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Biomedical subjects

J Cordey

Publications and source records attributed to J Cordey.

At least 19 recordsLinked to original sources
PubMed1992

Effect of bone size, not density, on the stiffness of the proximal part of normal and osteoporotic human femora.

Proximal femur fractures in the elderly lead to a high rate of hospitalization. In studying the operative treatment of such fractures, it is first necessary to understand the relationship between the morphologic properties of this part of the femur (related to both geometry and density) and its mechanical properties. Numerous investigations showed that femoral strength correlates with bone mass; however, the dimension of the bones was not taken into account. We measured the relationship between the stiffness of the proximal femur under physiologic load and its geometry and density. Conventional x-rays and quantitative computed tomography (QCT) were carried out on pairs of human cadaver femora. Eight pairs were instrumented with strain gauges. Bones were subjected to an eccentric load that simulates moderate weight bearing (single-leg stance), and the strain parallel to the bone axis was plotted as a function of the load applied. An apparent bone stiffness was calculated as the ratio between the strain gradient within the section and the load applied. Strong correlation was found between x-ray densitometry and QCT. The bone stiffness also correlates strongly with the geometry (area) and slightly with bone mass; however, an unexpectedly low correlation was found between stiffness and density. We chose stiffness as a mechanical parameter (not strength) because it describes the "normal" bone behavior under load. Our results clearly demonstrate that the cross-sectional size of the bones must be taken into account when establishing the relationship between the mechanical characteristics of the bone and its morphology. In accordance with previous predictions, our results support that bone loss due to osteoporosis is compensated for by an increase in bone diameter.

Absorptiometry, Photon↗
PubMed1992

Effect of animal species and age on plate-induced vascular damage in cortical bone.

Plates used for fracture fixation produce vascular injury to the underlying cortical bone. During the recovery of the blood supply, temporary osteoporosis is observed as a result of Haversian remodeling of the necrotic bone. This process temporarily reduces the strength of the bone. We tackled the postulate that quantitative differences exist between animal species, and in different bones within the same species, due to variations in the relative importance of the endosteal and periosteal blood supplies. Using implants scaled to the size of the bone, we found comparable cortical vascular damage in the sheep and in the dog, and in the tibia and femur of each animal. We observed a significant reduction in cortical vascular damage using plates that had a smaller contact area with the underlying bone. No significant difference in cortical vascular damage was noted in animals of different ages.

Age Factors↗
PubMed1991

Is there a mechanical difference between lag screws and double cerclage?

Comminuted fractures of the long bones present problems of mechanical instability. We therefore used a plate and six screws as the main osteosynthesis combined with supplementary lag screws or cerclage wire. These two supplementary methods were compared. As a model, we used 60 plastic tibias with standard midshaft butterfly fractures. These models, depending on the osteosynthesis applied for the fixation of the butterfly onto the main fracture, were split into three groups of 20 bones. Group A1 with two lag screws, group A2 with two lag screws and two double cerclages, and group A3 with two double cerclages with no lag screws. The models were tested in torque and axial load. The results were: 1. In torque, group A1 was the most unstable with significant statistical difference from group A2 (P less than 0.01) and from A3 (P less than 0.05). There was no significant statistical difference between groups A2 and A3. 2. In axial load, group A3 was stable with significant statistical difference from A2 (P less than 0.05). There was no difference between A1 and A3. The experiment showed that if the cerclage is used double, anchored at the end of the screws and tensioned, it acts like a spring and is mechanically more stable than lag screws in torque. In axial load, no mechanical difference exists between lag screws and double cerclage.

Biomechanical Phenomena↗
PubMed1991

A paradigm of delayed union and nonunion in the lumbosacral joint. A study of motion and bone grafting of the lumbosacral spine in sheep.

In a group of nine sheep (Group A), it was noted that when small, interlocking cancellous and cortical cancellous bone grafts are placed posteriorly on the lumbosacral spine, union always occurred in the interlumbar motion segments and almost never occurred at the lumbosacral joint. One of the main differences in these two areas is the amount of motion that occurs at each level with flexion and extension. Because nonunion following bone grafting for arthrodesis of the spine is a serious clinical problem, we have studied the amount of motion seen at the interlumbar and lumbosacral joints in sheep to ascertain how much motion is compatible with union and how much is associated with nonunion. In vivo studies were carried out in eight sheep (Group B), and five normal spine segments were studied in vitro to determine normal motion in this species. To simplify the complex in vivo motion that occurs at the lumbar motion segments, the simple linear displacement and strain of the fusion mass (consisting of fibrous tissue and bone grafts placed on and between the laminas posteriorly) was measured with the spine in flexion and extension. When the displacement and strain at the interlaminar level of the L6-S1 joint was measured, the linear displacement was found to be 5.2 mm and the associated linear strain 36%. The displacement at the L5-L6 interspace was 1.2 mm, and the strain 10%. The stiffness of the L5-L6 joint (which always fused) and the L6-S1 joint (which did not fuse, with one exception) were also studied. In a third group of four animals (Group C), internal fixation of the lumbosacral joint was attempted in addition to bone grafting.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[Treatment of defects of the long bones using distraction osteogenesis (Ilizarov) and intramedullary nailing. Theoretic principles, animal experiments, clinical relevance].

