures (2, 4 and 6 passes each; sutures knotted together as a loop) and (C) two sutures (2, 4 and 6 passes each, sutures knotted separately). The pull-out test was conducted using a validated electrodynamic testing machine. First occurrence of failure, maximum pull-out load and stiffness were measured. Suture failure was defined as pull-out of the ACL. Results: Two-point fixation, using two sutures, with at least two passes, showed the most favourable biomechanical stability. The maximum pull-out load was significantly higher with two sutures (529.5 N) used compared to one (310.4 N), p < 0.001. No significant differences were found for maximum pull-out loads between two-point fixation versus one-point fixation but stiffness was significantly higher with two-point fixation (107.4 N/mm vs. 79.4 N/mm, p < 0.001). More passes resulted in higher maximum pull-out loads. Conclusion: The results suggest using two independent sutures, refixed separately and at least two suture passes, is appropriate for ACL refixation. More suture passes provide additional strength but are technically challenging to achieve during surgery. Level of Evidence: Level IV.

Exploration of the Advanced VIVOTM Joint Simulator: An In-Depth Analysis of Opportunities and Limitations Demonstrated by the Artificial Knee Joint.

In biomechanical research, advanced joint simulators such as VIVOTM offer the ability to test artificial joints under realistic kinematics and load conditions. Furthermore, it promises to simplify testing with advanced control approaches and the ability to include virtual ligaments. However, the overall functionality concerning specific test setup conditions, such as the joint lubrication or control algorithm, has not been investigated in-depth so far. Therefore, the aim of this study was to analyse the basic functionality of the VIVOTM joint simulator with six degrees of freedom in order to highlight its capabilities and limitations when testing a total knee endoprostheses using a passive flexion-extension movement. For this, different test setup conditions were investigated, e.g., the control method, repeatability and kinematic reproducibility, waveform frequency, lubrication, and implant embedding. The features offered by the VIVOTM joint simulator are useful for testing joint endoprostheses under realistic loading scenarios. It was found that the results were highly influenced by the varying test setup conditions, although the same mechanical load case was analysed. This study highlights the difficulties encountered when using six degrees of freedom joint simulators, contributes to their understanding, and supports users of advanced joint simulators through functional and tribological analysis of joint endoprostheses.

Advanced Ti-Nb-Ta Alloys for Bone Implants with Improved Functionality.

The additive manufacturing of titanium-niobium-tantalum alloys with nominal chemical compositions Ti-xNb-6Ta (x = 20, 27, 35) by means of laser beam powder bed fusion is reported, and their potential as implant materials is elaborated by mechanical and biological characterization. The properties of dense specimens manufactured in different build orientations and of open porous Ti-20Nb-6Ta specimens are evaluated. Compression tests indicate that strength and elasticity are influenced by the chemical composition and build orientation. The minimum elasticity is always observed in the 90° orientation. It is lowest for Ti-20Nb-6Ta (43.2 ± 2.7 GPa) and can be further reduced to 8.1 ± 1.0 GPa for open porous specimens (p < 0.001). Furthermore, human osteoblasts are cultivated for 7 and 14 days on as-printed specimens and their biological response is compared to that of Ti-6Al-4V. Build orientation and cultivation time significantly affect the gene expression profile of osteogenic differentiation markers. Incomplete cell spreading is observed in specimens manufactured in 0° build orientation, whereas widely stretched cells are observed in 90° build orientation, i.e., parallel to the build direction. Compared to Ti-6Al-4V, Ti-Nb-Ta specimens promote improved osteogenesis and reduce the induction of inflammation. Accordingly, Ti-xNb-6Ta alloys have favorable mechanical and biological properties with great potential for application in orthopedic implants.

Systematic enhancement of microbial decontamination efficiency in bone graft processing by means of high hydrostatic pressure using Escherichia coli as a model organism.

