Symmetrical Insertion Research Articles

How does asymmetric tibial insert affect tibiofemoral kinematics and contact stresses in total knee Arthroplasty?

BackgroundAsymmetric tibial insert design is expected to restore normal knee kinematics better than symmetric design. A tri-condylar implant has asymmetric and symmetric tibial inserts with a ball-and-socket joint to replace the post-cam mechanism. The purpose of this study was to compare the knee kinematics of the two designs and to measure tibiofemoral contact stresses, including that of the ball-and-socket joint. MethodsUsing a computer simulation, the anteroposterior position and axial rotation of the femoral component were simulated during a weight-bearing deep knee bend for six validated models. Contact forces were simultaneously simulated in the medial, lateral, and ball-and-socket compartments. The relative position and the magnitude and direction of each contact force were applied to aforce/displacement control knee simulator. The contact stresses were measured individually using a pressure sensor. ResultsThe asymmetric tibial insert demonstrated a more posterior position of the femoral component in the lateral compartment during the entire range of motion and greater external rotation of the femoral component, compared to the symmetrical tibial insert. The mean peak contact stress of the medial and lateral compartments was < 9 Mpa, with no significant differences between the two designs except at 0°. The contact stress of the ball-and-socket joint was < 5 MPa. ConclusionsAsymmetry of the tibial insert shows significant kinematic difference and has little influence on the peak contact stress, which is considerably lower than the yield strength of polyethylene. The asymmetric tibial insert can lead to clinical benefits owing to its kinematic and kinetic properties.

Chemo‐ and Enantioselective Insertion of Furyl Carbene into the N−H Bond of 2‐Pyridones

AbstractAsymmetric carbene insertion reactions represent one of the most important protocols to construct carbon–heteroatom bonds. The use of donor–acceptor diazo compounds bearing an ester group is however a prerequisite for achieving high enantioselectivity. Herein, we report a chemo‐ and enantioselective formal N−H insertion of 2‐pyridones that has been accomplished for the first time with enynones as the donor–donor carbene precursors. DFT calculations indicate an unprecedented enantioselective 1,4‐proton transfer from O to C. The rhodium catalyst provides a chiral pocket in which the steric repulsion and the π–π interaction of the propeller ligand play a critical role in determining the selectivities.

Experimental and clinical analysis of the use of asymmetric vs symmetric polyethylene inserts in a mobile bearing total knee arthroplasty

PurposeThis study compared the effects of symmetric and asymmetric designs for mobile bearing polyethylene insert for total knee arthroplasty (TKA), both clinically and biomechanically through experimental cadaver tests. Methods303 patients implanted with a mobile bearing TKA were retrospectively analyzed up to 2-year follow-up with relative scores. The same femoral and tibial components were used for all the patients; 151 patients received a Symmetric Design (SD) insert and 152 an Asymmetric Design (AD). A biomechanical experimental test was performed to improve the comprehension of the clinical results, analyzing passive squat on 5 cadaveric knee specimens: internal-external rotations of femur and tibial insert respect to the tibia tray were analyzed in native and implanted configurations (with both symmetrical and asymmetrical inserts for each specimen). ResultsAfter surgery, patients' average flexion improved from 105° (with preoperative extension deficit of 5°), to 115° (SD-group) and 120° (AD-group) at the 2-year follow-up. There was no postoperative extension deficit. AD-group presented better ability to perform certain routines and wasn't affected by any pain, while antero-lateral pain was reported in some SD-group patients. The experimental tests returned no statistically relevant difference in tibio-femoral flexion-extension and internal-external rotations among all the three configurations tested; a statistically significant difference is found for insert-tray internal-external rotations between SD and AD configurations; in details, the AD insert showed insert-tray angles comparable to the ones found for femoral component-tibial tray, while the SD insert returned lower angular values. ConclusionClinically and biomechanically, an asymmetric mobile bearing insert could represent a valid alternative to symmetric mobile bearing insert. Level of evidenceIII, Case-control study Retrospective comparative study.

