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J Cordey

Publications and source records attributed to J Cordey.

At least 37 records · Page 2Linked to original sources
PubMed1999

Strain gauges used in the mechanical testing of bones. Part II: "In vitro" and "in vivo" technique.

How to choose and prepare the strain gauges for bonding on bones "in vitro" and "in vivo"? This communication aims to elucidate technical details and some applications: direct assessment of the axial load, the bending moment, and the torque applied to long bones by the physiological loads. As a typical example of application, we will show the assessment of stress protection due to plates on the bones in the sheep tibia.

Animals↗
PubMed1999

Strain gauges used in the mechanical testing of bones. Part III: Strain analysis, graphic determination of the neutral axis.

The problem addressed in this part is the analysis of the strain pattern within the bone, when the strain has been measured using strain gauges along the long axis of the diaphysis of a bone subjected to axial load, bending, or eccentric axial load. It is first necessary to obtain the position of the strain gauges using, for instance, computed tomography. The linear bending theory is then used to determine graphically the position of the neutral axis in a cross section and the strain field within the bone. An example of application is taken from the literature: Rybicky et al. (1) measured the reduction of strain within a plated horse metatarsus, relative to that of the intact bone. They made an analytical strain analysis. A comparison is made between the analytical results and the graphic ones, validating the graphic method.

Biomedical Engineering↗
PubMed1999

Loading model for the human femur taking the tension band effect of the ilio-tibial tract into account.

A loading model permitting the application of relevant loads to the diaphysis and constructed on the basis of current knowledge of the biomechanics of the femur will be presented. This model takes into account the force acting through the ilio-tibial tract in the frontal plane and the forces acting on the condyles in the sagittal plane. There is compression on the femoral head and on the condyles and tension on the greater trochanter. Experimental verification using human cadaveric femora instrumented with strain gauges has shown that the adequate loading condition is: a line of force tangential to the femoral head a line of force tangential to the dorsal aspect of the distal junction of the diaphysis and metaphysis. Under these conditions, the calculated forces will accord well with values assessed in vivo. The model described here represents a simple procedure for experimental load application, producing realistic strain values. The proximal part of the bone is placed under tension on the dorsal aspect; the medial aspect is under compression. The strain pattern develops such that the tensile forces affect the anterior aspect distally and compression the dorsal aspect.

Femoral Fractures↗
PubMed1999

The mechanics of internal fixation of fractures of the distal femur: a comparison of the condylar screw (DCS) with the condylar plate (CP).

Distal femoral fractures are rare and usually complex. Mostly, they are fixed with the Dynamic Condylar Screw (DCS) or the 95 degrees condylar plate (CP). The simplicity of applying the DCS compared with the CP led us to investigate whether any possible mechanical deficiencies of the CP would detract from its technical advantages, thus limiting the indications for its use in the treatment of fractures of the distal femur. An in vitro investigation was carried out to measure the stability of a Y-osteotomy (with and without medial metaphyseal bone defect) stabilized either with the CP or the DCS. 8 pairs of human cadaveric femora classified according to their bone density were used. CP and DCS were applied to 1 bone in each pair by means of three lag screws (anterior, posterior and through the plate). Physiological loading was simulated and measurements were taken at the level of the osteotomy in the frontal and sagittal planes in order to assess rotational instability and the amount of gap opening in the vertical branch of the osteotomy. There was no relevant difference in the mechanical properties of the two fixations for fractures without medial defect, even if the stability of the fixation was reduced by removing the distal screw. Furthermore, interfragmental movement was minimal. In the frontal plane, simulated closure resulted in closure of the medial branch of the osteotomy in every case without any opening of the vertical branch of the osteotomy. In the sagittal plane, the closure of all branches of the osteotomy was confirmed for 11 bones and a rotation of the condyle was observed in 5 bones (3 CP, 2 DCS). Removing the distal lag screw did not increase the instability. Even in osteoporotic bones, the DCS provided the same stability as the CP. For simple Y-osteotomies, the CP did not offer any technical or mechanical advantages. The stability in the frontal plane however was significantly reduced in osteotomies with medial defect. The amplitude of interfragmental movement on all bones fixed by the CP, except for 1 pair, was greater than those fixed by the DCS. The absence of the anterior lag screw did not reduce stability. However, the absence of the lag screw within the implant considerably weakend the fixation--more so for the CP than for the DCS. Instability reached a maximum without any lag screw at all, which again was more pronounced for the CP than for the DCS. The Dynamic Condylar Screw (DCS) must be regarded as the implant of choice both technically and mechanically even in osteoporotic bones, but the distal condylar block must be at least 4 cm in length.

