Mechanical compression of a fibrous membrane surrounding bone causes bone resorption.

Early micromovement and migration of a prosthesis of a hip or knee predicts late clinical loosening of the prosthesis. Such migration is likely to be associated with mechanical compression of the fibrous membrane interpositioned between bone and prosthesis during movement. Compression of the fibrous membrane by loading may lead to locally high fluid pressures reaching the underlying bone tissue. It has been established that high fluid pressures can lead to bone resorption. This resorption may eventually lead to clinical loosening of the prosthesis. We developed an experimental model to study the effects of compression of a soft tissue layer located between a titanium implant and cortical bone. In twelve rabbits, this device was implanted in the proximal tibia and allowed to osseointegrate. Next, a layer of soft tissue was allowed to form between titanium and bone. Subsequently, in six rabbits a cyclic load of 60 times in 2 min per day during 2 weeks was applied, leading to compression of the interpositioned soft tissue layer only. In the other six rabbits no load was applied. In all six loaded specimens, osteocyte death and bone resorption was observed underneath the area where compression of the fibrous membrane was exerted to a depth exceeding the amplitude of the loading device. Furthermore, formation of fibrocartilage was observed in the loaded areas. Formation of fibrocartilage, osteocyte death or bone resorption did not occur in the controls. Our results indicate that compression of a fibrous membrane surrounding bone can lead to resorption of the underlying bone primarily because of osteocyte death and subsequent resorption of dead bone tissue. This may explain the observation that early migration of a hip or knee prosthesis is predictive of clinical loosening of the prosthesis.     

Inhibitory effects of luteolin on titanium particle-induced osteolysis in a mouse model

Wear particles liberated from the surfaces of an implanted prosthesis are associated with peri-implant osteolysis and subsequent aseptic loosening. In the latter wear particle-induced inflammation and osteoclastogenesis have been identified as critical factors, and their inhibition as important steps in the treatment of affected patients, such as those undergoing total hip replacement. In this study the ability of luteolin to inhibit both titanium (Ti) particle-induced osteoclastogenesis in vitro and osteolysis in a murine calvaria Ti particle-induced model of osteolysis was examined. The results showed that luteolin, a highly potent and efficient inhibitor of tumor necrosis factor α (TNF-α) and interleukin-6 expression, inhibited Ti particle-induced inflammatory cytokine release, osteoclastogenesis, and bone resorption in bone marrow macrophages. Microcomputed tomography and histological analyses showed that the Ti particles caused significant bone resorption and increased TRAP(+) multinuclear osteoclasts in the murine calvarial model of osteolysis, whereas this was not the case in the luteolin treatment group, in which osteolytic suppression was accompanied by a decrease in both TNF-α production and serum levels of the osteoclast marker the C-terminal telopeptide fragment of type I collagen. These results support the use of luteolin as a natural compound in the prevention and treatment of aseptic loosening after total replacement arthroplasty.     

Cortical and interfacial bone changes around a non-cemented hip implant: Simulations using a combined strain/damage remodelling algorithm

Prostheses alter the loading pattern in bones. For example femoral hip implants cause the cortical bone to remodel and the implant/bone interface to react. To date, simulations of peri-prosthetic bone adaptations have succeeded for the bulk bone remodelling only. In this study we use an approach based on a combined strain/damage algorithm to simultaneously predict both bulk and interfacial peri-prosthetic bone adaptation around a non-cemented hip prosthesis. The influence of stem stiffness is investigated; a flexible iso-elastic stem (20 GPa), an titanium alloy stem (110 GPa), and a stiff cobalt chrome (CoCrMo) stem (210 GPa). The results predict that an iso-elastic stem reduces proximal bone loss because stress shielding is prevented but it increases proximal interface resorption due to damage-stimulated resorption. On the other hand, a stiff cobalt chrome stem increases proximal strain-stimulated resorption but does not induce proximal interfacial damage-stimulated resorption; however damage-stimulated resorption surrounding the distal tip is predicted to increase with stiffer stems. Simulations for the titanium stem were predicted to minimise both strain and damage related remodelling. We propose that this combined strain/damage remodelling algorithm can provide realistic simulations of the response of bone around load-bearing orthopaedic implants.     

