Bone-stem Interface Research Articles

Enhancing the fretting damage resistance of suspension plasma sprayed hydroxyapatite coating with Titania addition

The damage of the bioactive HAp ceramic coatings on titanium implants and debris generated at the implant stem-bone interface is a major concern as it causes osteolysis, metallosis, and loosening of implants. Attempts are made to develop strong and wear-resistant biocompatible HAp coatings through the addition of different ceramics and with better coating processes. The addition of titania to HAp was found to strengthen the coating, and this paper reports the fretting wear resistance of titania-added HAp suspension plasma spray coating. Expected micro motion between the stem–bone interface in the implants due to applied loads is estimated using numerical simulations. The fretting wear resistance of the titania-added coating was evaluated using the simulated ball-on-flat contacts. The titania-added HAp suspension plasma spray-coated samples exhibited reduced fretting friction coefficient and increased wear resistance. High hardness and modulus of the 50 % titania added HAp contribute to the reduced fretting damage and wear debris generation at the interface.

Demographic characteristics influencing the stem subsidence in total hip arthroplasty: an imaging study

IntroductionThe present study evaluated whether patient demographic characteristics influence the subsidence of the stem in total hip arthroplasty (THA). The following characteristics were evaluated: age, height, weight, and sex. The association between the time elapsed from the THA implantation and the amount of stem subsidence was also investigated.MethodsThe records of patients who underwent THA in the period between 2016 and 2023 were accessed. All patients underwent two-staged bilateral THA using cementless DePuy collarless Corail (DePuy Synthes, Raynham, MA, USA) stems. The following parameters were measured and compared to assess stem subsidence: distance from the proximal femur at the stem bone interface and the medial apex of the regular triangle built within the trochanter minor (point A); distance from the medial apex of the regular triangle built within the trochanter minor and the distal portion of the femoral stem (point B).ResultsOverall, 294 patients were included. 62% (182 of 294 patients) were women. 45% (134 of 296 THAs) were on the right side. The mean age was 64.9 ± 10.4 years. The mean BMI was 28.3 ± 5.1 kg/m2. The mean length of the follow-up was 14.4 ± 11.0 months. The mean subsidence in point A was 2.1 mm (P < 0.0001), and that in point B was 3.1 mm (P < 0.0001). There was evidence of a weak positive association between patient weight (P < 0.0001), age (P = 0.03), follow-up (P = 0.002) and the amount of stem subsidence. Patient height did not demonstrate any association with the amount of stem subsidence (P = 0.07). There was no difference in stem subsidence between women and men (P = 0.9).ConclusionStem subsidence in THA using cementless DePuy collarless Corail implants is approximately 2.6 mm after 14.4 months. Greater patient weight, age, and longer time elapsed from THA implantation were associated with greater stem subsidence. Patient height and sex did not demonstrate any influence on the amount of stem subsidence. These results must be considered in light of the limitations of the present study.

Does preclinical analysis based on static loading underestimate post-surgery stem micromotion in THA as opposed to dynamic gait loading?

The success of cementless hip stems depends on the primary stability of the implant quantified by the amount of micromotion at the bone-stem interface. Most finite element (FE)-based preclinical studies on post-surgery stem stability rely on static analysis. Hence, the effect of dynamic gait loading on bone-stem relative micromotion remains virtually unexplored. Furthermore, there is a paucity of research on the primary stability of grooved stems as opposed to plain stem design. The primary aim of this FE study was to understand whether transient dynamic gait had any incremental effect on the net micromotion results and to further draw insights into the effects of grooved texture vis-à-vis a plain model on micromotion and proximal load transfer in host bone. Two musculoskeletal loading regimes corresponding to normal walking (NW) and stair climbing (SC) were considered. Although marginally improved load transfer was predicted proximally for the grooved construct under static loading, the micromotion values (max: NW ~ 7μm; SC ~ 10μm) were found to be considerably less in comparison to plain stem (max: NW ~ 50μm; SC ~ 20μm). For both physiological load cases, a significant surge in micromotion values was predicted in dynamic analyses as opposed to static analyses for the grooved stem (~ 390% greater). For the plain model, the increase in these values from static to dynamic loading is relatively moderate yet clinically significant (~ 230% greater). This suggests that the qualitative similarities notwithstanding, there were significant dissimilarities in the quantitative trends of micromotion for different cases under both analyses.

