The biomechanics of plate fixation of periprosthetic femoral fractures near the tip of a total hip implant: cables, screws, or both?

Femoral shaft fractures after total hip arthroplasty (THA) remain a serious problem, since there is no optimal surgical repair method. Virtually all studies that examined surgical repair methods have done so clinically or experimentally. The present study assessed injury patterns computationally by developing three-dimensional (3D) finite element (FE) models that were validated experimentally. The investigation evaluated three different constructs for the fixation of Vancouver B1 periprosthetic femoral shaft fractures following THA. Experimentally, three bone plate repair methods were applied to a synthetic femur with a 5 mm fracture gap near the tip of a total hip implant. Repair methods were identical distal to the fracture gap, but used cables only (construct A), screws only (construct B), or cables plus screws (construct C) proximal to the fracture gap. Specimens were oriented in 15 degrees adduction to simulate the single-legged stance phase of walking, subjected to 1000 N of axial force, and instrumented with strain gauges. Computationally, a linearly elastic and isotropic 3D FE model was developed to mimic experiments. Results showed excellent agreement between experimental and FE strains, yielding a Pearson linearity coefficient, R2, of 0.92 and a slope for the line of best data fit of 1.06. FE-computed axial stiffnesses were 768 N/mm (construct A), 1023 N/mm (construct B), and 1102 N/mm (construct C). FE surfaces stress maps for cortical bone showed Von Mises stresses, excluding peaks, of 0-8 MPa (construct A), 0-15 MPa (construct B), and 0-20 MPa (construct C). Cables absorbed the majority of load, followed by the plates and then the screws. Construct A yielded peak stress at one of the empty holes in the plate. Constructs B and C had similar bone stress patterns, and can achieve optimal fixation.

The biomechanics of plate repair of periprosthetic femur fractures near the tip of a total hip implant: the effect of cable-screw position.

Optimal surgical positioning of cable-screw pairs in repairing periprosthetic femur fractures near the tip of a total hip implant still remains unclear. No studies in the literature to date have developed a fully three-dimensional finite element (FE) model that has been validated experimentally to assess these injury patterns. The aim of the present study was to evaluate the biomechanical performance of three different implant-bone constructs for the fixation of periprosthetic femoral shaft fractures following total hip arthroplasty. Experimentally, three bone-plate repair configurations were applied to the periprosthetic synthetic femur fractured with a 5 mm gap near the tip of a total hip implant. Constructs A, B, and C, respectively, had successively larger distances between the most proximal and the most distal cable-screw pairs used to affix the plate. Specimens were oriented in 15 degrees adduction, subjected to 1000 N of axial force to simulate the single-legged stance phase of walking, and instrumented with strain gauges. Computationally, a linearly elastic and isotropic three-dimensional FE model was developed to mimic the experimental setup. Results showed excellent agreement between experimental versus FE analysis strains, yielding a Pearson linearity coefficient, R2, of 0.90 and a slope for the line of best data fit of 0.96. FE axial stiffnesses were 601 N/mm (Construct A), 849 N/mm (Construct B), and 1359 N/mm (Construct C). FE surface stress maps for cortical bone showed maximum von Mises values of 74 MPa (Construct A), 102 MPa (Construct B), and 57 MPa (Construct C). FE stress maps for the metallic components showed minimum von Mises values for Construct C, namely screw (716MPa), cable (445MPa), plate (548MPa), and hip implant (154MPa). In the case of good bone stock, as modelled by the present synthetic femur model, optimal fixation can be achieved with Construct C.

The biomechanics of a validated finite element model of stress shielding in a novel hybrid total knee replacement.

