Abstract. Objectives. Young patients receiving metallic bone implants after surgical resection of bone cancer require implants that last into adulthood, and ideally life-long. Porous implants with similar stiffness to bone can promote bone ingrowth and thus beneficial clinical outcomes. A mechanical remodelling stimulus, strain energy density (SED), is thought to be the primary control variable of the process of bone growth into porous implants. The sequential process of bone growth needs to be taken into account to develop an accurate and validated bone remodelling algorithm, which can be employed to improve porous implant design and achieve better clinical outcomes. Methods. A bone remodelling algorithm was developed, incorporating the concept of bone connectivity (sequential growth of bone from existing bone) to make the algorithm more physiologically relevant. The algorithm includes adaptive elastic modulus based on apparent bone density, using a node-based model to simulate local remodelling variations while alleviating numerical checkerboard problems. Strain energy density (SED) incorporating stress and strain effects in all directions was used as the primary stimulus for bone remodelling. The simulations were developed to run in MATLAB interfacing with the commercial FEA software ABAQUS and Python. The algorithm was applied to predict bone ingrowth into a porous implant for comparison against data from a sheep model. Results. The accuracy of the predicted bone remodelling was verified for standard loading cases (bending, torsion) against analytical calculations. Good convergence was achieved. The algorithm predicted good bone remodelling and growth into the investigated porous implant. Using the standard algorithm without connectivity, bone started to remodel at locations unconnected to any bone, which is physiologically implausible. The implementation of bone connectivity ensures the gradual process of bone growth into the implant pores from the sides. The bone connectivity algorithm predicted that the full remodelling required more time (approximately 50% longer), which should be considered when developing post-surgical rehabilitation strategies for patients. Both algorithms with and without bone connectivity implementation converged to same final stiffness (less than 0.01% difference). Almost all nodes reached the same density value, with only a limited number of nodes (less than 1%) in transition areas with a strong density gradient having noticeable differences. Conclusions. An improved bone remodelling algorithm based on strain energy density that modelled the sequential process of bone growth has been developed and tested. For a porous metallic bone implant the same final bone density distribution as for the original adaptive elasticity theory was predicted, with a slower and more fidelic process of growth from existing surrounding bone into the porous implant. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Numerous papers present in-vivo knee kinematics data following total knee arthroplasty (TKA) from fluoroscopic testing. Comparing data is challenging given the large number of factors that potentially affect the reported kinematics. This paper aims at understanding the effect of following three different factors: implant geometry, performed activity and analysis method. A total of 30 patients who underwent TKA were included in this study. This group was subdivided in three equal groups: each group receiving a different type of posterior stabilized total knee prosthesis. During single-plane fluoroscopic analysis, each patient performed three activities: open chain flexion extension, closed chain squatting and chair-rising. The 2D fluoroscopic data were subsequently converted to 3D implant positions and used to evaluate the tibiofemoral contact points and landmark-based kinematic parameters. Significantly different anteroposterior translations and internal-external rotations were observed between the considered implants. In the lateral compartment, these differences only appeared after post-cam engagement. Comparing the activities, a significant more posterior position was observed for both the medial and lateral compartment in the closed chain activities during mid-flexion. A strong and significant correlation was found between the contact-points and landmarks-based analyses method. However, large individual variations were also observed, yielding a difference of up to 25% in anteroposterior position between both methods. In conclusion, all three evaluated factors significantly affect the obtained tibiofemoral kinematics. The individual implant design significantly affects the anteroposterior tibiofemoral position, internal-external rotation and timing of post-cam engagement. Both kinematics and post-cam engagement additionally depend on the activity investigated, with a more posterior position and associated higher patella lever arm for the closed chain activities. Attention should also be paid to the considered analysis method and associated kinematics definition: analyzing the tibiofemoral contact points potentially yields significantly different results compared to a landmark-based approach