Aseptic loosening following Custom Megaprosthesis Reconstruction presenting as a Pseudoarthrosis - A case report

IntroductionCustom megaprosthesis reconstruction is a common treatment modality used for the management of large bone defects. Aseptic loosening was found to be the third most common cause of failure of megaprosthesis. Case reportA 40 year old gentleman had recurrent left proximal tibia giant cell tumor. He underwent a resection of the tumor and reconstruction with cemented custom megaprosthesis of the knee. Two years following the surgery, abnormal movement was noted in middle 1/3rd of the leg. Radiographs revealed radiolucency between the tibial component and bone. He was managed conservatively, and the patient continued to mobilise with walker support. ConclusionAseptic loosening can occur isolated in the middle portion of the megaprosthesis tibial component, with an intact tibial stem-bone interface, resulting in a presentation mimicking pseudoarthrosis. The pseudoarthrosis can be managed conservatively unless there is loosening of the entire tibial component and stem.

Tibial implant fixation in TKA worth a revision?—how to avoid stress-shielding even for stiff metallic implants

In total knee arthroplasty (TKA), force is transmitted into the tibia by a combined plate-stem device along with cemented or cementless stem fixation. The present work analyzes this force transmission in finite element simulations with the main aim to avoid reported postsurgical bone density reduction as a consequence of a reduced tibial bone loading. In the numerical analysis different implant materials, stem/extension lengths and implant-to-stem interface conditions are considered, from a stiff fully cemented fixation to sliding contact conditions with a low friction coefficient. The impact of these variations on bone loading changes are measured by (i) decomposing the total force into parts mediated by the plate and by the stem and by (ii) post-surgery strain energy density (SED) deviations. Based on a bionics-inspired perspective on how nature in pre-operative conditions carries out force transfer from the knee joint into the tibia, a modified implant–bone interface is suggested that alters force transmission towards physiological conditions while preserving the geometries of the standard plate-stem endoprosthesis design. The key aspect is that the axial force is predominantly transmitted through the plate into proximal bone which requires a compliant bone-stem interface as realized by sliding friction conditions at a low friction coefficient. These interface conditions avoid stress shielding almost completely, preserve pre-surgery bone loading such that bone resorption is not likely to occur.

Three-dimensional structural optimization of a cementless hip stem using a bi-directional evolutionary method

A correct choice of stem geometry can increase the lifetime of hip implant in a total hip arthroplasty. This study presents a numerical methodology for structural optimization of stem geometry using a bi-directional evolutionary structural optimization method. The optimization problem was formulated with the objective of minimizing the stresses in the bone–stem interface. Finite element analysis was used to obtain stress distributions by three-dimensional simulation of the implant and the surrounding bone under normal walking conditions. To compare the initial and the optimal stems, the von Mises stress distribution in the bone–implant interface was investigated. Results showed that the optimization procedure leads to a decrease in the stress concentration in the implant and a reduction in stress shielding of the surrounding bone. Furthermore, periprosthetic bone adaptation was analyzed numerically using an adaptive bone remodeling procedure. The remodeling results showed that the bone mass loss could be reduced by 16% in the optimal implant compared to the initial one.

Measures of micromotion in cementless femoral stems-review of current methodologies

Stability and loosening of implanted femoral stems in Total Hip Replacement have been well established as barriers to the primary concerns of osseointegration and long term implant survival. In-vitro experiments and finite element modeling have for years been used as a primary tool to assess the bone stem interface with variable methodologies leading to a wide range of micromotion, interference fit and stress shielding values in the literature. The current study aims to provide a comprehensive review of currently utilized methodologies for in-vitro mechanical testing as well as finite element modeling of both micromotion and interference of implanted femoral stems. A total of 12 studies detailed in 33 articles were selected for inclusion. Experimental values of micromotion ranged from 12 to <TEX>$182{\mu}m$</TEX> while finite element analysis reported a wider range from 2.74 to <TEX>$1,277{\mu}m$</TEX>. Only two studies were found that modeled bone/implant contact with consideration for interference fit. In studies evaluating stem micromotion in THA, the reference surface at the bone/stem interface should be well defined. Additionally, the amount of penetration considered should be disclosed and associated with bone density and roughness.