To obtain bone allografts that are safe for transplantation, several processing steps for decellularization and decontamination have to be applied. Currently available processing methods, although well-established, may interfere with the biomechanical properties of the bone. High hydrostatic pressure (HHP) is known to devitalize tissues effectively while leaving the extracellular matrix intact. However, little is known about the inactivation of the contaminating microorganisms by HHP. This study aims to investigate the ability of high-pressure decontamination and to establish a treatment protocol that is able to successfully inactivate microorganisms with the final goal to sterilize bone specimens. Using Escherichia coli (E. coli) as a model organism, HHP treatment parameters like temperature and duration, pressurization medium, and the number of treatment cycles were systematically adjusted to maximize the efficiency of inactivating logarithmic and stationary phase bacteria. Towards that we quantified colony-forming units (cfu) after treatment and investigated morphological changes via Field Emission Scanning Electron Microscopy (FESEM). Additionally, we tested the decontamination efficiency of HHP in bovine cancellous bone blocks that were contaminated with bacteria. Finally, two further model organisms were evaluated, namely Pseudomonas fluorescens as a Gram-negative microorganism and Micrococcus luteus as a Gram-positive representative. A HHP protocol, using 350 MPa, was able to sterilize a suspension of stationary phase E. coli, leading to a logarithmic reduction factor (log RF) of at least -7.99 (±0.43). The decontamination of bone blocks was less successful, indicating a protective effect of the surrounding tissue. Sterilization of 100% of the samples was achieved when a protocol optimized in terms of treatment temperature, duration, pressurization medium, and number and/or interval of cycles, respectively, was applied to bone blocks artificially contaminated with a suspension containing 104 cfu/mL. Hence, we here successfully established protocols for inactivating Gram-negative model microorganisms by HHP of up to 350 MPa, while pressure levels of 600 MPa were needed to inactivate the Gram-positive model organism. Thus, this study provides a basis for further investigations on different pathogenic bacteria that could enable the use of HHP in the decontamination of bone grafts intended for transplantation.

Isolation of TiNbN wear particles from a coated metal-on-metal bearing: Morphological characterization and in vitro evaluation of cytotoxicity in human osteoblasts.

To improve the wear resistance of articulating metallic joint endoprostheses, the surfaces can be coated with titanium niobium nitride (TiNbN). Under poor tribological conditions or malalignment, wear can occur on these implant surfaces in situ. This study investigated the biological response of human osteoblasts to wear particles generated from TiNbN-coated hip implants. Abrasive particles were generated in a hip simulator according to ISO 14242-1/-2 and extracted with Proteinase K. Particle characteristics were evaluated by electron microscopy and energy dispersive x-ray spectroscopy (EDS), inductively coupled plasma mass spectrometry (ICP-MS) and dynamic light scattering (DLS) measurements. Human osteoblasts were exposed to different particle dilutions (1:20, 1:50, and 1:100), and cell viability and gene expression levels of osteogenic markers and inflammatory mediators were analyzed after 4 and 7 days. Using ICP-MS, EDS, and DLS measurements, ~70% of the particles were identified as TiNbN, ranging from 39 to 94 nm. The particles exhibited a flat and subangular morphology. Exposure to particles did not influence cell viability and osteoblastic differentiation capacity. Protein levels of collagen type 1, osteoprotegerin, and receptor activator of nuclear factor κB ligand were almost unaffected. Moreover, the pro-inflammatory response via interleukins 6 and 8 was minor induced after particle contact. A high number of TiNbN wear particles only slightly affected osteoblasts' differentiation ability and inflammatory response compared to metallic particles. Nevertheless, further studies should investigate the role of these particles in peri-implant bone tissue, especially concerning other cell types.

Computer-based analysis of the taper connection strength of different revision head and adapter sleeve designs.

OBJECTIVES: Ceramic revision heads, equipped with titanium adapter sleeves, are used in femoral head revision in total hip arthroplasty to avoid ceramic fracture due to the damaged taper. METHODS: A finite element analysis of the taper connection strength of revision heads with varying head diameters combined with adapter sleeves of different lengths was conducted. The influence of various assembly forces, head diameter, and length of the adapter sleeves was evaluated. For two combinations, the pattern of contact pressure was evaluated when applying a simplified joint load (3 kN, 45° load angle). Experimental validation was conducted with 36 mm heads and adapter sleeves in size S, as well as 28 mm heads and adapter sleeves in size XL. RESULTS: The pull-off force increased with higher assembly forces. Using larger head diameters and adapter sleeves led to decreased pull-off forces, a reduced contact surface, and less contact pressure. The contact pressure showed significant peaks and a diagonal pattern under 45° angle loading when assembly forces were less than 4 kN, and larger adapter sleeves were utilized. CONCLUSION: A sufficient assembly force should be ensured intraoperatively, especially with an increasing head diameter and adapter sleeve size, as lower assembly forces might lead to reduced taper connection strength.