Background. Finite element (FE) models have become a standard pre-clinical tool to study biomechanics of spine and are used to simulate and evaluate different strategies in scoliosis treatment: examine their efficacy as well as the effect of different implant design parameters. The goal of this study is to investigate, in a system of rods and laminar wires, the effect of the number of wires and their pre-stress on whole spine stiffness. Methods. A generic FE model was developed to represent a full human spine, including vertebrae, intervertebral discs, ligaments, facet and costovertebral joints, and ribcage. Intervertebral discs were modeled with 3D rebar elements with linear elastic material properties. Vertebrae, ribs, sternum, facet joints, cartilage and endplates were modeled with brick elements, and costal muscles with shell elements with linear elastic properties. Furthermore, ligaments were modeled with truss elements with nonlinear hypo-elastic properties. The spine model was instrumented from T7 to T12 with rods and wires modeled as titanium. Nonlinear contact properties were defined for rib neck-vertebra, transverse processes-rib and facet joint sets. The FE model was loaded in flexion and the whole spine instantaneous stiffness was calculated for different wire pre-stressing levels (0.1 to 2 MPa). Similar analyses were performed with changed numbers of wires and whole spine stiffness was calculated. Results. The results show that with increasing the pre-stress level the whole spine instantaneous stiffness increases by up to 6%. Reducing the number of wires decreases the whole spine stiffness almost linearly by 5%. These changes also alter center of rotation of the spine. The results suggest that pre-stressing and number of wires have an effect on whole spine stiffness. Conclusions. In summary, the develop FE model can be used to simulate different treatment strategies and to improve implant designs used in surgical treatment of scoliosis. Level of evidence. FEA study

Abstract. Objectives. Currently, total hip replacement surgery is an effective treatment for osteoarthritis, where the damaged hip joint is replaced with an artificial joint. Stress shielding is a mechanical phenomenon that refers to the reduction of bone density as a result of altered stresses acting on the host bone. Due to solid metallic nature and high stiffness of the current orthopaedic prostheses, surrounding bones undergo too much bone resorption secondary to stress shielding. With the use of 3D printing technology such as selective laser melting (SLM), it is now possible to produce porous graded microstructure hip stems to mimics the surrounding bone tissue properties. Method. In this study we have compared the physical and mechanical properties of two triply periodic minimal surface (TPMS) lattice structure namely gyroid and diamond TPMS. Based on initial investigations, it was decided to design, and 3D print the gyroid and diamond scaffolds having pore size of 800 and 1100 um respectively. Scaffold of each type of structure were manufactured and were tested mechanically in compression (n=8), tension (n=5) and bending (n=1). Results. Upon FEA validation of the scaffold in Abaqus, the desired scaffold for hip implant application was evaluated to have a young's modules of 12.15 GPa, yield strength of 242 MPa and porosity of 55%. Topology and lattice optimization were performed using nTopology to design an optimised graded porous hip implant based on stress shielding reduction. It was understood that the designed optimised hip implant can reduce the stress shielding effect by more than 65% when compared to the conventional generic implant. Conclusions. The designed hip implant presented in this work shows clinical promise in reducing bone loss while having enhanced osseointegration with the surrounding cortical bones. Hence, this will help reduce the risk of periprosthetic fracture and the probability of revision surgery

Total hip arthroplasty (THA) is one of the most successful surgery. However, patients' expectations have increased over the last two decades in regards to hip function after joint replacement, the patients assume to return their daily and sport activities without major limitations. This presentation will examine the effect of surgical approaches and implant designs as well as rehabilitation protocol on the clinical and biomechanical outcomes after THA. The new implant designs for THA aim to improve joint function whereas the surgical approaches intend to reduce muscle damage to regain muscle strength. One important determinant measured from gait analysis is the hip abduction moment as the abductors play a key role in stabilizing the pelvis in the frontal plane, particularly in phases of transition, such as the single leg stance in walking or stair climbing. This showed that muscle strength needs to be preserved. To minimize the risk of hip joint instability, a strong focus of implant development has been carried out. To illustrate this important concept within the context of gait analysis, I will present two studies that examine the influence of surgical approach and biomechanical reconstruction; and the second, is a prospective RCT comparing a dual mobility implant to a standard total hip replacement.

End-stage osteoarthritis is characterised by pain and reduced physical function, for which total knee arthroplasty (TKA) is recognised to be a highly effective treatment. Most implants are multi radius in design, though modern kinematic theory suggests a single flexion/extension axis is located in the femur. A recently launched TKA implant (Triathlon, Stryker US), is based on this theory, adopting a single radius of curvature femoral component. It is hypothesised that this design allows better function, and specifically, that it results in enhanced efficiency of the quadriceps group through a longer patello-femoral moment arm.

