Plane Stability Research Articles

Attraction centers and parity-time-symmetric delta-functional dipoles in critical and supercritical self-focusing media.

We introduce a model based on the one-dimensional nonlinear Schrödinger equation with critical (quintic) or supercritical self-focusing nonlinearity. We demonstrate that a family of solitons, which are unstable in this setting against the critical or supercritical collapse, is stabilized by pinning to an attractive defect, that may also include a parity-time (PT)-symmetric gain-loss component. The model can be realized as a planar waveguide in nonlinear optics, and in a super-Tonks-Girardeau bosonic gas. For the attractive defect with the delta-functional profile, a full family of the pinned solitons is found in an exact analytical form. In the absence of the gain-loss term, the solitons' stability is investigated in an analytical form too, by means of the Vakhitov-Kolokolov criterion; in the presence of the PT-balanced gain and loss, the stability is explored by means of numerical methods. In particular, the entire family of pinned solitons is stable in the quintic (critical) medium if the gain-loss term is absent. A stability region for the pinned solitons persists in the model with an arbitrarily high power of the self-focusing nonlinearity. A weak gain-loss component gives rise to intricate alternations of stability and instability in the system's parameter plane. Those solitons which are unstable under the action of the supercritical self-attraction are destroyed by the collapse. On the other hand, if the self-attraction-driven instability is weak and the gain-loss term is present, unstable solitons spontaneously transform into localized breathers, while the collapse does not occur. The same outcome may be caused by a combination of the critical nonlinearity with the gain and loss. Instability of the solitons is also possible when the PT-symmetric gain-loss term is added to the subcritical nonlinearity. The system with self-repulsive nonlinearity is briefly considered too, producing completely stable families of pinned localized states.

Three-Dimensional Takeoff Step Kinetics of Long Jumpers with and without a Transtibial Amputation.

The loads applied on the musculoskeletal system during the long jump takeoff step are not well established for nonamputee athletes or athletes with a lower extremity amputation. Information on joint loading and potential injury mechanisms is important for improving training or rehabilitation protocols, prosthetic design, and the general understanding of the long jump. Three-dimensional takeoff step kinematics and kinetics were used for inverse dynamic model calculations on three male athletes with and seven male athletes without a below the knee amputation (BKA). Athletes with BKA used their affected leg as their takeoff leg. Despite equivalent long jump performance, ground reaction force application characteristics were widely different, and calculated joint loads were significantly lower in athletes with BKA compared with nonamputee athletes during the takeoff step. The takeoff step of the long jump for athletes with BKA seems to be dominated by sagittal plane movements, whereas it involves sagittal plane movement and compensatory joint work in the frontal plane for nonamputee athletes. Coaches and athletes should adapt training protocols to the unique musculoskeletal loading patterns of long jumpers with or without a BKA. Specifically, nonamputee athletes should strengthen the muscles responsible for hip and knee extension, as well as for frontal plane stabilization, early in the season to avoid injuries. The presented data enable clinicians to identify potential causes of pain or injury more differentially in both groups of athletes and might stimulate future research in the field of robotics and prosthetic components. Furthermore, the altered joint mechanics of athletes with BKA versus nonamputees serves as an explanation for their previously described more effective takeoff step.

Neocrystallization of clay minerals in the Alhama de Murcia Fault (southeast Spain): implications for fault mechanics