Stiffness optimisation of cement and stem materials in total hip replacement

It is acknowledged that bone resorption and fatigue fracture of cement in total hip replacement may cause feature problems. The solution is frequently sought associated with the stiffness of cement and stem. The purpose of this paper is firstly to describe the effect of changes in modulus of elasticity of the cement material for the implanted prosthesis on the fatigue notch factor (Kf). The paper further describes a method of numerical optimisation to determine the optimal stiffness characteristics of cement and stem materials, which minimises the probability of fatigue fracture of cement at all interfaces with the stem and the bone, while limiting the amount of bone resorbed. The parameters describing the elastic moduli of cement and stem were considered as design variables. The method was applied to an equivalent 2D finite element model of femoral hip replacement in combination with an optimisation procedure using the ANSYS program. The results of the first study suggest that lower modulus of elasticity of cement material decreases Kf in the cement at all interfaces and proximal bone while higher values increase Kf. For the second aim, Young's moduli of about 0.6 and 22 GPa are optimal for cement and stem materials, respectively. These characteristics decreased the probability of fatigue fracture of cement at all interfaces with the stem and the bone as a result of decreasing Kf in cement at all interfaces, while limiting the amount of bone resorbed as a result of increasing Kf in the proximal bone.     

Bone remodelling analysis of the humerus after a shoulder arthroplasty

The shoulder arthroplasty has become an efficient treatment for some pathologies. However there are complications that can compromise its success. Among them, the stress shielding effect on the humerus has been reported as a possible cause of failure. The objective of this work was to investigate the bone remodelling in the humerus after a shoulder arthroplasty. For this purpose, computational models were developed to analyse the stress shielding contribution to the humeral component failure of shoulder arthroplasties, with a cemented and an uncemented prosthesis. A computational remodelling model was used to characterize the bone apparent density at each site of the humerus. The density distribution was obtained by the solution of a problem that takes into account both structural stiffness and the metabolic cost of bone maintenance. Bone was subjected to 6 load cases that include the glenohumeral reaction force and the action of 10 muscles. In the implanted models, different interface conditions were tested for the bone-implant and the cement-implant interfaces. Moreover, a pathological case defined by a poorer quality of bone was considered. In the healthy situation, the models that better model in vivo conditions showed no significant changes in bone mass. However, the results for the pathological case showed some bone resorption which supports the importance given to the quality of bone in the success of the joint replacement. Bearing in mind the conditions addressed, the results lead to conclude that the stress shielding is not a key factor for the humeral component failure of shoulder arthroplasties in a healthy situation though several issues, including muscle function and bone quality, may heighten its effect.     

A method for shape optimization of a hip prosthesis to maximize the fatigue life of the cement

The long term success of total joint replacement can be limited by fatigue failure of the acrylic cement and the resulting disruption of the bone-cement interface. The incidence of such problems may be diminished by reduction of the fatigue notch factor in the cement, so that stress concentrations are avoided and the fatigue crack initiation time maximized. This study describes a method for numerical shape optimization whereby the finite element method is used to determine an optimal shape for the femoral stem of a hip prosthesis in order to minimize the fatigue notch factor in the cement layer and at interfaces with the bone and stem.

A two-dimensional model of the proximal end of a femur fitted with a total hip prosthesis was used which was equivalent to a simplified three-dimensional axisymmetric model. Software was developed to calculate the fatigue notch factor in the cement along the cement/stem and cement/bone interfaces and in the proximal bone. The fatigue notch factor in the cement at the cement/stem interface was then minimized using the ANSYS finite element program while constraining the fatigue notch factor at the cement/bone interface at or below its initial level and maintaining levels of stress in the proximal bone to prevent stress shielding. The results were compared with those from other optimization studies.     