Change in power output was compared between single and multi radius implants as part of a larger ongoing randomised controlled trial to benchmark the new implant. Power output was assessed using a Leg Extensor Power Rig, well validated for use with this population, pre-operatively and at 6, 26 and 52 weeks post-operatively in 101 Triathlon and 82 Kinemax implants. All patients were diagnosed with osteoarthritis, and drawn from a single centre. Output was reported as maximal wattage (W) generated in a single leg extension, and expressed as a proportion of the contralateral limb power output to act as an internal control.

The results are shown in the table below. Two-way repeated measures ANOVA demonstrated a significant effect of TKA on the quadriceps power output, F = 249.09, p = <0.001 and also a significant interaction of the implant group on the output F = 11.33, p = 0.001. Independent samples t-tests of between group differences at the four assessment periods highlighted greater improvement in the single radius TKA group at all post-operative assessments (p <0.03), see table.

The theoretical enhanced quadriceps efficiency conferred by single radius design was found in this study. Power output was significantly greater at all post-operative assessments in the single radius compared to the multi radius group. This difference was particularly relevant at early 6 week and 1 year assessment. Lower limb power output is known to link positively to functional ability. The results support the hypothesis that TKAs with a single radius design have enhanced recovery and better function.

In severe cases of total knee arthroplasty which cannot be treated with off-the-shelf implants anymore custom-made knee implants may serve as one of the few remaining options to restore joint function or to prevent limb amputation. Custom-made implants are specifically designed and manufactured for one individual patient in a single-unit production, in which the surgeon is responsible for the implant design characteristics in consultation with the corresponding engineer. The mechanical performance of these custom-made implants is challenging to evaluate due to the unique design characteristics and the limited time until which the implant is needed. Nevertheless, the custom-made implant must comply with clinical and regulatory requirements. The design of custom-made implants is often based on a underlying reference implant with available biomechanical test results and well-known clinical performance. To support surgeons and engineers in their decision whether a specific implant design is suitable, a method is proposed to evaluate its mechanical performance. The method uses finite element analysis (FEA) and comprises six steps: (1) Identification of the main potential failure mechanism and its corresponding FEA quantity of interest. (2) Reproduction of the biomechanical test of the reference implant via FEA. (3) Identification of the maximum value of the corresponding FEA quantity of interest at the required load level. (4) Definition of this value as the acceptance criteria for the FEA of the custom-made implant. (5) Reproduction of the biomechanical test with the custom-made implant via FEA. (6) Conclusion whether the acceptance criteria is fulfilled or not. The method was applied to two exemplary cases of custom-made knee implants. The FEA acceptance criteria derived from the reference implants were fulfilled in both custom-made implants. Subsequent biomechanical tests verified the FEA results. This study suggests and applies a non-destructive and efficient method for pre-clinical testing of a single-unit custom-made knee implant to evaluate whether the design is mechanically suitable

Occlusal loading and muscle forces during mastication aids in assessment of dental restorations and implants and jaw implant design; however, three-dimensional bite forces cannot be measured with conventional transducers, which obstruct the native occlusion. The aim of this study was to combine accurate jaw kinematics measurements, together with subject-specific computational modelling, to estimate subject-specific occlusal loading and muscle forces during mastication. Motion experiments were performed on one male participant (age: 39yrs, weight: 82kg) with healthy dentition. Two low-profile magnetic sensors were fixed to the participant's teeth and the two dental arches digitised using an intra-oral scanner. The participant performed ten continuous of chewing on a polyurethane rubber sample of known material properties, followed by maximal compression (clenching). This was repeated at the molars, premolars of both the left and right sides, and central incisors. Jaw motion was simultaneously recorded from the sensors, and finite element modelling used to estimate bite force. Specifically, simulations of chewing and biting were performed by driving the model using the measured kinematics, and bite force magnitude and direction quantified. Muscle forces were then evaluated using a rigid-body musculoskeletal model of the patient's jaw. The first molars generated the largest bite forces during chewing (left: 309 N, right: 311 N) and maximum-force biting (left: 496 N, right: 495 N). The incisors generated the smallest bite forces during chewing (75 N) and maximum-force biting (114 N). The anterior temporalis and superficial masseter muscles had the largest contribution to maximum bite force, followed by the posterior temporalis and medial pterygoid muscles. This study presents a new method for estimating dynamic occlusal loading and muscle forces during mastication. These techniques provide new knowledge of jaw biomechanics, including muscle and occlusal loading, which will be useful in surgical planning and jaw implant design

