MRI Findings Associated With Anterior Cruciate Ligament Tears in National Football League Athletes.

Background: Anterior cruciate ligament (ACL) tears are a high-frequency injury requiring a lengthy recovery in professional American football players. Concomitant pathology associated with ACL tears as identified on magnetic resonance imaging (MRI) is not well understood in these athletes. Purpose: To describe the MRI findings of concomitant injuries associated with ACL tears among athletes in the National Football League (NFL). Study Design: Cross-sectional study; Level of evidence, 3. Methods: Of 314 ACL injuries in NFL athletes from 2015 through 2019, 191 complete MRI scans from the time of primary ACL injury were identified and reviewed by 2 fellowship-trained musculoskeletal radiologists. Data were collected on ACL tear type and location, as well as presence and location of bone bruises, meniscal tears, articular cartilage pathology, and concomitant ligament pathology. Mechanism data from video review were linked with imaging data to assess association between injury mechanism (contact vs noncontact) and presence of concomitant pathology. Results: Bone bruises were evident in 94.8% of ACL tears in this cohort, most often in the lateral tibial plateau (81%). Meniscal, additional ligamentous, and/or cartilage injury was present in 89% of these knees. Meniscal tears were present in 70% of knees, lateral (59%) more than medial (41%). Additional ligamentous injury was present in 71% of all MRI scans, more often a grade 1/2 sprain (67%) rather than a grade 3 tear (33%), and most often involving the medial collateral ligament (MCL) (57%) and least often the posterior cruciate ligament (10%). Chondral damage was evident in 49% of all MRI scans, with ≥1 full-thickness defect in 25% of all MRI scans, most often lateral. Most (79%) ACL tears did not involve direct contact to the injured lower extremity. Direct contact injuries (21%) were more likely to have a concomitant MCL tear and/or medial patellofemoral ligament injury and less likely to have a medial meniscal tear. Conclusion: ACL tears were rarely isolated injuries in this cohort of professional American football athletes. Bone bruises were almost always present, and additional meniscal, ligamentous, and chondral injuries were also common. MRI findings varied by injury mechanism.

Author Correction: A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements.

The electrochemical synthesis of ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative1-4 to the energy-intensive Haber-Bosch process, which dominates industrial ammonia production. However, there are considerable scientific and technical challenges5,6 facing the electrochemical alternative, and most experimental studies reported so far have achieved only low selectivities and conversions. The amount of ammonia produced is usually so small that it cannot be firmly attributed to electrochemical nitrogen fixation7-9 rather than contamination from ammonia that is either present in air, human breath or ion-conducting membranes9, or generated from labile nitrogen-containing compounds (for example, nitrates, amines, nitrites and nitrogen oxides) that are typically present in the nitrogen gas stream10, in the atmosphere or even in the catalyst itself. Although these sources of experimental artefacts are beginning to be recognized and managed11,12, concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments designed to identify and then eliminate or quantify the sources of contamination. Here we propose a rigorous procedure using 15N2 that enables us to reliably detect and quantify the electrochemical reduction of nitrogen to ammonia. We demonstrate experimentally the importance of various sources of contamination, and show how to remove labile nitrogen-containing compounds from the nitrogen gas as well as how to perform quantitative isotope measurements with cycling of 15N2 gas to reduce both contamination and the cost of isotope measurements. Following this protocol, we find that no ammonia is produced when using the most promising pure-metal catalysts for this reaction in aqueous media, and we successfully confirm and quantify ammonia synthesis using lithium electrodeposition in tetrahydrofuran13. The use of this rigorous protocol should help to prevent false positives from appearing in the literature, thus enabling the field to focus on viable pathways towards the practical electrochemical reduction of nitrogen to ammonia.

Dam trout: Genetic variability in Oncorhynchus mykiss above and below barriers in three Columbia River systems prior to restoring migrational access.

