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Biomedical subjects

B Rahn

Publications and source records attributed to B Rahn.

35 records · Page 2Linked to original sources
PubMed1995

Stabilization of the short sagittal split osteotomy: in vitro testing of different plate and screw configurations.

Using a 3-dimensional in vitro model, the stability of different types of osteosynthesis for the short sagittal osteotomy was tested. The following four groups of plate and screw configurations were evaluated: Group I: Fixation with miniplates using monocortical screws only, Group II: Fixation with miniplates, but with two of the screws engaging both fragments, Group III: Same as group II with an additional position screw, Group IV: Fixation with 3 position screws. The stability obtained with miniplate fixation using monocortical screws only (group I) was by a factor of 2.9 less than position screw fixation (group IV), which is considered to be an approved standard. In order to increase the stability of miniplate fixation, the screws in the area of overlapping bone should engage both fragments.

Bone Plates↗
PubMed1994

[Bone healing after unreamed intramedullary nailing].

Good clinical results of unreamed nailing have been observed primarily in cases of open fracture. However, it is still unclear whether unreamed nailing is a suitable procedure for fractures that have previously been treated with reamed nailing. Since histological findings on bone healing after unreamed nailing were not available, an animal experiment on sheep was undertaken. The aim was to investigate whether there were differences in the nature of bone healing following reamed and unreamed nailing procedures. Fluorescence microscopy clearly showed that maximal callus formation occurred within 4 weeks after unreamed nailing and within 6 weeks after reamed nailing. Callus formation was also more prolific after unreamed than after reamed nailing. It was demonstrated by microradiography that bone regeneration progressed more rapidly, in terms of both periosteal and interfragmentary callus, after unreamed nailing. No disturbances of bone healing and no greater risk of pseudarthrosis were observed following unreamed nailing. Histological investigations showed that bone healing was faster after unreamed nailing and there was a reduced loss of vitality. This is of particular clinical relevance in the surgical treatment of fractures with severe soft tissue injury and of open and comminuted fractures. These results indicate that an extension of the indications for unreamed nailing should be considered.

Animals↗
PubMed1994

[Animal experiment studies of "biological" plate osteosynthesis of multi-fragment fractures of the femur].

In three groups (A, B, C) of 12 sheep each, defined, reproducible comminuted subtrochanteric fractures were produced in three steps without devascularization of the bone: (1) longitudinal biocortical osteotomies limited by bore holes as breakpoints, (2) an external fixator producing a static lateral bending load of 0.20 kN, (3) sudden three-point antero-posterior compression. Sheep in group A were treated with direct reduction and anatomical reconstruction of each fracture according to the principles of the AO/ASIF group and with an angle blade plate. In group B the same plate was used, but no attempt was made to reduce fragments anatomically. Length and alignment were restored with indirect reduction techniques (distraction via external fixator and articulating tension device) only. The treatment applied in group C incorporated the same reduction modes as that in group B, but an experimental plate with point bone contact and unicortical, fixed screws were used. After 4, 8 and 12 weeks of full weight-bearing, the femurs were harvested for radiographic analysis and biomechanical testing. Subjective evaluation of fracture healing by 20 independent orthopaedic trauma surgeons resulted in significantly higher ratings for groups B and C than for group A after 8 (p = 0.07) and 12 weeks (p = 0.09). Density scan measurements showed little change in bone density as a percentage of that on the intact side over 12 weeks (108.1, 105.7, 104.4) in group A, but revealed marked changes in groups B and C (95.7, 117.5, 133.6 and 104.2, 125.6, 120.6), reflecting higher masses of callus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Healing of cancellous bone osteotomy in rabbits--Part I: Regulation of bone volume and the regional acceleratory phenomenon in normal bone.

We performed a simple, undisplaced, incomplete osteotomy of the distal medial condyle of mature New Zealand White rabbits and permitted healing without fixation for 4 weeks. During the recovery period, the rabbits received the bone label calcein in their drinking water. From ground stained and unstained sections, we determined histomorphometric parameters in five zones: osteotomy gap, juxtaosteotomy, lateral condyle, metaphysis, and diaphysis. At 4 weeks, newly formed cancellous bone had obliterated the osteotomy gap. Osteotomy also stimulated new bone formation in cancellous bone of the medial condyle around the osteotomy. At that site, we found a fivefold increase in new bone without a change in bone volume (BV). Stimulation of bone formation was not observed in cancellous bone of the lateral condyle that had not been operated on or in cortical bone of the metaphysis or diaphysis. The maintenance of BV, despite increased new bone formation in the osteotomized medial femoral condyle, was probably due to a local acceleration of bone remodeling.

Animals↗
PubMed1993

Healing of cancellous bone osteotomy in rabbits--Part II: Local reversal of arthritis-induced osteopenia after osteotomy.

With use of the intravital bone label calcein, we previously identified, by histomorphometry, greatly increased new bone formation and juxtaarticular osteopenia (a high turnover state) in carrageenan-induced experimental inflammatory arthritis of the knee in rabbits. In Part I of this paper, we showed that a large increase in new bone formation after a stable incomplete distal femoral condylar osteotomy of normal bone in the rabbit does not increase bone volume (BV) in normal tissue adjacent to the osteotomy (zone 1). In this study, we performed an osteotomy of bone made osteopenic by experimental inflammatory arthritis. After 4 weeks of healing, we examined new bone formation and BV in five zones around the osteotomy. In zone 0 (the osteotomy gap), new bone formation filled the gap to normal BV, as we found for the normal/osteotomy group. In zone 1 (adjacent to but excluding the osteotomy gap), we found greatly increased new bone formation and a return to normal BV, increased from the osteopenic level induced by experimental inflammatory arthritis. In this model, osteotomy apparently reversed the bone-wasting process of inflammatory arthritis. This effect was not observed in other zones: the lateral condyle that had not been operated on, the metaphysis, or the diaphysis.