Biomechanical Comparison of Posterior Fixation Combinations with an Allograft Spacer between the Lateral Mass and Pedicle Screws

Background: There are a few biomechanical studies that describe posterior fixation methods with pedicle screws (PS) and lateral mass screws (LMS); the combination of both screw types and their effect on an allograft spacer in a surgically treated cervical segment is unknown. Methods: Finite element model (FEM) analyses were used to investigate the effects of a hybrid technique using posterior PS and LMS. Stress distribution and subsidence risk from a combination of screws under hybrid motion control conditions, including flexion, extension, axial rotation, and lateral bending, were investigated to evaluate the biomechanical characteristics of different six-screw combinations. Findings: The load sharing on the allograft spacer in flexion mode was highest in the LMS model (74.6%) and lowest in the PS model (35.1%). The likelihood of subsidence of allograft spacer on C6 was highest in the screws from the distal LMS (type 5) model during flexion and extension (4.902 MPa, 30.1% and 2.189 MPa, 13.4%). In lateral bending, the left unilateral LMS (type 4) model screws on C5 (3.726 MPa, 22.9%) and C6 (2.994 MPa, 18.4%) yielded the greatest subsidence risks, because the lateral bending forces were supported by the LMS. In counterclockwise axial rotation, the left unilateral LMS (type 4) model screws on C5 (3.092 MPa, 19.0%) and C6 (3.076 MPa, 18.9%) demonstrated the highest subsidence risks. Conclusion: The asymmetrical ipsilateral use of LMS and posterior PS in lateral bending and axial rotation demonstrated the lowest stability and greatest subsidence risk. We recommend bilateral symmetrical insertion of LMS or posterior PS and posterior PS on distal vertebrae for increased stability and reduced risk of allograft spacer subsidence.

Asymmetric polyethylene inserts promote favorable kinematics and better clinical outcome compared to symmetric inserts in a mobile bearing total knee arthroplasty.

This study aims at comparing the effects of symmetric and asymmetric designs for the polyethylene insert currently available and also for mobile bearing total knee arthroplasty (TKA). The investigation was performed both clinically and biomechanically through finite element analysis. 303 patients, with a mobile bearing TKA, were analyzed retrospectively. All patients received the same femoral and tibial components; for the insert, 151 patients received a symmetric design (SD) and 152 an asymmetric design (AD). Additionally, a 3D finite element model of a lower leg was developed, resurfaced with the same TKAs and analysed during gait and squat activities. TKA kinematics, and bone-stresses were investigated for the two insert solutions. After surgery, patients' average flexion improved from 105°, with 5° of preoperative extension deficit, to 120° (AD-group) and 115° (SD-group) at the latest follow-up. There was no postoperative extension deficit. No pain affected the AD-group, while an antero-lateral pain was reported in some patients of the SD-group. Patients of the AD-group presented a better ability to perform certain physical routines. Biomechanically, the SD induced higher tibial-bone stresses than the AD. Both designs replicated similar kinematics, comparable to literature. However, SD rotates more on the tray, reducing the motion between femoral and polyethylene components, while AD permits greater insert rotation. The biomechanical analysis justifies the clinical findings. TKA kinematics is similar for the two designs, although the asymmetric solution shows less bone stress, thus resulting as more suitable to be cemented, avoiding lift-off issues, inducing less pain. Clinically, and biomechanically, an asymmetric mobile bearing insert could be a valid alternative to symmetric mobile bearing insert. Case-control study retrospective comparative study, III.

Ring-polymer molecular dynamics: rate coefficient calculations for energetically symmetric (near thermoneutral) insertion reactions (X + H2) → HX + H(X = C(1D), S(1D)).

Following our previous study of prototypical insertion reactions of energetically asymmetric type with the RPMD (Ring-Polymer Molecular Dynamics) method [Y. Li, Y. Suleimanov, and H. Guo, J. Phys. Chem. Lett. 5, 700 (2014)], we extend it to two other prototypical insertion reactions with much less exothermicity (near thermoneutral), namely, X + H2 → HX + H where X = C((1)D), S((1)D), in order to assess the accuracy of this method for calculating thermal rate coefficients for this class of reactions. For both chemical reactions, RPMD displays remarkable accuracy and agreement with the previous quantum dynamic results that make it encouraging for the future application of the RPMD to other barrier-less, complex-forming reactions involving polyatomic reactants with any exothermicity.