AbstractTwo preferred textures were observed in the Alhama de Murcia Fault rocks: (a) foliated bands (>100 µm thick) rich in well-crystallized dioctahedral micas, quartz, hematite and dolomite; and (b) ultrafine-grained bands (<100 µm thick) made of patches composed of small mica crystals (<15 µm) and dispersed Fe-oxides. In both textures, kaolinite forms intergrowths or patches of randomly oriented crystals filling gaps or opening layers of presumably inherited detrital mica crystals, which is interpreted as an epitaxial growth from fluids. The Na/K ratio of mica crystals in the thin ultrafine-grained bands shows a wider range than the micas from the foliated bands including muscovitic, intermediate Na/K and paragonitic compositions. The absence of the 0.98 nm intermediate peak in the diffractograms indicates that the small micas are submicroscopically paragonite and phengite intergrowths. The d001 values of the K-dioctahedral micas in the <2 µm and whole fractions are clearly different from each other. The d001 values of micas of the <2 µm fraction are larger, indicating a higher K and lower Na content in the small micas. Their composition corresponds to lower temperatures, suggesting their growth during a genetic episode in the fault. The textural relationships indicate a late growth of kaolinite, probably due to the fluid–rock interaction along fault planes and fractures. The neoformed clay minerals might alter the stability of the fault plane. The absence of expandable clay minerals and the relatively high frictional strength of kaolinite under wet conditions might explain the observed velocity-neutral behaviour of this gouge and earthquake propagation towards the surface.

The differences in sagittal plane whole-body angular momentum during gait between patients with hemiparesis and healthy people

Regulation of whole-body angular momentum (WBAM) is essential for maintaining dynamic balance during gait. Patients with hemiparesis frequently fall toward the anterior direction; however, whether this is due to impaired WBAM control in the sagittal plane during gait remains unknown. The present study aimed to investigate the differences in WBAM in the sagittal plane during gait between patients with hemiparesis and healthy individuals. Thirty-three chronic stroke patients with hemiparesis and twenty-two age- and gender-matched healthy controls walked along a 7-m walkway while gait data were recorded using a motion analysis system and force plates. WBAM and joint moment were calculated in the sagittal plane during each gait cycle. The range of WBAM in the sagittal plane in the second half of the paretic gait cycle was significantly larger than that in the first and second halves of the right gait cycle in the controls (P = 0.015 and P = 0.011). Furthermore, multiple regression analysis revealed the slower walking speed (P < 0.001) and larger knee extension moment on the non-paretic side (P = 0.003) contributed to the larger range of WBAM in the sagittal plane in the second half of the paretic gait cycle. Our findings suggest that dynamic stability in the sagittal plane is impaired in the second half of the paretic gait cycle. In addition, the large knee extension moment on the non-paretic side might play a role in the dynamic instability in the sagittal plane during gait in patients with hemiparesis.

Paradigm shift in geriatric fracture treatment.

The number of geriatric patients is increasing. These patients exhibit specific characteristics, which influence thetype of fracture care. Many patients have comorbidities, which make them more vulnerable to surgical procedures. The soft tissue envelope around the fracture often is compromised due to pre-existing diseases such as diabetes, chronic venous insufficiency or peripheral vascular disease. Bone mineral density has decreased, which enhances the risk of implant loosening. The goals of treatment differ from those, which are valid for younger adults. Primary goal is preserving independency of the elderly patient in his activities of daily life. Advantages and drawbacks of surgical procedures have to be balanced with those of conservative treatment. Fractures of the lower extremities will more often need surgical treatment than fractures of the upper extremities. Patient´s autonomy is best obtained by creating high stability in the fracture plane, which enables motion and weight-bearing. Second priority is prevention of general and local post-operative complications by the use of less invasive surgical procedures. Restoring anatomy and optimal function are less important goals. The implants, which are used, are inserted through small incisions, placed deep under the skin and use long anatomic or osseous corridors. Intramedullary devices have important advantages. This paradigm shift takes the special challenges and requirements of geriatric patients into account.

Modified approach for calculating individual energies of polar and semipolar surfaces of group-III nitrides