Denosumab prevents periprosthetic bone mineral density loss in the tibial metaphysis in total knee arthroplasty

BackgroundPeriprosthetic bone quality is one of the most important factors preventing early prosthesis migration and long-term failure. Although denosumab, which binds to the receptor activator of nuclear factor kappa-B ligand (RANKL), has been linked with periprosthetic bone mineral density (BMD), the effectiveness of denosumab against bone loss remains unclear. We hypothesized that denosumab treatment after total knee arthroplasty (TKA) could prevent periprosthetic bone resorption.MethodsIn this prospective cohort study, 28 patients with primary knee osteoarthritis were divided into two groups: denosumab (denosumab and vitamin D) and control (vitamin D only) groups. All patients underwent TKA with the same implant model and received medication after surgery. We used dual-energy X-ray absorptiometry to measure periprosthetic BMD after TKA.ResultsIn the control group, the BMD of the proximal medial tibia decreased drastically at 12 months after TKA (− 19.7%). Denosumab treatment significantly preserved this BMD loss (0.7%). The linear regression analysis revealed that denosumab intervention had the highest significantly positive relationship with BMD.ConclusionsOur results indicate that denosumab treatment significantly reduces periprosthetic BMD loss, even at the early stages after TKA. This therapeutic strategy may facilitate early stable fixation of the prosthesis which, in turn, may help to prevent early implant migration and reduce the need for revision surgery.     

Mast cells accumulate in rat bone marrow after ovariectomy

We have previously shown that mast cells (MC) may act as accessory cells of bone resorption in a synchronized model of resorption. The aim of this study was to verify whether bone marrow MC accumulated during the phase of rapid osteopenia development in estrogen-deprived rats. Sprague-Dawley rats, 90 days old, were subjected to bilateral ovariectomy (OVX) or sham surgery (controls). Bone histomorphometry was performed in the proximal tibia metaphysis. Thirty days after surgery, serum estradiol had dropped (p < 0.002), and osteopenia was well established in the OVX rats (trabecular bone volume decreased by 69%, p < 0.0001). The indices of bone resorption were strongly modified: the number (p < 0.0001) and individual activity (p < 0.001) of the trabecular osteoclasts were prominently increased in the OVX rats. Ovariectomy resulted in a dramatic increase in the number of bone marrow MC (p < 0.0001), 97% of which were of the mucosal subtype. These results show that MC accumulate concomitantly with osteoclast generation in estrogen-deficient rats. Although the biological significance of this MC increase is unknown from these results, we hypothesize that MC might play a role in ovariectomy-induced bone loss similar to that they we previously proposed in a mechanically activated model of resorption.     

全髋关节置换术对股骨近端骨重建的影响

目的 采用Wolff骨重建理论分析全髋关节置换（total hip arthroplasty,THA）对股骨近端骨重建进程的影响。方法 根据骨重建控制方程,利用Python语言编写骨重建程序。在ABAQUS软件中分别建立术前股骨模型与术后股骨及假体有限元模型。对比THA手术前后骨重建进程,分析假体植入对THA术后中远期股骨力学性能的影响。结果 假体植入后,股骨近端应力持续降低,受力点由股骨头转移到假体,出现明显的应力遮挡现象。应力遮挡区域内骨丢失现象严重。股骨干皮质骨变薄,应力遮挡有所缓解。假体底端内侧受挤压,应力显著高于外侧,此处骨质分布不均。结论 THA术后股骨近端内侧出现明显的应力遮挡,导致骨丢失,造成假体松动;假体底端两侧应力水平存在差异,引起骨质分布不均,导致假体与股骨配合不紧密,造成术后患者大腿中段的疼痛。     

Resorption patterns of calcium-phosphate cements in bone

Two calcium phosphate cements, one monophasic and the other biphasic, have been used as bone void filler in a sheep model. The cements were injected into a slot defect in the proximal tibia and into a cylindrical defect in the distal femur. In this study, we focused on the resorption pattern of the two cement formulations and the subsequent biologic reaction. Bone remodeling occurred synchronously with the resorption of the implant material in a creeping substitution process. Cracks and pores in the monophasic cement were filled with osseous tissues. The biphasic cement showed faster resorption of the matrix. The more slowly resorbing granules were surrounded by newly grown bone, thus providing an inverse scaffold for cancellous bone regeneration. In highly loaded areas, the long-term support function of the fixation appears to be critical. Because cortical bridging of the defects was seen in only one case, it can be concluded that calcium-phosphate cements are preferentially suitable as cancellous bone substitute materials.     

