Bending Of Rods Research Articles

Bent Telescopic Rods in Patients With Osteogenesis Imperfecta.

Telescopic rods require alignment of 2 rods to enable lengthening. A telescopic rod converts functionally into a solid rod if either rod bends, preventing proper engagement. Our goal was to characterize implant bending as a mode of failure of telescopic rods used in the treatment of osteogenesis imperfecta in children. We conducted a retrospective review of our osteogenesis imperfecta database for patients treated with intramedullary telescopic rods at our institution from 1992 through 2010 and identified 12 patients with bent rods. The 6 boys and 6 girls had an average age at the time of initial surgery of 3.1 years (range, 1.8 to 8.3 y) and a total of 51 telescoping rods. Clinic notes, operative reports, and radiographs were reviewed. The rods were analyzed for amount of lengthening, characteristics of bending, presence of cut out, or disengagement from an anchor point. Bends in the rods were characterized by their location on the implant component. The bent and straight rods were compared. Data were analyzed with the Mann-Whitney test (statistical significance set at P≤0.05). Of the 51 telescoping rods, 17 constructs (33%) bent. The average interval between surgery and rod bending was 4.0 years (range, 0.9 to 8.2 y). Before bending, 11 of 17 telescoping rods had routine follow-up radiographs for review. In 10 of the rods, bending was present when early signs of rod failure were first detected. Rod bending did not seem to be related to rod size. There was no area on the rod itself that seemed more susceptible to bending. Rod bending can be an early sign of impending rod failure. When rod bending is first noted, it may predispose the rod to other subsequent failures such as loss of proximal and distal fixation and cut out. Rod bending should be viewed as an indicator for closer monitoring of the patient and discussions regarding future need for rod exchange. Level III-retrospective review.

The Anterior Subcutaneous Pelvic Fixator (INFIX) in an Anterior Posterior Compression Type 3 Pelvic Fracture

The purpose of this video is to describe the equipment, anatomy, and surgical technique of anterior subcutaneous pelvic fixation (INFIX) using pedicle screws and a rod in an Anterior Posterior Compression 3 pelvic fracture, as well as how to distract in lateral compression fractures. The equipment required includes standard spine pedicle screw sets with long screws, 70-110 mm in length, and 7 or 8 mm in diameter. The approach is a mini open and one needs to be familiar with the iliac oblique, obturator outlet, and obturator inlet views. The length of the screw is measured from the sciatic notch to the skin, and they are placed so that the head sits just below the skin. The rod is passed just under the skin along the bikini line and the construct compressed or distracted against a c-clamp while monitored with fluoroscopy. In Orthopaedic Trauma Association C type injuries, we leave c-clamps on the outside the screws to reinforce them or use monoaxial screws. The implants are removed at 3-6 months postop. The patients tolerate the implants and are able to sit and stand with out difficulty. Complications include lateral femoral cutaneous nerve irritation, heterotopic bone, loss of fixation if the implants are applied incorrectly. The INFIX procedure for anterior pelvic fixation is based on standard techniques that are familiar to the Orthopaedic Pelvic Surgeon including supraacetabular screws. Rod bending, rod passing, determining the ideal height of the screws, and distraction/compression maneuvers are demonstrated in this video.

Pediatric forearm fractures with in situ intramedullary implants.

PurposeThe purpose of this investigation is to present our institutional experience with fractures of the pediatric forearm with in situ intramedullary nails.MethodsSix patients treated at our institution for forearm fracture with in situ intramedullary implants between 2004 and 2013 were reviewed. Patient demographics, injury and radiographic characteristics, method of treatment, time to union, and complications were collected from the medical record.Results485 patients with forearm fractures were treated with intramedullary implants and six patients presented with a fracture with in situ implants (1.2 %). Fractures in all six patients resulted from a second traumatic event after radiographic healing but before implant removal at a mean of 13.0 months from the initial procedure. One patient had an adequately aligned fracture and was treated with casting without reduction. The remaining five patients (83 %) returned to the operating room for treatment. Two patients underwent rod removal and placement of new intramedullary implants, and two patients were treated with rod removal and plating without attempt at closed reduction. One patient underwent closed reduction in the operating room with successful re-bending of the radial implant and replacement of the ulna implant. All patients went on to uncomplicated radiographic union at a mean 3.6 months.ConclusionsThe incidence of fracture of pediatric forearm with in situ intramedullary implants is low. This rare complication can be treated by several different methods, including revision TENS placement, revision to plate fixation, or in situ bending of rods, with the expectation for successful uncomplicated union.