Animals↗
PubMed1992

[The importance of the center of resistance for the biology of tooth movement].

The tooth movement of loaded premolars was investigated in four two-years-old beagle dogs under general anesthesia. Two supragingival registrations were performed to calculate the center of rotation in order to estimate the amount of tipping. Loads of 5 to 20 N were applied for two to four seconds. The amount of tipping was found to be load- and time-dependent. The discrepancy between these findings and the models of analytical mechanics were explained by bone bending in our experiments. Biology and localization of periodontal remodelling is supposed to be dependent on load magnitude, load duration and physical properties of all periodontal tissues including bone.

Animals↗
PubMed1991

Bridging of mandibular defects with two different reconstruction systems: an experimental study.

To compare two different mandibular reconstruction systems, a 5-cm angular resection was performed in nine adult sheep. The defect was reconstructed using either a classic AO plate or the AO-THORP reconstruction system. The animals were killed 5, 9, and 14 weeks after operation. Serial sections with the plates and screws in place were prepared and studied histologically and with microradiography and fluorescence microscopy. Twenty-six percent of the 2.7-mm AO cortical screws were adequately fixed. The corresponding percentage for AO-THORP hollow screws was 73%. The main advantage of the latter system is the screw-plate locking principle, which allows plate stability to be maintained even if bone is resorbed under the plate. Whether the existence of a screw lumen is an advantage has not yet been established.

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

Changes in the metaphysis and diaphysis of the femur proximal to the knee in rabbits with experimentally induced inflammatory arthritis.

We quantified the cross-sectional cortical bone area and remodeling rates in the ipsilateral femoral diaphysis and metaphysis of rabbits with carrageenan-induced inflammatory monarthritis of the knee. Although osteogenesis rates were significantly elevated (approximately threefold in diaphyses and sixfold in metaphyses), the cross-sectional bone area of the diaphysis was significantly diminished. Fivefold and sixfold increases in bone resorption rates were calculated in diaphyses and metaphyses, respectively. Other morphologic changes observed were porosity and net resorption of the anterior cortex and net accretion on the posteromedial cortex ("drift" of bone). These findings may have clinical significance with regard to the mechanisms and consequences of bone changes in patients with rheumatoid arthritis.

Animals↗
PubMed1988

Biomechanics of the craniocervical region: the alar and transverse ligaments.

In the treatment of spine fractures and fracture-dislocations, stability of the spine is one of the major objectives. In the craniocervical joint, the alar and transverse ligaments provide much of the stability of the healthy spine. Because the anatomy appears well described, the contribution of each of these structures so far has received little attention. The alar ligament restrains rotation of the upper cervical spine, whereas the transverse ligament restricts flexion as well as anterior displacement of the atlas. A lesion in one or both structures can produce damage to the neural structures and/or cause pain. To investigate the possible role of each of these ligaments, a mechanical and histologic study of the upper cervical spine was made. The bone-ligament-bone complex of the alar and transverse ligaments was subjected to uniaxial mechanical testing in seven specimens. The alar ligaments had an in vitro strength of 200 N, and the transverse ligaments had an in vitro strength of 350 N. Histologic analysis revealed a mainly collagenous nature of these ligaments. Clinical evidence (broken odontoid processes) suggests that the transverse ligament is strong enough to withstand physiologic loads. The alar ligament, on the other hand, due to its lower strength and its axial direction of loading, might be prone to injury and therefore require stabilization of the appropriate vertebra more often than normally is assumed.

Aged↗
PubMed1988

Juxtaarticular bone loss in experimental inflammatory arthritis.

The osteopenia associated with experimental inflammatory arthritis was studied by a histomorphometric method that exphasized net changes in bone composition. Juxtaarticular trabecular bone volume and turnover were studied in the carrageenan injection model of inflammatory arthritis of the mature rabbit knee. Trabecular bone volume was studied by histomorphometry of the femoral condyles and confirmed by photodensitometry on standard macroradiographs. Osteogenesis was studied by imaging of calcein fluorochrome-labeled newly formed bone in undecalcified histological sections. A significant net loss of cancellous bone (approximately 20%) occurred over 49 days in both the medial and the lateral femoral condyle in the arthritis group compared with normal controls. Total osteogenesis was increased fourfold and it was calculated that an even greater increase in total bone resorption was responsible for the negative bone balance. There is evidence that the periarticular bone loss of human rheumatoid arthritis is also associated with increased bone turnover. Quantitative studies of the kinetics of bone remodeling in inflammatory arthritis will provide the basis for therapeutic attempts to prevent or reverse arthritis-induced bone loss. Fracture risk in inflammatory arthritis may be increased not only by osteopenia, but additionally by the presence of a large proportion of newly formed (and presumably less mineralized) bone.

Animals↗
PubMedDate not supplied

Further development of titanium miniplate fixation for mandibular fractures. Experience gained and questions raised from a prospective clinical pilot study with 2.0 mm fixation plates.

Miniplate systems are often used instead of more rigid systems for the treatment of mandibular fractures. While the most stable fixation method for all mandibular fractures is the 2.7 mm plate, most fracture sites and types are eminently suitable for miniplate fixation via an intraoral approach. However, the relatively low stability of the miniplate systems compared with rigid plate systems limits the indications for their use in mandibular fracture treatment, especially when immediate postoperative function is desired. A more rigid miniplate which provides increased stability was studied. The results of a preliminary study and a clinical trial of a 2.0 mm titanium miniplate system are presented in this paper. The therapeutic consequences of the lesser stability afforded by small plate systems are discussed. Indications for miniplate fixation without additional immobilization are reviewed.

Adolescent↗