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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

At least 19 recordsLinked to original sources
PubMed1995

Intramedullary nailing and pulmonary embolism: does unreamed nailing prevent embolization? An in vivo study in rabbits.

Pulmonary embolism in reamed femoral nailing has been reported and discussed over recent years. Does an unreamed nailing technique with a solid nail prevent this rare but serious complication of intramedullary fixation? In an animal model in rabbits, we studied the pathophysiologic impact on pulmonary function and the impact on hemostasis of reamed and unreamed nailing of intact femora and tibiae, and of femoral fracture in relation to intramedullary pressure. No statistical difference of PaO2, PaCO2, and PCO2et was found in the femur whether a reamed or unreamed procedure was performed. Two of six animals with unreamed femoral nailing, one of six animal with reamed femoral nailing, and one of five animals with a femoral fracture fulfilled four of four or three of four criteria for embolization (increase of the difference of PaCO2 and PCO2et, decrease of PaO2, increase of blast cells in central-venous blood and bone marrow/fat in histologic section of the lungs and bone). Tibial nailing did not alter pulmonary function in either group. Intramedullary pressure was increased in all animals with perioperative impairment of pulmonary function (375 to 676 mbar). Analysis of the hemostatic results showed a significant difference of platelet activation in reamed versus unreamed nailing of the femur 1 hour after nailing (p < 0.01) and a significant decrease of fibrinogen and antithrombin III (p < 0.001/p < 0.01) in reamed femoral nailing. We conclude that unreamed nailing of the femur with a solid rod may also cause bone marrow embolization with alteration of pulmonary function as long as an important increase of the intramedullary pressure is generated during the nailing procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Influence of reaming versus nonreaming in intramedullary nailing on local infection rate: experimental investigation in rabbits.

The question of whether the impairment of the endosteal blood supply, which is induced by nailing with reaming of the medullary cavity, increases the risk of a postoperative infection cannot be conclusively answered by studying existing literature. The aim of this study was to investigate the effect of medullary reaming on the occurrence of local infection based on an infection model in the rabbit tibia (n = 44). An infection rate of 50% was found after unreamed nailing, as opposed to an infection rate of 64% after medullary reaming. The number of bacteria observed after reaming was significantly higher than after nail insertion without previous reaming. The differing susceptibilities to infection as observed in this model are statistically significant (p < or = 0.05).

Animals↗
PubMed1995

[Biomechanical reaction of the bones to intra- and extramedullary load bearers: the significance of implant contact].

Bone reacts very differently to changes in the environment relating to implant surgery. Since the advantages and disadvantages of implants have to be set against each other, the functions of implants and the demands made upon them will be considered first. The contact area between the bone and the implant will then be discussed. The contact surfaces and their induction of necrosis are at present in the forefront of our research in the area of biomechanics. The essential issues are: the avoidance of early temporary porosity, the possibilities of providing best conditions for "accelerated" bone healing, the reduction of refracture risks, and the improvement of infection resistance. Considerable opportunities for improvement of the most recent insights into the biology and biomechanics of the contact zones.

Bone Resorption↗
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↗
PubMed1992

Drill bit failure without implant involvement--an intraoperative complication in orthopaedic surgery.

The aetiology, frequency and consequences of drill bit failure during surgical intervention in human and animal bone tissue are investigated and discussed to provide the surgeon confronted with this problem with a scientifically based procedure. The literature on this subject is rather inadequate, i.e. only one publication in the last decade could be found dealing with this topic and this was a veterinary case. The Laboratory for Experimental Surgery in Davos has received several enquiries from the medical profession worldwide as to correct procedure in the case of drill bit failure. Three sources of information were investigated in order to furbish a reply to these enquiries, these were the AO/ASIF documentation centre in Berne, a survey of 280 surgeons and orthopedic doctors in Switzerland and a survey of 83 AO/ASIF foundation members. One broken tap (tool steel) was removed two years after the operation and metallographic investigations carried out. A frequency of 3 drill bit failure per 1000 internal fixations (0.3%) is apparent in nearly all data. The reasons for drill bit failure were investigated. Drill bit failure occurs more frequently in the proximal femur and when using angled plates. On the basis of this enquiry the following guidelines can be offered to the surgeon. A broken drill bit which is not in contact with an implant can be left in the body without any risk of delayed recovery. However, if the drill fragment is situated near a joint or if it can be easily removed without further trauma to the bone, then it should be removed. Once the fracture has healed the broken drill bit should be removed along with the implant provided no exceptional difficulties are involved.

