Periprosthetic bone remodelling of a collum femoris preserving cementless titanium femoral hip replacement

Total hip arthroplasty represents a major surgical achievement for pain relief and restoration of lifestyle quality due to the joint disease of osteoarthritis. Total hip replacement has evolved over the past 30 years utilising a variety of biocompatible materials, geometric shapes and fixation techniques. The main objective of this study is to investigate the long-term effects of strain adaptive bone remodelling due to the influence of a novel titanium cementless femoral hip replacement. The period of on-growth has been taken into account and the simulation has been run to predict the remodelling behaviour for a 36-month period. The main conclusion from this analysis is that the implant does shield the calcar to a similar degree as other cementless femoral hip designs. It does, however, tend to cause bone to be laid down along its length. This may, in part, be due to the novel geometry of the implant interlocking with and loading the bone.     

Activity intensity,assistive devices and joint replacement influence predicted remodelling in the proximal femur

Bone morphology and density changes are commonly observed following joint replacement, may contribute to the risks of implant loosening and periprosthetic fracture and reduce the available bone stock for revision surgery. This study was presented in the ‘Bone and Cartilage Mechanobiology across the scales’ WCCM symposium to review the development of remodelling prediction methods and to demonstrate simulation of adaptive bone remodelling around hip replacement femoral components, incorporating intrinsic (prosthesis) and extrinsic (activity and loading) factors. An iterative bone remodelling process was applied to finite element models of a femur implanted with a cementless total hip replacement (THR) and a hip resurfacing implant. Previously developed for a cemented THR implant, this modified process enabled the influence of pre- to post-operative changes in patient activity and joint loading to be evaluated. A control algorithm used identical pre- and post-operative conditions, and the predicted extents and temporal trends of remodelling were measured by generating virtual X-rays and DXA scans. The modified process improved qualitative and quantitative remodelling predictions for both the cementless THR and resurfacing implants, but demonstrated the sensitivity to DXA scan region definition and appropriate implant–bone position and sizing. Predicted remodelling in the intact femur in response to changed activity and loading demonstrated that in this simplified model, although the influence of the extrinsic effects were important, the mechanics of implantation were dominant. This study supports the application of predictive bone remodelling as one element in the range of physical and computational studies, which should be conducted in the preclinical evaluation of new prostheses.     

Long-term study of bone remodelling after femoral stem: a comparison between dexa and finite element simulation

A hip replacement with a cemented or cementless femoral stem produces an effect on the bone called adaptive remodelling, attributable to mechanical and biological factors. The objective of all of cementless prostheses designs has been to achieve a perfect transfer of loads in order to avoid stress-shielding, which produces an osteopenia. In order to quantify this, the long term and mass-produced study with dual energy X-ray absorptiometry (DEXA) is necessary. Finite element (FE) simulation makes possible the explanation of the biomechanical changes which are produced in the femur after stem implantation. The good correlation obtained between the results of the FE simulation and the densitometric study allow, on one hand, to explain from the point of view of biomechanical performance the changes observed in bone density in the long-term, where it is clear that these are due to a different transfer of load in the implanted model compared to the healthy femur; on the other hand, it validates the simulation model, in a way that it can be used in different conditions and at different time periods, to carry out a sufficiently precise prediction of the evolution of the bone density from the biomechanical behaviour in the interaction between the prosthesis and femur.     

Study of bone remodeling of two models of femoral cementless stems by means of DEXA and finite elements

Background  

A hip replacement with a cemented or cementless femoral stem produces an effect on the bone called adaptive remodelling, attributable to mechanical and biological factors. All of the cementless prostheses designs try to achieve an optimal load transfer in order to avoid stress-shielding, which produces an osteopenia.     

