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Biomedical subjects

B A Rahn

Publications and source records attributed to B A Rahn.

At least 19 recordsLinked to original sources
PubMed2005

Validation of speed of sound for the assessment of cortical bone maturity.

Bone changes its structural and physical properties during maturation. In order to validate ultrasound measurements with regard to their usefulness in assessing cortical bone maturation, speed of sound (SOS) data were compared with mechanical properties (elastic modulus, bending strength, and cortical surface hardness), density and water content. Thirty pig mandibles were selected from three different age groups. Rectangular specimens of the buccal cortical bone of the body of the mandible were prepared. SOS was measured with pulsed ultrasound at a frequency of 2 MHz in all three dimensions, bone mineral density (BMD) by quantitative computed tomography, breaking strength and apparent elastic modulus in a three-point bending test to failure, water content using the lyophilization technique, and micro-indentation hardness using a modified Vickers' technique. While SOS in all three directions, BMD, surface hardness, and bending strength increased significantly (P < 0.001), bone tissue water content decreased significantly (P < 0.001) with age. Changes in the elastic modulus were not significant. Changes in SOS in the antero-posterior and apico-occlusal directions can be partly explained by BMD. In a bucco-lingual direction the increase is inadequately explained by the physical parameters investigated, and has possibly to be attributed to structural differences. Maturation of the mandible implies changes in its architectural organization, in material composition, and in the mechanical properties of cortical bone. In vitro SOS measurements reflect different structural and physical properties that are all age dependent. It thus seems feasible that age-related changes in bone maturation could be monitored by SOS measurements.

Age Factors↗
PubMed2003

Intramedullary pressure increase and increase in cortical temperature during reaming of the femoral medullary cavity: the effect of draining the medullary contents before reaming.

BACKGROUND: Reaming is regarded as the most adverse aspect of the intramedullary nailing procedure since it leads not only to impairment of the vessels but also to an increase in intramedullary pressure and cortical temperatures which may in turn lead to aseptic cortical necroses and pulmonary dysfunction. Intramedullary pressure increase is considered to be the most detrimental of these factors. METHODS: The aim of this study was to investigate the effect on intramedullary pressure and cortical temperature of removing the medullary fat before reaming. The fat was removed through a suction tube inserted proximally. The measurements were made on pairs of human femora whereby in one group the contents of the medulla were drained by suction before reaming. The pressure was measured in the mid diaphysis and in the metaphysis. The temperature was measured in the mid diaphysis. The femora were reamed in a water bath at 37 degrees C and at a constant insertion force. RESULTS: In comparison to the group which was not drained, the pressure for the 9.0 mm reamer in previously drained femora was reduced as follows: positive diaphyseal pressure by 88% (reamer insertion); positive metaphyseal pressure by 78% (reamer insertion); negative diaphyseal pressure by 84% (reamer withdrawal); negative metaphyseal pressure by 65% (reamer withdrawal). No significant difference was determined for temperature increase (median suction, 39.7 degrees C; median without suction, 39.4 degrees C). CONCLUSION: The removal of the medullary contents by suction before inserting reaming instruments leads to a considerable and statistically significant pressure reduction. If the medullary contents are not sucked out before reaming or insertion of unreamed nails, high intramedullary pressure and the risk of embolization is unaltered. Consequently new instruments should be developed to facilitate the removal of the medullary contents before commencing the reaming procedure or insertion of unreamed nails.

Drainage↗
PubMed2001

Measurement of fibroblast and bacterial detachment from biomaterials using jet impingement.

Fibroblast and Staphylococcus aureus detachment strength from orthopaedic alloys and a tissue culture plastic (Thermanox) have been investigated with jet impingement. For S. aureus, unlike fibroblasts, detachment is caused more by pressure than shear. For these biomaterials, detachment strength is much higher for S. aureus than fibroblasts. Comparing materials under equivalent flow conditions, S. aureus attach to stainless steel and titanium with equal strength and more strongly than to Thermanox. For fibroblasts, detachment strength from all materials was similar. Fibroblast detachment strength from these biomaterials substantially decreases with time at equal flow rates and increases with flow rate at equal exposure times. Detachment strength is very similar for 3T3 and L929 fibroblasts on Thermanox for equivalent flow rate/time combinations, though enhanced adhesion of 3T3 cells was often noted for metals. Time effects are less evident for S. aureus. S. aureus adhesion to metals is more affected by flow rate than fibroblast adhesion.

