The transport of wear particles in the prosthetic hip joint: a computational fluid dynamics investigation

The joint fluid mechanics and transport of wear particles in the prosthetic hip joint were analyzed for subluxation and flexion motion using computational fluid dynamics (CFD). The entire joint space including a moving capsule boundary was considered. It was found that particles suspended in the joint space are drawn into the joint gap between prosthesis cup and head during subluxation, which was also documented by Lundberg et al. (2007; Journal of Biomechanics 40, 1676-1685), however, wear particles remain in the joint gap. Wear particles leave the joint gap during flexion and can finally migrate to the proximal boundaries including the acetabular bone, where the particle deposition can cause osteolysis according to the established literature. Thus, the present study supports the theory of polyethylene wear particle induced osteolysis of the acetabular bone as a major factor in the loosening of hip prosthesis cups.     

In vivo motion of the scaphotrapezio-trapezoidal (STT) joint

It has previously been shown that the articulation of the scaphotrapezio-trapezoidal (STT) joint can be modeled such that the trapezoid and trapezium are tightly linked and move together on a single path relative to the scaphoid during all directions of wrist motion. The simplicity of such a model is fascinating, but it leaves unanswered why two distinct carpal bones would have a mutually articulating surface if there were no motion between them, and how such a simplistic model of STT joint motion translates into the more complex global carpal motion. We performed an in vivo analysis of the trapezoids and trapeziums of 10 subjects (20 wrists) using a markerless bone registration technique. In particular, we analyzed the centroid spacing, centroid displacements, kinematics, and postures of the trapezoid and trapezium relative to the scaphoid. We found that, on a gross level, the in vivo STT motion was consistent with that reported in vitro. In addition, we found that the magnitude of trapezoid and trapezium motion was dependent upon the direction of wrist motion. However, we also found that when small rotations and displacements are considered there were small but statistically significant relative motions between the trapezoid and trapezium (0.4 mm in maximum flexion, 0.3 mm in radial deviation and at least 10 degrees in flexion extension and ulnar deviation) as well as slight off-path rotations. The results of this study indicate that the STT joint should be considered a mobile joint with motions more complex than previously appreciated.     

FE-analysis of surface stresses for the tribological system in total hip prostheses]

The implantation of a total hip prosthesis is an operation which is performed frequently due to advanced hip joint damage both in humans and in veterinary medicine in dogs. The long-term result of a hip prosthesis is mainly determined by aseptic loosening of the prosthesis; among other causes, abrasion particles of the tribological pairing are responsible for the loosening. For the analysis of the surface stresses with different tribological pairings, a finite element model was generated which was based on the CAD data of a commercial total hip prosthesis. After transmission of a physiological force in the components of the three tribological pairings ceramic/polyethylene, ceramic/ceramic and metal/polyethylene, stresses were calculated. Stresses in the ceramic/ceramic tribological pairings were conspicuously higher than in the other material pairings. In the future adapted prostheses have to be developed that ensure optimal friction and absorption characteristics of the components.     

Failure of Total Hip Arthroplasties. Numerical Modeling of Debris Formation through Plastic Strains

The life span of a total hip prosthesis is one of the main points on which the long-term success of arthroplasties depends. It is, by now, widely recognized that hip arthroplasty failure is mainly due to the aseptic loosening resulting from the presence of wear debris forming at the contact interface between the femoral head and the cup of the acetabulum. The size of these particles varies from a few micrometers to some tens of micrometers or more. The main aim of this study was therefore to investigate the formation of debris in the microscopic size range. For this purpose, a numerical study was carried out on various mechanisms leading to plastic deformations, which can lead to damage and wear in material. Numerical analyses were performed with a laboratory software program LMGC90, on the evolution of the plastic strains involved in various wear mechanisms on the microscopic scale.     

Method for the estimation of a double hinge kinematic model for the trapeziometacarpal joint using MR imaging

In this paper, we propose a method to estimate the parameters of a double hinge model of the trapeziometacarpal joint (TMC) by MRI-based motion analysis. The model includes two non-orthogonal and non-intersecting rotation axes accounting for flexion–extension (F–E) and adduction–abduction (A–A). We evaluated the quality of the estimated model parameters in the prediction of the relative motion of the first metacarpal bone with respect to the trapezium. As a result, we obtained that: (a) the estimated location and orientation of the F–E and A–A axes were in agreement with previous in vitro studies, (b) the motion of the first metacarpal predicted by the 2 degrees of freedom (2DoF) model exhibits a maximum surface distance error in the range of about 2 mm and (c) four thumb postures at the boundary of the TMC range of motion are sufficient to provide a good estimation of the 2DoF TMC kinematic model and good reproducibility (～1.7 mm) of the real thumb motion at TMC level.     

