The influence of femoral head surface roughness on the wear of ultrahigh molecular weight polyethylene sockets in cementless total hip replacement.

A theoretical relationship was recently proposed relating the wear behavior of polymetric bearing materials articulating against hard counterfaces.(1) This model attempts to predict the influence of surface roughness on wear. Laboratory-based studies have been used to establish the validity of these relationships, but their application to the clinical situation has not been investigated fully. Forty-two retrieved PCA hip joints have been assessed. The total wear volume was calculated from the penetration measured using the shadowgraph method, and roughness of the articulating surfaces was recorded using noncontacting profilometry. The roughness of the explanted femoral heads was observed to increase (median S(a) - 10. 35 nm worn region, 3.05 nm peripheral region), while that of the acetabular liner fell dramatically (median S(a) - 41 nm worn region, 212 nm unworn region). No evidence of a relationship between the topography of the worn regions of the femoral head and that of the acetabular liner could be found. Similarly, the strength of the association between the surface roughness and the clinical wear factor was considerably poorer than that achieved in laboratory experiments. A number of reasons for this observation are proposed. Most deleterious was considered to be the inability of the roughness parameters to describe the damaging features of the surface adequately. Uncertainty as to when the surface of the component degrades during its life serves to introduce further doubt as to the application of the wear models in the clinical environment. In conclusion, this study fails to provide clinical evidence to substantiate the relationship between surface finish and wear rate. The adoption of standardized measurement parameters and techniques would facilitate the direct comparison of joint types and the selection of the most advantageous materials.     

Effect of the initial implant fitting on the predicted secondary stability of a cementless stem

A numerical model able to investigate the influence of biomechanical factors on the long-term secondary stability of implants would be extremely useful for the design of new cementless prosthetic devices. A purely biomechanical model of osseo-integration has been developed, formulated as a rule-based adaptation scheme. Due to its complexity, the problem was divided into three steps: preliminary implementation of the model (proof of concept); implementation of the complete model and investigation of the model solution; and model validation. The paper describes the first of these three steps. The model was implemented as a discretestates machine, and the few parameters required were derived from the literature. It was then applied to a real clinical case. The study was conducted using the frictional contact finite element model of a human femur implanted with a cementless anatomical stem. A stable solution was achieved after between three and 15 iterations for all initial positions considered. Similar initial conditions yielded similar final configurations. The model predicted all initial configurations, with the exception of a partial osseo-integration, ranging between 62% (distal fit) and 78% (proximal fit) of the viable interface. This is in good agreement with the values reported in the literature that never exceed 75%, even in the best conditions, and report better clinical results for proximal fit. For the varus configuration, which lacks cortical support, the algorithm predicted a completed loosening.     

Load-transfer analysis after insertion of cementless anatomical femoral stem using pre- and post-operative CT images based patient-specific finite element analysis

Periprosthetic bone remodeling is commonly seen after total hip arthroplasty, but the remodeling pattern differs among patients even in those implanted with the same stem. Remodeling occurs mainly because of the difference in load transmitted from the stem to the femur. In this study, we evaluated the load-transfer pattern in eight female patients implanted with an anatomical stem on an individual basis by patient-specific finite element analysis that is based on pre- and postoperative computed tomography images. Load transfer was evaluated using interface stress between the stem and bone. One of eight patients demonstrated proximal dominant load transfer, while the other patients demonstrated a distal dominant pattern. The results of our biomechanical simulations reveal the differences in load-transfer pattern after surgery among patients with the same anatomical stem.     

