Rigid Cantilever Research Articles

Management of Severe Bilateral Nasal Wall Collapse

The aim of this study was to examine and analyze the pathology contributing to severe bilateral nasal wall collapse seen in certain revision rhinoplasty patients and identify those surgical maneuvers in the previous nasal surgery, which may have contributed to this complication; suggest alternatives or modifying steps in nasal surgery to prevent lateral wall collapse; analyze consecutive revision rhinoplasties and identify those patients who have complete bilateral nasal collapse at the internal nasal valve; and analyze the results achieved after surgical reconstruction of complete bilateral nasal collapse. We identified 49 patients, who presented from 1990 to 2000 for revision surgery, who had bilateral collapse of the upper lateral cartilage. All patients had at least one previous rhinoplasty and all but 14 patients had undergone two or more procedures. The patients were reconstructed with a conchal cartilage graft placed through an external rhinoplasty approach. All patients complained of nasal obstruction with forced nasal inspiration. The collapse was visualized on inspiration and when prevented with intranasal positioning of a bayonet, all patients experienced an immediate improvement in nasal breathing. Postoperatively, all patients experienced this same improvement in their nasal airway. Collapse was not identified in any of the patients after surgery. Two patients underwent revision because of cosmetic asymmetries. We strongly recommend a cartilage overlay to reconstitute the rigid midline continuity of the upper lateral cartilages. Unfortunately, with any significant hump removal, this structural interruption is, to varying degrees, inevitable in most rhinoplasty techniques. The upper lateral cartilages can be sutured to circumvent some of the inferior drift, but this will not reconstitute the rigid lateral cantilever effect of the intact cartilage.

C1–C2 Pedicle Screw Fixation with Rigid Cantilever Beam Construct: Case Report and Technical Note

C1–C2 Pedicle Screw Fixation with Rigid Cantilever Beam Construct: Case Report and Technical Note

Anatomic suitability of the C1-C2 complex for pedicle screw fixation.

A computed tomography (CT) study of 60 consecutive patients (120 sides) was performed to assess suitability for either transarticular or pedicle screw fixation. A C1 lateral mass and C2 pedicle screw fixation with a rigid cantilever beam system has been described. The anatomic constraints relevant for this technique have not. Fifty consecutive patients underwent standard CT of the cervical spine. Pedicle and transarticular screw trajectories were plotted, and the maximum safe diameter for screw placement was determined for each trajectory. Also, trajectories were plotted in 10 additional patients with known craniocervical junction abnormalities using three-dimensional (3-D) imaging and computer-aided navigation tools. Screw placement was considered feasible if a 4-mm diameter trajectory could be plotted without impingement on neural or vascular structures. Four-millimeter diameter pedicle screws could be placed in 91 of 100 C2 pedicles in the CT studies and in 20 of 20 pedicles in the 3-D studies. Four-millimeter diameter C1-C2 transarticular screws could be placed in 94 of 100 sides in the CT study and in 19 of 20 sides in the 3-D study. Four sides could tolerate a C2 pedicle screw and not a transarticular screw; the opposite situation existed in five sides. Placement of screws into C1 was not an issue in any patient. The mean maximum diameter of potential transarticular screws was 6.5 mm, and the mean maximum diameter of the pedicle screws was 5.3 mm (P < 0.01). C1-C2 pedicle screw fixation is a technique that appears to be widely applicable and may represent an alternative fixation technique in selected patients.

C1–C2 Pedicle Screw Fixation with Rigid Cantilever Beam Construct: Case Report and Technical Note

C1–C2 Pedicle Screw Fixation with Rigid Cantilever Beam Construct: Case Report and Technical Note

Dynamic pressures on rigid cantilever walls retaining poroelastic soil media. Part I. First method of solution

The problem of the determination of dynamic pressures and the associated forces on a rigid, vertical cantilever wall retaining a semi-infinite, uniform, fully-saturated poroelastic layer of soil is solved analytically under conditions of plane strain. Hysteretic damping in the soil skeleton may also be present. The rigid wall and the base of the soil layer are both excited by an acceleration harmonically varying with time and spatially invariant. The governing partial differential equations of motion, after separation of variables and the simplifying assumption of zero vertical normal stresses, reduce to a system of two ordinary differential equations for the amplitudes of the horizontal solid skeleton displacement and the pore water pressure, which are easily solved. Soil displacements and stresses, wall pressures and resultant forces as well as the pore water pressure are explicitly expressed. Their variation with frequency, hysteretic damping, porosity and permeability is numerically computed in order to assess the relative importance of the various parameters on the response.