Formula omitted] is rational

The cyclic insertion conjecture of Borwein, Bradley, Broadhurst and Lisoněk states that inserting all cyclic shifts of some fixed blocks of 2's into the multiple zeta value ζ(1,3,…,1,3) gives an explicit rational multiple of a power of π. In this paper we use motivic multiple zeta values to establish a non-explicit symmetric insertion result: inserting all possible permutations of some fixed blocks of 2's into ζ(1,3,…,1,3) gives some rational multiple of a power of π.

“N” structure for type-II superlattice photodetectors

In the quest to raise the operating temperature and improve the detectivity of type II superlattice (T2SL) photodetectors, we introduce a design approach that we call the “N structure.” N structure aims to improve absorption by manipulating electron and hole wavefunctions that are spatially separated in T2SLs, increasing the absorption while decreasing the dark current. In order to engineer the wavefunctions, we introduce a thin AlSb layer between InAs and GaSb layers in the growth direction which also acts as a unipolar electron barrier. Unlike the symmetrical insertion of AlSb into GaSb layers, N design aims to exploit the shifting of the electron and hole wavefunctions under reverse bias. With cutoff wavelength of 4.3 μm at 77 K, temperature dependent dark current and detectivity measurements show that the dark current density is 3.6 × 10−9 A/cm2, under zero bias. Photodetector reaches background limited infrared photodetection (BLIP) condition at 125 K with the BLIP detectivity (D*BLIP) of 2.6 × 1010 Jones under 300 K background and −0.3 V bias voltage.

Synthesis and Identification of a Trimethylenemethane Derivative π-Extended with Three Pyridinyl Radicals

A trimethylenemethane (TMM) derivative 1(2*), in which the parent TMM is pi-extended by the symmetric insertion of three pyridine rings into the C-C bonds of TMM, has been synthesized by the alkali metal reduction of the isolated corresponding dication. Although the frozen-glass X-band cw-ESR spectrum of 1(2*) gave unresolved fine structures due to the small ZFS parameters, pulsed ESR two-dimensional electron spin transient nutation (2D-ESTN) spectroscopy unambiguously can afford to identify diradical 1(2*) as a triplet species.

Magnetic properties of Fe/Pt films by symmetrical insertion of Ag

Ultrathin Ag (0.5 nm) pinning layers (APLs) were symmetrically inserted into [Fe/Pt] bilayers to introduce controllable defects on the interfaces between Ag and Fe/Pt multilayers. The highest coercivity 7700 Oe and remanent squareness 0.95 were obtained with five APLs. The large enhancement in coercivity (75% increment compared with that without APL) is due to the relative uniform defects that introduced pinning effects on the interfaces between the APLs and Fe/Pt multilayers. According to the distribution of angule- dependent coercivity of Fe/Pt multilayers without and with APLs, a tendency is suggested of weakened domain-wall motion while enhanced rotation of reverse domain mode.

Improving the life cycle of forging dies with active brazed ceramic inserts

The use of embedded ceramic inserts in forging tools has lately been investigated and successfully tested with model forging dies. However, there is a danger of the mechanical widening of the steel tool as a major problem of forging dies with embedded ceramic inserts. Furthermore, only rotation symmetric ceramic inserts can be embedded, which allows only a small variety in the construction of tools. A considerably larger number of designs are possible for active metal brazing of ceramic inserts in the die's body material. For achieving this, active brazed ceramic–metal compounds were developed and tested for their practical use in the forging process.

Soft body reconstructions of Palaeozoic corals: implications for the system of Anthozoa (Coelenterata)

The soft bodies and individual developmental sequences of the polyps of Palaeozoic corals are reconstructed on the basis of the functional, engineering and constructional morphology of Recent Anthozoa. Four types of body construction can be distinguished by the arrangement of mesenteries, the number of mesentery insertion zones and characteristic septal insertion patterns: (1) serial insertion of single mesenteries in four sectors, which has resulted in the serial insertion of septa, (2) symmetrical insertion of single mesenteries in four sectors, which has resulted in a symmetrical septal pattern or pseudo radial septal patterns, (3) exponential insertion of paired mesenteries in four sectors, which has resulted in septa bifurcation, and (4) exponential insertion of paired mesenteries in six sectors, which has resulted in a radial septal pattern. Suggestions for a constructional taxonomy are given on the basis of the arrangement of mesenteries and on individual development of the reconstructed polyps. Accordingly, new superorders are introduced: 'Seriales’ for the first body construction and 'Symmetricales’ for the second. The third body construction is that of the Heterocorallia and the fourth that of the Hexacorallia. Following a constructional taxonomy, new and stricter definitions are given for the new and already known taxonomic categories of Rugosa, Heterocorallia and Hexacorallia. A byproduct of this re-definition is that several Palaeozoic corals represent the body construction of the Hexacorallia and should therefore be revised as Hexacorallia; consequently, Hexacorallia must already have been present in the Palaeozoic.

