Pre-bent Plates Research Articles

Contact surfaces, compressive forces and pressure distribution in osteosynthesis. Model studies using pressure-sensitive foil

Previous pressure gauges have been unable to measure exactly the stress over the cross-section of fractures or osteotomies. This first became possible with the pressure sensitive foil. Known operative procedures were examined with this foil using a self-compressing plate and a synthetic tube model. Contact area, compressive force, pressure and pressure distribution were measured simultaneously and analogously. A straight plate produces extremely little force and pressure on the gap. Both are limited to about a quarter of the cross-section just below the plate. The consequence is no sufficient stability. Also, using a prebent plate results in inhomogeneous pressure distribution with high values, but a distinct decrease of the stress on the opposite side of the plate, especially by compression applied at the end of the plate. But compression from near the fracture side gives the highest values and a most homogeneous force distribution. In this case the force recorded 1700 N, the mean pressure 5,2 MPa and the contact 90% of the cross-section. The length thrust of the plate ends approximately at a torque of screw tightening at 1,0 Nm. Using torques up to 2,5 Nm, force and pressure increase isometrically. Higher torques have no influence. Converging screws result in smaller contact, force and pressure, because they produce a vector force away from the gap and a smaller length thrust.

One-Dimensional Analysis on the Dynamic Response of Cellular Chains to Pulse Loading

On the basis of our previous studies of a typical type II structure (i.e. a pair of prebent plates), a simplified one-dimensional mass-spring model is proposed to describe the uniaxial load-deformation characteristic of cellular materials and structures. When compared with the previous mass-spring model proposed by Shim et al., the present model employs fewer parameters (only two) to describe elastic-plastic behaviour, and the structural hardening/softening is represented by only one of the parameters. The model is then used to study the dynamic response of a cellular chain to a pulse loading of specified force intensity and duration. By adjusting the value of a single parameter adopted in the model, each cell of the cellular chain is identically assigned to possess either an elastic-hardening or an elastic-softening-consolidation property. The effects of material elasticity, cell compliance characteristic, cell number, and pulse intensity and duration are all examined by this model and discussed in detail. A special attention is paid to the initiation and propagation of the plastic collapse of the cells in the cellular chain so as to identify the governing parameters. Apart from the elastic wave speed, two other characteristic velocities, i.e. the particle velocity induced by the elastic wave and the plastic collapse propagation velocity, are defined and analytically evaluated. It is found that these three characteristic velocities completely govern the elastic and plastic dynamic behaviour of the cellular chains.

First Metatarsophalangeal Fusion with Ball-and-Socket Bone Preparation and a Dorsal Plate Fixation

The first metatarsophalangeal joint fusion is an accepted technique for hallux rigidus, severe hallux valgus deformity, and revision for failed hallux valgus surgery. In this article, the use of reamers for congruent convex concave surfaces is described. Together with a dorsal plate and an interfragmentary compression screw, this combination of the ball-and-socket bone preparation has operative advantages over other metatarsophalangeal fusion techniques. It is, on the one hand, technically simple to achieve congruent joint surfaces which is a requirement for good bone healing, and on the other hand, the prebent plate limits the risk for major malalignment of arthrodesis.

A study on type II structures. Part I:a modified one-dimensional mass–spring model

Abstract Most impact energy-absorbing structures can be classified into one of two types in terms of the shape of the overall quasi-static load–displacement curve in the early stages of deformation. Type I has a relatively “flat-topped” curve, while type II has an initial peak load followed by a “steeply falling” curve. The previous work showed that the deformation of type II specimens is much more sensitive to the impact velocity than that of type I specimens. That is, when the total kinetic energy remains the same for all specimens, smaller final deformations result from higher impact velocities; and this phenomenon is much more significant for type II specimens than for type I specimens. In order to explain this characteristic of type II structures, a one-dimensional mass–spring model with variable mass is proposed for a typical type II structure (i.e., a pair of pre-bent plates), and used to examine the effects of the lateral inertia of the structure under impact. Unlike conventional mass–spring models, our system contains an equivalent variable mass, which is a function of the rotational angle at plastic hinges and comes into effect during the second phase of the dynamic response. Predictions of this analytical model agree very well with an ABAQUS FE simulation of the dynamic response of the pre-bent plates to impact; and this verifies the validity of the mass–spring model proposed.

A study on type II structures. Part I:: a modified one-dimensional mass–spring model

Most impact energy-absorbing structures can be classified into one of two types in terms of the shape of the overall quasi-static load–displacement curve in the early stages of deformation. Type I has a relatively “flat-topped” curve, while type II has an initial peak load followed by a “steeply falling” curve. The previous work showed that the deformation of type II specimens is much more sensitive to the impact velocity than that of type I specimens. That is, when the total kinetic energy remains the same for all specimens, smaller final deformations result from higher impact velocities; and this phenomenon is much more significant for type II specimens than for type I specimens. In order to explain this characteristic of type II structures, a one-dimensional mass–spring model with variable mass is proposed for a typical type II structure (i.e., a pair of pre-bent plates), and used to examine the effects of the lateral inertia of the structure under impact. Unlike conventional mass–spring models, our system contains an equivalent variable mass, which is a function of the rotational angle at plastic hinges and comes into effect during the second phase of the dynamic response. Predictions of this analytical model agree very well with an ABAQUS FE simulation of the dynamic response of the pre-bent plates to impact; and this verifies the validity of the mass–spring model proposed.