Alloys↗
PubMed2000

[Comparative in vitro studies of self-boring and self-tapping screws. Histomorphological and physical-technical studies of bone layers].

Self-drilling screws are gaining increasing importance in maxillofacial surgery. This study assesses which screw design, self-drilling or self-tapping, is best suited to various locations of the human skull. With regard to different areas in the human midface, mandible, and cranium, the thickness of cortical bone varies as well as the relative proportion of cortical to cancellous bone. Criteria used to judge the success of screws were minimal insertion torque and minimum temperature, maximum pullout strength, and minimum deformation and destruction of the bone. To mimic the variations in anatomical conditions, 1-mm and 3-mm-thick cortical bone specimens and cancellous bone blocks were prepared. Eight screws of three types (self-tapping, self-drilling/self-tapping, conically shaped self-drilling) were inserted into the different bone specimens. Torque and temperature were measured during the insertion procedure. Subsequently, the screws were carefully removed and the specimens were processed for histological evaluation. The same insertion protocol was used to test the pull-out strength of the screws. The conically shaped screw showed best results in cancellous bone for all parameters. The self-tapping screw with a pilot hole performed best in thick cortical bone and the self-drilling/self-tapping screw performed better than did the others in thin bone. The results suggest the three screw designs to be optimal for different locations of the human skull. This project provides the data for a planned in vivo study that will evaluate the long-term influence of deformation and temperature on stability and osseointegration of the screws.

Animals↗
PubMed1999

Histology of the ligamentum flavum in patients with degenerative lumbar spinal stenosis.

The degree of calcification as well as the structural changes of the elastic fibres in the ligamentum flavum in patients with degenerative lumbar spinal stenosis were evaluated and the results were compared to those of patients without spinal stenosis. In 21 patients (13 male, 8 female) with lumbar spinal stenosis the ligamentum flavum was removed, histologically processed and stained. The calcification, the elastic/collagenous fibre ratio as well as the configuration of the fibres were evaluated with an image analyzing computer. As a control group, 20 ligaments of 10 human corpses were processed in the same way. The results were statistically analysed using the Mann-Whitney-Wilcoxon test (alpha = 0.05) and the t-test (alpha = 0.05). Nearly all the ligaments of patients with lumbar spinal stenosis were calcified (average 0.17%, maximum 3.8%) and showed relevant fibrosis with decreased elastic/collagenous fibre ratio. There was a significant correlation between age and histological changes (P<0.05). In the control group we only found minimal calcification in 3 of 20 segments (average 0.015%). No relevant fibrosis was found and the configuration of elastic fibres showed no pathologic changes. The results of this study illustrate the important role of histological changes of the ligamentum flavum for the aetiology of lumbar spinal stenosis.

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↗
PubMed1998

Fracture healing in biological plate osteosynthesis.

In order to gain a better understanding of the healing processes after plate fixation and indirect reduction, Baumgaertel designed a reproducible fracture model for the sheep femur in 1992 so that the differences between anatomical (rigid) and biological (bridging) fixation could be investigated. It was demonstrated that indirect reduction and bridge plating was superior to direct fragment reduction and anatomical fixation in respect to radiology, biomechanics and microangiography. In this study, it was shown that bony bridging of the fracture gap and mineralization of callus occurred faster and more efficiently after indirect than after direct and anatomical reduction. Bone healing was identified as beginning in the 2.-3. week after indirect and only in the sixth week after direct reduction. The increased breaking strength of the indirectly reduced femora at 8 weeks can be attributed to this process. In addition, the consequences of applying the PC-Fix for biological plating were investigated. The values for bone healing were improved by applying a plate with only point contact to the bone, thus conserving the periosteal blood supply.

Animals↗
PubMed1996

Fixation with reconstruction plates under critical conditions: the role of screw characteristics.