Restoration of access to lost habitat for threatened and endangered fishes above currently impassable dams represents a major undertaking. Biological monitoring is critical to understand the dynamics and success of anadromous recolonization as, in the case of Oncorhynchus mykiss, anadromous steelhead populations are reconnected with their conspecific resident rainbow trout counterparts. We evaluate three river systems in the Lower Columbia River basin: the White Salmon, Sandy, and Lewis rivers that are in the process of removing and/or providing passage around existing human-made barriers in O. mykiss riverine habitat. In these instances, now isolated resident rainbow trout populations will be exposed to competition and/or genetic introgression with steelhead and vice versa. Our genetic analyses of 2,158 fish using 13 DNA microsatellite (mSAT) loci indicated that within each basin anadromous O. mykiss were genetically distinct from and significantly more diverse than their resident above-dam trout counterparts. Above long-standing natural impassable barriers, each of these watersheds also harbors unique rainbow trout gene pools with reduced levels of genetic diversity. Despite frequent releases of non-native steelhead and rainbow trout in each river, hatchery releases do not appear to have had a significant genetic effect on the population structure of O. mykiss in any of these watersheds. Simulation results suggest there is a high likelihood of identifying anadromous x resident individuals in the Lewis and White Salmon rivers, and slightly less so in the Sandy River. These genetic data are a prerequisite for informed monitoring, managing, and conserving the different life history forms during upstream recolonization when sympatry of life history forms of O. mykiss is restored.

Butterflies of Guinea-Bissau: VIII. New data, new reports, corrections and biodiversity (Lepidoptera: Papilionoidea).

New records are added to the Papilionoidea of Guinea-Bissau, many of which were obtained within the country's Protected Areas. Examination of the collected material yielded 9 new genera and 47 new species for the country, significantly increasing the knowledge of local butterfly diversity. 99 genera and 244 species are now known to occur in Guinea-Bissau, representing an increase of almost 20 % in the number of species and 7 % in the genera in relation to previous data. For each species, the studied material, probable abundance and proposed conservation status in the country are reported; some corrections relative to a few previous misidentifications are added. A gazetteer of the prospected localities is included, as well as species' occurrences within the Protected Areas and previous bibliographic references in Guinea-Bissau. The known geographical range, primary habitat and host-plants of each species/subspecies are also provided.

The homotropenylium cation: a system with a pinched π ring current.

The homotropenylium cation (1, C8H9(+)) is a key species in the discussion of homoaromaticity. Constrained optimisations around the minimum structure have been performed, varying the size of the gap spanned by the CH2-bridge and optimising all other geometrical parameters. At each bridging distance, ab initio current-density maps have been calculated and plotted using the ipsocentric approach. Analysis of the maps, including decomposition into localised orbital contributions, gives a clear indication of a global diatropic ring current passing through the gap. The change in pπ-pπ interaction, from conventional π overlap around the conjugated seven-carbon perimeter to σ overlap (pσ-pσ) in the gap, results in a distinctive pinched topology, with two streams of current pinched down into one for part of the circuit. This ring current is diatropic and therefore the species 1 is aromatic on the magnetic criterion.

An efficient parallel algorithm for the calculation of unrestricted canonical MP2 energies.

We present details of our efficient implementation of full accuracy unrestricted open-shell second-order canonical Møller-Plesset (MP2) energies, both serial and parallel. The algorithm is based on our previous restricted closed-shell MP2 code using the Saebo-Almlöf direct integral transformation. Depending on system details, UMP2 energies take from less than 1.5 to about 3.0 times as long as a closed-shell RMP2 energy on a similar system using the same algorithm. Several examples are given including timings for some large stable radicals with 90+ atoms and over 3600 basis functions.

Isomerization of stilbene using enforced geometry optimization.

Using our recently proposed quantum chemical model to simulate the effect of external forces acting on a molecule (Wolinski and Baker, Mol Phys 2009, 107, 2403), which we subsequently termed enforced geometry optimization (EGO), we investigate structural isomerism in C(14) H(12) , starting from cis-stilbene. By applying an external force to pairs of carbon atoms, one from each "half" of the molecule, we have generated 10 different structural isomers. Each was characterized as a minimum by vibrational analysis. Not only can EGO generate potentially new, metastable isomers it can also provide good initial guesses for transition states connecting the starting and final structures, thus giving an estimate of the stability of the new isomers to rearrangement back to the starting material. In addition to the new isomers, we provide a full set of vibrational fundamentals for cis- and trans-stilbene and 4a,4b-dihydrophenanthrene. The agreement with experimental assignments is excellent, with mean average deviations for the stilbenes of 5.0 cm(-1) or less.