The influence of contact ratio and its location on the primary stability of cementless total hip arthroplasty: A finite element analysis

Cementless hip stems are fixed to the surrounding bone by means of press-fit. To ensure a good press-fit, current surgical technique specifies an under-reaming of the bone cavity using successively larger broaches. Nevertheless, this surgical technique is inaccurate. Several studies show that the contact ratio (percentage of stem interface in contact with bone) achieved after surgery can vary between 20% and 95%. Therefore, this study aimed to investigate the influence of the contact ratio and its location on the primary stability of a cementless total hip arthroplasty using finite element analysis. A straight tapered femoral stem implanted in a composite bone was subjected to stair climbing. Micromotion of 7600 nodes at the stem-bone interface was computed for different configurations of contact ratios between 2% and 98%) along the hip stem. Considering the 15 configurations evaluated, the average micromotion ranges between 27μm and 54μm. The percentage of the porous interface of the stem having micromotion below 40μm that allows bone ingrowth range between 25–57%. The present numerical study shows that full contact (100%) between stem and bone is not necessary to obtain a good primary stability. The stem primary stability is influenced by both the contact ratio and its location. Several configurations with contact ratio lower than 100% and involving either the proximal or the cortical contact provide better primary stability than the full contact configuration. However, with contact ratio lower than 40%, the stem should be in contact with cortical bone to ensure a good primary stability.

Radiological Evaluation of Treatment of Periprosthetic Femoral Fractures.

Periprosthetic fracture of the femur is a common complication of total hip replacement surgery. There are several risk factors, including the female gender, an uncemented implant, the use of a straight or revision stem and secondary osteoarthritis. The aim of the study was a radiological evaluation of treatment of periprosthetic femoral fractures Material and methods. The study group consisted of patients who underwent hip replacement surgery at the Department of Orthopaedics and Traumatology, Medical University of Silesia, between 2002 and 2006. Radiologic evaluation of outcomes was based on the scheme developed by HIP Society, SICOT, AAOS and, additionally, on Beals and Tower's classification. The incidence of pathological findings, such as lucent zones along the stem-bone interface, crack of the cement and focal osteolysis of the greater trochanter and around the cement, did not exceed 10%. Lucent zones were most frequently seen in radiographs of cemented prostheses in Gruen's zones 2, 3 , 4 and 5. Cortical hypertrophy was seen medially in Gruen's zones 4, 5 and 6. Adams' arc osteolysis was found in 15.5% of patients with intraoperative fractures and almost 40% of patients with late fractures. Heterotopic ossification was noted only in 7 patients. 1. Radiological evaluation of treatment of periprosthetic femoral fractures after hip replacement surgery is one of the most difficult parts of patient status assessment in post-surgical patients. 2. The most common pathological radiographic findings were stem subsidence and the presence of osteolytic foci around Adams` arc. 3. The occurrence of a periprosthetic fracture did not significantly affect Beals and Tower scores.

An In Vitro Comparison of the Primary Stability of 2 Tapered Fluted Femoral Stem Designs

BackgroundProximal bony deficiencies present a biomechanical challenge to achieving primary stability in revision hip arthroplasty. Long tapered fluted stems have been engineered to span these defects but concerns of early subsidence are well documented. This work aimed primarily to investigate the issue of subsidence with this design using a cadaveric model. A secondary aim was to compare the stability of 2 versions of this design. MethodsSeven pairs of cadaveric femora were obtained, dual emission x-ray absorpitometry scanned, with calibration radiographs taken for digital templating. Each bone was potted according to the ISO standard for fatigue testing and a Paprosky type 3 defect was simulated. The established cone-conical Restoration Modular (Stryker) system and a novel design with a chamfered tip and flute configuration (Redapt, Smith & Nephew) were examined. Movement at the stem-bone interface was measured using radiostereometric analysis and micromotion transducers. ResultsAll restoration stems and 85% of the Redapt stems achieved stability by recognized criteria, micromotion < 150 μm and migration less than 2 mm. A Fisher exact test comparing the proportion of stems which were stable or unstable was not significant, P = .055. Mean axial subsidence (SD) was 0.17 mm (0.32) and 0.1 mm (0.131) for the Restoration and Redapt stems respectively. ConclusionThis study has demonstrated minimal subsidence in the immediate post-operative period using tapered fluted stems. Both designs achieved excellent stability despite simulation of Paprosky type 3 bony defects in the cadaveric model. This geometry appears satisfactory for use in revision surgery in the presence of significant proximal bony deficiencies.

