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Strain Gradient Elasticity Solution for Functionally Graded Micro-cylinders  [PDF]
H. Sadeghi,M. Baghani,R. Naghdabadi
Physics , 2013,
Abstract: In this paper, strain gradient elasticity formulation for analysis of FG (Functionally Graded) micro-cylinders is presented. The material properties are assumed to obey a power law in radial direction. The governing differential equation is derived as a fourth order ODE. A power series solution for stresses and displacements in FG micro-cylinders subjected to internal and external pressures is obtained. Numerical examples are presented to study the effect of the characteristic length parameter and FG power index on the displacement field and stress distribution in FG cylinders. It is shown that the characteristic length parameter has a considerable effect on the stress distribution of FG micro-cylinders. Also, increasing material length parameter leads to decrease of the maximum radial and tangential stresses in the cylinder. Furthermore, it is shown that the FG power index has a significant effect on the maximum radial and tangential stresses.
The effect of endoskeleton on antibiotic impregnated cement spacer for treating deep hip infection
Kuo-Ti Peng, Liang-Tseng Kuo, Wei-Hsiu Hsu, Tsan-Wen Huang, Yao-Hung Tsai
BMC Musculoskeletal Disorders , 2011, DOI: 10.1186/1471-2474-12-10
Abstract: From Jan. 2004 to Dec. 2007, we collected a prospective cohort of consecutive 34 patients who treated with two-stage revision total hip arthroplasty for deep infection of hip joint. In group 1, fifteen patients were treated by a novel design augmented with hip compression screw while nineteen patients were treated by traditional design in group 2.No fracture of cement spacer occurred in group 1 while 6 cases developed spacer failure in group 2. (p < 0.05) There were significant differences in bodily pain and general health perception between groups (p < 0.05).Patients being treated for deep infection of hip joint using cement spacer augmented with stronger endoskeleton have lower pain levels and better joint function between stages.A two-stage revision arthroplasty was suggested as the gold standard treatment among many therapeutic alternatives for deep infections in the hip joint[1-6] Various design of antibiotics impregnated cement prosthesis, either custom made or commercially available[7], reported advantages such as effective local antibiotics delivery, continuation of patient mobility, maintenance of limb alignment, and facilitation of re-implantation, contributed to the good functional recovery after revision total hip arthroplasty(THA) [8-12]. However, fracture of the cement spacer occurred which might decrease ambulation ability and leg length discrepancy [10,11,13], and demand an additional surgery for exchange [9] (Figure 1). The introduction of metallic endoskeleton such as Kirschner wires [11,14], Rush rod[8,10], hip compression screws, intramedullary nail[15],and even custom made rod[16] aimed to increase the strength of the construct. Among those designs of endoskeleton, hip compression screw was of particular interest because it was privileged by providing angular stability that augmented the weakest link of the cement spacer [17]. It was possible that mechanical instability, pain, and cement spacer dislocation might be avoided through increasing the
Contact stresses in the human hip joint - review  [cached]
Matej Daniel
Bulletin of Applied Mechanics , 2007,
Abstract: This review gives an overview of various method used to determine hip joint contact stress: from direct measurement using implanted instrumented endoprosthesis to several methods of mathematical modeling.
Finite element study on the predicted equivalent stresses in the artificial hip joint  [PDF]
Mamdouh M. Monif
Journal of Biomedical Science and Engineering (JBiSE) , 2012, DOI: 10.4236/jbise.2012.52007
Abstract: The subsurface fatigue that occurs in the Ultra-High Molecular Weight Polyethylene (UHMWPE) hip joint cup has been identified to be correlated with the contact stress at that cup. This cup stress is known to be affected by the implant design, dimensions and materials. In this study, a 3D finite element modeling has been used to investigate the effects on the cup contact stress when using low stiffness Titanium alloy (Ti) as a femur head. Also, the effects on the cup contact stress due to using different sizes of femur heads, and the presence of metal backing shell with different thicknesses are studied. The finite element results show that the use of low stiffness Ti alloy femur head results in a significant decrease in the cup contact stress compared with Stainless Steel (SS) and Cobalt Chromium (Co Cr Mo) femur heads. The presence of metal backing shell up to 1 mm thickness results in a remarkable decrease in the cup contact stresses especially for small femur heads. Finally, the use of larger femur heads, up to 32 mm diameter, results in significant decrease in the overall predicted hip joint contact. The present results indicate that any changes in design and geometrical parameters of the hip joint have significant consequences in the long term behaviour of the artificial hip joint and should be taken into consideration.