We propose an approach for simultaneously calculating absolute surface energies of polar and semipolar planes without invoking the similarity between hexagonal and cubic structures. Our approach is based on the calculations of total energy differences between two identical wedge-shaped geometries with ideal surfaces using density functional calculations in conjunction with the evaluations of surface dangling bonds for various orientations. The calculations demonstrate characteristic features of the surface stability depending on the crystal orientation: For both GaN and AlN, the surface energy of semipolar $(11\overline{2}2)$ plane under H-rich condition is lower than that of nonpolar $(11\overline{2}0)$ plane. The lower surface energy on the $(11\overline{2}2)$ plane compared with the $(11\overline{2}0)$ plane implies that the semipolar $(11\overline{2}2)$ surface is preferentially formed for high ${\mathrm{H}}_{2}$ pressures during the metal-organic vapor phase epitaxy, consistent with the experimental results of selective-area growth of GaN. Similar trends can also be found in the surface energies of semipolar $(1\overline{1}01)$ plane in both GaN and AlN, and the absolute surface energy on the $(1\overline{1}01)$ plane is found to be lower than that on the $(11\overline{2}2)$ plane. These calculated results suggest that all of the phenomena related to the stability of polar and semipolar planes of group-III nitrides would benefit from these accurate values of surface energies.

Design and tailoring of one-dimensional ZnO nanomaterials for photocatalytic degradation of organic dyes: a review

Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies. The advantages of ZnO nanomaterials over other semiconductors, and their structure-dependent properties, make them important building blocks in nanotechnology as multifunctional materials. Moreover, it has been confirmed that ZnO nanomaterials can exhibit high performance in photodegradation of organic dyes for treatment of industrial effluent. The wurtzite structure of ZnO contains polar and nonpolar planes; the low surface energy and thermodynamic stability of the nonpolar planes enable formation of one-dimensional (1D) ZnO structures, which are desirable compared with zero-dimensional (0D) and two-dimensional (2D) nanoarchitectures. Also, relative to other forms, the superiority of 1D ZnO nanostructures in dye photodegradation makes them promising as a future research direction and for commercial use. Therefore, understanding the design and synthesis of 1D ZnO nanomaterials is of critical importance for the development of novel and high-performance photocatalysts. Rational design of 1D ZnO nanophotocatalysts is thus required to enhance their photodegradation activity via efficient separation of charge carriers, increased surface-to-volume ratio, enhanced light absorption capacity, and improved stability/reusability. We briefly describe herein the most widely applied synthesis methods, including vapor-phase and solution-based strategies, to understand different methods for tailoring 1D ZnO nanophotocatalysts. Moreover, to elucidate the effect of their physical/chemical properties on the photodegradation efficiency, all the modification methods are categorized into four different approaches, viz. (1) morphology control, (2) induction of defects, (3) modulation by doping, and (4) formation of hybrids and heterojunctions. An overview of all aspects of charge generation, separation, and transfer during dye photodegradation by engineered 1D ZnO nanomaterials is also provided.

Oxidation of Suspended Graphene: Etch Dynamics and Stability Beyond 1000 °C.

We study the oxidation of clean suspended mono- and few-layer graphene in real time by in situ environmental transmission electron microscopy. At an oxygen pressure below 0.1 mbar, we observe anisotropic oxidation in which armchair-oriented hexagonal holes are formed with a sharp edge roughness below 1 nm. At a higher pressure, we observe an increasingly isotropic oxidation, eventually leading to irregular holes at a pressure of 6 mbar. In addition, we find that few-layer flakes are stable against oxidation at temperatures up to at least 1000 °C in the absence of impurities and electron-beam-induced defects. These findings show, first, that the oxidation behavior of mono- and few-layer graphene depends critically on the intrinsic roughness, cleanliness and any imposed roughness or additional reactivity from a supporting substrate and, second, that the activation energy for oxidation of pristine suspended few-layer graphene is up to 43% higher than previously reported for graphite. In addition, we have developed a cleaning scheme that results in the near-complete removal of hydrocarbon residues over the entire visible sample area. These results have implications for applications of graphene where edge roughness can critically affect the performance of devices and more generally highlight the surprising (meta)stability of the basal plane of suspended bilayer and thicker graphene toward oxidative environments at high temperature.

Reproducibility of cone-beam computed tomographic measurements of bone plates and the interdental septum in the anterior mandible.