Biomechanical Phenomena↗
PubMed1999

A biomechanical comparison of the antegrade inserted universal femoral nail with the retrograde inserted universal tibial nail for use in femoral shaft fractures.

Femoral shaft fractures with and without bony contact were simulated in cadaver specimens fixed with one of two different types of intramedullary locked nail systems; conventional antegrade nail fixation of the femur with the universal AO femoral nail or retrograde insertion in the femur with the universal tibial nail (a smaller diameter slotted nail) were utilized. Mechanical testing simulated one leg stance, and resultant deformation was measured in bending, torsion, and shortening. In stable fractures, fracture stability was similar to both devices, while in unstable fractures, the larger femoral nail was more stable. Furthermore, the simulation of single leg stance led to a coupled deformation of varus bending, axial shortening, and external rotation, which was dependent on bone geometry.

Adult↗
PubMed1999

Fracture healing of the sheep tibia treated using a unilateral external fixator. Comparison of static and dynamic fixation.

It is generally accepted that when a fracture is treated with external fixation, dynamization of the fixation accelerates formation of the bony callus by transferring part of the functional loads. The aim of the research presented here was to validate this principle using in vivo measurements of callus stiffness. We created a transverse fracture in the mid third of the tibial shaft in 12 sheep and maintained a 3 mm gap between the fragments for 3 weeks. Two types of unilateral external fixators were applied. Axial loading was permitted (dynamization) from the fourth week onwards in 6 animals. In the other 6 animals, fixation remained static for both types of fixation. Weekly measurements of callus stiffness were obtained using a goniometer and load cell to assess bending stiffness. Two slightly different fixators were used. Callus formed in all 12 animals. Callus stiffness increased exponentially to reach the degree of stiffness measured on the contralateral side. There was no clear difference in healing between the two types of fixations nor between dynamic and static fixation. If a unilateral fixator was applied which did not maintain absolutely rigid fixation, the fracture generally healed well even without contact between the fragment ends. If the process of callus formation had begun normally, dynamic fixation offered no further benefit. Measuring the stiffness of the callus with an adequate measurement apparatus in vivo indicated that the fixator could be removed earlier than would have been authorized on the basis of radiological evidence alone.

Animals↗
PubMed1999

Type of screw does not influence holding power in the femoral head: a cadaver study with shearing test.

We studied the holding power during cut-out tests of 4 different screw fixation devices of the femoral head, correlated to head size and bone density, on 48 paired deep frozen proximal femurs of fresh gross specimens. We found no significant effect of the device on the holding power. There was a significantly higher maximal load at failure in large and dense heads. It seems then unnecessary to advocate more sophisticated but also more expensive devices to fix femoral neck fractures.

Aged↗
PubMed1998

Biomechanical behaviour at the distal third of the femur: possible use of a medial metaphyseal plate.

The incidence of fractures in the distal femur is becoming more frequent and they are often associated to complex lesions with potential complications. Operative treatment is mandatory for elderly people and several methods of internal fixation with appropriate implants have been developed, generally approaching the lateral aspect of the femur. An alternative antero-medial access was proposed several years ago but the biomechanical aspects of its application must be debated. The aim of the present study is to establish if adverse biomechanical effects should be expected when the plate is affixed at the medial side of the femur metaphysis, by analysing the strain pattern of a human cadaver femur submitted to loads simulated in different experimental conditions. Application of load resulted, as expected, in tension in the lateral aspect and compression in the medial aspect of the femur diaphysis but it turned more and more toward the anterior aspect and the compression turned toward the posterior aspect when the levels measured changed from proximal to distal. The plate was next to the neutral axis and produced a moderate stress protection effect (approx. 70 per cent). No biomechanical disadvantages have been observed as a result of the plate being apposed at the medial aspect instead of the conventional lateral aspect of the distal femur.

Aged↗
PubMed1998

[Method for measuring the comparative stability of osteosynthesis in the dorsal pelvic ring].