Implant manufacturers develop new products to improve existing fracture fixation methods or to approach new fracture challenges. New implants are commonly tested and approved with respect to their corresponding predecessor products, because the knowledge about the internal forces and moments acting on implants in the human body is unclear. The aim of this study was to evaluate and validate implant internal forces and moments of a complex physiological loading case and translate this to a standard medical device approval test. A finite elements model for a transverse femur shaft fracture (AO/OTA type 32-B2) treated with a locked plate system (AxSOS 3 Ti Waisted Compression Plate Broad, Stryker, Kalamazoo, USA) was developed and experimentally validated. The fractured construct was physiologically loaded by resulting forces on the hip joint from previously measured in-vivo loading experiments (Bergmann et. al). The forces were reduced to a level where the material response in the construct remained linear elastic. Resulting forces, moments and stresses in the implant of the fractured model were analysed and compared to the manufacturers’ approval data. The FE-model accurately predicted the behaviour of the whole construct and the micro motion of the working length of the osteosynthesis. The resulting moment reaction in the working length was 24 Nm at a load of 400 N on the hip. The maximum principle strains on the locking plate were predicted well and did not exceed 1 %. In this study we presented a protocol by the example of locked plated femur shaft fracture to calculate and validate implant internal loading using finite element analysis of a complex loading. This might be a first step to move the basis of development of new implants from experience from previous products to calculation of mechanical behaviour of the implants and therefore, promote further optimization of the implants’ design

Prosthetic joint infection (PJI) is an important cause of arthroplasty failure. There is no method to disclose the presence or map the distribution of the in vivo biofilm on infected arthroplasty despite the recognition that such a tool would aid intraoperative decision making and improve novel implant design. The aim of this study was to test the efficacy of four dyes to disclose bacterial biofilm in an in vitro setting. Four dyes with known affinity to bacterial biofilm were assessed to determine their efficacy to disclose biofilms in an in vitro model of PJI. Three dyes (Methylene Blue, Indocyanine Green and Rose Bengal) have established clinical utility and the other, Thioflavin T, is known to fluoresce in the presence of amyloid a known biofilm constituent. The efficacy of the dyes to discriminate between biofilms of different mass and vitality (high, low or the non-inoculated control) was determined after three minutes exposure of the biofilm to the dyes by calculating the amount of dye bound to the biofilm via sonication and spectrophotometry, quantification of the dye through standardised photographic imaging of the stained biofilm and the calculation of inter-observer agreement. Each experiment was performed in triplicate for each dye and repeated three times. For each of the disclosure dyes assessed there was significant difference demonstrated between the amount of dye bound to the high and low mass biofilms (p<0.05) as well as in the amount of dye quantified in photographic and fluorescent image assessment between biofilms of differing mass (p<0.01). There was excellent agreement between three observers, for each disclosure dye, in determining the biofilm mass of each stained disc (Kappa>0.91). This study demonstrates the efficacy of biofilm disclosure dyes in an in vitro PJI model which could one day be used to disclose and map the clinical biofilm in vivo

Total temporomandibular joint (TMJ) replacements reduce pain and improve quality of life in patients suffering from end-stage TMJ disorders, such as osteoarthritis and trauma. Jaw kinematics measurements following TMJ arthroplasty provide a basis for evaluating implant performance and jaw function. The aim of this study is to provide the first measurements of three-dimensional kinematics of the jaw in patients following unilateral and bilateral prosthetic TMJ surgeries. Jaw motion tracking experiments were performed on 7 healthy control participants, 3 unilateral and 1 bilateral TMJ replacement patients. Custom-made mouthpieces were manufactured for each participant's mandibular and maxillary teeth, with each supporting three retroreflective markers anterior to the participant's lip line. Participants performed 15 trials each of maximum jaw opening, lateral and protrusive movements. Marker trajectories were simultaneously measured using an optoelectronic tracking system. Laser scans taken of each dental plate, together with CT scans of each patient, were used to register the plate position to each participant's jaw geometry, allowing 3D condylar motion to be quantified from the marker trajectories. The maximum mouth opening capacity of joint replacement patients was comparable to healthy controls with average incisal inferior translations of 37.5mm, 38.4mm and 33.6mm for the controls, unilateral and bilateral joint replacement patients respectively. During mouth opening the maximum anterior translation of prosthetic condyles was 2.4mm, compared to 10.6mm for controls. Prosthetic condyles had limited anterior motion compared to natural condyles, in unilateral patients this resulted in asymmetric opening and protrusive movements and the capacity to laterally move their jaw towards their pathological side only. For the bilateral patient, protrusive and lateral jaw movement capacity was minimal. Total TMJ replacement surgery facilitates normal mouth opening capacity and lateral and inferior condylar movements but limits anterior condylar motion. This study provides future direction for TMJ implant design