Effects of Materials of Cementless Femoral Stem on the Functional Adaptation of Bone

The objective of this paper is to identify the effects of materials of cementless femoral stem on the functional adaptive behaviors of bone.The remodeling behaviors of a two-dimensional simplified model of cementless hip prosthesis with stiff stem,flexible 'iso-elastic' stem,one-dimensional Functionally Graded Material (FGM) stem and two-dimensional FGM stem for the period of four years after prosthesis replacement were quantified by incorporating the bone remodeling algorithm with finite element analysis.The distributions of bone density,von Mises stress,and interface shear stress were obtained.The results show that two-dimensional FGM stem may produce more mechanical stimuli and more uniform interface shear stress compared with the stems made of other materials,thus the host bone is well preserved.Accordingly,the two-dimensional FGM stem is an appropriate femoral implant from a biomechanical point of view.The numerical simulation in this paper can provide a quantitative computational paradigm for the changes of bone morphology caused by implants,which can help to improve the design of implant to reduce stress shielding and the risk of bone-prosthesis interface failure.     

A long-lasting bisphosphonate partially protects periprosthetic bone,but does not enhance initial stability of uncemented femoral stems: A randomized placebo-controlled trial of women undergoing total hip arthroplasty

Low bone quality may compromise the success of cementless total hip arthroplasty in high-risk patients such as elderly women. Zoledronic acid is a long-lasting antiresorptive agent, which is known to reduce short-term periprosthetic bone loss. However, its effect on femoral stem stability is not well known. Forty-nine female patients with a mean age of 68 years (range, 51–85 years) scheduled to undergo cementless total hip arthroplasty due to osteoarthritis were randomized in this double-blind, placebo-controlled trial to receive a single postoperative infusion of zoledronic acid or placebo. Patients were evaluated for up to four years postoperatively for femoral stem migration measured by radiostereometric analysis, bone mineral density (BMD) measured by dual X-ray absorptiometry, functional recovery, and patient-reported outcome scores. Implant survival was determined at nine years postoperatively. Zoledronic acid did not reduce the femoral stem migration that occurred predominantly during the settling period of the first 3–6 months. Subsequently, all femoral stems were radiographically osseointegrated. Zoledronic acid maintained periprosthetic BMD, while the expected loss of periprosthetic bone during the first 12 months was found in controls. Thereafter, periprosthetic BMD of Gruen zone 7 decreased even in the zoledronic acid group but remained 14.6% higher than that in the placebo group at four years postoperatively. Functional recovery was comparable across the groups. At nine years postoperatively, no revision arthroplasty had been performed. In conclusion, in women at high-risk for low BMD, zoledronic acid had a long-lasting, partially protective effect on periprosthetic bone loss, but the treatment did not enhance the initial femoral stem stability.     

Implant–bone interface healing and adaptation in resurfacing hip replacement

Hip resurfacing demonstrates good survivorship as a treatment for young patients with osteoarthritis, but occasional implant loosening failures occur. On the femoral side there is radiographic evidence suggesting that the implant stem bears load, which is thought to lead to proximal stress shielding and adaptive bone remodelling. Previous attempts aimed at reproducing clinically observed bone adaptations in response to the implant have not recreated the full set of common radiographic changes, so a modified bone adaptation algorithm was developed in an attempt to replicate more closely the effects of the prosthesis on the host bone. The algorithm features combined implant–bone interface healing and continuum bone remodelling. It was observed that remodelling simulations that accounted for progressive gap filling at the implant–bone interface predicted the closest periprosthetic bone density changes to clinical X-rays and DEXA data. This model may contribute to improved understanding of clinical failure mechanisms with traditional hip resurfacing designs and enable more detailed pre-clinical analysis of new designs.     

Influence of ingrowth regions on bone remodelling around a cementless hip resurfacing femoral implant

Hip resurfacing arthroplasty is an alternative to traditional hip replacement that can conserve proximal bone stock and has gained popularity but bone resorption may limit implant survival and remains a clinical concern. The goal of this study was to analyze bone remodelling patterns around an uncemented resurfacing implant and the influence of ingrowth regions on resorption. A computed tomography-derived finite element model of a proximal femur with a virtually implanted resurfacing component was simulated under peak walking loads. Bone ingrowth was simulated by six interface conditions: fully bonded; fully friction; bonded cap with friction stem; a small bonded region at the stem-cup intersection with the remaining surface friction; fully frictional, except for a bonded band along the distal end of the cap and superior half of the cap bonded with the rest frictional. Interface condition had a large influence on remodelling patterns. Bone resorption was minimized when no ingrowth occurred at the bone-implant interface. Bonding only the superior half of the cap increased bone resorption slightly but allowed for a large ingrowth region to improve secondary stability.     