Establishing safe high hydrostatic pressure devitalization thresholds for autologous head and neck cancer vaccination and reconstruction.

High hydrostatic pressure specifically devitalizes cells and tissues without major changes in their molecular structure. Hence, high hydrostatic pressure may enhance the development of whole-cell anti-tumor vaccines, representing tumor heterogeneity and thus (neo-) antigen diversity. Moreover, safe devitalization of tumor-infiltrated supporting tissue may facilitate reimplantation for functional reconstruction. However, precise high hydrostatic pressure thresholds for safe cancer cell killing are unknown. Here, we show that high hydrostatic pressure of at least 450 MPa is necessary to safely devitalize head and neck squamous cell cancer. A pressure of 300 MPa, which has been used frequently in cancer vaccine preparation, resulted in partial devitalization with 27% live cells in flow cytometry and 4% remaining autofluorescence in cell culture after one week. The remaining cells could form vital tumors in the chorioallantoic membrane assay. In contrast, 450 MPa killed all cells in vitro and prevented tumor outgrowth in ovo. The effectiveness of 450 MPa was attributed to the induction of DNA double-strand breaks, independent of apoptosis, autophagy, or methuosis. Furthermore, 450 MPa continued to induce immunogenic cell death. Our results demonstrate that 450 MPa of high hydrostatic pressure induces safe and sustained devitalization of head and neck cancer cells and tissues. Because of the heterogeneity in pressure resistance, we propose our approach as a starting point for determining the precise thresholds for other cancer entities. Further studies on head and neck cancer should focus on immunological co-cultures, combinations of immune checkpoint inhibition, and accurate anatomical reconstruction with pressure-treated autografts.

Pre-clinical characterization of a novel flexible surface stem design for total knee replacements.

Primary stability is crucial for implant osseointegration and the long-term stability of cementless total joint replacements. Biomechanical studies have shown the potential of femoral stems for total knee replacements to reduce micromotions at the bone-implant interface. However, approaches such as focusing on the structural elasticity of the femoral stems are rarely described. Three groups with different femoral stem designs were investigated: group 1: flexible surface stem, group 2: flexible surface stem with open-porous structured lamellas, and group 3: solid stem (reference). The stems were implanted into bone substitute material and dynamically loaded for 1000 cycles. Relative movement and subsidence were measured optically, and axial pull-out forces were determined after dynamic testing. Relative movements increased to 0.10 mm (groups 1 and 2) compared to 0.03 mm (group 3). Subsidence increased to 0.08 mm (group 1) and 0.11 mm (group 2) compared to 0.06 mm (group 3). For each group, subsidence mainly occurred during the first 500 cycles. A similar convergence was observed in the further course. Pull-out forces increased to 1815.0 N (group 1) and 1347.1 N (group 2) compared to 1306.4 N (group 3). The flexible surface stem design resulted in higher relative movements and subsidence, but also exhibited increased pull-out forces. The relative movements were below the critical limit of 0.15 mm and represent a superposition of the elastic deformations of the interacting implant components as well as the micromotion at the bone-implant interface. Therefore, the novel flexible surface stem design appears to offer promising primary implant fixation.

Corrosion Products from Metallic Implants Induce ROS and Cell Death in Human Motoneurons In Vitro.

Due to advances in surgical procedures and the biocompatibility of materials used in total joint replacement, more and younger patients are undergoing these procedures. Although state-of-the-art joint replacements can last 20 years or longer, wear and corrosion is still a major risk for implant failure, and patients with these implants are exposed for longer to these corrosive products. It is therefore important to investigate the potential effects on the whole organism. Released nanoparticles and ions derived from commonly used metal implants consist, among others, of cobalt, nickel, and chromium. The effect of these metallic products in the process of osteolysis and aseptic implant loosening has already been studied; however, the systemic effect on other cell types, including neurons, remains elusive. To this end, we used human iPSC-derived motoneurons to investigate the effects of metal ions on human neurons. We treated human motoneurons with ion concentrations regularly found in patients, stained them with MitoSOX and propidium iodide, and analyzed them with fluorescence-assisted cell sorting (FACS). We found that upon treatment human motoneurons suffered from the formation of ROS and subsequently died. These effects were most prominent in motoneurons treated with 500 µM of cobalt or nickel, in which we observed significant cell death, whereas chromium showed fewer ROS and no apparent impairment of motoneurons. Our results show that the wear and corrosive products of metal implants at concentrations readily available in peri-implant tissues induced ROS and subsequently cell death in an iPSC-derived motoneuron cell model. We therefore conclude that monitoring of neuronal impairment is important in patients undergoing total joint replacement.