Total knee replacement (TKR) design aims to restore normal kinematics with emphasis on flexion range. The survivorship of a TKR is dependent on the kinematics in six-degrees-of-freedom (6-DoF). Stepping up, such as stair ascent is a kinematically demanding activity after TKR. The debate about design choice has not yet been informed by 6-DoF in vivo kinematics. This prospective randomised controlled trial (RCT) compared kneeling kinematics in three TKR designs. 68 participants were randomised to receive either cruciate retaining (CR-FB), rotating platform (CR-RP) or posterior stabilised (PS-FB) prostheses. Image quality was sufficient for 49 of these patients to be included in the final analysis following a minimum 1-year follow-up. Patients completed a step-up task while being imaged using single-plane fluoroscopy. Femoral and tibial computer-aided design (CAD) models for each of the TKR designs were registered to the fluoroscopic images using bespoke software OrthoVis to generate six-degree-of-freedom kinematics. Differences in kinematics between designs were compared as a function of flexion. There were no differences in terminal extension between the groups. The CR-FB was further posterior and the CR-RP was more externally rotated at terminal extension compared to the other designs. Furthermore, the CR-FB designs was more posteriorly positioned at each flexion angle compared to both other designs. Additionally, the CR-RP design had more external femoral rotation throughout flexion when compared with both fixed bearing designs. However, there were no differences in total rotation for either step-up or down. Visually, it appears there was substantial variability between participants in each group, indicating unique patient-specific movement patterns. While use of a specific implant design does influence some kinematic parameters, the overall patterns are similar. Furthermore, there is high variability indicating patient-specific kinematic patterns. At a group level, none of these designs appear to provide markedly different step-up kinematic patterns. This is important for patient expectations following surgery. Future work should aim to better understand the unique patient variability

Introduction and Objective. Kinematic Alignment (KA) is a surgical technique that restores the native knee alignment following Total Knee Arthroplasty (TKA). The association of this technique with a medial pivot implant design (MP) attempts to reestablish the physiological kinematics of the knee. Aim of this study is to analyze the clinical and radiological outcomes of patients undergoing MP-TKA with kinematic alignment, and to assess the effect of the limb alignment and the orientation of the tibial component on the clinical outcomes. Materials and Methods. We retrospectively analyzed 63 patients who underwent kinematic aligned medial pivot TKA from September 2018 to January 2020. Patient-Related Outcomes (PROMs) and radiological measures were collected at baseline, 3 months and 12 months after surgery. Results. We demonstrated a significant improvement in the clinical and functional outcomes starting from 3 months after surgery. This finding was also confirmed at the longest follow-up. The clinical improvement was independent from the limb alignment and from the orientation of the tibial component. The radiological analysis showed that the patient's native limb alignment was restored, and that the joint line orientation maintained the parallelism to the floor when standing. This latter result has a particular relevance, as it may positively influence the outcomes, reducing the risk of wear and mobilization of the implant. Conclusions. The association of kinematic alignment and a medial pivot TKA implant allows for a fast recovery, good clinical and functional outcomes, independently from the final limb alignment and the tibial component orientation

Introduction and Objective. Difficult primary total knee arthroplasty (TKA) and revision TKA are high demanding procedures. Joint exposure is the first issue to face off, in order to achieve a good result. Aim of this study is to evaluate the clinical and radiological outcomes of a series of patients, who underwent TKA and revision TKA, where tibial tubercle osteotomy (TTO) was performed. Materials and Methods. We retrospectively reviewed a cohort of 79 consecutives TKAs where TTO was performed, from our Institution registry. Patients were assessed clinically and radiographically at their last follow-up (mean, 7.4 ± 3.7 years). Clinical evaluation included the Knee Society Score (KSS), the pain visual analogue scale (VAS), and range of motion. Radiological assessment included the evaluation of radiolucent lines, osteolysis, cortical bone hypertrophy, time of bone healing of the TTO fragment, and the hardware complication. Results. KSS raised from 40.7 ± 3.1 to 75 ± 4.3 (p < 0.0001). Knee flexion increased from 78.7 ± 9.9° to 95.0 ± 9.5° (p < 0.0001), and VAS improved from 7.9 ± 0.9 to 3.8 ± 1 (p < 0.0001). No signs of loosening or evolutive radiolucency lineswere found. Osteolytic areas around the stem were detected. No significant association was found between the implant design and the outcomes, while aseptic loosening showed significantly better results. Complications were: 4 painful hardware, 3 late periprosthetic infections, 1 extension lag of 5°, and 3 flexion lag. Conclusions. Our experience suggests the use of TTO to improve the surgical approach in difficult primary TKA or revision TKA. A strict surgical technique leads to good results with low risk of complications