PurposeThis study aimed to introduce a novel method to evaluate the alveolar bone and interdental septum in the anterior mandible using cone-beam computed tomography (CBCT).Materials and MethodsFifty-six CBCT scans from adult patients were selected. The CBCT scans were obtained before and after orthodontic treatment. The following measurements were taken: width of the alveolar bone and the interdental septum, height of the interdental septum, height of the bone plates, distance between the cementoenamel junction and marginal bone crests, and vertical positioning of the mandibular incisor, using the lingual plane as a reference. To test the reproducibility and the stability of the lingual plane, a triangle was traced in the anterior mandible. The intra-class correlation coefficient (ICC) was used to determine intra- and inter-examiner agreement. The paired Student t-test was used to evaluate the area of the triangle and the reproducibility of all measurements.ResultsThe ICC was excellent for the alveolar bone and dental measurements (0.9989 and 0.9977, respectively), as well as for the interdental septum (0.9987 and 0.9961, respectively). The area of the triangles showed stability in the lingual plane (P>0.05). For the alveolar bone, mandibular incisor, and interdental septum measurements, no statistically significant differences were found between the 2 examiners (P>0.05), confirming the technical reliability of the measurements.ConclusionThe method used in this study provides a valid and reproducible assessment of alveolar bone dimensions in the anterior mandible measured on CBCT images.

Postural instability in cognitively impaired elderly during forward and backward body leans.

[Purpose] The aim of this study was to determine whether there are differences in postural stability control while leaning forward and backward between healthy elderly participants and elderly participants with cognitive impairment. [Participants and Methods] Postural stability was analyzed in 36 participants. According to the Mini-Mental State Examination results, participants were divided into the cognitive impairment group and the control group. A force plate was used to register the center of pressure in the sagittal and frontal plane, during two trials of maximum forward and backward body leaning. [Results] Significant differences were shown in both forward and backward leaning between the control and cognitive impairment groups. [Conclusion] The control of stability in the sagittal plane during maximum forward and backward lean of the body in cognitively impaired patients is similar to the results obtained by their healthy peers. However, individuals with cognitive impairment demonstrated larger lateral oscillations, which may be the reason for postural instability in this group, leading to an increased occurrence of falls.

The Role of Initial Conditions and Parameters of the Model in Evolution of the Universe. Case Study: Brans-Dicke Theory in Einstein Frame

The dynamics of the Brans-Dicke (BD) cosmology in the Einstein frame is studied. We implement phase-space analysis in order to investigate the role of initial conditions and model parameters in the evolution of the universe. The phase plane algorithm and stability of the model are considered in the Einstein Frame where the cosmological background is described in Λ-Cold Dark Matter (ΛCDM) and is supplemented by a Jordan-Fierz-Brans-Dicke field. Our results show: (1) The model parameter α (the coupling strength of the BD scalar field to matter sources) in the Einstein frame plays an important role in the model stability whereas the initial conditions significantly affect the cosmic dynamics. (2) Using type Ia SNIa data, we fit the parameters of the model with observation and show that the current value of the effective equation of state (EoS) parameter is within the range supported by observations. (3) The phase space analysis implies that the universe approaches an attractor in the near future.

Differences in EMG-moment relationships between ACL-injured and uninjured adults during a weight-bearing multidirectional force control task.

Anterior cruciate ligament injury (ACLi) reduces mechanical knee joint stability. Differences in muscle activation patterns are commonly identified between ACLi individuals and uninjured controls (CON); however, how and which of these differences are adaptations to protect the knee or adversely increase risk of joint instability remain unclear. Since the neuromuscular system integrates activity of all muscles crossing the knee to create a moment-of-force that opposes an external load, this study sought to quantify differences in individual muscle electromyography (EMG)-moment relationships between ACLi and CON. Participants isometrically modulated ground reaction forces during a standing force matching protocol to elicit combinations of sagittal, frontal and transverse plane moments. Partial least squares regressions determined which internal joint moment(s) predicted activation of 10 leg muscles for each group. Compared to CON, ACLi demonstrated greater contribution of rectus femoris to knee extension, semitendinosus and gastrocnemii to knee flexion, and lateral gastrocnemii to knee external rotation moments. ACLi also showed lower contributions of biceps femoris to knee flexion, medial gastrocnemius to internal rotation, and varied hip muscle contributions to frontal plane hip moments. Between group differences in EMG-moment relationships during static conditions suggest neuromuscular contributions to sagittal plane stability increases after ACL injury, while knee stability during knee abduction and external rotation is reduced. Clinical Significance: Clinical assessments of ACLi should account for deficits in frontal and rotational plane stability by including tasks that elicit such loads. Improving hamstring muscle balance, hip abductor and gastrocnemius function may benefit ACLi rehabilitation interventions and should be studied further. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Experimental study of the effect of liquid nitrogen pretreatment on shale fracability