Bending testing and characterization of surrogate nuclear fuel rods made of Zircaloy-4 cladding and aluminum oxide pellets

Behavior of surrogate nuclear fuel rods made of Zircaloy-4 (Zry-4) cladding with alumina pellets under reversed cyclic bending was studied. Tests were performed under load or moment control at 5 Hz. The surrogate rods fractured under moment amplitudes greater than 10.16 Nm with fatigue lives between 2.4 × 103 and 2.2 × 106 cycles. Fatigue response of Zry-4 cladding was characterized by using flexural rigidity. Degradation of flexural rigidity was shown to depend on the moment and the prefatigue condition of specimens. Pellet-to-pellet interface (PPI), pellet-to-cladding interface (PCI), and pellet condition affect surrogate rod failure. Both debonding of PPI/PCI and pellet fracturing contribute to surrogate rod bending fatigue. The effect of sensor spacing on curvature measurement using three-point deflections was studied; the method based on effective gauge length is effective in sensor spacing correction. The database developed and the understanding gained in this study can serve as input to analysis of SNF (spent nuclear fuel) vibration integrity.

Management of tibial diaphyseal fractures with linear external skeletal fixators using carbon connecting rods in dogs

Dogs (12) with unstable tibial diaphyseal fractures, selected for this study, were stabilized with bilateral uniplanar Type II external skeletal fixators using stainless steel positive profile centrally threaded transfixation full pins, 2- way AO clamps and indigenously designed carbon fiber rods. Clinical lameness evaluation and radiographic evaluation for fixator stability, fragment alignment and callus formation were studied. Post-operatively, no breakage or bending of the carbon fiber rods was seen throughout the fixation period. Fixator staged disassembly and complete removal was done on an average 4–9 weeks in all cases which showed grade I lameness after removal. Complications like pin tract infection, wound at suture site due to wound dehiscence and wound at pin-skin interface were seen, which subsided later without any affect on bone healing. Lameness grading, pain score and radiographic evaluation of healing were estimated in all the cases throughout the fixation period. ESF using carbon fiber connecting rod appears as a practicable method for repair of tibial diaphyseal fractures with minimum risk of fixator destabilization. Fixator staged disassembly at 4 weeks accelerated bone healing and promoted earlier limb function.

Stereoradiography imaging motion artifact: does it affect radiographic measures after spinal instrumentation?

Stereoradiography imaging (SRI) is an accurate and reliable low-dose radiographic method. However, patients must remain motionless during image acquisition. Motion artifacts are frequently noted. The aims of the study were to determine the incidence of the SRI motion artifact and assess if motion during SRI acquisition affects radiographic measurements. In this retrospective study, 198 patients with spinal instrumentation had biplanar SRI radiographs performed, of whom 39 had concomitant conventional radiographs. Eight coronal and sagittal spinal parameters were independently measured on SRI and conventional radiographs for the 39 patients by 2 observers. Inclusion criteria were: presence of spinal instrumentation of more than six levels and an SRI motion artifact identified on the coronal and/or the sagittal views on either the spinal rods or on the limbs. Means were compared between both types of radiographs using the Student's t test; intraclass correlation coefficients (ICCs) were used for intraobserver reproducibility and interrater reliability. A motion artifact was identified in 19.7% (n=39, mean age 19.5±1.7years) of the cases. There were no differences in any of the coronal or sagittal plane measurements between SRI and X-rays. Intraobserver reliability and interrater reproducibility was high (range 0.81-0.98). Motion artifact during full-spine stereoradiography imaging acquisition is frequent, but does not affect spinal measurements. SRI with a motion artifact can be used to produce reliable measurements of the sagittal and coronal parameters. Some SRI images with a motion artifact may suggest loss of fixation or bending of the rods. However, after becoming familiar with the appearance of the motion artifact, repeat radiographs are rarely indicated. 14-004872. Level IV.