In the last years, 3d printing has progressively grown and it has reached a solid role in clinical practice. The main applications brought by 3d printing in orthopedic surgery are: preoperative planning, custom-made surgical guides, custom-made im- plants, surgical simulation, and bioprinting. The replica of the patient's anatomy, starting from the elaboration of medical volumetric images (CT, MRI, etc.), allows a progressive extremization of treatment personalization that could be tailored for every single patient. In complex cases, the generation of a 3d model of the patient's anatomy allows the surgeons to better understand the case — they can almost “touch the anatomy” —, to perform a more ac- curate preoperative planning and, in some cases, to perform device positioning before going to the surgical room (i.e. joint arthroplasty). 3d printing is also commonly used to produce surgical cutting guides, these guides are positioned intraoperatively on given landmarks to guide the surgeon to perform a specific surgical act (bone osteotomy, bone resection, implant position, etc.). In total knee arthroplasty, custom-made cutting guides have been developed to help the surgeon align the femoral and tibial components to the pre-arthritic condition with- out the use of the intramedullary femoral guide. 3d printed custom-made implants represent an emerging alternative to biological reconstructions especially after oncologic resection surgery or in case of complex arthroplasty revision surgery. Custom-made implants are designed to re- place the original shape and size of the patient's bone and they allow an extreme personalization of the treatment for every single patient. Patient-specific surgical simulation is a new frontier that promises great benefits for surgical training. a solid 3d model of the patient's anatomy can faithfully reproduce the surgical complexity of the patient and it allows to generate surgical simulators with increasing difficulty to adapt the difficulties of the course with the level of the trainees performing structured training paths: from the “simple” case to the “complex” case

Although 3D-printed porous dental implants may possess improved osseointegration potential, they must exhibit appropriate fatigue strength. Finite element analysis (FEA) has the potential to predict the fatigue life of implants and accelerate their development. This work aimed at developing and validating an FEA-based tool to predict the fatigue behavior of porous dental implants. Test samples mimicking dental implants were designed as 4.5 mm-diameter cylinders with a fully porous section around bone level. Three porosity levels (50%, 60% and 70%) and two unit cell types (Schwarz Primitive (SP) and Schwarz W (SW)) were combined to generate six designs that were split between calibration (60SP, 70SP, 60SW, 70SW) and validation (50SP, 50SW) sets. Twenty-eight samples per design were additively manufactured from titanium powder (Ti6Al4V). The samples were tested under bending compression loading (ISO 14801) monotonically (N=4/design) to determine ultimate load (F. ult. ) (Instron 5866) and cyclically at six load levels between 50% and 10% of F. ult. (N=4/design/load level) (DYNA5dent). Failure force results were fitted to F/F. ult. = a(N. f. ). b. (Eq1) with N. f. being the number of cycles to failure, to identify parameters a and b. The endurance limit (F. e. ) was evaluated at N. f. = 5M cycles. Finite element models were built to predict the yield load (F. yield. ) of each design. Combining a linear correlation between FEA-based F. yield. and experimental F. ult. with equation Eq1 enabled FEA-based prediction of F. e. . For all designs, F. e. was comprised between 10% (all four samples surviving) and 15% (at least one failure) of F. ult. The FEA-based tool predicted F. e. values of 11.7% and 12.0% of F. ult. for the validation sets of 50SP and 50SW, respectively. Thus, the developed FEA-based workflow could accurately predict endurance limit for different implant designs and therefore could be used in future to aid the development of novel porous implants. Acknowledgements: This study was funded by EU's Horizon 2020 grant No. 953128 (I-SMarD). We gratefully acknowledge the expert advice of Prof. Philippe Zysset