IL-6-induced response of human osteoblasts from patients with rheumatoid arthritis after inhibition of the signaling pathway.

Interleukin (IL-) 6 is a critical factor in inflammatory processes of rheumatoid arthritis (RA). This is of high interest as the progression of RA may lead to the implantation of joint endoprostheses, which is associated with a pro-inflammatory increase in IL-6 in the periprosthetic tissue. Biological agents such as sarilumab have been developed to inhibit IL-6-mediated signaling. However, IL-6 signaling blockade should consider the inhibition of inflammatory processes and the regenerative functions of IL-6. This in vitro study investigated whether inhibiting IL-6 receptors can affect the differentiation of osteoblasts isolated from patients with RA. Since wear particles can be generated at the articular surfaces of endoprostheses leading to osteolysis and implant loosening, the potential of sarilumab to inhibit wear particle-induced pro-inflammatory processes should be investigated. Both in monocultures and indirect co-cultures with osteoclast-like cells (OLCs), human osteoblasts were stimulated with 50 ng/mL each of IL-6 + sIL-6R and in combination with sarilumab (250 nM) to characterize cell viability and osteogenic differentiation capacity. Furthermore, the influence of IL-6 + sIL-6R or sarilumab on viability, differentiation, and inflammation was evaluated in osteoblasts exposed to particles. Stimulation with IL-6 + sIL-6R and sarilumab did not affect cell viability. Except for the significant induction of RUNX2 mRNA by IL-6 + sIL-6R and a significant reduction with sarilumab, no effects on cell differentiation and mineralization could be detected. Furthermore, the different stimulations did not affect the osteogenic and osteoclastic differentiation of co-cultured cells. Compared to the osteoblastic monocultures, a decreased release of IL-8 was triggered in the co-culture. Among these, treatment with sarilumab alone resulted in the greatest reduction of IL-8. The co-culture also showed clearly increased OPN concentrations than the respective monocultures, with OPN secretion apparently triggered by the OLCs. Particle exposure demonstrated decreased osteogenic differentiation using different treatment strategies. However, sarilumab administration caused a trend toward a decrease in IL-8 production after stimulation with IL-6 + sIL-6R. The blockade of IL-6 and its pathway have no significant effect on the osteogenic and osteoclastic differentiation of bone cells derived from patients with RA. Nonetheless, observed effects on the reduced IL-8 secretion need further investigation.

Do hip resurfacing and short hip stem arthroplasties differ from conventional hip stem replacement regarding impingement-free range of motion?

Total hip joint replacement (THR) is clinically well-established. In this context, the resulting range of motion (ROM) is crucial for patient satisfaction when performing joint movements. However, the ROM for THR with different bone preserving strategies (short hip stem and hip resurfacing) raises the question of whether the ROM is comparable with conventional hip stems. Therefore, this computer-based study aimed to investigate the ROM and type of impingement for different implant systems. An established framework with computer-aided design 3D models based on magnetic resonance imaging data of 19 patients with hip osteoarthritis was used to analyse the ROM for three different implant systems (conventional hip stem vs. short hip stem vs. hip resurfacing) during typical joint movements. Our results revealed that all three designs led to mean maximum flexion higher than 110°. However, hip resurfacing showed less ROM (-5% against conventional and -6% against short hip stem). No significant differences were observed between the conventional and short hip stem during maximum flexion and internal rotation. Contrarily, a significant difference was detected between the conventional hip stem and hip resurfacing during internal rotation (p = 0.003). The ROM of the hip resurfacing was lower than the conventional and short hip stem during all three movements. Furthermore, hip resurfacing shifted the impingement type to implant-to-bone impingement compared with the other implant designs. The calculated ROMs of the implant systems achieved physiological levels during maximum flexion and internal rotation. However, bone impingement was more likely during internal rotation with increasing bone preservation. Despite the larger head diameter of hip resurfacing, the ROM examined was substantially lower than that of conventional and short hip stem.

Osteogenic differentiation of mesenchymal stem cells cultured on allogenic trabecular bone grafts treated with high hydrostatic pressure.