When cryogenic liquid nitrogen (LN2) comes into contact with deep reservoirs, it will bring about serious thermal damage to rock pore structure. Therefore, LN2 pretreatment on reservoirs can contribute to further improving the stimulated reservoir volume (SRV) during large-scale hydraulic fracturing. To investigate the effect of LN2 pretreatment on the SRV of shale reservoirs, a series of physical and mechanical experiments related to shale reservoir fracability were conducted. A quantitative fracability evaluation model suitable for different confining pressures was developed from the perspective of fracturing mechanisms. The changes in shale fracability due to LN2 pretreatment were discussed in detail. The responses in P-wave velocities and T2 spectrum curves demonstrate that shale pore structure is subjected to serious damage after freeze-thaw cycles, and some micro-pores are aggregated to form micro-cracks or even macro-cracks. The decreases in tensile, compressive and shear strength and elastic modulus show that the mechanical properties of shales are deteriorated due to cryogenic damage effect. The changes in physical and mechanical properties of shales reveal respectively that LN2 pretreatment can lead to a slight reduction in shale brittleness, a significant improvement in micro-crack development, a moderate decrease in stability of the bedding planes, a relative increase in the propagation ability of fractures. Based on the result of the analytic hierarchy process, it can be concluded that shale fracability is efficiently enhanced due to LN2 pretreatment, especially under high confining pressure condition. Finally, the hydraulic fracturing experiments under tri-axial stress were carried out to further validate the feasibility of LN2 pretreatment to improve the SRV of shale reservoirs. Compared with the experimental results without LN2 pretreatment, it is found that the initiation pressure and initiation time decline by about 54% and 60% respectively. Both the size and complexity of the SRV of shales are enhanced obviously.

Spontaneous doping of the basal plane of MoS2 single layers through oxygen substitution under ambient conditions.

The chemical inertness of the defect-free basal plane confers environmental stability to MoS2 single layers, but it also limits their chemical versatility and catalytic activity. The stability of pristine MoS2 basal plane against oxidation under ambient conditions is a widely accepted assumption however, here we report single-atom-level structural investigations that reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure. The use of scanning tunnelling microscopy reveals a slow oxygen-substitution reaction, during which individual sulfur atoms are replaced one by one by oxygen, giving rise to solid-solution-type 2D MoS2-xOx crystals. Oxygen substitution sites present all over the basal plane act as single-atom reaction centres, substantially increasing the catalytic activity of the entire MoS2 basal plane for the electrochemical H2 evolution reaction.

Structurally and environmentally favorable masonry units for infilled frames

Infill in frames can have detrimental or beneficial effects, and among parameters that influence interaction, infill type stands out as a common element. Masonry units utilized for masonry structures are also frequently utilized as a frame infill. Consequently, their higher strength and stiffness greatly influence the surrounding frame, which can often lead to undesired effects. Therefore, a different approach is proposed – designing a masonry unit with structurally favorable properties for an infill. Lower stiffness and strength of infill can generally benefit the structure as in comparison to a bare frame such infill provides stiffness, but has a higher potential to sustain enough damage to prevent significant detrimental effects on the frame. Out of plane stability, compactness and lightweight are favorable, which is necessary to combine with environmental aspects. To encompass favorable goals, a new masonry unit was developed, based on research of 13 self-compacting concrete mixtures with recycled materials in their composition. Utilizing recycled crushed brick and ground expanded polystyrene enabled reductions in weight, carbon footprint, stiffness and strength. Among various mixtures, based on key material properties, two were selected for production and further testing of masonry units. Units’ density, stiffness and strength showed potential for application as non-structural infill. With a mortar mixture that showed favorable and reliable experimental results, masonry wallets were tested for compression strength and modulus of elasticity, which confirmed developed units potential. From available literature collected results of modulus of elasticity and compressive strength on masonry wallets indicate that developed units are very similar to AAC units, but with significant environmental advantages. Designed mixtures of self-compacting concrete with developed unit shape show great potential for use as non-structural infill, with highlighted positive interaction aspects of a frame-infill composite. This enables the engineer to take a more active role in design, by preventing detrimental effects through choice of constituents in a frame-infill composite.