人工半骨盆假体置换联合腰椎椎弓根螺钉固定术后生物力学的有限元分析

目的:建立人工半骨盆假体置换与联合腰椎椎弓根螺钉固定后的三维有限元模型,评价腰骶段生物力学改变后半骨盆假体力学结构的特点。方法:采用CT薄层扫描采集原始数据,分别建立正常骨盆、半骨盆假体置换术后以及半骨盆假体置换联合腰椎椎弓根螺钉固定术后骨盆的三维有限元模型,分别在第4腰椎上终板平面施以500 N的垂直纵向载荷,分析不同骨盆模型的应力分布特点。结果:与正常骨盆有限元模型相比,半骨盆假体置换术后健侧骨盆应力分布以骶髂关节、髋臼窝及耻骨为主,置换侧半骨盆假体以耻骨连接棒、髋臼杯及髂骨座为主,最大应力出现在耻骨连接棒,应力峰值为65.62 MPa。联合腰椎椎弓根螺钉固定后健侧应力相对减小,置换侧髂骨固定座与骶骨固定处应力相对减小,应力分布以腰椎椎弓根钉棒、耻骨连接棒及髋臼杯为主,最大应力出现在椎弓根螺钉,应力峰值为107 MPa。结论:半骨盆假体置换联合腰椎椎弓根螺钉固定后钉棒分担了半骨盆置换后健侧骨盆及置换侧髂骨固定座与骶骨固定处附近的部分应力,缓解应力集中现象,降低术后骨盆破坏风险,一定程度上增加了半骨盆置换后骨盆的稳定性。     

Numerical analysis of the effects of material parameters on the lubrication mechanism for knee prosthesis

The tibial component of current knee prostheses made of ultra high molecular weight polyethylene (UHMWPE) has a high degree of wear that causes knee inflammation, prosthesis loosening and subsequent replacement in not more than 15 years. In order to know which UHMWPE material properties have more influence on wear, a steady state lubrication model with non-Newtonian synovial fluid has been studied through numerical solution. The results show that UHMWPE has a very high elastic modulus that makes difficult a well lubricated artificial joint and induces the formation of very thin lubricating films between the moving surfaces with the same magnitude of roughness components. This study shows that the use of deformable porous materials in the tibial component could cause the lubricating film thickness to be higher than the average roughness and the pressure levels to be lower than the one predicted for UHMWPE. These two facts imply friction and wear reduction.     

Effect of cup inclination on predicted contact stress-induced volumetric wear in total hip replacement

In order to increase the lifetime of the total hip endoprosthesis, it is necessary to understand mechanisms leading to its failure. In this work, we address volumetric wear of the artificial cup, in particular the effect of its inclination with respect to the vertical. Volumetric wear was calculated by using mathematical models for resultant hip force, contact stress and penetration of the prosthesis head into the cup. Relevance of the dependence of volumetric wear on inclination of the cup (its abduction angle ?_A) was assessed by the results of 95 hips with implanted endoprosthesis. Geometrical parameters obtained from standard antero-posterior radiographs were taken as input data. Volumetric wear decreases with increasing cup abduction angle ?_A. The correlation within the population of 95 hips was statistically significant (P = 0.006). Large cup abduction angle minimises predicted volumetric wear but may increase the risk for dislocation of the artificial head from the cup in the one-legged stance. Cup abduction angle and direction of the resultant hip force may compensate each other to achieve optimal position of the cup with respect to wear and dislocation in the one-legged stance for a particular patient.     

Incidence of metal sensitivity in patients with total joint replacements.

Sensitivity to chromium, cobalt, nickel, molybdenum, vanadium, and titanium was studied by patch tests in 50 patients who had received total joint replacements. Nineteen (38%) were sensitive to one or more of the metals. In 23 patients non-traumatic failure of the prosthesis had occurred, and 15 of these patients were sensitive to metal. Out of 27 patients with no evidence of prosthesis loosening, four were sensitive to nickel and cobalt or nickel only. Dermatological reactions occurred in 13 patients after surgery; in only eight, however, was there evidence of metal sensitivity. These findings indicate that metal-on-metal total joint replacements may sensitise the patient to metals contained in the prosthesis. Although there is a high incidence of prosthesis failure among metal-sensitive patients it remains uncertain whether the loosening causes the sensitisation or vice versa.     