Exact Solutions for Thermal Stresses in a Rotating Thick-Walled Cylinder of Functionally Graded Materials  [PDF]
G.H. Rahimi,M. Zamani Nejad
Journal of Applied Sciences , 2008,
Abstract: In this study, thermal stresses in a hollow rotating thick-walled cylinder made of functionally graded material under internal and external pressure are obtained as a function of radial direction to an exact solution by using the theory of elasticity. Material properties are considered as a function of the radius of the cylinder and the Poisson`s ratio as constant. The distributions of the thermal stresses are obtained for different values of the powers of the module of elasticity.
J Li,QS Zhang,YQ Lai,SL Ye,YX Liu,

金属学报(英文版) , 2005,
Abstract: The thermal stresses relaxation of Ni/NiFe2O4 system functionally graded cermet inert anode for aluminum electrolysis was optimally designed. The transient thermal stresses of the inert anode under complex boundary condition during high-temp (955℃) electrolysis were calculated using the finite-element software ANSYS, the influence of different parameters on the distribution of the thermal stresses were analyzed. The results showed that, during the process of thermal shock,the thermal hoop tensile stress on the surface of the anode is very large, which is possibly the major cause of anode crack; when the radius of the anode is between 0.05-0.15m, a range that can be realized by recent manufacturing technology, the optimum composition distribution exponent p is 0.25; The hoop tensile stresses reduce with the decrease of anode scale and also decrease with the decrease of the convection coefficient between the electrolyte and the anode.
Displacements, Strains, and Stresses Investigations in an Inhomogeneous Rotating Hollow Cylinder Made of Functionally Graded Materials under an Axisymmetric Radial Loading  [PDF]
Elise Rose Atangana Nkene, Luc Leroy Mambou Ngueyep, Joseph Ndop, Emma Sandring Djiokeng, Jean-Marie Bienvenu Ndjaka
World Journal of Mechanics (WJM) , 2018, DOI: 10.4236/wjm.2018.83005
Abstract: In this paper, an analytical and numerical study of strain fields, stress fields and displacements in a rotating hollow cylinder, whose walls were completely made in Functionally Graded Materials (FGM), was conducted. We have considered the rotating hollow cylinder submitted to an asymmetric radial loading. It is assumed that, because of the functional graduation of the material, the mechanical properties such as Young elastic modulus and the density varies in the radial direction, in accordance with a the power law function. The inhomogeneity parameter was selected between -1 and 1. On the basis of the second law of Newton, Hooke’s law and the strain-stress relationship, we established the differential equation which governs the equilibrium for a rotating hollow cylinder. We found the analytical solution and compared to the numerical solution obtained by using the shooting method and the fourth order Runge-Kutta algorithm. The analytical and numerical results lead to the conclusion that the magnitude of the tangential stresses is greater than that of the radial stresses. The changes due to the graduation of FGM does not produce consistent variations in the distribution of radial stresses, but strongly affects the distribution of tangential stresses. The tangential stresses, tangential strains and displacements are much higher at the inner surface of the cylinder wall. The internal radial pressure intensely affects the radial stresses and the radial strain.
Femoral and obturator nerves palsy caused by pelvic cement extrusion after hip arthroplasty.  [cached]
Pawel Zwolak,Peer Eysel,Joern William-Patrick Michael
Orthopedic Reviews , 2011, DOI: 10.4081/or.2011.e6
Abstract: Cement extrusion into the pelvis with subsequent palsy of the obturator and femoral nerves is a rare entity after hip replacement surgery. Cemented fixation of the acetabular cup has been considered as a safe and reliable standard procedure with very good long term results. We present a case of fifty year old female patient after hip arthroplasty procedure which suffered an obturator and femoral nerve palsy caused by extrusion of bone cement into the pelvis. Postoperative X-rays and CT-scan of the pelvis demonstrated a huge mass consisted of bone cement in close proximity of femoral and obturator nerves. The surgery charts reported shallow and weak bony substance in postero-superior aspect of the acetabulum. This weak bony acetabular substance may have caused extrusion of bone cement during press-fitting of the polyethylene cup into the acetabulum, and the following damage of the both nerves produced by polymerization of bone cement. The bone cement fragment has been surgically removed 3 weeks after arthroplasty. The female patient underwent intensive postoperative physical therapy and electro stimulation which resulted in full recovery of the patient to daily routine and almost normal electromyography results.