Large deflection and post-buckling analysis of non-linearly elastic rods by wavelet method

We propose a wavelet method in the present study to analyze the large deflection bending and post-buckling problems of rods composed of non-linearly elastic materials, which are governed by a class of strong non-linear differential equations. This wavelet method is established based on a modified wavelet approximation of an interval bounded L2-function, which provides a new method for the large deflection bending and post-buckling problems of engineering structures. As an example, in this study, we considered the rod structures of non-linear materials that obey the Ludwick and the modified Ludwick constitutive laws. The numerical results for both large deflection bending and post-buckling problems are presented, illustrating the convergence and accuracy of the wavelet method. For the former, the wavelet solutions are more accurate than the finite element method and the shooting method embedded with the Euler method. For the latter, both bifurcation and limit loads can be easily and directly obtained by solving the extended systems. On the other hand, for the shooting method embedded with Runge–Kutta method, to obtain these values usually needs to choose a good starting value and repeat trial solutions many times, which can be a tough task.

Biomechanical analysis of Ponte and pedicle subtraction osteotomies for the surgical correction of kyphotic deformities.

Biomechanical analysis of Ponte (PO) and pedicle subtraction osteotomies (PSO) in kyphotic deformity instrumentation. Patient-specific biomechanical model was used to computationally simulate seven hyperkyphotic instrumentation cases with three osteotomy strategies-1-level PSO, 3-level PO, or 6-level PO; forces within the instrumented spine were assessed and results were analyzed through rANOVA tests. Corrections with multi-level PO were close to those with one-level PSO. In upright position, average implant forces were from 225 to 280N and rod bending moments were around 10 Nm with no significant difference between the three strategies (p<0.05). In simulations of 30° flexion, rod bending moments increased by 38, 2, and 8%, implant forces increased by 28, 23 and 26% for the 1-level PSO, 3-level PO, and 6-level PO, respectively. Correction per vertebral level was smaller than the maximum correction allowed by PO and PSO. Multi-level PO allows similar kyphotic correction to 1-level PSO in spinal deformities with mixed indications for PO and PSO. Loads on the instrumentation constructs in PSO were higher than multi-level PO and higher in 6-level PO than 3-level PO. High loads were located more on the osteotomy sites. The rod shape should be adapted to the anticipated spine correction on the osteotomy sites.

Non-periodic homogenization of bending–torsion theory for inextensible rods from 3D elasticity

We derive, by means of \(\Gamma \)-convergence, the equations of homogenized bending rod starting from 3D nonlinear elasticity equations. The main assumption is that the energy behaves like \(h^2\) (after dividing by \(h^2\), the order of vanishing volume), where h is the thickness of the body. We do not presuppose any kind of periodicity and work in the general framework. The result shows that, on a subsequence, we always obtain the equations of the same type as in bending–torsion rod theory and identifies, in an abstract formulation, the limiting quadratic form connected with that model. This result is the generalization of periodic homogenization of bending–torsion rod theory already present in the literature.

Total wrist arthrodesis with wrist fusion rod in patients with rheumatoid arthritis.