含抗生素骨水泥股骨柄与非骨水泥髋臼金属托结合全髋置换治疗中老年股骨颈骨折内固定失败19例

背景：中老年股骨颈骨折内固定失败后的治疗充满挑战性,最佳治疗方法尚未达到一致。 目的：观察含抗生素骨水泥股骨柄与非骨水泥髋臼金属托组合的全髋关节置换治疗股骨颈骨折内固定失败的效果。 方法：纳入股骨颈骨折内固定失败后行人工全髋关节置换患者19例,假体均为含抗生素骨水泥股骨柄与非骨水泥髋臼金属托组合的全髋关节。髋臼侧采用生物性假体压配固定,股骨侧采用带抗生素骨水泥假体固定。12例选取金属-聚乙烯承重界面,7例选取陶瓷-聚乙烯承重界面。置换后随访,定期摄片监测假体位置,并指导功能锻炼,记录髋关节功能恢复状况。 结果与结论：手术时间(110±55) min,术中出血量(510±60) mL,置换后出血量(310±40) mL。切口均一期愈合,未见局部红肿,脓性渗出。双下肢畸形恢复,长度相差均小于1 cm。19例全部获得随访,随访期间所有病例均未见假体松动征象。置换后1年随访Harris髋关节评分显著高于置换前(P < 0.05),其中优10例,良8例,中1例,差0例,优良率为94.7%。提示全髋关节置换治疗股骨颈骨折内固定失败有一定困难,采用含抗生素骨水泥股骨柄与非骨水泥髋臼金属托组合,可加强围手术期处理以及针对性的功能锻炼,患者关节疼痛以及活动度可得到明显改善。     

Effects of anodic oxidation parameters on a modified titanium surface

Bioactive ceramics used as coating materials combine the conductive properties of a bioceramic with the mechanical stability of the metal implant. We studied a calcium zirconium phosphate-containing coating material, FA-CZP [Ca(5)(PO(4))(3)F, CaZr(4)(PO(4))(6)], that is relatively insoluble in the biological milieu. The reaction of bone to this material was investigated histologically and histomorphometrically in an animal trial. Cylindrical Ti6Al4V specimens that had been coated with FA-CZP by plasma spraying were implanted in the femoral condyles of rabbits. The implants were left in place for 2, 4, 6, 12, and 14 weeks. FA-CZP led to impaired mineralization of the newly formed bone at the interface. Noncalcified osteoid was found throughout the whole study period. The layer seemed to become thicker with time. The mineralization disorder is evidently caused by zirconium ions. The presence of zirconium in the osteoid in contact with the implant was demonstrated by means of two different staining methods.     

Long-term follow-up results of a second-generation cementless femoral prosthesis with a collar and straight distal fixation channels

Purpose

We evaluated the results of more than 10 years of follow-up of total hip arthroplasty using a second-generation cementless femoral prosthesis with a collar and straight distal fixation channels.

Materials and Methods

One hundred five patients (129 hips) who underwent surgery between 1991 and 1996 for primary total hip arthroplasty using cementless straight distal fluted femoral stems were followed for more than 10 years. Ninety-four hips in 80 patients were available for clinical and radiologic analysis. The mean age at the time of surgery was 47 years, and the mean duration of follow-up was 14.3 years.

Results

The mean Harris hip scores had improved from 58 points to 88 points at the time of the 10-year follow-up. Activity-related thigh pain was reported in nine hips (10%). At the last follow-up, 93 stems (99%) were biologically stable and one stem (1%) was revised because of loosening. No hip had distal diaphyseal osteolysis. Proximal femoral stress-shielding was reported in 86 hips (91%). We found no significant relationship between collar-calcar contact and thigh pain, stem fixation status, or stress-shielding. The cumulative survival of the femoral stem was 99% (95% confidence interval, 98-100%) after 10 years.

Conclusion

The long-term results of total hip arthroplasty using a second-generation cementless femoral prosthesis with a collar and straight distal fixation channels were satisfactory; however, the high rate of proximal stress-shielding and the minimal effect of the collar indicate the need for some changes in the stem design.     