Pattern Formation in Reaction–Diffusion Models with Nonuniform Domain Growth

Recent examples of biological pattern formation where a pattern changes qualitatively as the underlying domain grows have given rise to renewed interest in the reaction–diffusion (Turing) model for pattern formation. Several authors have now reported studies showing that with the addition of domain growth the Turing model can generate sequences of patterns consistent with experimental observations. These studies demonstrate the tendency for the symmetrical splitting or insertion of concentration peaks in response to domain growth. This process has also been suggested as a mechanism for reliable pattern selection. However, thus far authors have only considered the restricted case where growth is uniform throughout the domain. In this paper we generalize our recent results for reaction–diffusion pattern formation on growing domains to consider the effects of spatially nonuniform growth. The purpose is twofold: firstly to demonstrate that the addition of weak spatial heterogeneity does not significantly alter pattern selection from the uniform case, but secondly that sufficiently strong nonuniformity, for example where only a restricted part of the domain is growing, can give rise to sequences of patterns not seen for the uniform case, giving a further mechanism for controlling pattern selection. A framework for modelling is presented in which domain expansion and boundary (apical) growth are unified in a consistent manner. The results have implications for all reaction–diffusion type models subject to underlying domain growth.

Structural–functional Aspects in the Evolution of Operculate Corals (Rugosa)

Among the Rugosa operculae were developed by only a few genera. One is the slipper–shaped Calceola and another is the pyramidal shaped Goniophyllum. On the basis of biological and morphological knowledge of recent corals, the two different bauplans of the soft bodies of Calceola and Goniophyllum have been reconstructed. The soft body (i.e. the polyp) of a rugose coral is thought to have all the basic structures of anthozoan polyps: a barrel–like body shape, a flat oral disc with tentacles, and a mouth from which a pharynx reaches inside the gastric cavity. Furthermore, as in all Anthozoa, Rugosa had internal mesenteries that act as tensile cords; during growth in the diameter further mesenteries were inserted. In contrast to all other Anthozoa, in the Rugosa new single mesenteries were added in four insertion sectors. The bauplans of Calceola and Goniophyllum differ in the pattern of mesentery insertion into these four sectors. Calceola had a serial insertion pattern and Goniophyllum had a symmetrical insertion pattern. They are representatives of the two different bauplans within the Rugosa. The lid corals are examples of convergent evolved genera; Calceola as well as Goniophyllum originated by quite simple modifications of the ancestral type. The peculiar shapes, the operculae and especially the straight hinges between the calyx and the lid(s) result only from mechanical necessity. Under special conditions (such as high sedimentation rates) these modifications of the corallites represent suitable tactics for survival.

Comparison of the perturbative convergence with multireference Möller–Plesset, Epstein–Nesbet, forced degenerate and optimized zeroth order partitionings: The excited BeH2 surface

High order perturbation energies are computed for excited 1A1 states of BeH2 at geometries near the Be→H2 symmetric insertion transition state. The equations of multireference perturbation theory are solved through 30th order to study the difficulties in selecting the appropriate zeroth order Hamiltonian, orbitals, orbital energies, and reference functions for the computations of smooth molecular potential energy surfaces. The origin of the perturbative divergence produced by Möller–Plesset and Epstein–Nesbet partitionings is analyzed using a conceptually simple two-state model constructed using one state each from the reference and orthogonal spaces. The optimized zeroth order partitioning scheme (OPT) for double reference space computations with configurations 1a122a123a12 and 1a122a121b22 produces a truly convergent perturbation expansion through 30th order. The OPT energies are accurate in low orders as compared to the exact (197 dimensional) solution within the basis. The forced valence orbital degeneracy partitioning method (FD) also generates a truly convergent expansion for the same double reference space calculation, with slightly poorer low order energies than the OPT scheme. The BeH2 system facilitates the consideration of larger reference spaces (constructed using three through six orbitals) where the FD method produces highly accurate energies in low orders despite the asymptotic nature of the FD perturbation expansion. The “delayed’’ perturbative divergence behavior with the FD partitioning scheme (for large reference spaces) is shown to occur due to the incorrect ordering between the zeroth order energies of some reference and complementary space levels.