Kinetically stable high-energy isomers of C14H12 and C12H10N2 derived from cis-stilbene and cis-azobenzene.

Following on from our recent enforced geometry optimization (EGO) investigation of isomerization in cis-stilbene (J Comput Chem, in press) we report the discovery of two interesting new, symmetrical "fused sandwich" isomers of both cis-stilbene and the related cis-azobenzene. The isomers were obtained by applying external forces to pairs of carbon atoms from each of the benzene rings in cis-stilbene and cis-azobenzene simultaneously, and are all at least 100 kcal mol(-1) higher in energy than the starting material. Each new structure was characterized as a minimum by vibrational analysis. Despite their high energy, all of the new isomers appear to be kinetically stable with respect to rearrangement back to cis-stilbene or cis-azobenzene, respectively.

A reliable and efficient first principles-based method for predicting pK(a) values. 2. Organic acids.

In part 1 of this series, we developed a protocol for the large-scale calculation of pK(a) values in aqueous solutions from first principles calculations, with the goal of striking a compromise between accuracy and computational efficiency. Following previous workers in the field, pK(a) values are calculated from a linear regression fit to deprotonation energies: pK(a)(f) = alpha(f)(E(A)(-) - E(HA)) + beta(f), where f denotes a family of functional groups. In this paper, we derive (alpha(f), beta(f)) values for the acidic functional groups -COOH, -POOH, alcoholic and phenolic -OH, -SH, -NHOH/ horizontal lineNOH, and -NROH, using a data set of 449 experimental pK(a) values. Several groupings of these functional groups were explored; our final recommended method uses five families (10 empirical parameters). Mean absolute deviations between our fits and experiment are 0.4 pK(a) units or less for each with a maximum error range of +/-1.5 pK(a) units. In certain subgroups, such as monocarboxylic acids, considerably better fits (mean absolute deviation approximately 0.20 pK(s) units) were obtained at the cost of more empirical parameters. Almost 70% of pK(a)'s calculated by our protocol lie within +/-0.4 pK(a) units and over 90% within +/-0.8 pK(a) units of the experimental reference value. Our results compare favorably with previous similar models which have greater computational cost.

A reliable and efficient first principles-based method for predicting pK(a) values. 1. Methodology.

We have developed an efficient and reliable protocol for the calculation of pK(a) values in aqueous solution from density functional calculations. We establish a standard linear regression fit using only calculated energies of deprotonation and experimental pK(a) values; all other factors, including most entropic effects, are absorbed into the fitting constants. In this article we fit a small training set of 34 experimentally well-characterized molecules to determine the best level of theory among those tested (i.e., the optimum compromise between efficiency and accuracy for the basis set, the exchange-correlation functional, the (continuum) solvation model and the level of geometry optimization). Our main findings are that a relatively modest basis set (6-311+G**) suffices for the calculation of the energy differences, with an even small basis set (3-21G*) sufficient for the preceding geometry optimization. Using a solvation model (COSMO in our case) throughout is essential to achieve reliable results. The exchange-correlation functional plays only a modest role; in particular, pure DFT functionals that allow the efficient calculation of the Coulomb term are perfectly adequate. The final protocol will be applied subsequently to data sets much larger than commonly used in such studies.

Comments on the molecular geometry of ferrocene: The dangers of using quantum chemistry programs as black boxes.

The dangers of using standard quantum chemistry programs as black boxes is illustrated by analyzing some results in a recent paper published in this journal (Zhang et al., J Comput Chem 2007, 28, 2260). The main danger is that nonlinear optimizations of both the wavefunction and the molecular geometry may converge to higher local minima or to saddle points, producing misleading results. For instance, some of the calculated molecular geometries of ferrocene in the aforementioned paper correspond to an SCF solution that converged to an excited state. This is the cause of the apparent large variation in the calculated iron-ring distance with the basis set. Another problem we noticed is that the source of the diffuse functions used in the earlier work in connection with the 6-31G and 6-311G basis sets for transition metals is not specified in the literature or the program manual. They are also a poor match for the 6-31G basis set. We re-emphasize that the 6-31G basis set used in this paper lacks the necessary diffuse d-type functions for the late first-row transition metals, and ought to be replaced by the m6-31G basis that offers a more balanced description of the atomic valence states.

