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Biomedical subjects

B A Rahn

Publications and source records attributed to B A Rahn.

At least 37 records · Page 2Linked to original sources
PubMed1993

Influence of the compression force on the intramedullary pressure development in reaming of the femoral medullary cavity.

The reaming process is considered the main damage factor in intramedullary nailing, as there are repeated increases in intramedullary pressure and cortical temperature, which can lead to aseptic cortex necroses and fat embolisms. In this study, the influence of the compression force on the increase in pressure is to be examined. The intramedullary pressure was measured in the middle of the diaphysis and in the metaphysis of human femora reamed under various compression forces. The compression force exerted by the surgeon was measured on polyurethane femora. It was observed that an increase in the compression force of 1.8 times led to an increase in the diaphyseal pressure of 4.7 times and of the metaphyseal pressure of 3.1 times. As surgeons exert high compression forces, peak pressures of 970 mmHg diaphyseally and 1150 mmHg metaphyseally must be expected in the hospital. If reaming is carried out with less compression force, the intramedullary pressure can easily be reduced by 79% in the area of the diaphysis and by 68% in the metaphysis.

Femoral Fractures↗
PubMed1993

Fixation of vascularized bone grafts.

In 24 patients, fixation of isolated or combined bone grafts has been performed exclusively with miniplates. Other than the lateral displacement of one osteomyocutaneous iliac crest graft, no complication occurred with regard to the fixation method chosen. In contrast to the clinical findings, our results of an animal experiment demonstrate less complications by fixation of vascularized bone grafts to mandibular angle defects (guinea pig) when THORP plates are used instead of miniplates. Whereas we consider miniplate fixation of vascularized bone grafts to be the method of choice, selected patients may require more stable fixation systems, especially when a high postoperative mobility may be expected or large amounts of the mandible including the condyle have to be reconstructed.

Animals↗
PubMed1993

The role of corticotomy and osteotomy in the treatment of bone defects using the Ilizarov technique.

Posttraumatic bone defects are usually bridged using autogenous or exogenous cancellous bone grafts. These grafts consolidate to form a solid bone structure that is mechanically stiffer than natural bone. Likewise, the procedure of corticotomy and distraction is appropriate for treatment of bone defects. In our experiment, a 2-cm bone defect was created in 25 sheep tibiae. We performed corticotomy or osteotomy of the intact bone, thus creating a bone segment that was drawn across the defect using a specially designed traction device. The limb was stabilized using an external fixator. Four groups were formed for comparison: corticotomy and osteotomy with distraction at a rate of 1 mm/day; corticotomy and osteotomy with immediate transportation of the segment to the docking site. The animals were killed after 4, 8, 12, 16 and 52 weeks. Evaluation of the results was based on standard radiographs. In the two groups involving gradual transportation, spontaneous bone regeneration occurred in all cases whereby after corticotomy the new bone was tubular (around the medulla). Following osteotomy, bone regeneration occurred initially on the dorsal and lateral sides of the tibia leaving a defect on the ventral and medial sides. This defect subsequently closed. At the end of segment transportation, healing was observed at the docking site. In Groups 3 and 4, the bone did not regenerate at all. Therefore, this procedure, immediate transportation, was not investigated further because no clinical success could be expected from its application.

Animals↗
PubMed1993

A new method for investigating the undersurface of cell monolayers by scanning electron microscopy.

Glow discharge is commonly used for cleaning the inside of coating units and for cleaning hard surfaces before carbon or metal evaporation procedures. In this study it has been used to remove the embedding medium to reveal, for scanning electron microscope (SEM) study, the undersurfaces of Balb/c 3T3 fibroblastic cells that have been cultured on Thermanox discs and embedded in LR White resin. Ten to twenty-minute ionization times were found to reveal the largest area of the undersurface without causing damage to the cells. Chemical etching of the resin was also shown to reveal the undersurface of the cells, but caused some damage, preventing successful re-embedding for transmission electron microscopy, and at higher magnifications revealed less detail. A circular impression within the main outline of the cells was observed in many cells, which is considered to reflect the presence of a nucleus. The undersurfaces of most cells, after applying both methods of etching, displayed a number of very short processes. Subsequent transmission electron microscopy of ultrathin sectioned, re-embedded, areas of the gold sputter-coated blocks revealed the depth of ionization that had occurred and confirmed that the specimens observed in SEM were the undersurfaces of cells. This method can be modified to study the attaching surface of any organism to a substratum.

3T3 Cells↗
PubMed1993

The effect of fracture on femoral head blood flow. Osteonecrosis and revascularization studied in miniature swine.