The influence of the scaffold design on the distribution of adhering cells after perfusion cell seeding

In natural tissues, the extracellular matrix composition, cell density and physiological properties are often non-homogeneous. Here we describe a model system, in which the distribution of cells throughout tissue engineering scaffolds after perfusion seeding can be influenced by the pore architecture of the scaffold. Two scaffold types, both with gyroid pore architectures, were designed and built by stereolithography: one with isotropic pore size (412 ± 13 μm) and porosity (62 ± 1%), and another with a gradient in pore size (250-500 μm) and porosity (35%-85%). Computational fluid flow modelling showed a uniform distribution of flow velocities and wall shear rates (15-24 s(-1)) for the isotropic architecture, and a gradient in the distribution of flow velocities and wall shear rates (12-38 s(-1)) for the other architecture. The distribution of cells throughout perfusion-seeded scaffolds was visualised by confocal microscopy. The highest densities of cells correlated with regions of the scaffolds where the pores were larger, and the fluid velocities and wall shear rates were the highest. Under the applied perfusion conditions, cell deposition is mainly determined by local wall shear stress, which, in turn, is strongly influenced by the architecture of the pore network of the scaffold.     

股骨前面血供分布特点与骨膜（骨）瓣设计

目的：为股骨干骨折骨不连、骨缺损设计骨膜（骨）瓣修复术式提供解剖学基础。方法：在４０侧成人下肢标本上，对股骨前面骨膜血管的来源、走行、分支、分布及其吻合进行观测，并在标本上进行摹拟术式设计。结果：股骨前面骨膜血供，来自股外侧肌支、股中间肌支、膝降动脉、膝上外动脉、股动脉和股深动脉肌间隔支呈节段性分布的肌骨膜支和骨膜支。肌骨膜支外径１．４～１．７ｍｍ，长度１．７～５．６ｃｍ；骨膜支外径０．４～０．６ｍｍ，长度１．２～１．５ｃｍ。骨膜血管多呈向下或水平走行，达骨膜后分出升支、降支及吻合支，相互吻合成网。结论：可以节段骨膜支为蒂设计股骨前面骨膜瓣，修复股骨干骨折骨不连、骨缺损     

全髋关节置换术中臼杯水平位移对股骨侧非骨水泥型假体-骨界面应力影响的有限元分析

目的　利用三维有限元力学分析方法, 研究全髋关节置换术中臼杯水平位移对股骨侧非骨水泥型假体-骨界面应力分布的影响。 方法　选取正常人体的骨盆及股骨为实验对象, 螺旋CT 扫描,利用计算机仿真技术对CT图像进行三维重建,建立髋关节及股骨模型,进行全髋关节置换的模拟手术, 臼杯位置从髋关节旋转中心外侧10mm处起,水平内移,每隔2 mm为一个实验组,至内移至旋转中心内侧10 mm,共分11个实验组。加载关节负荷,观察股骨侧假体-骨界面间的Von Mises应力分布情况, 对结果进行统计分析。 结果　臼杯的水平位移没有改变股骨总体的应力云分布;各组假体-骨界面应力均值（4.728±2.152）-（5.431±2.465）MPa,均值有差异,差异有统计学意义;应力均值、极差、标准差均随内移而降低,呈高度的负相关。近端假体-骨界面的应力变化,与整个股骨的应力变化相似。 结论　假体的水平内移可以降低股骨侧假体-骨界面间的Von Mises应力,内移可以使界面的应力分布更均匀。     

The effect of cyclic strain on embryonic stem cell-derived cardiomyocytes

Cardiomyocytes in the body are subjected to cyclic mechanical strain induced by the rhythmic heart beating. In this study, we tested the hypothesis that cyclic strain promotes cardiomyogenesis of embryonic stem cell-derived cardiomyocytes (ESCs). ESCs cultured on elastic polymer [poly(lactide-co-caprolactone), PLCL] scaffolds subjected to cyclic strain in vitro displayed elevated cardiac gene expression compared to unstrained controls. Six weeks after implantation into infarcted rat myocardium, the elastic cardiac patches (ESC-seeded PLCL scaffolds) showed reduced fibrotic tissue formation, likely due to a combination of lower apoptotic activity, higher vascular endothelial growth factor (VEGF) expression, and more extensive angiogenesis in the strained versus unstrained control [ESC-seeded, non-elastic poly(lactide-co-glycolide) scaffolds] patches. Importantly, cardiac gene expression was upregulated in the elastic patches compared to control, with evidence for cardiomyocyte-specific microstructures including myofibrillar bundles and Z-lines. This study shows that the use of an elastic polymer scaffold designed to permit mechanical strain transduction as a cell transplantation vehicle significantly increases cardiomyogenesis of the implanted ESCs.     