First insight on the impact of an osteoblastic layer on the bio-tribocorrosion performance of Ti6Al4V hip implants

In uncemented Ti6Al4V hip implants, the bone–stem interface is subjected to cyclic loading motion driven by the daily activities of the patients, which may lead to the complete failure of the implant in the long term. It may also compromise the proliferation and differentiation processes of osteoblastic cells (bone-forming cells). The main objective of this work is to approach for the first time the role of these organic materials on the bio-tribocorrosion mechanisms of cultured Ti6Al4V alloys. The colonized materials with MG63 osteoblastic-like cells were characterized through cell viability/proliferation and enzymatic activity. Tribocorrosion tests were performed under a reciprocating sliding configuration and low contact pressure. Electrochemical techniques were used to measure the corrosion kinetics of the system, under free potential conditions. All tests were performed at a controlled atmosphere. The morphology and topography of the wear scar were evaluated. The results showed that the presence of an osteoblastic cell layer on the implant surface significantly influences the tribocorrosion behavior of Ti6Al4V alloy. It was concluded that the cellular material was able to form an extra protective layer that inhibits further wear degradation of the alloy and decreases its corrosion tendency.

Effect of femoral mechanical properties on primary stability of cementless total hip arthroplasty: a finite element analysis

With the goal of increasing the survivorship of the prosthesis and anticipating primary stability problems of new prosthetic implants, finite element evaluation of the micromotion, at an early stage of the development, is mandatory. This allows assessing and optimizing different designs without manufacturing prostheses. This study aimed at investigating, using finite element analysis (FEA), the difference in the prediction of the primary stability of cementless hip prostheses implanted into a <TEX>$Sawbones^{(R)}$</TEX> 4th generation, using the manufacturer's mechanical properties and using mechanical properties close to that of human bone provided by the literature (39 papers). FEA was carried out on the composite <TEX>$Sawbones^{(R)}$</TEX> implanted with a straight taper femoral stem subjected to a loading condition simulating normal walking. Our results show that micromotion increases with a reduction of the bone material properties and decreases with the augmentation of the bone material properties at the stem-bone interface. Indeed, a decrease of the cancellous Young modulus from 155MPa to 50MPa increased the average micromotion from <TEX>$29{\mu}m$</TEX> up to <TEX>$41{\mu}m$</TEX> (+42%), whereas an increase of the cancellous Young modulus from 155MPa to 1000MPa decreased the average micromotion from <TEX>$29{\mu}m$</TEX> to <TEX>$5{\mu}m$</TEX> (-83%). A decrease of cortical Young modulus from 16.7GPa to 9GPa increase the average global micromotion from <TEX>$29{\mu}m$</TEX> to <TEX>$35{\mu}m$</TEX> (+33%), whereas an increase of the cortical Young modulus from 16.7GPa to 21GPa decreased the average global micromotion from <TEX>$29{\mu}m$</TEX> to <TEX>$27{\mu}m$</TEX> (-7%). It can also be seen that the material properties of the cancellous structure had a greater influence on the micromotion than the material properties of the cortical structure. The present study shows that micromotion predicted at the stem-bone interface with material properties of the <TEX>$Sawbones^{(R)}$</TEX> 4th generation is close to that predicted with mechanical properties of human femur.