Miniature swine were used to study the effect of cervical fracture on femoral head blood flow. Laser Doppler flowmetry was used to evaluate femoral head blood flow before and after the fracture, after internal fixation with or without compression, and 8 weeks post-fracture. Fluorescent bone-labeling was performed at 2, 4 and 6 weeks post-fracture. Femoral head blood flow decreased to 40 percent of baseline following fracture, partly from the disruption of venous drainage. Histologically, all femoral heads showed some degree of trabecular thinning, microfracture, and neovascularization when compared with controls. Analyses of the laser Doppler flowmetry data, fluorescent label histology, microradiography and bone densitometry indicated that late (4-6 weeks) revascularization produces severe trabecular mechanical weakening and resultant femoral head collapse. Femoral head ischemia following fracture probably falls along a continuum, with only the more severe cases proceeding to mechanical collapse. Femoral neck fractures in the minipig produce femoral head necrosis of a severity and incidence which closely parallels that of the human population; thus, the minipig is a useful model for further study of complications following femoral neck fracture in humans.

Animals↗
PubMed1993

[Histological changes in the ligamentum flavum in patients with spinal stenosis].

In 21 patients with spinal stenosis the ligamentum flavum was removed, histologically processed and the calcification was measured with an image analyzing computer. Nearly all the ligaments were calcified: on average 0.17%, with a maximum of 3.8%. There was a significant correlation between age and calcification. We compared these findings with those of a group of "normals". There we only found minimal calcification in 3 of 20 segments (0.025%, 0.049%, 0.22%). As these people were on average 85 years of age, this can be looked upon as normal degenerative changes. This illustrates the important role of calcification of the ligamentum flavum for spinal stenosis.

Aged↗
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

[The effect of static magnetic fields on osteoblast activity: an in-vitro study].

The aim of the present study was to investigate whether the influence of static magnetic fields can be demonstrated in an osteoblast cell culture. For this in-vitro study we used osteoblasts originating from the embryonal calvariae of rats. The total material (n = 41) was divided in four groups: a) cell cultures submitted to the fields of attracting magnets (n = 11), b) cell cultures in the fields of repelling magnets (n = 10), c) cell cultures under the influence of demagnetized magnets (sham group, n = 11), d) control cultures (n = 9). The cell cultures were subjected for 21 days to magnetic fields (intensity 178 ml) using Neodynium magnets. Osteoblast activity was histo-chemically determined by staining the alkaline phosphatase produced. The quantitative evaluation was performed by measuring the optical density of the cell cultures and the results were statistically analysed. The results of these in-vitro study are: 1. The optical density of the cell cultures was nearly the same in samples with or without the influence of magnetic fields. 2. No divergent reaction could be found between the application of homogeneous and heterogeneous magnetic fields. 3. The different orientation of homogeneous magnetic fields in vertical or horizontal direction did not effect the osteoblast cell culture. 4. The cellular distribution in the osteoblast cultures does not follow the orientation of the magnetic field lines. 5. The form of the osteoblasts was nearly the same among all four groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The effects of horizontal tooth loading on the circulation and width of the periodontal ligament--an experimental study on beagle dogs.

The third premolars of Beagle dogs were subjected to tipping force of 20N, applied for between 20 minutes and 7 hours. Ten minutes before the end of the experiment the animals were injected intravenously with disulphine blue in order to show the capillary circulation and the tissue perfusion in the PDL under loading. The animals were then killed, and vertical histological sections were made of the loaded and the control teeth. The width of the PDL of the loaded and control teeth was measured at seven levels along the root surface and an analysis of variance was carried out. There was no circulatory disturbance and only slight irreversible changes in the shape of the PDL with loading for up to 3 hours. Only the teeth which had been loaded for at least 3 hours showed clear zones of irreversible compression and expansion. As the amount of irreversible compression increased so the blood supply and the circulation were impaired. Further increased compression of the periodontal ligament caused by long-term force application resulted in localized blood clotting.

Animals↗
PubMed1992

[Fat embolism and fracture, a review of the literature].