Dynamic pressures on rigid cantilever walls retaining poroelastic soil media. Part II. Second method of solution

The problem of the determination of the dynamic pressures and the associated forces on a rigid, vertical cantilever wall retaining a semi-infinite, uniform, fully-saturated poroelastic (with or without hysteretic damping) layer of soil under conditions of plane strain is considered. The rigid wall and the base of the soil layer are both excited by an acceleration harmonically varying with time and spatially invariant. The method of solution is based on the theory of Mei and Foda and considers the total field to be approximated by the superposition of an elastodynamic problem with modified elastic constants and mass density for the whole domain and a diffusion problem for the pore fluid pressure confined to a boundary layer at the free boundary (top) of the soil layer. Both problems are solved analytically in the frequency domain. Extensive parametric and comparison studies are conducted in order to assess the range of values of the various parameters (frequency, shear modulus, Poisson's ratio, porosity and permeability) for which the accuracy of the present method against the direct one, reported in a companion paper, is satisfactory.

Interactions Between Micron-sized Glass Particles and Poly(dimethyl siloxane) in the Absence and Presence of Applied Load

A technique using a scanning electron microscope to view a fine particle in contact with a flat substrate whilst under load and during its removal is described. The particle is attached to an atomic force microscope cantilever so that the magnitude of the load can be estimated directly from the imaged deflection. Interactions between 5 to 60 μm spherical glass particles and cross-linked poly(dimethyl siloxane) were studied in the presence and absence of load. WA was estimated to be 74 mJ/m2 from the size of the contact area in the absence of load. Using highly flexible cantilevers to apply load resulted in large shear displacements and forces, which distorted the contact area and assisted in particle removal. These shear effects were eliminated by using a more rigid cantilever to measure a normal pull-off force for which the interface toughness, Gc , exceeded 950 mJ/m2. The large adhesion hysteresis indicated the presence of chemical bonding, presumed to occur between silanol and siloxane groups. The mode of particle detachment varied significantly with the choice of cantilever, showing evidence of both cohesive failure and interfacial crack propagation. The relevance of these results to the interpretation of AFM data is discussed.

Triple plastic hinge mechanism for a bent cantilever beam subjected to an out-of-plane tip force pulse of finite duration

In Ref. [1], the need was demonstrated for a deformation mechanism consisting of three plastic hinges (triple-hinge mechanism) to complete the range of possible deformation modes for a bent, rigid perfectly-plastic cantilever beam subjected to a suddenly applied constant tip force applied perpendicular to the plane of the cantilever. This paper provides the analysis of the transient behaviour of such a mechanism when a rectangular force pulse (constant force applied for a finite duration) is applied to the beam. The kinematics of the various hinges are described and the partitioning, of the input energy between the five phases of the motion is evaluated.

A mechanical model of metatarsal stress fracture during distance running

A model of metatarsal mechanics has been proposed as a link between the high incidence of second and third metatarsal stress fractures and the large stresses measured beneath the second and third metatarsal heads during distance running. Eight discrete piezoelectric vertical stress transducers were used to record the forefoot stresses of 21 male distance runners. Based upon load bearing area estimates derived from footprints, plantar forces were estimated. Highest force was estimated beneath the second and first metatarsal head (341.1 N and 279.1 N, respectively). Considering the toe as a hinged cantilever and the metatarsal as a proximally attached rigid cantilever allowed estimation of metatarsal midshaft bending strain, shear, and axial forces. Bending strain was estimated to be greatest in the second metatarsal (6662 mu epsilon), a value 6.9 times greater than estimated first metatarsal strain. Predicted third, fourth, and fifth metatarsal strains ranged between 4832 and 5241 mu epsilon. Shear force estimates were also greatest in the second metatarsal (203.0 N). Axial forces were highest in the first metatarsal (593.2 N) due to large hallux forces in relationship to the remaining toes. Although a first order model, these data highlight the structural demands placed upon the second metatarsal, a location of high metatarsal stress fracture incidence during distance running.

Motion of a rigid plastic cantilever in a damping medium under transverse impact

The motion of a rigid plastic cantilever beam which is surrounded by a damping medium and struck transversely at the tip by a moving mass is studied. The elementary theory, which disregards effects due to rate of straining and geometry changes is used. The governing equations of motion are integrated numerically. For comparison the case of discrete damping provided at the tip only is also solved. Results are presented for a wide range of parameters.