Energy transfer mechanisms in a dipole chain: From energy equipartition to the formation of breathers.

We study the energy transfer in a classical dipole chain of N interacting rigid rotating dipoles. The underlying high-dimensional potential energy landscape is analyzed in particular by determining the equilibrium points and their stability in the common plane of rotation. Starting from the minimal energy configuration, the response of the chain to excitation of a single dipole is investigated. Using both the linearized and the exact Hamiltonian of the dipole chain, we detect an approximate excitation energy threshold between a weakly and a strongly nonlinear dynamics. In the weakly nonlinear regime, the chain approaches in the course of time the expected energy equipartition among the dipoles. For excitations of higher energy, strongly localized excitations appear whose trajectories in time are either periodic or irregular, relating to the well-known discrete or chaotic breathers, respectively. The phenomenon of spontaneous formation of domains of opposite polarization and phase locking is found to commonly accompany the time evolution of the chaotic breathers. Finally, the sensitivity of the dipole chain dynamics to the initial conditions is studied as a function of the initial excitation energy by computing a fast chaos indicator. The results of this study confirm the aforementioned approximate threshold value for the initial excitation energy, below which the dynamics of the dipole chain is regular and above which it is chaotic.

An exploration of the use of Inertial Measurement Units in the assessment of dynamic postural control of the knee and the effect of bracing and taping

© 2018 IOS Press and the authors. BACKGROUND: The Star Excursion Balance Test (SEBT) is a common clinical test that can provide information about dynamic movement, but does not reflect movement quality or postural-control strategies, and does not report kinematics of the lower limb. PURPOSE: To assess the dynamic postural control of healthy subjects using inertial measurement units (IMUs) and clinical SEBT scores to determine the effect of knee bracing and taping. METHODS: Twenty-four healthy individuals performed the SEBT under three randomised conditions (patellar bracing, patellar taping, and control condition (no intervention). Clinical SEBT scores were recorded and normalised to leg length and angular velocities were measured using IMUs during SEBT. Composite scores were calculated as the sum of clinical scores in each direction divided by three. Descriptive statistics (mean±sd) were calculated for each variable and repeated measures ANOVA were used to identify differences between limb (dominant, non-dominant) and condition. MAIN RESULTS: Compared to the control condition, bracing and taping significantly improved dynamic postural control in the sagittal plane by 6% (1.5-10.5%) P = 0.011 and 8% (2.9-13%) P = 0.004 respectively. Bracing significantly improved coronal plane stability compared to the control condition by 9% (3.8-14.1%) P = 0.002, and taping by 7% (1.6-12.6%) P = 0.013. SEBT scores revealed small but statistically significant differences (P < 0.05) between conditions in the anterior, posteromedial and composite scores, all showing a difference of between 1-2%. PRINCIPAL CONCLUSIONS: Patellar soft bracing and taping can improve dynamic postural stability during SEBT. It is possible to detect clinically important changes in lower limb stability from angular velocity using IMUs.