The requirements for bone substitute materials are multifaceted. Beside biomechanical stability, these materials should provide osteoconductive and osteoinductive properties to promote integration into the host tissue. So far, autologous bone is the only material, which combines all properties, but is naturally limited. Allogenic bone grafts have to be decellularized prior to implantation. This causes the reduction of biomechanical properties and the loss of osteoinductive qualities. High hydrostatic pressure (HHP) offers a gentle alternative for processing and supply of allogenic bone substitute materials while preserving biomechanical integrity. To determine whether osteogenic properties are retained by HHP treatment, mesenchymal stem cells (MSCs) were cultured with HHP-treated and untreated allogenic trabecular bone blocks up to 28 days. Both, gene expression and protein analysis showed that HHP-treated bone positively influenced differentiation of MSCs into osteoblasts and mineralization of bone matrix. This effect was greater in samples cultivated with HHP-treated bone blocks. The present study shows that HHP treatment does not result in the reduction of osteoinductivity, thus serving as an alternative approach for processing allogeneic bone substitute materials.

Combining Electrostimulation with Impedance Sensing to Promote and Track Osteogenesis within a Titanium Implant.

(1) Background: Electrical stimulation is a promising alternative to promote bone fracture healing but with the limitation of tracking the osteogenesis progress in vivo. To overcome this issue, we present an opportunity to combine the electrical stimulation of a commercial titanium implant, which promotes osteogenesis within the fracture, with a real-time readout of the osteogenic progress by impedance sensing. This makes it possible to adjust the electrical stimulation modalities to the individual patient's fracture healing process. (2) Methods: In detail, osteogenic differentiation of several cell types was monitored under continuous or pulsatile electrical stimulation at 0.7 V AC/20 Hz for at least seven days on a titanium implant by electric cell-substrate impedance sensing (ECIS). For control, chemical induction of osteogenic differentiation was induced. (3) Results: The most significant challenge was to discriminate impedance changes caused by proliferation events from those initiated by osteogenic differentiation. This discrimination was achieved by remodeling the impedance parameter Alpha (α), which increases over time for pulsatile electrically stimulated stem cells. Boosted α-values were accompanied by an increased formation of actin stress fibers and a reduced expression of the focal adhesion kinase in the cell periphery; morphological alterations known to occur during osteogenesis. (4) Conclusions: This work provided the basis for developing an effective fracture therapy device, which can induce osteogenesis on the one hand, and would allow us to monitor the induction process on the other hand.

The effect of a digital-assisted group rehabilitation on clinical and functional outcomes after total hip and knee arthroplasty-a prospective randomized controlled pilot study.

BACKGROUND: The rising number of total hip and knee arthroplasties and the decreasing availability of physiotherapists require clinically and economically effective rehabilitation approaches. Therefore, the present pilot study investigated the effect of a novel digital-assisted individualized group rehabilitation program on clinical and functional outcomes after total hip and knee arthroplasty. METHODS: In this randomized controlled pilot study, 26 patients undergoing total knee or hip replacement were randomly assigned to either the intervention group (IG, novel digital-assisted group therapy) or the control group (CG, standard postoperative physiotherapy currently carried out in Germany). The IG received the novel digital-assisted group therapy twice per week for a six-months period, while the CG received individual outpatient therapy depending on the prescription of the supervising physician. The number of therapy sessions was recorded. Moreover, subjective outcomes (EuroQol-5Dimensions (EQ-5D) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)), functional outcome (30 s sit to stand test and timed up and go test (TUG)), as well as gait parameters were quantified preoperatively as well as at three and six months after surgery. Data were analyzed using an analysis of covariance with baseline-adjustment. RESULTS: No patient-reported falls, pain, and hospital readmissions were recorded. On average, the IG received more therapy sessions. The clinical and functional outcomes were mainly not significantly different between groups at three- and six-months follow-up, but medium to large effect sizes for the differences in quality of life (EQ-5D) as well as pain, stiffness, and physical function (WOMAC), and TUG performance were observed in favor of the IG. However, the IG showed a higher variability of gait velocity after total joint replacement. CONCLUSION: The digital-assisted rehabilitation had positive effects on quality of life, pain, stiffness, physical function, and TUG performance. Nevertheless, the therapy concept may be improved by adding exercises focusing on gait performance to reduce gait variability. The results indicate that the digital-assisted therapy concept is effective and safe. Therefore, a consecutive full-scaled randomized controlled clinical trial is recommended. TRIAL REGISTRATION: This study was retrospectively registered on 14/02/2022 in the German Clinical Trial Register (DRKS00027960).