螺旋型髋臼与压配型髋臼的临床应用分析

背景：在人工全髋关节置换髋臼假体的选择上,多数研究认为螺旋型髋臼较压配型髋臼能的稳定性好。 目的：对比螺旋型髋臼与压配型髋臼两种不同全髋关节置换的临床疗效。 方法：回顾性分析选择螺旋型髋臼与压配型髋臼两种不同人工全髋关节置换39例患者临床资料。 结果与结论：①随访时间：随访4~51个月,平均32.6个月。②Harris评分：末次随访时两组Harris评分均较置换前明显提高(P < 0.05),且螺旋型髋臼假体组稍高于压配型髋臼假体组,但差异无显著性意义。③不良反应：压配型髋臼假体组置换1年后松动1例,术后行走疼痛3例,髋臼假体周围成骨6例,髋臼假体周围出现透亮带3例,髋臼假体周围骨硬化1例,髋臼假体周围骨吸收1例;螺旋型髋臼假体组髋臼假体周围成骨3例,髋臼假体周围出现透亮带1例,髋臼假体周围骨吸收1例。表明螺旋型髋臼假体的初始稳定性优于压配型髋臼假体。      

影响人工全髋关节置换稳定性的因素

背景：人工全髋关节置换后出现假体松动的现象较常见,了解影响人工全髋关节稳定性的因素对提高人工全髋关节置换疗效是十分必要的。 目的：总结近年人工全髋关节置换稳定性影响因素的最新研究进展,进一步认识人工全髋关节的稳定性。 方法：应用计算机检索中国期刊全文数据库1997-01/2010-12有关人工髋关节置换后假体无菌性松动的相关文章,检索词“人工关节,置换,稳定性”。检索文献量总计98篇,最终纳入符合标准的文献30篇。 结果与结论：人工全髋关节置换稳定性的影响因素及发病机制较为复杂,其主要原因是力学因素,其次是生物学因素,它们共同结果是造成骨吸收、骨溶解,最终导致假体松动、骨质破坏。其过程还与许多细胞因子的参与密切相关。针对引起人工全髋关节稳定性的影响因素,可以从关节材料、安放角度、抑制磨损颗粒移动、促进成骨及抑制骨吸收等方面来防治。     

Repair of a proximal femoral bone defect in dogs using a porous surfaced prosthesis in combination with recombinant BMP-2 and a synthetic polymer carrier

Total hip arthroplasty (THA) has become an almost standard procedure for the treatment of various hip lesions. However, one of the limitations has been the mechanical loosening of the prosthesis, a condition termed peri-prosthetic osteolysis. Consequently, at revision surgery, various grades of bone defect are often noted. Alternative approaches aimed at overcoming this problem have included a special design of the revision prosthesis and allo- or autogeneic bone grafting in combination with or without biomaterials. In a further attempt to address the loosening of the prosthesis, we have combined human bone morphogenetic protein-2, produced by DNA recombination (rhBMP-2) with a new synthetic biodegradable polymer (poly-D,L-lactic-acid-para-dioxanone-polyethyleneglycol block co-polymer; PLA-DX-PEG). We present data on the efficacy of the rhBMP-2 laden prosthesis to reconstruct a bone defect in a canine model. In this model, medial half of the proximal femur was surgically resected to create a bone defect that was repaired with the rhBMP-2/PLA-DX-PEG composite. Twelve weeks after implantation, the original bone defects in the rhBMP-2 treatment groups had been repaired. Thus, this type of 'hybrid' prosthesis may provide a new modality to repair bone defects or restore lost bone mass encountered in revision arthroplasty.     

The effect of different humeral prosthesis fin designs on shoulder stability: A computational model

Humeral prostheses commonly use a fin structure as an attachment point for the supraspinatus muscle in total shoulder arthroplasty (TSA), but these fins may cause injury to the muscle during implantation, inadvertently influencing stability. In order to prevent supraspinatus injury, the effect of different humeral prostheses on shoulder joint stability needs to be investigated. A commercially available prosthesis and two modified humeral prostheses that substituted the fin structure for 2 (2H) or 3 holes (3H) were evaluated using computational models. Glenohumeral abduction was simulated and the superioinferior/anterioposterior stability of the shoulder joint after TSA was calculated. The results revealed that the 2H design had better superioinferior stability than the other prostheses, but was still less stable than the intact shoulder. There were no obvious differences in anterioposterior stability, but the motion patterns were clearly distinguishable from the intact shoulder model. In conclusion, the 2H design showed better superioinferior stability than the 3H design and the commercial product during glenohumeral joint abduction; the three prostheses show similar results in anterioposterior stability. However, the stability of each tested prosthesis was not comparable to the intact shoulder. Therefore, as a compromise, the 2H design should be considered for TSA because of its superior stability.     