Mandibular angular ostectomy defects in 12 sheep were bridged with a titanium plate system (THORP), designed according to the screw-plate-locking principle. Two screw designs (hollow and solid) and two rough (plasma-coated, sand-blasted)-surface and one smooth (anodized)-surface structure were tested in a critical two-screw anchorage model. Fixation with two screws only per fragment was successful in only one-third of the cases. The fixation results were superior for screws with a rough surface, either sand-blasted or plasma-coated. The hollow-screw design did not seem to offer special advantages over the solid screws with identical surface structure. In the successful cases, the bone-screw contact was maintained continuously over a period of 8 weeks, and anchorage was even enhanced by reinforcement of the cancellous structures. In the unsuccessful cases, peri-implant bone resorption seemed to be related to jeopardized bone perfusion in the vicinity of the implants. It is presumed that a plating system with locked screws has the advantage that only two screws will hold a relatively short condylar process. This study proved the assumption to be questionable. However, in view of the problems related to prosthetic replacement of the temporomandibular joint, an attempt to salvage the articular portion may still be justified in selected cases, even if the chance of success is as low as 30%.

Animals↗
PubMed1996

Autogenous cancellous bone graft incorporation in a gap defect in the canine femur.

While gap defect models provide greater graft stability and are more representative of many clinical situations than segmental defect models, the healing in these models has not been well documented. To study the histologic course of cancellous bone graft healing in a long bone gap defect, 12 adult mongrel dogs were killed in groups of two at 1, 2, 3, 4, 6, and 12 weeks. Graft incorporation in these dogs was studied using macro- and microradiography, histologic sections, and computer-assisted digital surface analysis; results are described. Unlike that seen in segmental defect models, the pattern of repair in a cancellous bone grafted gap defect provides consistent healing at 12 weeks and follows the same healing process seen with stable defects.

Animals↗
PubMed1996

Bone growth and remodelling after fracture.

We used a rabbit model to investigate the mechanism by which the angulation of fractures is corrected in children. We produced a transverse proximal tibial fracture in one leg of 12 eight-week-old New Zealand white rabbits and measured bone alignment and length and the patterns of bone growth and remodelling. The angle between the joint surfaces changed rapidly to correct the alignment of the limb as a result of asymmetrical growth of epiphyseal plates. In an adult with closed plates, the angle between the joint surfaces cannot therefore improve. The angle at the fracture itself showed slow improvement because of bone drift and the asymmetrical growth of the epiphyseal plates. Remodelling corrected the shape of the bone in the region of the fracture. Periosteal division on the convex side increased the growth of the epiphyseal plate on that side, thus slowing the correction. The effect was relatively small, providing an indication that factors other than the periosteum are important in inducing correction. External torsional deformities developed because of helical growth at the plate. This was probably caused by abnormal posture which induced a torque at the growth plate. Helical growth is the mechanism by which rotational deformities can occur and correct.

Age Factors↗
PubMed1995

Microjet impingement followed by scanning electron microscopy as a qualitative technique to compare cellular adhesion to various biomaterials.

Adhesion of cells to biomaterial surfaces is one of the major factors which mediates their biocompatibility. Quantitative or qualitative cell adhesion measurements would be useful for screening new implant materials. Microjet impingement has been evaluated by scanning electron microscopy, to determine to what extent it measures cell adhesion. The shear forces of the impingement, on the materials tested here, are seen to be greater than the cohesive strength of the cells in the impinged area, causing their rupture. The cell bodies are removed during impingement, leaving the sites of adhesion and other cellular material behind. Thus the method is shown not to provide quantification of cell adhesion forces for the metals and culture plastic tested. It is suggested that with highly adherent biomaterials, the distribution and patterns of these adhesion sites could be used for qualitative comparisons for screening of implant surfaces.

3T3 Cells↗
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

[Bone remodeling after reamed and unreamed intramedullary nailing. A histomorphometric study].