Effects of prosthesis design and impression techniques on human cortical bone strain around oral implants under load

PurposeThe purpose of this study was to evaluate the effects of two different prosthetic designs (screw-retained versus cement-retained) and two impression techniques (open versus closed tray) on bone-level strains around implants.Materials and methodsTwo Ø 4.1 mm × 10 mm Straumann implants were placed in the bilateral fibulas of six fresh cadavers; bone segments were removed en bloc. Twelve implant-level and six abutment-level (18 total) working casts were made to fabricate fixed partial dentures, resulting in three test groups: Group 1: closed-tray technique/implant-level model/screw-retained prostheses; Group 2: closed-tray technique/abutment-level model/cement-retained prostheses; Group 3: open-tray technique/implant-level model/screw-retained prostheses. Linear strain-gauges were bonded to the cortical bone between implants and the lateral wall of the fibula in close proximity to the implant necks in each bone fragment. Strain-gauge signals were digitized by a data acquisition system and corresponding software at a sample rate of 10 KHz, simultaneously monitored from the computer during application of an external static load of 150 N on the middle of the pontic, using a loading frame.ResultsThe approximal and lateral strains were extremely similar in both prosthetic groups (p > 0.05). Within-group comparisons for the indirect impression technique showed that approximal and lateral strains in screw- and cement-retained prostheses were similar (p > 0.05). Neither the prostheses design nor the impression technique had any discernable effect on bone-level strain.ConclusionStrains on the cortical bone around two implant supported, 3-unit screw- or cement-retained fixed prostheses, fabricated either by direct or indirect impression techniques on Straumann dental implants, are similar under a 150 N static load.     

股骨内髁参数对单髁置换中截骨及假体设计的参考意义

BACKGROUND: Knee-parameter measurements play an important role in the designing of the knee prosthesis. Currently, we have more and more research of the total knee replacement, while uni-condylar knee replacement study is few.  OBJECTIVE: To obtain the parameters of the normal femoral condyles and explore its correlation with osteotomy and prosthesis design of the knee joint during uni-condylar knee replacement. METHODS: Normal knee joints of 60 cases (60 knees) were selected. We measured the parameters by using thin-section CT scan and post-processing techniques, including arc diameter of the lowest point of the femoral condyle on the coronal plane, arc diameter of the distal point of the posterior condyle of the femur on the transverse plane, arc diameter of the distal point of the posterior condyle of the femur on the sagittal plane, and arc diameter of the lowest point of the femoral condyle on the sagittal plane, and analyzed the correlation with sex and height.  RESULTS AND CONCLUSION: The diameter of the arc that passes through the lowest point of femoral medial condyle in the coronal plane was (42.685±1.389) mm. The diameter of the arc that passes through the farthest point of posterior of femoral medial condyle in the cross-section was (42.732±1.440) mm. The diameter of the arc that passes through the lowest point of femoral medial condyle on the sagittal plane was (45.473±1.332) mm. The diameter of the arc that passes through the farthest point of posterior of femoral medial condyle on the sagittal plane was (42.587±1.446) mm. The results illustrate that knee condyle related parameters were positively correlated with height. Parameters in males were significantly greater than in females. The diameter of the arc that passes through the lowest point of femoral medial condyle on the sagittal plane was significantly larger than that of the farthest point of femoral posterior medial condyle on the sagittal plane (P < 0.001). There was no significant difference among the diameter of the arc that passes through the lowest point of femoral medial condyle on the coronal plane, the diameter of the arc that passes through the farthest point of posterior of femoral medial condyle on the cross-section and that of the farthest point of femoral posterior medial condyle on the sagittal plane.       