平台转移设计种植体植入1年后下颌后牙区的骨丧失

背景：传统两段式种植体修复后种植体颈部牙槽骨的吸收一直被认为是种植术后的正常反应。 目的：评价下颌后牙区两段式种植体应用平台转移设计后周围骨丧失情况。 方法：50例患者共植入88颗种植体,实验组植入40颗Ankylos种植体,采用平台转移设计;对照组植入48颗3i种植体,采用传统对接设计。所有种植体均为潜入式植入,肩台均平齐牙槽嵴顶水平,3个月后完成最终修复。 结果与结论：所有种植体均完成骨结合。与种植体植入时相比,功能负重12个月后,实验组种植体周围骨丧失高度为(0.31± 0.39) mm,对照组种植体周围骨丧失高度为(0.94±0.43) mm,两者差异有非常显著性意义。随访期内,种植体无松动、脱落,牙龈组织健康,成功率为100%。结果显示种植体功能负重12个月后,平台转移设计可以减少种植体颈部骨吸收,保持种植体周围骨组织的稳定性。     

Iron lactate-induced osteopenia in male Sprague-Dawley rats.

Osteopenia was induced in rats fed a diet containing 50,000 ppm (5%) iron lactate for 2 or 4 weeks. Blood chemistry, urinalysis, and bone histomorphometry of the proximal tibial metaphysis were performed. Urinary pyridinoline and deoxypyridinoline and the osteoclast number per bone surface were selected for the measurement of dynamic resorption. The osteoclast surface, eroded surface, and osteoblast surface increased at both ends of the exposure periods, and bone resorption and formation both increased. The bone volume, trabecular thickness, and trabecular number decreased, and the secondary spongiosa of proximal metaphysis showed a marked bone loss. However, no mineralization defect was observed. At the end of the 2-week exposure period, biomarkers of osteoclasts and osteoblasts had increased the most, and the osteoblast surface, osteoclast surface, and osteoclast number per bone surface increased with prolonged exposure. The pathological changes of the bone lesion in iron lactate-overloaded rats were similar to those in rats of the osteoporotic model, because they consisted of changes reflecting the increase of bone resorption and formation without an osteomalacic change. However, the decline of serum parathyroid hormone (PTH) levels was different from that of the osteoporosis model rat. We concluded iron-induced bone lesions probably differ from those of low turnover bone diseases.     

In vivo histologic and biomechanical characterization of a biodegradable particulate composite bone cement

A biodegradable particulate composite bone cement consisting of a crosslinked gelatin matrix and tricalcium phosphate particles was implanted intraosseously in rabbits for up to 12 weeks. Cured cylindrical implants were inserted in holes drilled in the proximal tibial metaphysis. Sequential fluorochrome labeling and radiographs were done, and specimens were processed for decalcified and nondecalcified histology. At 4 weeks, the cross-sectional diameter of the implant was slightly greater than at implantation. There was considerable dissolution of the matrix and some new bone ingrowth. At 12 weeks, the diameter was reduced to half the original diameter and bone had grown throughout the matrix. In the distal femur, freshly mixed cement was used to stabilize an osteochondral fracture. Mechanical testing of the cement-stabilized fracture revealed a decrease in compressive strength and modulus at 4 weeks followed by an increase to greater than initial values at 12 weeks. Over time, the osteochondral fragment subsided into the underlying cement, but the subsidence did not correlate with mechanical strength. This osteochondral fracture model permits measurement of the overall material properties of a cement simultaneously weakened by resorption and reinforced by ingrowing bone.     