Experimental findings after unreamed nailing have indicated certain advantages for new bone formation in comparison to reamed nailing. It would be of interest to establish whether any essential differences can be determined in the extent and course of callus formation. To investigate this question, thin sections of bone from 16 tibiae (nailing after transverse osteotomy in sheep) were examined histomorphometrically the progress at the periosteal and interfragmentary surfaces of the remodelling callus being recorded separately after 4, 6 and 8 weeks. After unreamed nailing, more extensive and earlier formation of interfragmentary callus was observed. At 4 weeks postoperatively the remodelled periosteal bone surface was 158 mm2, which was 1.6 times that after the unreamed procedure (95 mm2). By 4 weeks after unreamed nailing the periosteal callus surface was already greater than 6 weeks after reamed nailing. On the basis of these experimental results the use of unreamed nailing can be recommended, especially for open fractures and fractures with severe soft tissue damage.

Animals↗
PubMed1994

The incidence, pathogenesis, diagnosis, and treatment of fat embolism.

Fat embolism syndrome is a potentially serious and life threatening complication of long bone trauma, blunt trauma, and intramedullary manipulation. In long bone fractures, fat embolism is encountered in 0.9% to 2.2% of cases. During intramedullary manipulations, such as prosthetic stem insertion or reaming, the incidence is typically lower (range, 0.5% to 0.8%). Diagnosis is dependent upon the clinical recognition of dyspnea, petechiae, and cognitive dysfunction in the first several days following fracture, trauma, or intramedullary surgery. Treatment consists of pulmonary support and aggressive resuscitation. Studies support early fracture fixation, but the role of systemic steroids, heparin, and other modalities remains speculative.

Brain Diseases↗
PubMed1993

Intramedullary pressure, strain on the diaphysis and increase in cortical temperature when reaming the femoral medullary cavity--a comparison of blunt and sharp reamers.

Clinical application has shown intramedullary nailing to be a safe therapeutic procedure, although damage to the vascular system and fat embolism have been demonstrated in animal experiments. The main negative factors were presumed to be the increase in intramedullary pressure and the increase in cortical temperature. In this study, the effect of the blunting of the reamers on the increase in intramedullary pressure, the tangential strain on the diaphysis and the increase in cortical temperature was to be clarified. The measurements were carried out on pairs of human femora reamed with sharp and blunt AO reamers. The pressure was measured in the middle of the diaphysis and in the metaphysis, the strain in the middle of the femur and the temperature on four aspects of the femur. The femora were reamed with identical compression and traction forces in a water bath at 37 degrees C. In comparison with the sharp reamer, the blunt reamer develops 2.1 times the positive diaphyseal pressure, 1.7 times the positive metaphyseal pressure, 1.6 times the negative diaphyseal pressure, 1.5 times the positive tangential strain, 55 times the negative tangential strain and 2.8 times the increase in cortical temperature. There is no difference in the negative metaphyseal pressure. Since blunt reamers produce greater intramedullary pressure values, greater tangential strain on the diaphysis and a greater increase in cortical temperature, the attention of surgeons and operating staff must be drawn to the fact that they should treat the reamers gently and replace them whenever necessary.

Equipment Failure↗
PubMed1993

Extent of bluntness and damage to reamers from hospitals.

The negative effects of intramedullary nailing, such as aseptic cortical necroses and fat embolisms, are mainly caused by an increase in intramedullary pressure and an increase in cortical temperature during the reaming process. The degree of bluntness of the reamers has a negative influence on these two parameters. The objective of this study was to examine the degree of bluntness and damage to intramedullary reamers in clinical use. 10 sets of intramedullary reamers returned from Swiss clinics were examined with regard to the radius of the cutting edge and the degree of damage. The following results were established (MN = medullary nailings): Sharpest reamers: hospitals with 300-400 beds. Hospitals with < 5 MN per year. Bluntest reamers: hospitals with > 1000 beds. Hospitals with 40-60 MN/year. Least damaged reamers: hospitals with 300-400 beds. Hospitals with 40-60 MN/year Most damaged reamers: hospitals with > 1000 beds. Hospitals with 40-60 MN/year Due to the fact that some of the reamers in clinical use are of inadequate quality both with regard to the sharpness of the milling lips and the degree of damage, doctors and operating staff should be instructed to check the quality of cutting tools before using them, to treat them carefully and to replace them if necessary.

Equipment Failure↗