The reasons of fat embolism as well as the following fat embolism syndrome are most likely long bone fractures, especially if the femur is participated. On the other hand there are cases, where a severe concussion of the entire body caused fat embolism. But it is also supposed, that intramedullary reaming as well as the insertion of knee- and hip-prostheses could be a releasing factor, because the applicated pressure on the medullary canal can cause a fat release in the systemic blood system. The morbidity depends on age and fracture, which is on fractures between 0.9 and 2%. The most affected group are people between 18 and 28 years of age. The fat embolism is manifesting at 46-60% of the patients in the first 24 hours and over 90% of the patients are affected in the first three days. If you look at the metabolic changes, you will find shortly after the fracturing process a rapid increase of free fatty acids (FFA), as well as an increase of the plasmatic enzyme levels (lipase, GPT, GOT, GLDH, LDH, etc.), catecholamines and glucocorticoids. In order to discuss the pathogenesis in a fairly complete way, you have to take different theories into consideration, because several parallel running processes--which are influencing each other--are leading to the syndrome. Infloating theory: Proceeding on the assumption that contents of the bone marrow are floating out of the fracture gap into the venous system and are leading to fat embolism in the lungs. Lipase theory: You can diagnose in 50-70% of the fracture patients an increase of the lipase level, which is correlating with the manifestation of the fat embolism. The lipase releases fat from the body depositories in addition to the fat, who is coming out of the fracture gap. Shock and coagulation theory: During shock the microcirculation is decelerated, the blood viscosity is increased and the suspension stability of the cellular blood components is decreased, which is leading to the sludging phenomenon. So the capillaries of the lungs and the brain are a kind of sludge filter of the blood, that is changed in its suspensions stability. Free fatty acids theory: Primary existing capillary defects are reasonable caused by free fatty acids (FFA). They are hydrolyzed of the neutral fats and are histotoxic for the walls of the blood vessels.(ABSTRACT TRUNCATED AT 400 WORDS)

Embolism, Fat↗
PubMed1992

[The temporal behavior of the anchorage of a cement-free implanted acetabular cup in animal experiments].

The mechanical qualities of the cementless press-fit cup of a hip prosthesis were examined in sheep. Primary anchorage of the cup is achieved by relative oversize of the cup in relation to the acetabulum, causing a press-fit effect. The surface of the cup consists of Sulmesh, a titanium net, which allows bony ingrowth. The quality of the mechanical anchorage in the acetabular bone was tested by measurements of the torque and cranio-caudal tilting moment needed to pull out the cup. It was shown that the secondary biological anchorage of the press-fit cup exceeds the primary mechanical anchorage (measured in previous in vitro experiments) by a factor of three. This improvement of the mechanical fixation of the press-fit cup in the acetabular bone can be explained by bony ingrowth into the Sulmesh and can be confirmed by histological findings.

Acetabulum↗
PubMed1991

The use of miniplates in mandibular fractures. An in vitro study.

To test the stability of miniplate osteosynthesis in the mandible, a three-dimensional in vitro model was developed. Four clinically relevant fracture situations were simulated by osteotomies in polyurethane mandibles. The stability of the osteosyntheses was tested according to a reproducible procedure of unilateral loading under conditions of static equilibrium. The mandible was supported at the condyles in silicon rubber fossae and was held in position by traction on the coronoid processes in combination with preloading in the region of the incisors with a force of 10 N. Six points were tested to register the effects of unilateral loading on bending and torsion at the sites of the osteotomies. The following results were obtained. The preliminary results show that in cases of jaw angle fracture neither bending nor torsional forces are sufficiently controlled by miniplate-fixation in the commonly proposed position. Furthermore, it was confirmed that fracture treatment in the canine region requires two plates instead of one to resist displacement of the fracture fragments during function.

Bite Force↗
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

Induction of monocyte chemotaxis in devascularized rabbit bone.

Temporary impairment of blood supply has been suggested to cause bone remodeling. The degradation of cells and matrix and the attraction of resorbing cells were examined in this study. Bone specimens of rabbits were stored in vitro for 2-20 days. At the end of this aging process the probes were tested for their chemotactic activity toward autologous leukocytes in a diffusion chamber. Both supernatant from the aged bone specimens and ground bone particles exhibited significant chemotactic activity that was specifically attracting monocytes. It is suggested that soluble bone matrix proteins or degeneration products liberated during ischemic damage to cortical bone initiate the resorptive process.

Animals↗
PubMed1990

Reaming versus non-reaming in medullary nailing: interference with cortical circulation of the canine tibia.

Medullary nails have only been used with reluctance in the treatment of open fractures since reaming interferes with the cortical circulation. The technique of interlocking offers the interesting possibility of inserting a relatively stiff nail which does not necessarily require reaming. The effects of reaming prior to nail insertion upon the cortical circulation was investigated in the canine tibia. Intravital staining with procion red was used to trace areas of disturbed circulation. Nail insertion without reaming provided clear advantages for the bone's blood supply, while reaming disturbed perfusion in two-thirds of the cortical area and regionally extended through the entire thickness of the cortex. The disturbance without reaming was limited to the inner layer of the cortex and involved only one-third of the cortical cross-section.

Animals↗