Modular hip prostheses were introduced to optimize the intra-surgical adaptation of the implant design to the native anatomy und biomechanics of the hip. The downside of a modular implant design with an additional modular interface is the potential susceptibility to fretting, crevice corrosion and wear. For testing hip implants with proximal femoral modularity according to ISO & ASTM, sodium chloride solutions are frequently used to determine the fatigue strength and durability of the stem-neck connection. The present study illustrate that the expansion of standard requirements of biomechanical testing is necessary to simulate metal ion release as well as fretting and crevice corrosion by using alternative test fluids. To assess the primary stability of tibial plateaus in vitro, different approaches had been undergone: cement penetration depth analysis, static tension or compression loading until interface failure. However, these test conditions do not reflect the in vivo physiologic loading modes, where the tibial plateau is predominantly subjected to combined compression and shear forces. The objectives were to evaluate the impact of the tibial keel & stem length on the primary stability of a posterior-stabilised tibial plateau under dynamic compression-shear loading conditions in human tibiae

Hip resurfacing arthroplasty (HRA) became a popular procedure in the early 90s because of the improved wear characteristic, preserving nature of the procedure and the optimal stability and range of motion. Concerns raised since 2004 when metal ions were seen in blood and urine of patients with a MoM implant. Design of the prosthesis, acetabular component malpositioning, contact-patch-to-rim distance (CPR) and a reduced joint size all seem to play a role in elevated metal ion concentrations. Little is known about the influence of physical activity (PA) on metal ion concentrations. Implant wear is thought to be a function of use and thus of patient activity levels. Wear of polyethylene acetabular bearings was positively correlated with patient's activity in previous studies. It is hypothesized that daily habitual physical activity of patients with a unilateral resurfacing prosthesis, measured by an activity monitor, is associated with habitual physical activity. A prospective, explorative study was conducted. Only patients with a unilateral hip resurfacing prosthesis and a follow-up of 10 ± 1 years were included. Metal ion concentrations were determined using ICP-MS. Habitual physical activity of subjects was measured in daily living using an acceleration-based activity monitor. Outcome consisted of quantitative and qualitative activity parameters. In total, 16 patients were included. 12 males (75%) and 4 females (25%) with a median age at surgery of 55.5 ± 9.7 years [43.0 – 67.9] and median follow-up of 9.9 ± 1.0 years [9.1 – 10.9]. The median cobalt and chromium ion concentrations were 25 ± 13 and 38 ± 28 nmol/L. A significant relationship, when adjusting for age at surgery, BMI, cup size and cup inclination, between sit-stand transfers (p = .034) and high intensity peaks (p = .001) with cobalt ion concentrations were found (linear regression analysis). This study showed that a high number of sit-stand transfers and a high number of high intensity peaks is significantly correlated with high metal ion concentrations, but results should be interpreted with care. For patients it seems save to engage in activities with low intensity peaks like walking or cycling without triggering critical wear or metal ions being able to achieve important general health benefits and quality of life, although the quality (high intensity peaks) of physical activity and behaviour of patients (sit-stand-transfers) seem to influence metal ion concentrations