Reactivity of molybdenum and tungsten disilene complexes

The reactions of the η 2 -disilene complexes Cp 2M(η 2-Me 2SiSiMe 2) (M = Mo, 1a; W, 1b) with a variety of inorganic and organic substrates are reported. Compound 1a reacts with methanol to yield Cp 2Mo(SiMe 2H)(SiMe 2OMe) ( 2,> 80%) and Cp 2Mo(H)(Si Me 2SiMe 2OMe) ( 3, < 20%), products of SiSi and MoSi bond cleavages. Nucleophilic attack by methylenetrimethylphosphorane leads to opening of the MoSi 2 ring and yields the disilyl-substituted ylide Cp 2Mo(H)(SiMe 2SiMe 2CHPMe 3) ( 4). Although oxygen atom sources such as O 2, N 2O, epoxides and Ph 3PO do not react cleanly with 1, reaction with elemental sulphur yields the symmetrical sulphur-atom insertion product cyclo-Cp 2MO (SiMe 2SSiMe 2) ( 5). In contrast, reaction with triphenylphosphine sulphide principally yields the unsymmetrical insertion product cyclo-Cp 2Mo(SiMe 2SiMe 2S) ( 6). Compounds 5 and 6 have been characterized by X-ray diffraction studies. Insertion into the SiSi bond of 1a and 1b is also observed in reactions with trimethylsilylazide and carbon dioxide, which yield cyclo-Cp 2Mo(SiMe 2N(TMS)SiMe 2) ( 7) and cyclo-Cp 2W(SiMe 2C(O)OSiMe 2) ( 10), respectively. Benzophenone also appears to insert between the two silicon atoms in 1a to yield a five-membered ring compound, but the instability of this product has precluded a definitive assignment of the structure. The four-membered ring compound cylo-Cp 2Mo (SiMe 2) 3 ( 8) has been identified in the reaction of 1a with dimethylsilylene, generated by the thermolysis of hexamethylsilacyclopropane. Dimethylsilylene insertion is relatively unselective in non-coordinating solvents such as benzene, and the secondary insertion product cyclo-Cp 2Mo(SiMe 2) 4 ( 9) is also produced. However, only 8 is formed in tetrahydrofuran, an observation which can be attributed to the higher selectivity of the intermediate silylene-base adduct formed in the coordinating solvent.

UHF filter with symmetrical or unsymmetrical insertion of two dielectric disk resonators in the transmission line

UHF filter with symmetrical or unsymmetrical insertion of two dielectric disk resonators in the transmission line

The Synthesis of a Class of Wide-Band Lattice Crystal Filter With Symmetrical Insertion Loss characteristics

A general synthesis procedure based on the Darlington technique is described for the lattice-crystal-filter which incorporates shunt inductors to widen the bandwidth. Specifically, it is shown how equivalent low-pass insertion functions may be obtained for all filters with (approximately) symmetrical band-pass insertion functions; these low-pass functions may be expressed by the ratio of two polynomials of even degree in complex frequency with the degree of the numerator polynomial exceeding that of the denominator by at least two. Starting with two such polynomials, corresponding to the desired insertion function, it is shown how a set of crystal constants may be found.

On the Synthesis of the Crystal-Capacitor Lattice-Filter with Symmetrical Insertion Loss Characteristics

A general synthesis procedure is described for the very narrow-bandwidth lattice crystal filter. Specifically, it has been shown that equivalent low-pass insertion functions for all (almost) symmetrical insertion functions of lattice, crystal-capacitor filters may be expressed by the ratio of two polynomials of even degree in complex frequency. Starting with two such polynomials corresponding to the desired insertion function, it is shown how a set of corresponding crystal constants may be found.