A Biomimetic Hip Joint Simulator and its Application in in vitro Study of the Integrity of Replacement Cemented Hip

1IntroductionAseptic loosening is a major clinical probleminterfering with long term success of arthroplasty inhumans.When this occurs,the stem will migrate withinthe cortical bone.The migration of the stem after hiparthroplasty is an unavoidable phenomenon and is one ofthe major cause of late aseptic loosening of the hiparthroplasty[1-5].Many factors,such as cement mantle performance,stem type and surface finish,cementing and surgerytechniques affect the subsidence or migration of thefemoral …     

Experimental method for the in vitro testing of the initial stability of cementless hip prostheses

Micromotions at the interface between bone and prosthesis are believed to induce bone resorption and ultimately lead to loosening of the implant. Thus the initial stability achieved by a hip prosthesis is an important factor for the long-term function of the implant. Knowing the biological consequences of the mechanical conditions, it appears to be mandatory to measure the extent of these three-dimensional movements. An in vitro dynamic method for measurement of the micromotion of the femoral component of hip prostheses has been developed. Tests in cemented prostheses have confirmed that the use of cement reduces sinkage and rotation manyfold and have yielded reference values for stability. Comparison with two types of cementless prostheses has shown that certain cementless implants may achieve stability comparable to cemented ones in some load directions.     

The influence of uncemented femoral stem length and design on its primary stability: a finite element analysis

One of the crucial factors for short- and long-term clinical success of total hip arthroplasty cementless implants is primary stability. Indeed, motion at the bone–implant interface above 40 μm leads to partial bone ingrowth, while motion exceeding 150 μm completely inhibits bone ingrowth. The aim of this study was to investigate the effect of two cementless femoral stem designs with different lengths on the primary stability. A finite element model of a composite Sawbones^® fourth generation, implanted with five lengths of the straight prosthesis design and four lengths of the curved prosthesis design, was loaded with hip joint and abductor forces representing two physiological activities: fast walking and stair climbing. We found that reducing the straight stem length from 146 to 54 mm increased the average micromotion from 17 to 52 μm during fast walking, while the peak value increased from 42 to 104 μm. With the curved stem, reducing length from 105 to 54 mm increased the average micromotion from 10 to 29 μm, while the peak value increased from 37 to 101 μm. Similar findings are obtained for stair climbing for both stems. Although the present study showed that femoral stem length as well as stem design directly influences its primary stability, for the two femoral stems tested, length could be reduced substantially without compromising the primary stability. With the aim of minimising surgical invasiveness, newer femoral stem design and currently well performing stems might be used with a reduced length without compromising primary stability and hence, long-term survivorship.     

人工髋关节置换术在320例股骨头缺血性坏死中的治疗体会

目的：探讨人工髋关节置换术在治疗股骨头缺血性坏死（ANFH）中的临床疗效。方法：选择2007年2月-2011年2月我院收治的320例（340髋）股骨头缺血性坏死患者,均采用人工髋关节置换术对患者进行治疗,其中160例（172髋）患者应用骨水泥型假体进行治疗,另外160例（168）患者采用非骨水泥型假体进行治疗。采用Harris评分对患者手术前后的髋关节功能情况进行评价,并比较骨水泥治疗组和非骨水泥治疗组的临床疗效。结果：患者均获得随访,随访时间为3～18个月。全部患者手术后的Harris评分明显高于手术前,差异有统计学意义（P〈0．05）。骨水泥治疗组和非骨水泥治疗组在术后出血量、术后Harris评分及住院时间方面的差异无统计学意义（P〉0．05）,但非骨水泥治疗组的并发症发生率明显低于骨水泥治疗组（P〈0．05）。结论：采用人工髋关节置换术治疗ANFH疗效显著,能明显改善患者的生活质量,骨水泥型假体与非骨水泥型假体的治疗效果相当,应根据患者的具体情况进行合理的选择。     