Hybrid Fixation Restores Tibiofibular Kinematics for Early Weightbearing after Syndesmotic Injury

Category: Ankle Introduction/Purpose: Injury to the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane (IOM) of the syndesmosis is a predictive measure of residual symptoms after an ankle injury. Unstable syndesmotic injuries are typically treated surgically with constructs consisting of cortical screw and/or suture button fixation. Previous studies have shown contradicting findings regarding the effects of different surgical fixation methods on tibiofibular kinematics. Thus, the objective of this study was to quantify tibiofibular joint motion with different syndesmotic screw and suture button fixation constructs after disruption of the syndesmosis compared to the intact ankle during simulated weight bearing. Methods: Five fresh-frozen human cadaveric specimens were tested using a six degree-of-freedom robotic testing system. After subtalar joint fusion, the tibia and calcaneus were rigidly fixed to a robotic manipulator, while complete fibular length was maintained and fibular motion was unconstrained. A constant 200 N compressive load was applied to the ankle while an additional 5 Nm external rotation and 5 Nm inversion moment applied independently to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. Fibular motion with respect to the tibia was tracked using an optical tracking system. Outcome variables included fibular medial-lateral (ML) translation, anterior-posterior (AP) translation, and external rotation (ER) in the following states: intact ankle, complete injury (AITFL, PITFL, and IOM transected), single tricortical screw fixation double tricortical screw fixation, hybrid fixation (single tricortical screw and single suture button), suture button fixation, and divergent suture button fixation. Repeated measures ANOVA was performed for statistical analysis. Results: The external rotation moment produced significant differences in fibular motion between the injury and fixation states compared to the intact state. A complete syndesmotic injury caused significantly increased fibular lateral translation, posterior translation, and external rotation in all ankle positions except 30° plantarflexion compared to the intact ankle. Single suture button and single screw fixation resulted in significantly higher fibular lateral translation at 10° dorsiflexion compared the intact ankle, while single suture button fixation also resulted in significantly higher external rotation at 10° dorsiflexion compared the intact ankle. Fibular posterior translation was significantly higher with hybrid, suture button, and divergent suture button fixation at 0° flexion and with single tricortical screw and double screw fixation at 10° dorsiflexion compared to the intact ankle (Figure 1). Conclusion: Complete injury to the syndesmosis results in significantly higher fibular lateral translation, external rotation, and posterior translation compared to the intact ankle. Hybrid or divergent suture button fixation would be recommended to restore tibiofibular motion without over-constraint. However, none of the fixation methods were able to restore AP translation in all ankle positions. Thus, it is important to evaluate syndesmotic stability in the sagittal plane at different ankle positions. Findings of this study suggest that physicians should evaluate fibular AP translation in a neutral position when using suture button fixation constructs and in dorsiflexion when using tricortical screw fixation constructs.

Posterior Translation of the Fibula is a Critical Factor in the Stability of the Syndesmosis After Injury and Repair