Multi-body simulation of a canine hind limb: model development, experimental validation and calculation of ground reaction forces

Background  

Among other causes the long-term result of hip prostheses in dogs is determined by aseptic loosening. A prevention of prosthesis complications can be achieved by an optimization of the tribological system which finally results in improved implant duration. In this context a computerized model for the calculation of hip joint loadings during different motions would be of benefit. In a first step in the development of such an inverse dynamic multi-body simulation (MBS-) model we here present the setup of a canine hind limb model applicable for the calculation of ground reaction forces.     

The cementless artificial hip cup--implant components with reliable long-term stability?

A hip joint simulator was developed to analyse the mechanism of loosening of cementless artificial hip cups. The machine induces vibrating motions and asymmetrical tilt shock loadings of the artificial cup. On measuring the primary stability of threaded cups, the simulation tests performed on pelvis substitute models, and animal and human acetabula failed to show any loosening of threaded cups fixed in place with a screw-in torque of more than 10 Nm. Instable cups became loose all the sooner, the lower the preload between the cup and femoral head. This demonstrates the importance of both the screw-in torque of the cup and the training status of the periarticular muscles.     

大直径陶瓷假体用于全髋关节置换术的稳定性和安全性

目的:探讨大直径陶瓷-陶瓷假体对髋关节置换患者术后假体磨损,稳定性和髋关节功能的影响。方法:选取我院2010年1月-2014年1月间采用大直径陶瓷-陶瓷假体行关全髋置换的股骨头坏死患者46例作为研究组。另选40例采用标准金属-聚乙烯假体手术患者作为对照组。观察并比较两组患者假体磨损情况、髋关节稳定性和功能评分。结果:研究组患者术后无一例脱位,发生假体松动1例,Harris评分为(82.04±1.92)分;对照组术后发生假体脱位4例,松动4例,Harris评分为(81.37±1.27)分;研究组假体稳定性和磨损程度优于对照组,差异具有统计学意义(P0.05),但两组髋关节功能评分无显著差异(P0.05)。发生假体松动的患者术后血沉、IL-1和IL-6浓度均高于正常值,差异具有统计学意义(P0.05)。结论:与标准假体相比,大直径陶瓷-陶瓷假体稳定性好,磨损率低,是全髋置换手术的良好假体。     

Finite element analysis of shear stresses at the implant-bone interface of an acetabular press-fit cup during impingement.

After total hip replacement (THR) impingement of the implant components causes shear stresses at the acetabular implant-bone interface. In the current study the finite element method (FEM) was applied to analyse the shear stresses at a fully bonded implant-bone interface assuming total ingrowth of the cup. The FE model of a press-fit acetabular component and the proximal part of the femoral component incorporates non-linear material and large sliding contact. The model was loaded with a superior-medial joint load of 435 N simulating a two-legged stance. Starting at initial impingement, the femoral component was medially rotated by 20 degrees . The peak tilting shear stress of -2.6 MPa at the impingement site takes effect towards the pole of the cup. The torsional shear stress at the impingement site is zero. On each side of the impingement site, there are extrema of torsional shear stress reaching -1.8 and 1.8 MPa, respectively. The global peak shear stress during impingement may indicate a possible starting point for cup loosening. The pattern of the torsional shear stresses suggests that besides the symmetric lever-out, an additional asymmetrical tilting of the cup occurs that can be explained by the orientation of the applied joint load.     