Best estimation of spectrum profiles for diagnosing femoral prostheses loosening

For the past few years, some authors have proposed several vibration analysis techniques to detect the prosthetic femoral stem loosening, having found some differences in the frequency response between secure and loose stems. Classical methods like periodogram have been used in most studies for the spectral estimation, and their conclusions have been reached only by visual inspection. A new metric called Non-linear Logarithmic Weighted Distance (NLWD), based on log-spectral distance is presented. As its name suggests, the spectral power is weighted in order to highlight discriminatory patterns of the spectral profiles. A Generalized Discriminant Ratio (GDR) based on NLWD metric has been also defined. In this study, experiments on a cadaveric dried bone with two kinds of fixation, Loose Stem class (LS) and Secure Stem class (SS), have been analyzed. To select the most discriminating approach to spectral estimation, five well known algorithms (Welch's, Burg's Auto-Regressive (AR), Auto-Regressive Moving Average (ARMA), Multiple Signal Classification (MUSIC) and Thomson's Multi-taper (MTM)) have been compared by using GDR. Finally, the use of the MTM method is proposed for the analysis of bone–stem interface vibratory signals, since it yields the most discriminatory profiles.

Numerical simulation of the insertion process of an uncemented hip prosthesis in order to evaluate the influence of residual stress and contact distribution on the stem initial stability

The long-term success of a cementless total hip arthroplasty depends on the implant geometry and interface bonding characteristics (fit, coating and ingrowth) and on stem stiffness. This study evaluates the influence of stem geometry and fitting conditions on the evolution and distribution of the bone–stem contact, stress and strain during and after the hip stem insertion, by means of dynamic finite element techniques. Next, the influence of the mechanical state (bone–stem contact, stress and strain) resulted from the insertion process on the stem initial resistance to subsidence is investigated. In addition, a study on the influence of bone–stem interface conditions (friction) on the insertion process and on the initial stem stability under physiological loading is performed. The results indicate that for a stem with tapered shape the contact in the proximal part of the stem was improved, but contact in the calcar region was achieved only when extra press-fit conditions were considered. Changes in stem geometry towards a more tapered shape and extra press fit and variation in the bone–stem interface conditions (contact amount and high friction) led to a raise in the total insertion force. A direct positive relationship was found between the stem resistance to subsidence and stem geometry (tapering and press fit), bone–stem interface conditions (bone–stem contact and friction interface) and the mechanical status at the end of the insertion (residual stress and strain). Therefore, further studies on evaluating the initial performance of different stem types should consider the parameters describing the bone–stem interface conditions and the mechanical state resulted from the insertion process.

Theoretical Study on Stem Implants Behaviour

The paper presents a complex study on hip joint endoprosthesis. The model for the femur was obtained by CT scanner and Mimics, the endoprosthesis was designed in proEngineer. This study has two stages: obtaining the 3D model for the bone and endoprosthesis, analysing the model in Ansys to obtain stress and strain state information. The paper also presents some interesting aspects of the contact between the bone and the implant in case of different types of endoprosthesis (two standardized types and one personalized). A good contact between the bone and the stem indicates a long life solution for an endoprosthesis. A personalized stem is very useful for persons with disabilities is designed taking in consideration the particularities of the patient. The contact results from Ansys illustrate the aspects from the bone stem interface. With this information the orthopaedist can take better decisions for a proper hip joint endoprosthesis used for a named patient.

Simultaneous and multisite measure of micromotion, subsidence and gap to evaluate femoral stem stability

The initial stability of cementless femoral components is crucial for the long-term success of total hip arthroplasty. This has been reported in animal and clinical studies. Until now, the stability was evaluated by the measurement of relative micromotion on a few simultaneous locations around the stem in cadaveric experiments. This paper presents an extended experimental setup to measure simultaneously local micromotion, subsidence and gap on hundreds of points at the bone–stem interface. This technique we applied to anatomical and straight stems in three pairs of cadaveric femurs. Measurements were in agreement with typically reported values. Conversely to other methods, which measure micromotion between implant and bone anchoring points of the measuring device, our method provides local micromotion between stem surface and adjacent bone surface. The observed variation of micromotion at the peri-implant surface confirms the importance of this simultaneous measure on a lot of points around the implant.