Loss in mechanical contact of cementless acetabular prostheses due to post-operative weight bearing: a biomechanical model

The primary stability of cementless acetabular components is a prerequisite for their clinical success. The target of the present study was to analyse possible effects of post-operative joint loading on the initial mechanical stability of a press-fitted acetabular prosthesis. For this purpose, a three-dimensional finite element model of the pelvic bone with acetabular reconstruction was set-up. The analysis included two steps: (1) simulation of the prosthesis press-fit implantation and (2) simulation of the instant of peak resultant hip loading during the one-legged stance. The difference between the contact pressures at the bone/implant interface, at the end of the second step and those at the end of the first step was calculated and assumed as an index of variation in mechanical contact due to post-operative weight bearing. The results show that, due to hip loading, contact pressures given by press-fit increase in the postero-superior acetabular region but decrease in the antero-inferior acetabular region. The calculated area in which the contact pressures decrease extend to about 30% of the total contact surface. These results imply that post-operative joint loading significantly reduces the mechanical stability given by press-fit. The decrease in contact pressures at the bone/implant interface may result in a lack of osteointegration, possibly hindering the implant secondary stability. It may also create a route for wear debris, possibly favouring periprosthetic osteolysis, which may lead to further loss in contact and clinical failure of the implant due to loosening.     

Bone formation is not coupled to bone resorption in site-specific manner in adult rats

The trabecular bone of the secondary spongiosa of mature rats shows a coupling of bone formation to resorption. It has been clearly shown that in adult man the coupling of formation and resorption involves a site-specific sequence of events, in which bone resorption is normally followed, at the same site, by bone formation. Whether the coupled processes of bone resorption and formation also occur at the same site in the rat is controversial. To elucidate the spatial relationship between bone formation and resorption in the rat, we compared the percentage of crenated and non-crenated cement lines with the percentage of crenated and non-crenated bone surfaces in the proximal tibia of adult rats aged 16 weeks to 2 years. A similar comparison was also made using bone from adult human iliac crest. We found that the trabecular bones of 16-week-old and 7-month-old rats exhibited a low percentage (7–11%) of crenated cement lines, which is opposite to the proportion (88%) we observed in human trabecular bone. In contrast, the surfaces of rat bone trabeculae showed a similar low proportion of crenated surface to human bone (rat 1.1–1.4% vs. 5% in humans). In older (2 years) rats, in which bones have ceased to grow in length, the percentage of cement lines that were crenated increased to 45%. These results imply that the major proportion of bone formation in the trabecular bone of growing rats occurs on non-resorbed surfaces. Thus, although there is substantial evidence that bone formation is coupled to resorption in the rat, such that increased resorption is associated with increased formation, and suppression of resorption suppresses bone formation, bone formation does not necessarily occur on a previously resorbed site. This suggests that in the rat, the processes are not coupled by local release of cytokines or local cell interactions but by some other signal, such as mechanical stimulation. Since site-specificity appears not to be crucial to the coupling of formation to resorption, the greater site-specificity of coupling in man, and in older rats, may be attributable to a more static skeleton, which engenders a closer spatial correlation between bone formation and the resorption that induced it. © 1993 Wiley-Liss, Inc.     

Long-Term Results of Total Hip Arthroplasty with an Extensively Porous Coated Stem in Patients Younger than 45 Years Old

Purpose

This study analyzed the long-term results of cementless total hip arthroplasty using an extensively porous coated stem in patients younger than 45 years old.

Materials and Methods

The clinical and radiographic results of 45 hips from 38 patients who underwent cementless total hip replacement arthroplasty with an AML prosthesis were reviewed retrospectively. The average follow-up was 12 years (range, 10-15 years).

Results

The average Harris hip score at the time of final follow-up was 87.3 (range 77-94) points. Forty two hips (93.3%) showed excellent and good clinical results. Osteolysis occurred around the stem in 20 hips (44.4%) and around the cup in 26 hips (57.8%). Stress-mediated femoral resorption was observed in 33 hips (73.3%) at 10 years. There was no incidence of resorption progressing after 5 years postoperatively. There was no stem loosening. Five hips were revised for osteolysis, cup loosening and polyethylene wear.

Conclusion

The long term results of total hip arthroplasty using an extensively porous coated stem were acceptable, and there was no case involving the progression of proximal bone resorption.