A study on type II structures. Part II:dynamic behavior of a chain of pre-bent plates

From the energy-absorption point of view, in general a cellular material may be composed of a number of type I and type II cells. A comprehensive study of the mechanisms, by which these two types of cells undergo large deformation under impact loading , will help to deepen our understanding of the dynamic behavior of cellular materials. In this paper, special attention is paid to the dynamic response of a chain of type II cells under a projectile impact. Both the FE analysis and the equivalent mass–spring model proposed in part I of the paper are employed, and the results agree well with each other while the mass–spring model is much more efficient than the FE simulation. Three collapse modes of type II chain are identified, depending on the initial impact velocity. Furthermore, based on the equivalent mass–spring model, the local contact behavior between the striker and the first cell of the type II chain, and the effects of the associated parameters (e.g., the effects of cell number, cell wall inertia, mass ratio, input energy, etc.) are discussed in detail.

A study on type II structures. Part II:: dynamic behavior of a chain of pre-bent plates

From the energy-absorption point of view, in general a cellular material may be composed of a number of type I and type II cells. A comprehensive study of the mechanisms, by which these two types of cells undergo large deformation under impact loading, will help to deepen our understanding of the dynamic behavior of cellular materials. In this paper, special attention is paid to the dynamic response of a chain of type II cells under a projectile impact. Both the FE analysis and the equivalent mass–spring model proposed in part I of the paper are employed, and the results agree well with each other while the mass–spring model is much more efficient than the FE simulation. Three collapse modes of type II chain are identified, depending on the initial impact velocity. Furthermore, based on the equivalent mass–spring model, the local contact behavior between the striker and the first cell of the type II chain, and the effects of the associated parameters (e.g., the effects of cell number, cell wall inertia, mass ratio, input energy, etc.) are discussed in detail.

Dynamic buckling of an imperfect elastic, visco-plastic plate

Finite element analyses of dynamic buckling of an initially pre-bent plate are compared with static and dynamic experiments on type II columns investigated by Tam and Calladine (Int J Impact Engng 1991;11: 349–77). We employ an elastic–visco-plastic material model of the Cowper–Symonds type, which includes the measured quasi-static effective-stress plastic–strain curve. The striker is represented by a point mass impacting a contact surface on the end of a plate. The analysis considers models composed of two-dimensional beam- and three-dimensional shell-elements and discusses the effects caused by the finite width of the plate, the strain- and strain-rate hardening material properties and inertia. The calculated static and dynamic response is in good agreement with the experimental curves. Having shown the accuracy of our finite element model, the effect of the impact velocity on the structural response is analysed.

Application of reconstruction plates to the mandible

Reconstruction plates are a viable repair option for a variety of clinical indications, including segmental and comminuted fractures, traumatic bone loss, bone loss secondary to infection, and repair of non-union, atrophic bone, and tumor defects. Because of their design as load-bearing plates, immediate restoration of function can be provided with the absence of postoperative intermaxillary fixation. Application of reconstruction plates requires careful adaptation of the plate to the contour of the mandible using proper bending instrumentation, templates, and pre-bent plates. Placement of sufficient screws is also a consideration. This article provides information concerning use of reconstruction plates and highlights critical application techniques for the clinical indications noted above.

Degradation kinetics of biodegradable dl-polylactic acid biodegradable implants depending on the site of implantation

A recently developed biodegradable system made of dl-polylactic acid ( dl-PLA) for internal fixation of non-weight-bearing bones of the craniofacial skeleton was investigated. The plates were used for rigid fixation of experimental nasal bone fractures in 20 New Zealand white rabbits. In addition, prebent plates were placed in subcutaneous pockets in the backs of the animals. The material was removed after 7, 14, 28, and 42 days, and bending angles, plate stability, molecular weights (MW), and histologic analyses were studied. A significant decrease of MW over time and a difference in MW loss, showing a faster degradation subcutaneously, were observed. Plate stability did not decrease during the interval of 6 weeks, but a loss of bending angle was found in all prebent implants. This effect was caused by memory of DL-PLA. The results suggest that memory of biodegradable materials should be investigated before clinical application and that degradation rates differ according to the site of implantation.

An experimental approach to the problem of increasing the blood supply to the lungs: Hurwitt, E. S.: Surg., Gynec. and Obst. 87:313 (Sept.), 1948

This study evaluated the accuracy of mandibular reconstruction and assessed clinical outcomes in both virtual planning and conventional surgery patients. ProPlan CMF surgical planning software was used preoperatively in the virtual planning group. In the virtual planning group, fibula flaps were harvested and osteotomized, and the mandibles were resected and reconstructed assisted by the prefabricated cutting guides and templates. The main outcome measures included the operative time, postoperative computed tomography (CT) scans, facial appearance, and occlusal function. The ischemia time and total operation time were shorter in the virtual planning group than in the conventional surgery group. High precision with the use of the cutting guides and templates was found for both the fibula and mandible, and a good fit was noted among the pre-bent plate, mandible, and fibula segments in the virtual planning group. Postoperative CT scans also showed excellent mandibular contours of the fibula flaps in accordance with virtual plans in the virtual planning group. This study demonstrated that virtual surgical planning was able to achieve more accurate mandibular reconstruction than conventional surgery. The use of prefabricated cutting guides and plates makes fibula flap moulding and placement easier, minimizes the operating time, and improves clinical outcomes.