In the past, biomechanical investigations on the dorsal pelvic ring have generally been performed on a small number of cadaveric pelves in various non-standardized procedures. Significant differences in stability between different internal fixation methods of unstable pelvic ring fractures were not found. The experimental design presented here was based as closely as possible on the physiological loading of the pelvis in one-leg stance. This method made it possible to carry out standardized, reproducible tests on different osteosytheses of the sacroiliac joint. Furthermore, the suitability of artificial bones for such investigations can be assessed on the basis of a larger number of similar experiments on artificial and human pelves and the number of human pelves required for such studies could be reduced.

Biomechanical Phenomena↗
PubMed1997

Positional stability of polylactide pins with various surface textures in sheep tibia.

Resorbable pins with a smooth or textured surface were produced from poly(L-lactide) P(L)LA poly(L/D-lactide) 95/5% P(L/D)LA, and poly(L/DL-lactide) 95/5% P(L/DL)LA by injection molding. The pins were implanted in sheep tibiae to establish whether the pin surface geometry and the polymer composition used for the pin preparation affect their positional stability in bone; i.e., can the pin design and its ability to swell in body fluids protect against loosening. Three of the 32 P(L)LA pins with a smooth surface loosened but none of the P(L/D)LA and P(L/DL)LA pins with a smooth surface did. This may indicate that expansion of the pin upon swelling protects against loosening, even if the pin's surface geometry is not optimal. None of the pins with a textured surface were loose, independent of the polymer used for the pin preparation. The textured surface of these pins allowed the ongrowth of new bone and hence, implant anchoring, secured the positional stability of the implant in the bone.

Animals↗
PubMed1997

The use of a resorbable augmentation device to secure plating of osteoporotic bones. An in vitro study.

Osteotomies in porotic human cadaveric humeri were fixed with metallic plates and screws in 3 experimental groups. In group I, osteotomies of the 3 arbitrarily chosen humeri were plated without reinforcement. The osteotomies of the contralateral 3 humeri were plated after reinforcement with a poly(L-lactide) augmentation device. In group II, osteotomies on one side were plated without reinforcement, but those of the contralateral humeri were plated after reinforcement with methylmethacrylate. In group III, the osteotomies of 3 humeri were plated and reinforced with poly(L-lactide) and in the 3 contralateral humeri were plated after reinforcement with methylmethacrylate. The pullout strength for screws from bones augmented with poly(L-lactide) was identical to those where methylmethacrylate had been used. The bones with poly(L-lactide) augmentation had a higher torsional stiffness than those with methylmethacrylate cement and those which were not reinforced. Resorbable polymeric medullary augmentation devices can be used to enhance plating of osteoporotic bones.

Bone Cements↗
PubMed1997

Resorbable polymeric inserts as a means of enhancing fixation of fractures of porotic bones. I. Stability of mechanical properties and viscoelasticity of the inserts aged in vitro.

A titanium screw-poly(L-lactide) medullary insert system intended for use in the fixation of porotic bone fractures was subjected to in vitro ageing at 37 degrees C and pH = 7.4 for up to 6 months. The pull-out force of the screw from the insert and the viscoelastic properties of the insert were measured. The pull-out force did not change up to 6 months of ageing, indicating that the polymeric insert provides a good purchase for the screws. The viscoelastic properties of the insert provides of bone and did not change substantially with temperatures up to 52 degrees C. This indicates that the medullary insert would maintain its properties in vivo even if the body temperature was increased. The molecular weight of the insert at 6 months was reduced by 60%, but the molecular weight reduction did not affect the mechanical properties of the insert.

Bone Screws↗
PubMed1997

The hybrid ring tubular external fixator: a biomechanical study.

OBJECTIVE: To measure and compare the mechanical properties in bending of the four-ring, and three-ring/one-tube hybrid external fixation frames. DESIGN. IN VITRO: measurements of the mechanical behaviour of ring and ring-tubular external fixation frames. In the latter, one ring of the full circular frame was replaced by one tube and Schanz screws. BACKGROUND: The mechanical properties of the classical Ilizarov four-ring external fixation frames has been compared to those of other external fixation frames by various authors. However, in clinical practice the hybrid fixation frame is being used with increasing frequency. Therefore the mechanical properties of the latter are of immediate interest and clinical value. METHODS: On explanted sheep tibiae with single and double osteotomies, frame stiffness in the four-point bending mode was measured at different K-wire tensions, comparing the values obtained from four-ring frames, to those of three-ring-tubular hybrid frames. These measurements were made under conditions of (a) bone distraction (BD), and (b) segment transport (ST), both at the initial and final stages of this procedure. RESULTS: In circular frames, frame stiffness in bending for increasing K-wire tension showed a Gaussian distribution both in distraction and post-ST with an optimum at 1000 N. In ring tubular hybrid frames, however, frame stiffness showed a more linear relationship to K-wire tension. CONCLUSIONS: In the four-ring Ilizarov external fixation frame, the exchange of one ring with one tube and one Schanz screw both reduced frame stiffness in bending and converted to linear its relationship to K-wire tension. RELEVANCE: Under clinical conditions, the use of a similar ring tubular hybrid external fixator allows the adjustment of frame stiffness in a simple and practical way. This is not the case with the original ring fixation frame.