This study aims to retrospectively review the short-term surgical outcome of wrist fusion using wrist fusion rod (WFR). Six wrists of four female patients (mean age 56 years; range 51 to 62 years) with advanced stage rheumatoid arthritis of Larsen IV or V were performed total wrist fusion using WFR. Clinical outcome was assessed using a numeric rating scale of pain satisfaction level. Bony fusion, correction of palmar subluxation and ulnar deviation, rod bending angle, wrist fusion angle, and complications were assessed from radiographs. All wrists achieved painless wrist stability with bony fusion of the radiocarpal joint. Both the palmar subluxation and ulnar deviation were corrected in all patients. Two radiographic complications were observed: rod fracture in one patient and a radiolucent line in proximal metacarpal bone in another patient. Both complications might have occurred as a result of instability of the third carpometacarpal joint, but neither influenced clinical outcome. Wrist fusion angle was smaller than rod bending angle at final observation. Wrist fusion using WFR is an option for the treatment of advanced stage rheumatoid arthritis of wrist. According to our experience, the stability of third carpometacarpal joint should be assessed before surgery, and this joint should be fused if required. The bending angle of the intramedullary rod does not directly form the wrist fusion angle in contrast to the case with a dorsal wrist fusion plate.

Method of Static Characteristics Calculation of Vibroinsulators with Rectilinear and Circular Working Sections in a Non-Linear Approach

An implementation of full-metal vibroinsulators is one of the most effective measures for an elimination of harmful effects of vibration in mechanical systems. However, in a contemporary literature an issue of an analytical calculation of vibroinsulators of that type, considering a non-linearity of the characteristics, is addressed insufficiently. In the presented study, by an implementation of exact theory of bending of elastic rods, the methodology of load characteristics calculation of full-metal vibroinsulators with elastic elements of rectilinear and circular shape of initial axial lines was developed. A groundlessness of Euler equation's implementation was demonstrated in a case of large displacement of linear rods, commensurable with their length. The method allows to increase designer's capabilities, to improve an accuracy of the calculation and to reduce time spent for a final adjustment of a product, which will ultimately lead to cost reduction final products.

Longitudinal Bending of Polymer Rods with Account Taken of Creep Strains and Initial Imperfections

An investigation was made of the loss of stability of polymer rods exposed to disturbances in the form of camber of the rod and eccentricity of load application.

Long Construct Pedicle Screw Reduction and Residual Forces are Decreased Using a Computer-Assisted Spinal Rod Bending System

Long Construct Pedicle Screw Reduction and Residual Forces are Decreased Using a Computer-Assisted Spinal Rod Bending System

A Second-Gradient Theory of Dilute Suspensions of Flexible Rods in a Newtonian Fluid

Mostsuspensiondescriptionsusednowadaysare based on Jeffery's model or some phenomenological modi- fications of it that do not take into account size effects: the kinematics and stresses do not involve a micro-mechanical characteristiclengthandthus,thepredictedrheologicalprop- ertiesarenecessarilyindependentofrodlength.Moresophis- ticatedmodelsabletoenrichfirst-gradientkinematicsaswell as to activate rod-bending mechanisms are needed, in partic- ulartoexplainthemildelasticityobservedexperimentally.In thispaperweproposeasecond-gradienttheoryfordilutesus- pensions of flexible rods in a Newtonian fluid that is indeed able to activate rod bending and predict viscoelastic behav- iour.

Intrasacral rod fixation for pediatric lumbopelvic fusion

This paper reports the authors' 19 years experience with pediatric intrasacral rod fixation. After insertion of two cannulated screws in S1 with and an original template guiding them into the anterior third of the endplate, two short fusion rods were inserted into the sacrum according to Jackson's technique distally to S3. In neuromuscular scoliosis, pelvic obliquity was reduced by connecting the proximal and distal constructs, distraction or compression, and in situ rod bending. In children with high-grade spondylolisthesis, lumbosacral kyphosis was reduced by rotation of the sacrum and in situ bending. There were no direct neurological or vascular injuries. The main complication was infection (7%). No pseudarthrosis or significant loss of correction at the lumbosacral junction was observed during follow-up. Intrasacral rod fixation appears to be safe and reliable for lumbopelvic fusion in pediatric patients.

Long Construct Pedicle Screw Reduction and Residual Forces are Decreased Using a Computer-assisted Rod Bending System

Long Construct Pedicle Screw Reduction and Residual Forces are Decreased Using a Computer-assisted Rod Bending System Previous biomechanical studies have shown that reduction loads placed on pedicle screws during assembly of the construct, with a rod that does not adequately fit the screw locations, can reduce the strength of the screw-bone interfaces. In this bench top study, axial pedicle screw forces on a unilateral 7-level construct were evaluated for 2 rod bending techniques: manual and computerassisted.