A model of bone adaptation as a topology optimization process with contact

Topology optimization is presently used in most diverse scientific, technologic and industrial areas, including biomechanics. Bone remodelling models and structural optimization has mutually provided inspiration for new developments in biomechanics and biomedicine. Considering that bone has the ability to adapt its internal structure to mechanical loading (Wolff’s law and Roux’s paradigm), it is possible to model the behaviour of the bone structure by the use of a topology optimization methodology whose optimization variables can be the relative densities and the orthotropic directions. In this work, the internal bone adaptation of a proximal femur is considered. The bone-remodelling scheme is numerically described by a time-dependent evolutionary procedure with anisotropic material parameters. The remodelling rate equation is obtained from the structural optimization task of maximizing the stiffness subject to a biological cost associated with metabolic maintenance of bone tissue in time. The situation of multiple load conditions is considered for a three-dimensional finite element model of the proximal femur. The bone density distribution of a real femur is used as the initial design for the onset of the remodelling mechanism. Examples of bone adaptation resulting from load changes are presented. The three-dimensional finite element model of the proximal femur with initial bone density distribution was adapted to implant a cementless stem. A remeshing technique is used to assign the bone relative density distribution to the new geometry and mesh. The time adaptation of the bone is assessed considering contact with friction at the bone-stem interface. Results of bone density evolution and osteointegration distribution are obtained.

Femoral stem-bone interface analysis of logical uncemented stem

This paper evaluates the mechanical behavior of an uncemented hip stem using finite element analysis. The analysis is focused on the stem-bone interaction which is assessed by simulation of distinct conditions encountered daily on orthopedic practice of hip implants. Logical uncemented femoral stem was used in this work. Three distinct conditions have been modeled: a) exposed neck with fully embedded fins, b) partially exposed anti-rotational fins and c) fully exposed fins, representing real femoral hip conditions. Anthropometric variations and different angulations for the stem neck were investigated for typical body weight of populations submitted to implants. The ratio of mobilized stress to yield stress is shown to be lower than 55% indicating a safety factor against stem failure. Although small displacements are observed in all conditions, the displacement increases with the increase of both the length of exposed fins and the magnitude of applied forces. Even for the extreme condition of fully exposed fins, the prostheses will support the working loads, and the risk of bone fracture still has a safety factor. Stresses and displacements change considerably with neck angulations suggesting that anthropometric variations should be considered in the future to optimize prostheses performance. Numerical analysis of the used uncemented femoral stem demonstrated that small stresses and strains are generated under working load conditions indicating that a proper factor of safety is obtained for the static conditions tested in the present study.

Design considerations for ceramic resurfaced femoral head: effect of interface characteristics on failure mechanisms

Ceramic hip resurfacing may offer improved wear resistance compared to metallic components. The study is aimed at investigating the effects of stiffer ceramic components on the stress/strain-related failure mechanisms in the resurfaced femur, using three-dimensional finite element models of intact and resurfaced femurs with varying stem–bone interface conditions. Tensile stresses in the cement varied between 1 and 5 MPa. Postoperatively, 20–85% strain shielding was observed inside the resurfaced head. The variability in stem–bone interface condition strongly influenced the stresses and strains generated within the resurfaced femoral head. For full stem–bone contact, high tensile (151–158 MPa) stresses were generated at the cup–stem junction, indicating risk of fracture. Moreover, there was risk of femoral neck fracture due to elevated bone strains (0.60–0.80% strain) in the proximal femoral neck region. Stresses in the ceramic component are reduced if a frictionless gap condition exists at the stem–bone interface. High stresses, coupled with increased strain shielding in the ceramic resurfaced femur, appear to be major concerns regarding its use as an alternative material.

Multilayered learning architecture applied to humanoid locomotion

This work presents a computational model for the concurrent study of bone remodelling and ingrowth around cementless femoral stems in total hip arthroplasty. It is assumed that biological fixation depends upon the magnitude of relative displacement at the bone-stem interface as well as an ongoing updating of interface conditions during the remodelling process. The remodelling model determines the distribution of bone density by producing the stiffest structure for a given set of biological conditions at the point of equilibrium in bone turnover. Changes in bone density and patterns of ingrowth are compared for different stem geometries, materials and lengths of surface coating. Patterns of bone ingrowth on the tapered stem were independent of extent of porous coating, while ingrowth varied with the length of coating on the cylindrical stem. This model integrates knowledge of under what mechanical conditions bone ingrowth occurs on prosthetic stem surfaces with remodelling behaviour over time.