This study proposes a novel hybrid total knee replacement (TKR) design to improve stress transfer to bone in the distal femur and, thereby, reduce stress shielding and consequent bone loss. Three-dimensional finite element (FE) models were developed for a standard and a hybrid TKR and validated experimentally. The Duracon knee system (Stryker Canada) was the standard TKR used for the FE models and for the experimental tests. The FE hybrid device was identical to the standard TKR, except that it had an interposing layer of carbon fibre-reinforced polyamide 12 lining the back of the metallic femoral component. A series of experimental surface strain measurements were then taken to validate the FE model of the standard TKR at 3000 N of axial compression and at 0 degreeof knee flexion. Comparison of surface strain values from FE analysis with experiments demonstrated good agreement, yielding a high Pearson correlation coefficient of R(2)= 0.94. Under a 3000N axial load and knee flexion angles simulating full stance (0O degree, heel strike (200 degrees, and toe off (600 degrees during normal walking gait, the FE model showed considerable changes in maximum Von Mises stress in the region most susceptible to stress shielding (i.e. the anterior region, just behind the flange of the femoral implant). Specifically, going from a standard to a hybrid TKR caused an increase in maximum stress of 87.4 per cent (O0 degree from 0.15 to 0.28 MPa), 68.3 per cent (200 degrees from 1.02 to 1.71 MPa), and 12.6 per cent (600 degrees from 2.96 to 3.33 MPa). This can potentially decrease stress shielding and subsequent bone loss and knee implant loosening. This is the first report to propose and biomechanically to assess a novel hybrid TKR design that uses a layer of carbon fibrereinforced polyamide 12 to reduce stress shielding.

The effect of cortex thickness on intact femur biomechanics: a comparison of finite element analysis with synthetic femurs.

Biomechanical studies on femur fracture fixation with orthopaedic implants are numerous in the literature. However, few studies have compared the mechanical stability of these repair constructs in osteoporotic versus normal bone. The present aim was to examine how changes in cortical wall thickness of intact femurs affect biomechanical characteristics. A three-dimensional, linear, isotropic finite element (FE) model of an intact femur was developed in order to predict the effect of bicortical wall thickness, t, relative to the femur's mid-diaphyseal outer diameter, D, over a cortex thickness ratio range of 0 < or = t/D < or = 1. The FE model was subjected to loads to obtain axial, lateral, and torsional stiffness. Ten commercially available synthetic femurs were then used to mimic 'osteoporotic' bone with t/D = 0.33, while ten synthetic left femurs were used to simulate 'normal' bone with t/D = 0.66. Axial, lateral, and torsional stiffness were measured for all femurs. There was excellent agreement between FE analysis and experimental stiffness data for all loading modes with an aggregate average percentage difference of 8 per cent. The FE results for mechanical stiffness versus cortical thickness ratio (0 < or = t/D < or = 1) demonstrated exponential trends with the following stiffness ranges: axial stiffness (0 to 2343 N/mm), lateral stiffness (0 to 62 N/mm), and torsional stiffness (0 to 198 N/mm). This is the first study to characterize mechanical stiffness over a wide range of cortical thickness values. These results may have some clinical implications with respect to appropriately differentiating between older and younger human long bones from a mechanical standpoint.

[The clinico-immunological characteristics of myasthenia patients]. / Kliniko-immunologicheskaia kharakteristika bol'nykh miasteniei.

Data are submitted of examination of 480 patients with myasthenia. The host protective mechanisms were studied, with the immunodeficiency (both cellular and humoral) having been ascertained. The above event were found out to be associated with severity of myasthenia, being more apparent in gravely ill patients.

[The characteristics of the synthesis of specific antihemagglutinins and antihemolysins in subjects inoculated with live measles vaccine in different climatic and geographical areas]. / Osobennosti sinteza spetsificheskikh antigemaggliutininov i antigemolizinov u lits, privitykh zhivoi korevoi vaktsinoi, v raznykh klimatogeograficheskikh zonakh.

The examination of children in the Far North and moderate zones has revealed essential differences in the formation of humoral antimeasles postvaccinal immunity. After booster immunization with live measles vaccine specific anti-hemolysins are more intensively synthesized than anti-hemagglutinins under the conditions of the Far North. In the moderate climatic zone the repeated injection of live measles vaccine induces more intensive synthesis of specific anti-hemagglutinins, rather than anti-hemolysins. Serological examination made prior to booster immunization is also of great importance, as the most intensive synthesis of antimeasles antibodies is observed among children, seronegative to measles virus and children with low titers of antimeasles antibodies in their blood sera.

[Effectiveness of combined spinal anesthesia]. / Effectivnost primeneniia kombinirovannoi spinnomozgovoi anestezii.