Distal Forelimb Kinematics in <Emphasis Type="Italic">Erythrocebus patas</Emphasis> and <Emphasis Type="Italic">Papio anubis</Emphasis> During Walking and Galloping

When using symmetrical gaits, terrestrial digitigrade monkeys adopt less digitigrade, i.e., more palmigrade-like, hand postures as they move with faster speeds. Accordingly, it appears that, in contrast to other mammals, digitigrady is unrelated to cursoriality in primates. However, researchers have not documented the effects of speed on distal forelimb kinematics in faster asymmetrical gaits, i.e., galloping, when ground reaction forces are typically increased owing to the decreased number of contact points during a stride, combined with higher speed. Thus, it remains possible that primates use digitigrade hand postures during these higher-speed asymmetrical gaits. We investigated 3D angles in the wrist joint and metacarpophalangeal joint of 2 habitually digitigrade terrestrial monkeys, Erythrocebus patas and Papio anubis, across a large range of walking and galloping speeds on a motorized treadmill. Nonparametric analyses reveal that angles, and therefore hand postures, are not different at the subject’s walk-gallop transition. Regression analyses show that when walking, digitigrade postures are adopted at slow speeds and more palmigrade-like postures are adopted at fast speeds. Contrary to expectations, there is little change in hand postures across galloping speeds; both subjects maintained palmigrade-like hand postures with substantial joint yield and reextension during support. These results indicate that the hands are always less digitigrade at faster speeds because the joints of the distal forelimb cannot resist the higher ground reaction forces that accompany these higher speed gaits.     

Three-dimensional finite element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems

Glenoid component loosening is the dominant cause of failure in total shoulder arthroplasty. It is presumed that loosening in the glenoid is caused by high stresses in the cement layer. Several anchorage systems have been designed with the aim of reducing the loosening rate, the two major categories being "keeled" fixation and "pegged" fixation. However, no three-dimensional finite element analysis has been performed to quantify the stresses in the cement or to compare the different glenoid prosthesis anchorage systems. The objective of this study was to determine the stresses in the cement layer and surrounding bone for glenoid replacement components. A three-dimensional model of the scapula was generated using CT data for geometry and material property definition. Keeled and pegged designs were inserted into the glenoid, surrounded by a 1-mm layer of bone cement. A 90 deg arm abduction load with a full muscle and joint load was applied, following van der Helm (1994). Deformations of the prosthesis, stresses in the cement, and stresses in the bone were calculated. Stresses were also calculated for a simulated case of rheumatoid arthritis (RA) in which bone properties were modified to reflect that condition. A maximum principal stress-based failure model was used to predict what quantity of the cement is at risk of failure at the levels of stress computed. The prediction is that 94 percent (pegged prosthesis) and 68 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival in normal bone. In RA bone, however, the situation is reversed where 86 percent (pegged prosthesis) and 99 percent (keeled prosthesis) of the cement has a greater than 95 percent probability of survival. Bone stresses are shown to be not much affected by the prosthesis design, except at the tip of the central peg or keel. It is concluded that a "pegged" anchorage system is superior for normal bone, whereas a "keeled" anchorage system is superior for RA bone.     

Effects of implant design parameters on fluid convection, potentiating third-body debris ingress into the bearing surface during THA impingement/subluxation

Aseptic loosening from polyethylene wear debris is the leading cause of failure for metal-on-polyethylene total hip implants. Third-body debris ingress to the bearing space results in femoral head roughening and acceleration of polyethylene wear. How third-body particles manage to enter the bearing space between the closely conforming articulating surfaces of the joint is not well understood. We hypothesize that one such mechanism is from convective fluid transport during subluxation of the total hip joint. To test this hypothesis, a three-dimensional (3D) computational fluid dynamics (CFD) model was developed and validated, to quantify fluid ingress into the bearing space during a leg-cross subluxation event. The results indicated that extra-articular joint fluid could be drawn nearly to the pole of the cup with even very small separations of the femoral head (<0.60mm). Debris suspended near the equator of the cup at the site of maximum fluid velocity just before the subluxation began could be transported to within 11 degrees from the cup pole. Larger head diameters resulted in increased fluid velocity at all sites around the entrance to the gap compared to smaller head sizes, with fluid velocity being greatest along the anterosuperolateral cup edge, for all head sizes. Fluid pathlines indicated that suspended debris would reach similar angular positions in the bearing space regardless of head size. Increased inset of the femoral head into the acetabular cup resulted both in higher fluid velocity and in transport of third-body debris further into the bearing space.     