Poor soft tissue balance in total knee arthroplasty (TKA) is one of the most primary causes of dissatisfaction and reduced joint longevity, which are associated with postoperative instability and early implant failure. 1. Therefore, surgical techniques, including mechanical instruments and 3-D guided navigation systems, in TKA aim to achieve optimum soft tissue balancing in the knee to improve postoperative outcome. 2. Patella-in-Place balancing (PIPB) is a novel technique which aims to restore native collateral ligament behaviour by preserving the original state without any release. Moreover, reduction of the joint laxity compensates for the loss of the visco-elastic properties of the cartilage and meniscus. Following its clinical success, we aimed to evaluate the impact of the PIPB technique on collateral ligament strain and laxity behaviour, with the hypothesis that PIPB would restore strains in the collateral ligaments. 3. . Eight fresh-frozen cadaveric legs were obtained (KU Leuven, Belgium, H019 2015-11-04) and CT images were acquired while rigid marker frames were affixed into the femur, and tibia for testing. After carefully removing the soft tissues around the knee joint, while preserving the joint capsule, ligaments, and tendons, digital extensometers (MTS, Minnesota, USA) were attached along the length of the superficial medial collateral ligament (MCL) and lateral collateral ligament (LCL). A handheld digital dynamometer (Mark-10, Copiague, USA) was used to apply an abduction or adduction moment of 10 Nm at fixed knee flexion angles of 0°, 30°, 60° and 90°. A motion capture system (Vicon Motion Systems, UK) was used to record the trajectories of the rigid marker frames while synchronized strain data was collected for MCL/LCL. All motion protocols were applied following TKA was performed using PIPB with a cruciate retaining implant (Stryker Triathlon, MI, USA). Furthermore, tibiofemoral kinematics were calculated. 4. and combined with the strain data. Postoperative tibial varus/valgus stresses and collateral ligament strains were compared to the native condition using the Wilcoxon Signed-Rank Test (p<0.05). Postoperative tibial valgus laxity was lower than the native condition for all flexion angles. Moreover, tibial valgus of TKA was significantly different than the native condition, except for 0° (p=0.32). Although, tibial varus laxity of TKA was lower than the native at all angles, significant difference was only found at 0° (p=0.03) and 90° (p=0.02). No significant differences were observed in postoperative collateral ligament strains, as compared to the native condition, for all flexion angles, except for MCL strain at 30° (p=0.02) and 60° (p=0.01). Results from this experimental study supported our hypotheses, barring MCL strain in mid-flexion, which might be associated with the implant design. Restored collateral ligament strains with reduced joint laxity, demonstrated by the PIPB technique in TKA in vitro, could potentially restore natural joint kinematics, thereby improving patient outcomes. In conclusion, to further prove the success of PIPB, further biomechanical studies are required to evaluate the success rate of PIPB technique in different implant designs

Understanding the long-term effects of total knee arthroplasty (TKA) on joint kinematics is vital to assess the success of the implant design and surgical procedure. However, while in vitro cadaveric studies quantifying post-operative biomechanics primarily reflect joint behaviour immediately after surgery,. 1. in vivo studies comprising of follow-up TKA patients often reflect joint behaviour a few months after surgery. 2. Therefore, the aim of this cadaveric study was to explore the long-term effects of TKA on tibiofemoral kinematics of a donor specimen, who had already undergone bilateral TKA, and compare them to post-operative kinematics reported in the literature. Two fresh-frozen lower limbs from a single donor (male, age: 83yr, ht: 1.83m, wt: 86kg), who had undergone bilateral TKA (Genesis II, Smith&Nephew, Memphis, USA) 19 years prior to his demise, were obtained following ethical approval from the KU Leuven institutional board. The specimens were imaged using computed tomography (CT) and tested in a validated knee simulator. 3. replicating active squatting and varus-valgus laxity tests. Tibiofemoral kinematics were recorded using an optical motion capture system and compared to various studies in the literature using the same implant – experimental studies based on cadaveric specimens (CAD). 1,4. and an artificial specimen (ART). 5. , and a computational study (COM). 6. . Maximum tibial abduction during laxity tests for the left leg (3.54°) was comparable to CAD (3.30°), while the right leg exhibited much larger joint laxity (8.52°). Both specimens exhibited valgus throughout squatting (left=2.03±0.57°, right=5.81±0.19°), with the change in tibial abduction over the range of flexion (left=1.89°, right=0.64°) comparable to literature (CAD=1.28°, COM=2.43°). The left leg was externally rotated (8.00±0.69°), while the right leg internally rotated (−15.35±1.50°), throughout squatting, with the change in tibial rotation over the range of flexion (left=2.61°, right=4.79°) comparable to literature (CAD=5.52°, COM=4.15°). Change in the femoral anteroposterior translation over the range of flexion during squatting for both specimens (left=14.88mm, right=6.76mm) was also comparable to literature (ART=13.40mm, COM=20.20mm). Although TKA was reportedly performed at the same time on both legs of the donor by the same surgeon, there was a stark difference in their post-operative joint kinematics. A larger extent of intraoperative collateral ligament release could be one of the potential reasons for higher post-operative joint laxity in the right leg. Relative changes in post-operative tibiofemoral kinematics over the range of squatting were similar to those reported in the literature. However, differences between absolute magnitudes of joint kinematics obtained in this study and findings from the literature could be attributed to different surgeons performing TKA, with presumable variations in alignment techniques and/or patient specific instrumentation, and the slightly dissimilar ranges of knee flexion during squatting. In conclusion, long-term kinematic effects of TKA quantified using in vitro testing were largely similar to the immediate post-operative kinematics reported in the literature; however, variation in the behaviour of two legs from the same donor suggested that intraoperative surgical alterations might have a greater effect on joint kinematics over time