Combined spinal anesthesia with the use of hyperbaric solution of lignocaine at an average dose of (69.4 +/- 1.4) mg and morphine hydrochloride at a dose of 0.3 mg was used in 50 patients with II-IV degree anesthesiologic risk during one-stage appendectomy. Effective intraoperative anesthesia was achieved in (96.2 +/- 2.5) % of cases. Duration of postoperative analgesia was (26.8 +/- 1.1) h. Suppression of breathing, hyperalgesia on termination of the effect of a local anesthetic were not noted. In (50.1 +/- 1.7) % of the patients, intraoperative hypotension was revealed. After the operation, nausea was noted in (20 +/- 11.5) % of these patients, vomiting--in (6.0 +/- 2.3) %, itch at the site of puncture--in (22.0 +/- 10.4) %, shiver--in (2.0 +/- 1.4) %.

[Use of magnesium sulfate for controlling postoperative shivering]. / Ispol'zovanie magniia sul'fata dlia kupirovaniia posleoperatsionnogo oznoba.

In intravenous administration of magnesium sulphate, the postoperative shivering was cupped off in 87.8% of the patients. The mean effective dosage of the preparation was 32.2 mg/kg of body weight. In rapid intravenous administration of the preparation, in 3% of the patients, the nausea and vomiting+ occurred. Hypotension (3% of cases) and ++re-curarization of the mandibular muscles (3%) were eliminated by means of the intravenous administration of calcium chloride. Cupping off the shivering permitted to prevent the hypothermal reaction after the operation and narcosis.

[Infectious complications after splenectomy in patients with cirrhosis of the liver]. / Infektsionnye oslozhneniia posle splenéktomii u bo'lnykh tsirrozom pecheni.

Based on an examination of 105 patients with cirrhosis of the liver with the syndrome of portal hypertension complicated by gastroduodenal bleedings who were subjected to splenectomy (in 86 patients there were proximal splenorenal anastomoses) the authors make a conclusion that infectious complications in the postoperative period in the group under analysis were developing against the background of the concomitant and predisposing conditions and can be compared in their incidence with infectious complications after other similar in severity operative interventions on organs of the abdominal cavity. In remote terms after operation the normalization of the indices of both cellular and humoral immunity was noted.

[A method of rapid cytodiagnosis of cytomegalic virus infections in pregnant women]. / Metod tsitologicheskoi ékspress-diagnostiki tsitomegalovirusnoi infektsii u beremennykh.

A cytologic method for rapid detection of specific cytomegaloviral cells (CMC) in cervicovaginal secretion is suggested. This method is more effective than similar CMC detection in salivary and urinary sediments by 1.5 and 3.4 times, respectively. Detection of CMC in the cervicovaginal secretion and not in the salivary or urinary sediments considerably improves the informative value of the method, since it permits a more accurate estimation of the risk of fetal viral infection.

[Characteristics of the immune response of children in the Arctic to live measles vaccine]. / Osobennosti immunnogo otveta detei v Zapoliar'e na zhivuiu korevuiu vaktsinu.

The intensity of immune response to live measles vaccine varies in children living in different climatic and geographical regions. The least intensive immunogenesis is registered in children living in the Arctic regions. The level of seroconversion in children living in these regions rises in response to measles vaccine containing a 10-fold amount of the virus per immunization dose.

[Epidemiological and immunological research on cytomegaly in parturients and newborn infants among the indigenous and immigrant population in the Far North]. / Epidemiologicheskie i immunologicheskie issledovaniia tsitomegalii u rozhenits i novorozhdennykh sredi korennogo i prishlogo naseleniia na Krainem Severe.

In the immigrant population of the Central Yakutiya, cytomegalic cells in the saliva and urine are found much more frequently than in the indigenous population (P less than 0.001). Significant differences were found in the content of complement-fixing antibody to CMV in parturients and newborns in the Extreme North as compared with the European USSR. While in the latter complement-fixing antibodies to CMV are more frequently found in newborn babies (86% in newborns and 69.8% in parturients), in the Extreme North it is vice versa (52.53% in parturients and 32.73% in newborns). Large numbers of seronegative women of the indigenous and immigrant population becoming pregnant get into the group of risk of infection with CMV which is explained by a high rate of detection of IgM in newborn babies of the indigenous (8.69%) and immigrant (9.8%) population and indicates congenital CMV infection.