CAST3M modelling of a spent fuel assembly bending during a handling accident Rod failure risk evaluation from the experimental results of spent fuel rod bending test

The fuel handling operating rules exclude any accidental risk. However in the framework of the PRECCI R&D project, the bending of a spent fuel assembly resulting from its locking during a translation displacement is taken into account. This enabled us to develop an approach based on experiments and calculations that allows us to simulate the behaviour of an assembly under such loading. This study was carried out in CEA laboratories with the funding and the technical support of EDF. A three points bending test on a spent fuel rod segment was performed at the Laboratory for Mechanical Behaviour of Irradiated Materials (LCMI). From the experimental strength-displacement curve, a maximum failure strain, a maximum failure curvature and an equivalent constitutive equation were determined. CAST3M modelling of the fuel rod taking into account the elasto-plastic behaviour of the clad and the cracking of the UO2 fuel pellets was verified by the experimental results. Consequently, the identification of the respective contributions of the clad and of the pellets to the rod global behaviour was made possible. A two dimensional assembly with beam elements was modelled with CAST3M. The properties of the beams modelling the different parts of the assembly (top and bottom nozzle, grids) were chosen and adjusted according to their materials (zirconium alloys, steel) in order to obtain stiffness, tensile and shear behaviour, sliding and holding functions close to the experimental ones. Assembly bending calculations were performed. In order to obtain a rod integrity estimator, their maximum calculated strains and curvatures as a function of the bending angles can be compared to the failure experimental ones.

Distribution of zeros of solutions of self-adjoint fourth order differential equations

In this paper, for self-adjoint fourth order differential equations, we establish some lower bounds on the distance between zeros of a nontrivial solution and also lower bounds on the distance between zeros of a solution and/or its derivatives. We also give new results related to boundary value problems which arise in the bending of rods. The main results will be proved by making use of some generalizations of Hardy, Opial and Wirtinger type inequalities.

Theoretical Analysis of the Impact on the Rod Bending about the Axial Force

Starting from the basic theory, to deduce the balance equations of the rod under the vertical and horizontal loads. Concerning the boundary problem, to analyze of this most general conditions, that is, the elastic rod ends are fixed on the elastic supports, thus to summary the common simplified boundary conditions.

Cilia-Mimetic Hairy Surfaces Based on End-Immobilized Nanocellulose Colloidal Rods

We show a simple method toward nanoscale cilia-like structures, i.e., functional hairy surfaces, upon topochemically functionalizing nanorods of cellulose nanocrystals (CNCs) with thiol end groups (CNC-SHs), which leads to their immobilization onto a gold surface from one end, still allowing their orientational mobility. CNCs having a lateral dimension of 3-5 nm and length of 50-500 nm incorporate the native crystalline structure with hydrogen-bonded cellulose chains in the parallel configuration. This facilitates asymmetric, selective chemical modification of the reducing ends through reductive amination. Successful thiol functionalization is demonstrated using cryo transmission electron microscopy based on selective attachment of silver nanoparticles to the CNC-SH ends to form Janus-like colloidal rod-sphere adducts. The extent of thiol modification of CNC-SHs is quantified using X-ray photoelectron spectroscopy. The promoted binding of CNC-SHs on gold surfaces is shown by atomic force microscopy and quartz crystal microbalance, where the high dissipation suggests pronounced orientational mobility due to flexible joints at one rod end onto the surfaces. That the joints are flexible is also shown by the bending and realignment of the CNC-SH rods using a receding triple-phase evaporation front of a drying drop of water. The ability of the hairy surface to size-selectively resist particle binding was also investigated. As the CNCs are piezoelectric and allow magnetic functionalization by nanoparticles, we foresee a general platform for nanosized artificial cilia for fluid manipulation and controlled adsorption/desorption.