中药防治假体周围骨溶解的研究进展

现如今人工关节置换术越来越多的应用于重建关节功能改善关节疾病患者的生活质量,但是术后并发症严重影响了手术的效果,人工假体周围骨溶解及假体无菌性松动又是人工关节置换术后失败的主要原因之一,所以如何预防以及发病后如何去治疗成为现今关节医生面临的重要课题。OPG/RANKL/RANK系统,炎性因子的产生,破骨细胞、成骨细胞这些都是影响人工假体术后产生无菌性松动,和引发假体周围骨溶解的重要因素,有效药物的干预治疗成为现如今关节置换术后以及围手术期的热门话题,中药因其副作用小,疗效独特,及深入的研究逐渐受到广大医生的注意,因此中药在治疗人工假体松动及骨溶解方面也得到了重大突破,本文从中医肾藏精,精生髓,髓能养骨理论着手总结中药作用于OPG/RANKL/RANK系统,抑制炎性因子、破骨细胞及促进成骨细胞增殖的研究现状。     

Failure of total hip arthroplasties. Numerical modeling of debris formation through plastic strains

The life span of a total hip prosthesis is one of the main points on which the long-term success of arthroplasties depends. It is, by now, widely recognized that hip arthroplasty failure is mainly due to the aseptic loosening resulting from the presence of wear debris forming at the contact interface between the femoral head and the cup of the acetabulum. The size of these particles varies from a few micrometers to some tens of micrometers or more. The main aim of this study was therefore to investigate the formation of debris in the microscopic size range. For this purpose, a numerical study was carried out on various mechanisms leading to plastic deformations, which can lead to damage and wear in material. Numerical analyses were performed with a laboratory software program LMGC90, on the evolution of the plastic strains involved in various wear mechanisms on the microscopic scale.     

Analysis of bone–prosthesis interface micromotion for cementless tibial prosthesis fixation and the influence of loading conditions

A lack of initial stability of the fixation is associated with aseptic loosening of the tibial components of cementless knee prostheses. With sufficient stability after surgery, minimal relative motion between the prosthesis and bone interfaces allows osseointegation to occur thereby providing a strong prosthesis-to-bone biological attachment. Finite element modelling was used to investigate the bone–prosthesis interface micromotion and the relative risk of aseptic loosening. It was anticipated that by prescribing different joint loads representing gait and other activities, and the consideration of varying tibial–femoral contact points during knee flexion, it would influence the computational prediction of the interface micromotion. In this study, three-dimensional finite element models were set up with applied loads representing walking and stair climbing, and the relative micromotions were predicted. These results were correlated to in-vitro measurements and to the results of prior retrieval studies. Two load conditions, (i) a generic vertical joint load of 3×body weight with 70%/30% M/L load share and antero-posterior/medial-lateral shear forces, acted at the centres of the medial and lateral compartments of the tibial tray, and (ii) a peak vertical joint load at 25% of the stair climbing cycle with corresponding antero-posterior shear force applied at the tibial–femoral contact points of the specific knee flexion angle, were found to generate interface micromotion responses which corresponded to in-vivo observations. The study also found that different loads altered the interface micromotion predicted, so caution is needed when comparing the fixation performance of various reported cementless tibial prosthetic designs if each design was evaluated with a different loading condition.     

The interplay between speed,kinetics, and hand postures during primate terrestrial locomotion

Nonprimate terrestrial mammals may use digitigrade postures to help moderate distal limb joint moments and metapodial stresses that may arise during high‐speed locomotion with high‐ground reaction forces (GRF). This study evaluates the relationships between speed, GRFs, and distal forelimb kinematics in order to evaluate if primates also adopt digitigrade hand postures during terrestrial locomotion for these same reasons. Three cercopithecine monkey species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway instrumented with a force platform. Three‐dimensional forelimb kinematics and GRFs were measured when the vertical force component reached its peak. Hand posture was measured as the angle between the metacarpal segment and the ground (MGA). As predicted, digitigrade hand postures (larger MGA) are associated with shorter GRF moment arms and lower wrist joint moments. Contrary to expectations, individuals used more palmigrade‐like (i.e. less digitigrade) hand postures (smaller MGA) when the forelimb was subjected to higher forces (at faster speeds) resulting in potentially larger wrist joint moments. Accordingly, these primates may not use their ability to alter their hand postures to reduce rising joint moments at faster speeds. Digitigrady at slow speeds may improve the mechanical advantage of antigravity muscles crossing the wrist joint. At faster speeds, greater palmigrady is likely caused by joint collapse, but this posture may be suited to distribute higher GRFs over a larger surface area to lower stresses throughout the hand. Thus, a digitigrade hand posture is not a cursorial (i.e. high speed) adaptation in primates and differs from that of other mammals. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.