Improving stress shielding following total hip arthroplasty by using a femoral stem made of β type Ti-33.6Nb-4Sn with a Young’s modulus gradation

Stress shielding-related bone loss occurs after total hip arthroplasty because the stiffness of metallic implants differs from that of the host femur. Although reducing stem stiffness can ameliorate the bone resorption, it increases stress at the bone–implant interface and can inhibit fixation. To overcome this complication, a novel cementless stem with a gradient in Young’s modulus was developed using Ti-33.6Nb-4Sn (TNS) alloy. Local heat treatment applied at the neck region for increasing its strength resulted in a gradual decrease in Young’s modulus from the proximal to the distal end, from 82.1 to 51.0 GPa as calculated by a heat transfer simulation. The Young’s modulus gradient did not induce the excessive interface stress which may cause the surface debonding. The main purpose of this study was to evaluate bone remodeling with the TNS stem using a strain-adaptive bone remodeling simulation based on finite element analysis. Our predictions showed that, for the TNS stem, bone reduction in the calcar region (Gruen zone 7) would be 13.6% at 2 years, 29.0% at 5 years, and 45.8% at 10 years postoperatively. At 10 years, the bone mineral density for the TNS stem would be 42.6% higher than that for the similar Ti-6Al-4V alloy stem. The stress–strength ratio would be lower for the TNS stem than for the Ti-6Al-4V stem. These results suggest that although proximal bone loss cannot be eliminated completely, the TNS stem with a Young’s modulus gradient may have bone-preserving effects and sufficient stem strength, without the excessive interface stress.     

人工髋关节置换术在320 例股骨头缺血性坏死中的治疗体会

目的：探讨人工髋关节置换术在治疗股骨头缺血性坏死（ANFH）中的临床疗效。方法：选择2007 年2 月-2011 年2 月我院收 治的320 例（340 髋）股骨头缺血性坏死患者,均采用人工髋关节置换术对患者进行治疗,其中160 例（172 髋）患者应用骨水泥型 假体进行治疗,另外160 例（168）患者采用非骨水泥型假体进行治疗。采用Harris评分对患者手术前后的髋关节功能情况进行评 价,并比较骨水泥治疗组和非骨水泥治疗组的临床疗效。结果：患者均获得随访,随访时间为3～18 个月。全部患者手术后的 Harris评分明显高于手术前,差异有统计学意义（P<0.05）。骨水泥治疗组和非骨水泥治疗组在术后出血量、术后Harris 评分及住 院时间方面的差异无统计学意义（P>0.05）,但非骨水泥治疗组的并发症发生率明显低于骨水泥治疗组（P<0.05）。结论：采用人工 髋关节置换术治疗ANFH疗效显著,能明显改善患者的生活质量,骨水泥型假体与非骨水泥型假体的治疗效果相当,应根据患者 的具体情况进行合理的选择。     

Effect of interface conditions on the behaviour of a Freeman hip endoprosthesis

The femoral element of a total hip replacement is a composite structure of two, or perhaps three, components — the endoprosthesis, the bone and, where present, the cement. The interfacial conditions are such that complete structural continuity does not necessarily obtain. That this is so has often been suspected due to the observed loosening which can occur in vivo. In modelling the system, typically for finite element analysis, it has usually been considered to be monolithic, such that tensile and shear stresses could be transmitted across the interfaces as well as the normal compressive stress. Here the femoral component of a Freeman hip replacement is considered, implanted without bone cement, and analyses are carried out under monolithic, i.e. fully bonded, and non-bonded assumptions. Simultaneously the effect of retaining the neck of the femur, one of the features of using this particular prosthesis, is also examined.     