For large shaft defects of tibia and femur, distraction-compression osteosynthesis (Ilizarov) provides an ideal autologous bone graft. Combination of this with an intramedullary interlocking nail instead of an external fixator could improve patient comfort, because transport with a small external device takes only one-third of the total fixation period. Using 21 adult female sheep we created standardized tibia shaft defects 20 mm (medium size) and 45 mm (large size) in length. The tibiae were stabilized with non-reamed intramedullary interlocking nails. Following corticotomy by chisel, segments were transported using subcutaneous traction wires with a screw as a fulcrum to maintain stationary skin exit points without soft tissue problems. The external traction devices were removed after 12 or 16 weeks. Animals were sacrificed after 12 or 24 weeks with medium-size defects, and after 16 or 32 weeks with large defects. We evaluated the results clinically, by standardized weekly X-rays and, after sacrifice, by quantitative computed tomography (QCT). No animals had to be excluded from the study. Despite primary destruction of the intramedullary circulation all distraction gaps were spanned with bone. X-Rays showed typical signs of good quality of distraction bone regeneration (narrow radiolucent zone in the middle of the regenerate, longitudinal structure), continuous calcification, and cortex formation. QCT cross sections showed completely circular bone regeneration with small and large defects. Bone regeneration was faster on the dorsal side, where more bone was formed than ventrally. Small defects can remain ventrally in the regenerate; these close secondarily.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

[Bone morphology following plate osteosynthesis as measured by axial tomography].

Previous examinations using computed tomography have shown that no geometrical changes in the cross-section was induced by the plate fixation; bone density was slightly reduced (10% in average) in the entire cross-section and not only next to the plate. A tomographic analysis is presented here about the quality and the amount of bone in the affected leg, compared to the contralateral one.

Adolescent↗
PubMed1989

[Stress protection in plate osteosynthesis: myth or reality?].

It is generally admitted that plate fixation of fractures results in reduced stress (stress protection) and subsequent structural adaptation of bone (bone loss). The analysis of the stress pattern and the reduction of deformation work in plated bones is a prerequisite for the assertion that bone loss is stress related. The strain field within bones under eccentric axial load has been analyzed theoretically and verified experimentally. The difference between the reduction of stress obtained using the flexible plate materials is small. Reduction of plate stiffness does not result in proportional improvement of the bone strain.

Bone Plates↗
PubMed1988

Early temporary porosis of bone induced by internal fixation implants. A reaction to necrosis, not to stress protection?

Stabilization of the fracture using implants requires contact surfaces between implant and bone. Such contact has been observed to induce bone porosis first seen at one month after surgery. Bone loss in the vicinity of implants has hitherto been explained as being induced by mechanical unloading of the bone (stress protection). Experiments in sheep, dogs, and rabbits combining intravital staining of blood circulation and polychrome fluorescent labeling of bone remodeling leads to the conclusion that early bone porosis in the vicinity of the implants is the result of internal remodeling of cortical bone and is induced by necrosis rather than by unloading. This theory is favored by the evidence that (1) the bone porosis is of a temporary nature, an intermediate stage in internal bone remodeling; (2) the pattern of the remodeling zone is closely related to that of the disturbed circulation, and not to that of unloading; (3) plastic plates may produce more porosis than steel plates; and (4) improved blood circulation using modified plates resulted in reduced porosis. The clinical relevance of these findings is related first to the temporary weakening of the bone, and second to the possibility of sequestration. Sequestration may be the result of intensified remodeling activity in the presence of inflammation or infection.

Animals↗
PubMed1979

[Inclined plate screws - in vitro measurement of the stability of transverse osteotomy of tibia].

A compression plate which is exactly contoured to the bone surface produces asymmetric compression: only part of the cortex near the plate is compressed. Therefore a compression plate is not meant to be used selfstanding, it will rather be combined with additional means. Two of these have been studied: the increased stability provided by the use of lagging, inclined plate screws was compared to the one provided by the spring effect of a plate prebent for central elevation. 7-hole dynamic compression plates (DCP) and 4.5 mm cortex screws were used to stabilize transverse osteotomies in human tibiae in vitro. Flexural and torsional testing revealed that the use of an inclined lag screw or a prebent plate increases stability compared to the one achieved with an exactly contoured plate alone. Preliminary tests suggest, that a combination of plate lag-screw and prebending offers stability up to high loads.

Biomechanical Phenomena↗
PubMed1979

[Importance of the friction between plate and bone in the anchoring of plates for osteosynthesis. Determination of the coefficient of metal-bone friction in animal in vivo].

In mechanical devices in general the friction plays an important role in force transmission. To find out about the magnitude of frictional forces between internal fixation plate and bone in vivo, simultaneous strain recording in plated bone and instrumented plate were performed. After 3 weeks of implantation the torque applied to a single plate-screw was set to definite levels. Thus it could be determined at what level of screw compression and at what tangential load of the related surface bone-plate, gliding occurred. The coefficient of friction was found to be 0.2 +/- 0.09 (x +/- Sx). It can be concluded that in vivo friction produced at the plate-bone contact surface is able to guarantee stability of fixation.

Animals↗
PubMed1979

[Registration of fibular movements in vivo in relation to the tibia at the level of the ankle joint].

Fibular movements in relation to the tibia are known on extension and dorsiflexion of the ankle-joint and have been proved by experiences on cadaveric preparates using outstanding points of relation. To registrate fibular movements in vivo a special trigonometric system has been developed permitting calculation of definite movement in frontal and sagittal plane as well as a rotation around axis. Twelve healthy volunteers were examined in this way during extension and dorsiflexion of the ankle, with and without weight-bearing. The results showed that we should not consider isolated fibular movement but analyse simultaneous complexity of movements in a graphic comparison. Under these conditions we observe a very high significance of fibular movements depending each of other. The emphasis can be designed in a field covering all the points reached by fibular movement in frontal and sagittal plane of the twelve healthy volunteers during movement of the ankle; it shows that the fibula functions like a guide-stick for ankle movement. Reflecting on the designed fields of healthy persons, some patients with posttraumatic pathological alterations of the ankle-joint have been analysed.

Ankle Injuries↗