Cement mantle defects in total hip arthroplasty: influence of stem size and cementing technique
A. Katzer,A. Ince,M. Hahn,M. M. Morlock,W. Steens
Journal of Orthopaedics and Traumatology , 2007, DOI: 10.1007/s10195-007-0084-x
Abstract: The cause of isolated osteolysis in the femoral shaft around stem implants in patients with cemented THR has so far not been established. A number of factors have been considered such as torsional stability of the femoral stem implant, the time of reduction intraoperatively after cementing and iatrogenic and load-induced defects in the cement mantle. The aim of this in vitro investigation was to determine if the cementing technique or the thickness of the prosthesis stem, and thus its bending strength, influences the formation, extent and localisation of cement mantle defects. In vitro biomechanical loading tests were performed on twelve anatomically shaped femoral stem prostheses of two different thicknesses which were implanted in artificial bone. Six of the implants were fixed by conventional cementing technique, the other six by means of the vacuum technique. Compared with thicker implant stems, the slimmer stems fixed with the conventional cementing technique had a higher number of cracks in the cement mantle. Pore formation was localised predominantly in the interface area between the bone cement and the “cancellous” bone or “cortex” of the artificial bone. This was observed especially in the non-vacuum mixed cement, regardless of stem thickness. Large pores were found mainly in the cement around the thicker stems which had been mixed by the conventional method. The thickness of the stems, whether fixed with vacuum-mixed or non-vacuum mixed cement, had no significant influence on the percentage of pore area in the cement. In the nonvacuum mixed cement, there was no significant difference between the percentages of pore area in the proximal and distal parts of the shafts, whereas in the vacuum mixed cement the percentage of pore area was significantly larger in the distal than in the proximal part of the shafts. In the specimens of both stem sizes, the percentage of pore area in the vacuum mixed cement was significantly smaller than in the nonvacuum mixed cement. This explains the greater fatigue strength of vacuum mixed cement. The cyclic loading on the thicker stem prostheses, especially in those fixed with vacuum mixed cement, resulted in fracture between the prosthesis tip and the clamping device due to the local stiffness of the artificial bone. Due to this unfavourable biomechanical property of the artificial bone, further studies will be carried out on human femurs. Nevertheless, in view of the results presented here, the vacuum mixing technique has to recommended as the “state of the art” method in cemented total hip arthroplasty.
Occlusion of the common femoral artery by cement after total hip arthroplasty: a case report
Mikel L Reilingh, Koen J Hartemink, Arjan WJ Hoksbergen, Rachid Saouti
Journal of Medical Case Reports , 2009, DOI: 10.1186/1752-1947-3-86
Abstract: A 59-year-old Caucasian woman presented with rest pain, numbness and cramps in the operated limb after hip replacement. Cement leakage under the transverse ligament had caused occlusion of the common femoral artery necessitating vascular reconstruction. She had a good functional recovery at follow-up.To the best of our knowledge, this is the first well-documented case reporting this pathomechanism of vascular lesion to the femoral artery. This case report highlights the potential risk of such a limb-threatening complication, and awareness should lead to prevention by meticulous surgical technique (correct technique of pressurization) or to early detection of the lesion.Total hip arthroplasty (THA) is a successful procedure with a satisfactory outcome in patients with coxarthrosis. Vascular injuries are a rare complication after orthopedic surgery of the hip. The complication rate is reported to be approximately 0.2-0.3% [1-4]. The most commonly injured vessels are the external iliac artery and vein and the common femoral artery [5,6]. Vascular complications are usually caused by direct trauma due to an osteotome, retractor, screws or powered reamer [7]. Direct injury from cement has been reported due to intrapelvic wall penetration, with thermal injury to the external iliac artery causing occlusion by thrombosis [8-10].An unusual pattern of injury to the common femoral artery after THA is presented. Cement leakage under the transverse ligament caused occlusion of the common femoral artery necessitating vascular reconstruction.An obese 59-year-old Caucasian female patient with a history of symptomatic osteoarthritis of the left hip received an Exeter total hip arthroplasty (THA) (Stryker?) by the posterolateral approach. The acetabulum was prepared with several anchorage holes and low viscosity Simplex P (Stryker?) cement was pressurized. Cerclage wiring was used to control a trochanteric fissure. At that time, no further complications were noted. Postoperatively, th
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