The influence of the valence state of titanium in MgCl2-supported titanium catalysts on olefin polymerization

The relationships between the valence state of titanium in MgCl₂-supported titanium catalysts and polymerization performances for ethylene and propylene were studied. When the titanium species of the supported titanium catalyst 1 was preliminarily reduced by treating it with AlEt₃, the resulting catalyst system 2 had lost the activity for propylene polymerization completely. The catalyst activity for ethylene polymerization was found to be reduced to 20% of that of the original catalyst 1. In the AlEt₃-pretreated catalyst 2 no Ti⁴⁺ is found and 80% of the total titanium is present as Ti²⁺. The catalyst system 2 plus AlEt₃, however, does exhibit activity towards ethylene-propylene copolymerization, propylene insertion being possible if the end of the growing polymer chain is an ethylene unit. The titanium in the AlEt₃-reduced catalyst 2 could be oxidized again by treatment with various agents. The oxidized catalysts 3, in conjunction with freshly added AlEt₃ as cocatalyst, are active for propylene polymerization and show increased activity for ethylene polymerization in relation to the extent of oxidation.     

The thalamic projection to cortical area 17 in a congenitally anophthalmic mouse strain

The thalamocortical projection innervating area 17 in the congenitally anophthalmic ZRDCT-An mouse was compared with its counterpart in normal-eyed mice of different strains by the horseradish peroxidase method. The results indicate that, despite absence of retinal afferents and a reduction of its neuronal population to 76% of normal, the dorsal nucleus of the lateral geniculate body in the ZRDCT-An mouse projects to area 17 in an essentially normal topographic pattern. Our evidence also indicates the existence, both in normal-eyed and ZRDCT-An mice, of an extrageniculate thalamocortical projection to area 17, arising in particular from the nucleus lateralis posterior but in lesser degree also from the nucleus lateralis dorsalis. In both normal and anophthalmic mice, this extrageniculate projection favors the lateral and posterior parts of area 17; however, the projection to these parts is considerably greater in the congenitally anophthalmic than in the normal-eyed mouse.Compensatory innervation thus appears to occur in the anophthalmic mouse not only at the level of the primary retinorecipient nucleus of the geniculostriate system, but also at the level of the visual cortex that is once removed from the direct effects of congenital denervation.     

The effect of strain rate on fracture toughness of human cortical bone: a finite element study

Evaluating the mechanical response of bone under high loading rates is crucial to understanding fractures in traumatic accidents or falls. In the current study, a computational approach based on cohesive finite element modeling was employed to evaluate the effect of strain rate on fracture toughness of human cortical bone. Two-dimensional compact tension specimen models were simulated to evaluate the change in initiation and propagation fracture toughness with increasing strain rate (range: 0.08–18 s⁻¹). In addition, the effect of porosity in combination with strain rate was assessed using three-dimensional models of micro-computed tomography-based compact tension specimens. The simulation results showed that bone’s resistance against the propagation of a crack decreased sharply with increase in strain rates up to 1 s⁻¹ and attained an almost constant value for strain rates larger than 1 s⁻¹. On the other hand, initiation fracture toughness exhibited a more gradual decrease throughout the strain rates. There was a significant positive correlation between the experimentally measured number of microcracks and the fracture toughness found in the simulations. Furthermore, the simulation results showed that the amount of porosity did not affect the way initiation fracture toughness decreased with increasing strain rates, whereas it exacerbated the same strain rate effect when propagation fracture toughness was considered. These results suggest that strain rates associated with falls lead to a dramatic reduction in bone’s resistance against crack propagation. The compromised fracture resistance of bone at loads exceeding normal activities indicates a sharp reduction and/or absence of toughening mechanisms in bone during high strain conditions associated with traumatic fracture.     