Stress changes in the femoral head due to porous ingrowth surface replacement arthroplasty

Finite element stress analyses were conducted of the canine femoral head before and after implantation of various surface replacement-type components. The femoral head was replaced by four implant geometries; (a) shell, (b) shell with peg, (c) shell with rod, and (d) a new epiphyseal replacement design. All implants were modelled to simulate bony ingrowth along the underside of the shell and along the surfaces of the peg and rod. The results indicated that in the normal femur the forces are transferred from the articular surface through the femoral head cancellous bone to the inferior cortical shell of the femoral neck. After shell-type surface replacement, forces were transferred more distally at the rim of the shell and at the end of the peg or rod, thereby reducing the stresses in the proximal head cancellous bone. Computer simulation of bone remodelling due to proximal bone stress reduction was shown to accentuate the abnormality of the stress fields. Surface replacement with a lower modulus material created a less abnormal redistribution of bone stresses. The new epiphyseal replacement design resulted in stress distributions similar to those in the normal femoral head and minimal shear stresses at the implant/bone interface. These findings suggest that the epiphyseal replacement concept may provide better initial mechanical integrity and create a more benign milieu for adaptive bone remodelling than conventional, shell-type surface replacement components.     

A numerically validated probabilistic model of a simplified total hip replacement construct

Hip replacement constructs are paradigms of uncertain systems, and as such are suited to the application of probabilistic methods to assess their structural integrity. In order to gain confidence in a probabilistic model, it would be useful to verify the findings with experimental data; however, this is difficult to achieve in practice because of the exhaustive number of parameter combinations that need to be tested. As an alternative to experimental testing, benchmarking can be carried out provided a known analytical solution is available. To this end, a simplified 2D two-beam model of the femoral part of a total hip replacement construct was utilised to analyse uncertainties and variability in the construct as it is subjected to load. The use of a simplified model enabled geometric parameters to be investigated; these are commonly not considered in probabilistic models due to the increased complexity involved. Analytical and finite element representations of the model were developed and compared. The probabilistic study used the Monte Carlo simulation technique and the first-order reliability method to look at the inducible displacement of a hip implant, a phenomenon that has been linked to the most common cause of hip implant failure, aseptic loosening. Excellent correlation was observed between the analytical and probabilistic solutions, and it was shown that probabilistic approaches could efficiently predict the response of the simplified beam model while readily identifying the parameters most likely to compromise the structural integrity of the construct.     

Sensitivity Analysis and Optimal Shape Design for Bone-Prosthesis Interfaces in a Femoral Head Surface Replacement

A numerical optimization procedure has been applied for the shape optimal design of a femoral head surface replacement. The failure modes of the prosthesis that were considered in the formulation of the objective functions concerned the interface stress magnitude and the bone remodelling activity beneath the implant. In order to find a compromising solution between different requirements demanded by the two objective functions, a two step optimization procedure has been developed. Through step 1 the minimization of interface stress was achieved, through step 2 the minimization of bone remodelling was achieved with constraints on interface stresses. The results obtained provided an optimal design that generates limited bone remodelling activity with controlled interface stress distribution. The computational procedure was based on the application of the finite element method, linked to a mathematical programming package and a design sensitivity analysis package.     

A finite element analysis of the vibration behaviour of a cementless hip system

An early diagnosis of aseptic loosening of a total hip replacement (THR) by plain radiography, scintigraphy or arthography has been shown to be less reliable than using a vibration technique. However, it has been suggested that it may be possible to distinguish between a secure and a loose prosthesis using a vibration technique. In fact, vibration analysis methods have been successfully used to assess dental implant stability, to monitor fracture healing and to measure bone mechanical properties. Several studies have combined the vibration technique with the finite element (FE) method in order to better understand the events involved in the experimental technique. In the present study, the main goal is to simulate the change in the resonance frequency during the osseointegration process of a cementless THR (Zweymüller). The FE method was used and a numerical modal analysis was conducted to obtain the natural frequencies and mode shapes under vibration. The effects were studied of different bone and stem material properties, and different contact conditions at the bone–implant interface. The results were in agreement with previous experimental and computational observations, and differences among the different cases studied were detected. As the osseointegration process at the bone–implant interface evolved, the resonance frequency values of the femur–prosthesis system also increased. In summary, vibration analysis combined with the FE method was able to detect different boundary conditions at the bone–implant interface in cases of both osseointegration and loosening.     

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.