Adult↗
PubMed1992

Drill bit failure with implant involvement--an intraoperative complication in orthopaedic surgery.

This paper aims to investigate whether drill bit fragments which are in contact with an implant behave differently to those without contact to the implant and if so in what way. There is particular emphasis on whether two metals in contact are subject to corrosion and whether the products of such a corrosion lead to undesirable tissue reactions. The orthopaedic surgeon must know whether a drill bit fragment should be removed if it is in contact with an implant, in particular, whether there will be negative consequences for the tissue if it is left in the body. It is necessary to establish how much additional trauma is justified in removing a broken fragment and how the surgeon can determine intraoperatively whether there is contact between the fragment and the implant. Finally, this investigation aims to establish whether the fragment can be left in the body until implant removal or whether it can be left permanently in situ.

Animals↗
PubMed1992

[Limited Contact Dynamic Compression Plate (LC-DCP)--biomechanical research as basis to new plate design].

Our continuously evolving understanding of bone biology has led to a new approach to plate fixation. In comminuted fractures, anatomical reduction of all fragments is no longer a goal in itself. Preservation of the viability of the bone fragments seems to be the key to unimpaired fracture healing in internal fixation. The rapid integration of unreduced but vital fragments into the fracture callus functions as a bio-buttress system and prevents fatigue fracture of the implant. To realize the new concept of biological internal fixation, the limited contact dynamic compression plate, which minimizes vascular damage to the plated bone segment, has been developed.

Animals↗
PubMed1992

[Mechanical properties of PDS-augmented patellar tendon transplants in reconstruction of the anterior cruciate ligament].

In 25 sheep the anterior cruciate ligament (ACL) was reconstructed after resection. Twelve modified "Jones procedures" were performed (transplantation of the central third of the patellar tendon with an initial load of 50 N) and 13 polydioxanone (PDS) augmentations. In 15 cases the ACL was resected from the right knee. Twenty-one sheep survived for 1 year and were then evaluated. Loss of the ACL leads to instable joints in this experiment. Within the first 6 months anterior translation occurs; after 1 year subluxations can be seen on the X-ray films. Macroscopical signs of extensive arthrosis were seen in the femorotibial and femoropatellar joints; the menisci were totally destroyed. Macroscopically strong ligaments were seen 1 year after PDS-augmented reconstruction as well as after transplantation of the patellar tendon with an initial load of 50 N. There was no difference between the two groups. The mechanical strength reached 54% of the maximum load of a control group in the Jones reconstructions and 61% after additional augmentation with a 2-mm biodegradable PDS cord. There was no statistically significant difference. Both methods are suitable for reconstruction of the ACL; the patellar tendon replaces the ACL very well.

Animals↗
PubMed1991

Role of interfragmentary strain in fracture healing: ovine model of a healing osteotomy.

It has been hypothesized that the histological pattern of fracture healing is controlled at least in part by the local mechanical strains in the interfragmentary region. To test this "interfragmentary strain hypothesis," we applied cyclic bending deformations to tibial osteotomies in 11 sheep. An instrumented flexible plate spanning a 1-mm osteotomy gap was deformed to create a gradient of tissue elongation from 10% under the plate to 100% at the opposite cortex. The cyclic deformations were applied three times per minute, 24 h per day, for 1-5 weeks. However, as a result of tissue differentiation, the bone-plate complex increased in stiffness with healing time, resulting in a marked reduction of the gap deformation at approximately 4 weeks. Fracture healing was evaluated using vascular injection of India ink and conventional histology. A nonlinear three-dimensional finite element model of the interfragmentary tissue at the initial stage of healing was used to predict the complex tissue strains. The ingrowth of vascularized soft tissue into the interfragmentary gap, as well as the subsequent differentiation of this tissue, occurred earlier and to a greater degree in regions of lower strain. In contrast, the proliferation of callus tissue was greatest at the periosteal and endosteal surfaces of the cortex opposite the plate. Direct comparison of the finite element predictions with the histology demonstrated that the spatial distribution of bone resorption at the fracture fragment ends directly corresponded to the locations of elevated tissue strain and stress. However, there was no consistent numerical relationship between the magnitude of these local peak strains and the corresponding volume of cortical bone resorption over the bone cross section.