Journal Article↗
PubMed1995

[A method for inducing standardized spiral fractures of the tibia in the animal experiment].

A method for the deliberate weakening of cortical bone has been developed on the basis of an already established technique for creating butterfly fractures. It enables one to create the same type of fracture, i.e., a spiral fracture, every time. The fracturing process is recorded as a force-strain curve. The results of the in vitro investigations form a basis for the preparation of experimental tasks aimed at demonstrating internal fixation techniques and their influence on the vascularity of the bone in simulated fractures. Animal protection law lays down that this fracture model must not fail in animal experiments.

Animal Testing Alternatives↗
PubMed1995

[Healing of spiral fractures in the sheep tibia comparing different methods--osteosynthesis with internal fixation, interlocking nailing and dynamic compression plate].

The healing process of spiral fractures of the sheep tibia was investigated in an experiment with simulated clinical conditions. The effects of conventional internal fixation techniques with the DCP and the intramedullary nail are compared with those of internal fixation with the spine fixator. The internal fixation techniques are described in terms of their bending stiffness when mounted on the fractured bone. The in vivo investigation was documented clinically and radiographically and the post mortem specimens were evaluated histologically. The bending stiffness of the healed bone was assessed in relation to the contralateral side. After application of the DCP, primary healing took place and extensive transcortical necrosis occurred in the implant bed. Intramedullary nailing led to secondary healing and to necrosis of the inner cortex close to the endosteum. After internal fixation with the spine fixator, gap healing took place and no cortical necrosis was observed. The clinical course was generally good after all procedures. The histological evaluation shows that damage to the vascularity of the bone can only be avoided by using the spine fixator. This principle seems to be appropriate for the purposes of biological internal fixation.

Animals↗
PubMed1994

Cancellous bone graft for skeletal reconstruction. Muscular versus periosteal bed--preliminary report.

The purpose of this project was to verify the value of perfused periosteum as a possibly ideal bed for autogenous cancellous bone graft. The model consisted of a 7 cm defect in the sheep tibia, stabilized with a locked intramedullary nail. The defect was filled with conventional cortico-cancellous bone graft covered either with a muscle or a perfused osteoperiosteal flap. The incorporation of the graft was analysed by a series of radiological and mechanical examinations. The graft embedded in perfused osteo-periosteum was rapidly remodelled to a strong, circular bone. Mechanical testing revealed even better values than for normal bone. The graft embedded in muscle showed an important resorptive phase before scanty, incomplete, reconstitution of bone appeared. Mechanical properties were poor. The study supports the hypothesis that perfused osteo-periosteum is an ideal bed for cancellous bone graft and that perfused muscle is not the ideal environment for incorporation of the graft.

Animals↗
PubMed1994

A retrospective analysis of plate contouring in the tibia using the conventional 4.5 (narrow) dynamic compression plate.

Plate contouring is an essential part of plate osteosynthesis. Its safety and technical ease is dependent on plate factors (material and design) and the complexity of the contouring. Our purpose was to determine the range of plate contouring; estimate the strain on the plate from the radius of curvature in the area of contouring; and determine whether shaped plates had a reduction in their load carrying capacity. A retrospective analysis of 500 radiographed tibias that had undergone osteosynthesis with the conventional dynamic compression plate was conducted to evaluate the radius of curvature and degree of bend in the plates, and to determine whether plates were bent at screw holes. Contouring of the plate to fit the bone was done by the surgeon at the time of application. Postoperative radiographs were evaluated. We found that (a) the shorter the length of plate contoured, the greater the strain; (b) plates were bent at screw holes, and these tended to be the areas of highest strain; (c) the range of plate strain was 0.6-16% (average 1.6%); and (d) plates were bent from 10 to 90 degrees (average 20 degrees).

Biophysical Phenomena↗