Objectives:Anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane (IOM) disruption is a predictive measure of residual symptoms after an ankle injury. Unstable syndesmotic injuries are typically treated surgically with cortical screw or suture button fixation. Previous studies have shown contradicting findings regarding the effects of partial syndesmotic injuries and different surgical fixation methods on tibiofibular kinematics. Thus, the objective of this study was to quantify tibiofibular joint motion with sequential disruption of the syndesmosis and with syndesmotic screw and suture button fixation compared to the intact ankle.Methods:Nine fresh-frozen human cadaveric specimens (mean age 60 yrs.; range 38-73 yrs.) were tested using a six degree-of-freedom robotic testing system. The subtalar joint was fused and the tibia and calcaneus were rigidly fixed to a robotic manipulator, while complete fibular length was maintained and fibular motion was unconstrained. A 5 Nm external rotation moment and 5 Nm inversion moment were independently applied to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. Fibular motion with respect to the tibia was tracked by a 3D optical tracking system. Outcome variables included fibular medial-lateral (ML) translation, anterior-posterior (AP) translation, and external rotation (ER) in the following states: 1) intact ankle, 2) AITFL transected, 3) AITFL, PITFL, and IOM transected (complete injury), 4) 3.5 mm cannulated tricortical screw fixation, 5) suture button fixation. An ANOVA with a post-hoc Tukey analysis was performed for statistical analysis (*p < 0.05).Results:All significant differences in fibular motion between ankle states occurred during the inversion moment. An isolated AITFL injury caused significant increases in fibular posterior translation at 15° and 30° plantarflexion compared to the intact ankle. A complete syndesmotic injury caused significant increases in fibular posterior translation in all 4 ankle positions and in fibular ER at 0° flexion and 15° plantarflexion compared to the intact ankle. No significant differences were detected in fibular motion between an isolated AITFL injury and complete injury at any ankle positions. No significant differences existed between the tricortical screw fixation and the intact ankle. Significantly higher fibular posterior translation was observed with the suture button compared to the intact ankle at 0° flexion, 30° and 15° plantarflexion. (Figure 1)Conclusion:An isolated AITFL injury resulted in a significant increase in fibular posterior translation relative to the tibia, comparable to that a complete injury, especially in positions of plantarflexion. Current diagnostic protocols after injury focus on the evaluation of fibular ML translation. However, these findings show that it is important to also evaluate syndesmotic stability in the sagittal plane and at different ankle positions. Restoration of native tibiofibular kinematics is essential to prevent post-traumatic arthritis. Tricortical screw fixation was able to restore tibiofibular kinematics in all planes. However, suture button fixation was not able to restore tibiofibular AP translation, which suggests that physicians should critically evaluate fibular AP translation and individualize treatment of unstable ankle injuries when reconstructing the syndesmosis with suture button fixation.Figure 1.Posterior translation of the fibula relative to the tibia (mean ± standard deviation) during a 5Nm inversion moment at 0° flexion, 15° and 30° plantarflexion, and 10° dorsiflexion in different ankle states: intact ankle, isolated AITFL injury, complete injury, tricortical screw flixation using a 3.5mm screw, suture button fixation. *p < 0.05

Structures at Risk from an Intermetatarsal Screw for Lapidus Bunionectomy

Category: Midfoot/Forefoot Introduction/Purpose: The Lapidus procedure is a common procedure for the treatment of hallux abducto valgus. Traditional fixation consists of two crossing screws in the sagittal plane. Despite arthrodesis of the first tarsometatarsal joint, recurrence of the hallux abducto valgus deformity remains a concern. A transverse screw spanning the base of the first metatarsal to the base of the second metatarsal has been advocated to provide transverse plane stability. However, the neurovascular bundle is located within the proximity of this screw. The literature is sparse with a standard technique to safely provide appropriate fixation. An anatomic cadaver study was undertaken to assess the risk of injury to the neurovascular bundle. Methods: Ten unmatched cadaveric limbs that had been disarticulated at the knee were used. Under fluoroscopic guidance, the guide wire to a 4.0-mm screw was driven across the base of the first metatarsal and into the second metatarsal. A 4.0-mm screw was inserted, taking care to obtain osseous purchase into the second metatarsal. A longitudinal incision was made and careful dissection was carried to identify the neurovascular bundle and screw. The neurovascular bundle was inspected for trauma and the proximity of the screws was measured using a digital caliper. Results: There were three left-sided and seven right-sided specimens. Five of the specimens were male and five were female. The mean age of the specimens at date of death was 71.4 years. The mean body mass index was 20.5. The mean distance from the 4.0-mm screw to the first metatarsal base 11.24 mm distal to the first tarsometatarsal joint. The deep plantar artery and deep peroneal nerve was free from injury in 10/10 (100%) specimens. However, the screw was measured to be less than 5 mm in three specimens. In these instances, the average distance of the screw distal to the first tarsometatarsal joint was 12.1 mm. Conclusion: The addition of the intermetatarsal screw for Lapidus bunionectomy is widely accepted clinical practice. Descriptions of the operative technique for the placement of hardware into the second metatarsal have not included specific recommendations to avoid potential risk to the neurovascular bundle as it courses between the bases of the first and second metatarsals. According to this cadaveric study, the neurovascular bundle was avoided with placement of the intermetatarsal screw, if placed approximately 11.24 mm distal to the first tarsometatarsal joint. Further study is warranted to evaluate the optimal distance distal to the first tarsometatarsal joint.