Quantum chemistry in parallel with PQS.

This article describes the capabilities and performance of the latest release (version 4.0) of the Parallel Quantum Solutions (PQS) ab initio program package. The program was first released in 1998 and evolved from the TEXAS program package developed by Pulay and coworkers in the late 1970s. PQS was designed from the start to run on Linux-based clusters (which at the time were just becoming popular) with all major functionality being (a) fully parallel; and (b) capable of carrying out calculations on large-by ab initio standards-molecules, our initial aim being at least 100 atoms and 1000 basis functions with only modest memory requirements. With modern hardware and recent algorithmic developments, full accuracy, high-level calculations (DFT, MP2, CI, and Coupled-Cluster) can be performed on systems with up to several thousand basis functions on small (4-32 node) Linux clusters. We have also developed a graphical user interface with a model builder, job input preparation, parallel job submission, and post-job visualization and display.

Parallel DFT gradients using the Fourier Transform Coulomb method.

The recently described Fourier Transform Coulomb (FTC) algorithm for fast and accurate calculation of Density Functional Theory (DFT) gradients (Füsti-Molnar, J Chem Phys 2003, 119, 11080) has been parallelized. We present several calculations showing the speed and accuracy of our new parallel FTC gradient code, comparing its performance with our standard DFT code. For that part of the total derivative Coulomb potential that can be evaluated in plane wave space, the current parallel FTC gradient algorithm is up to 200 times faster in total than our classical all-integral algorithm, depending on the system size and basis set, with essentially no loss in accuracy. Proposed modifications should further improve the overall performance relative to the classical algorithm.

The interpretation of compliance constants and their suitability for characterizing hydrogen bonds and other weak interactions.

Compliance constants (or their inverses, relaxed force constants) have frequently been proposed as replacements for internal coordinate force constants because of their invariance properties. Recently, Grunenberg and co-workers have proposed using compliance constants as bond strength descriptors, particularly for weak bonds. In this paper, we critically assess this claim and conclude that the use of compliance constants in this regard is inappropriate.

Advances in methods and algorithms in a modern quantum chemistry program package.

Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.

A critical assessment of the use of compliance constants as bond strength descriptors for weak interatomic interactions.

Inverse compliance constants (inverse diagonal elements of the inverse Hessian matrix) have frequently been proposed as replacements for regular internal coordinate force constants, as the former are invariant to the choice of internal coordinates while the latter are not. Recently, Grunenberg and co-workers have proposed using compliance constants as descriptors of bond strength, primarily based on their invariance properties. This article critically assesses the use of compliance constants as bond strength descriptors, highlighting reasons why their use for this purpose is considered inappropriate, particularly for weak bonding interactions.

Rare-gas insertion compounds of perfluorobenzene: aromaticity of some unstable species.

Calculations on the novel argon insertion compounds C6F6Ar(n), n = 1-6, where the argon atoms are inserted into the C-F bonds in perfluorobenzene, suggest that all possible species, with one to six inserted argon atoms, occupy minima on their respective potential energy surfaces. Ring-current plots using the ipsocentric model indicate that there is no disruption of the aromatic pi system upon argon insertion, and consequently all insertion compounds are aromatic according to the magnetic criterion. The barrier height for decomposition of the single-insertion compound, C6F6Ar, into C6F6+Ar is 19.5 kcal/mol at HF6-311G** and 29.5 kcal/mol at B3LYP6-311G**, suggesting that, although clearly thermodynamically unstable, argon-perfluorobenzene insertion compounds may be stable kinetically. Preliminary calculations indicate that other rare gas-perfluorobenzene insertion compounds may also be metastable. Both C6F6Ne and C6F6He are predicted to occupy minima on their respective potential energy surfaces.