The influence of mechanical properties of subchondral plate, femoral head and neck on dynamic stress distribution of the articular cartilage

A few finite element models have addressed the dynamic juxtaarticular stress transmission but none focused the investigation on the combined influence of the individual moduli of the underlying bones, including the subchondral plate, the femoral head and the femoral neck of the proximal femur. A finite element model including the acetabulum and the proximal femur was analyzed with dynamic loadings to study the effects of mechanical property changes in the underlying bones of the proximal femur on the stress distribution in the cartilage at the hip joint. We found the stress distribution was most sensitive to the subchondral plate stiffening, while the overall stiffening of the underlying bones had mild effect on the shear stress on the cartilage surface (or at the subchondral bone/cartilage interface) and on the strain energy density in the cartilage. Our results indicate that the subchondral plate plays a predominant mechanical role in the initial degeneration of the cartilage. The results may offer a mechanical explanation as to why the cartilage failure is common in patients with osteoarthritis but rare in patients with osteoporosis.     

Finite element analysis of a three-dimensional model of a proximal femur-cemented femoral THJR component construct: influence of assigned interface conditions on strain energy density

A finite element analysis of the stresses in a construct, comprising a three-dimensional model of the proximal human femur in which the stem of a total hip joint replacement was cemented, was performed. The one-legged standing condition was used, with all applied forces on the proximal femur being considered. These forces were the resultant hip joint reaction force and the forces due to the activation of the abductor, ilio-psoas, and ilio-tibialis muscles. The cortical and cancellous bones were assigned anisotropic elastic properties. It was found that the mean value of the strain energy density at each of the regions considered was considerably higher when debonding was considered at both the cancellous bone-acrylic bone cement and bone cement-stem interfaces (represented using surface-to-surface Coulomb friction, coefficient of friction = 0.22) compared to when perfect bonding conditions were taken to exist at these interfaces. The significance of this finding, together with the study limitations, is discussed.     

The in-vivo wear performance of prosthetic femoral heads with titanium nitride coating

This paper reports the study performed on four titanium nitride (TiN) coated prosthetic femoral heads collected at revision surgery together with patient data. Surface topology has been examined using Scanning Electron Microscopy (SEM) and elemental analysis of both coating and substrate have been evaluated using energy-dispersive X-ray spectrometry. Quantitative assessment of the surface topography is achieved using contacting profilometry. The average Ra roughness value is calculated at five different locations for each femoral head. The UHMWPE counterface worn volume has been measured directly on the acetabular components. TiN fretting and coating breakthrough occurred in two of the four components examined. In the damaged coating areas the surface profile is macroscopically saw-toothed with average tooth height 1.5 microm. The average Ra value is 0.02 microm on the undamaged surfaces and 0.37 microm on the damaged ones. Failure of the coating adhesion resulted in the release of TiN fragments and of metallic particulate from the substrate fretting corrosion and in the increase of the head surface roughness affecting counterface debris production. Our results suggest that TiN-coated titanium alloy femoral heads are inadequate in the task of resisting third body wear mechanisms in vivo.     

The influence of electrolytes on the volume of non-metabolizing renal cortical cells

1. The metabolism of rat renal cortex slices was inhibited by iodoacetate and anoxia, and swelling was prevented by the presence in the medium of 7.2 g polyethylene glycol 6000/100 ml. (referred to as PEG medium).2. Slices were incubated for up to 12 hr in PEG medium, and in PEG media containing 440 m-osmole/kg H(2)O of an electrolyte (LiCl, NaCl, KCl or RbCl), or a non-electrolyte (glucose).3. It was concluded that the slices in all media were at equilibrium with the medium after incubation for 8 hr.4. Slices in the medium containing glucose reached the same equilibrium water content as those in the PEG medium, but slices in all the electrolyte media had significantly lower equilibrium water contents, although these did not differ significantly from each other.5. It is suggested that the results demonstrate a non-specific effect of electrolytes on the swelling of non-metabolizing cells.