Animals↗
PubMed1991

Deformation of the distal femur: a contribution towards the pathogenesis of osteochondrosis dissecans in the knee joint.

Osteochondrosis dissecans (OD) is a process of subchondral bone necrosis occurring predominantly in young individuals at specific sites. The aetiology of this disease remains controversial with mechanical processes due to trauma and/or ischaemic factors being proposed. This study aims at explaining the aetiology of OD in the knee joint as a result of the particular deformation of the condyles. A finite element analysis of the distal third of the femur was performed. A three-dimensional model was developed based on computed tomography scans of a normal femur, consisting of cortical bone, cancellous bone and articular cartilage. This model was subjected to physiological loads at 0, 30, 60 and 90 degrees of knee flexion. A complex deformation was found within each condyle as well as between the two condyles. Both medial and lateral condyles are deformed in the medio-lateral direction and at the same time compressed between the patella and the tibia in the antero-posterior direction. This effect is highest at 60 degrees of knee flexion. In both planes, the medial condyle is distorted more than the lateral one. Strain concentration in the subchondral bone facing the patella varies with flexion, especially for angles exceeding 60 degrees. The deformation of the femur in the predominant locus of OD in the medial condyle exceeds that of the lateral condyle considerably. The analysis shows that repeated vigorous exercise including extreme knee flexion may produce rapidly changing strains which in turn could ultimately be responsible for local subchondral bone collapse.

Biomechanical Phenomena↗
PubMed1991

Value of coining on the improvement of endurance in slotted intramedullary nails.

Cracking of intramedullary nails, starting at the proximal end of the partial slot and propagating in a circumferential direction, has been observed. These partial cracks are relatively frequent, although full failures are very rare and do not disturb fracture healing. Coining is a cold-working process used to improve the endurance of structures with residual compressive stresses generated by plastic deformation. The influence of coining was investigated to evaluate its practical value in controlling these fatigue cracks. Bending and torsional tests were performed on high frequency machines. Coined zones of different shapes and depths were examined, comparing the elapsed number of load cycles with crack initiation. The results showed that the endurance of coined nails was improved by factors of approximately 10 and 5 in bending and torsion, respectively. This increase in fatigue life corresponds to a more than 50% larger dynamic load after a million cycles. Variations in coining shape and depth did not yield any significant differences.

Bone Nails↗
PubMed1991

Internal fixation with a self-compressing plate and lag screw: improvements of the plate hole and screw design. 1. Mechanical investigation.

For a number of years, self-compressing plates, with oval holes and using special drill guides, have been in use. Recently, the advantages offered by lag screw interfragmentary compression inserted through the plate have gained prominence. Often such screws are inserted in an inclined position toward the fracture plane for better efficiency. It has also become evident that inclined screws placed into oval holes undergo a displacement toward the fracture. Efforts to improve the effect of this technique have led to a new plate and screw interaction that is described herein. The result is versatility and efficiency of the fracture fixation.

Biomechanical Phenomena↗
PubMed1991

Internal fixation with a self-compressing plate and lag screw: improvements of the plate hole and screw design. 2. In vivo investigations.

A mechanically improved design of bone plate and screw was compared in vivo with conventional plate fixation. This method was investigated biologically in a standardized osteotomy model on sheep tibiae. It was found that maintenance of reduction of an osteotomy was facilitated and there was no adverse effect of this fracture fixation system on bone remodeling. The modified implant permits the reduced surgical approach to the bone through one plane and optimal fixation of the fracture or osteotomy.

Animals↗
PubMed1991

Induction and prevention of pin loosening in external fixation: an in vivo study on sheep tibiae.

In external fixation of fractures, pin loosening is a major concern. Preloading the pins is generally done to ensure their stability within the bone cortex. The effect of radial preload and bending preload in reducing resorption at the pin/bone interface was tested. Schanz screws were fixed to live sheep tibiae using a pneumatically operated external fixator frame. Evaluation was based on radiological observation and fluorochrome histology using sequential labels. Though not completely absent, bone resorption was minimal in the radial preload group, compared with the two other groups. More important, the bone-to-pin contact surface in the radial preload group was found to be almost intact after 5 weeks. In this study, radial preload appears to be superior to bending preload in terms of minimizing the problems of pin loosening.

Animals↗
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↗