Biomedical subjects

B Rahn

Publications and source records attributed to B Rahn.

At least 19 recordsLinked to original sources

PubMed2006

Mineralization and mechanical properties of the canine mandible distraction wound following acute molding.

To investigate the influence of an acute single step callus manipulation immediately after distraction on mechanical properties and mineralization of the regenerate, custom made distraction devices were bilaterally placed in the mandibular angle of 15 beagle dogs, allowing to simultaneously compress and stretch the regenerate after completed linear distraction. The animals were divided in three groups (n=5): Group 1 and 2 underwent manipulation of the regenerate, group 3 remained in a linear position. After 42 (group1) and 90 (group 2 and 3) days of consolidation the animals were sacrificed. The mechanical properties were assessed in an Instron testframe and bone density quantified by quantitative computed tomography and three- dimensionally assessed (Scion Image processing and analysis software). After 6 weeks of consolidation 25% of the specimens reached a stiffness which was >/=90% of the mean values of the unoperated reference hemi-mandibles. After a 13 week consolidation period, 62.5% were as stiff as the referenced specimens. Manipulated regenerates, allowed to heal under stable conditions for 13 weeks, had the same mechanical properties as specimens that underwent pure linear distraction. A temporary but not significant delay of osseous healing had to be postulated for the stretched zone after 6 weeks, indicating this area to be more critical than the compressed area.

Animals↗

PubMed2006

Intra-articular calcium phosphate cement: Its fate and impact on joint tissues in a rabbit model.

Clinical application of injectable ceramic cement in comminuted fractures revealed penetration of the viscous paste into the joint space. Not much is known on the fate of this cement and its influence on articular tissues. The purpose of this experimental study was to assess these unknown alterations of joint tissues after intra-articular injection of cement in a rabbit knee. Observation periods were from 1 week up to 24 months, with three rabbits per group. Norian SRS cement was injected into one knee joint, the contralateral side receiving the same volume of Ringers' solution. Light microscopic evaluation of histologic sections was performed, investigating the appearance of the cement, inflammatory reactions, and degenerative changes of the articular surface. No signs of pronounced acute or chronic inflammation were visible. The injected cement was mainly found as a single particle, anterior to the cruciate ligaments. It became surrounded by synovial tissues within 4 weeks and showed signs of superficial resorption. In some specimens, bone formation was seen around the cement. Degeneration of the articular surface showed no differences between experimental and control side, and no changes over time became apparent. No major degenerative changes were induced by the injected cement. The prolonged presence of cement still seems to make it advisable to remove radiologically visible amounts from the joint space.

Animals↗

PubMed2005

[Evaluation of potential damage to the regenerate during callus molding after mandibular distraction osteogenesis. Experimental study using an animal model].

BACKGROUND: Molding the regenerate created by distraction osteogenesis has clinically been shown to be an efficient lifeboat, good enough that for complex three-dimensional deformities final adjustments by molding the regenerate may be part of the treatment plan. The study assessed the limits of molding a regenerate, taking into consideration compressive and tensile forces acting simultaneously on the fresh callus. MATERIAL AND METHODS: Distraction osteogenesis was performed in 15 beagle mandibles using custom-made devices which allowed for lengthening as well as for angulation. After linear distraction of 10 mm, a defined 20 degrees angulation was performed in one acute step. The position of the fulcrum of the device allowed the regenerate to be compressed and stretched simultaneously. The effects on bone healing were assessed after 6 or 13 weeks of consolidation and compared to a control group where only linear distraction was performed. RESULTS: Radiological and histological investigations demonstrated that no significant difference between the biological behavior of the compressed and the stretched zone of the regenerate could be found. However, there were signs, showing the more critical character of the stretched area. After 6 weeks of consolidation, some specimens revealed delayed ossification of the stretched zone. Under stable conditions, this delay was compensated after 13 weeks of consolidation and complete osseous healing occurred. CONCLUSIONS: Under stable conditions, a fresh regenerate can be molded to a considerable extent without endangering osseous healing permanently. Nevertheless, tensile forces acting on the regenerate should be minimized to prevent damage to the new bone. This can be achieved by overdistraction prior to callus molding or by gradually changing the vector of distraction during the lengthening process.

Animals↗

PubMed2005

Histology of the porcine mandibular distraction wound.

The purpose of this study was to document the progression and pattern of endosteal bone formation in a porcine mandibular distraction wound. Bone formation was assessed in a 0-day latency model (n=24 pigs) using distraction rates of 1, 2, or 4 mm/day to create a 12-mm gap. Macro-radiographs and sagittal histologic sections, from the center of the mandible, were evaluated by computer morphometrics (% bone fill) and by a semi-quantitative bone formation score. Mean percent area of new bone was 12.4% (0-25.9%), 7.5% (0-21.3%) and 3.8% (0-10.5%) in mandibles distracted at 1, 2 or 4 mm/day respectively. At all time points, percent area of new bone was highest in mandibles distracted at 1 mm/day. Bone was deposited from the margins of the osteotomy toward the center of the wound and occurred first around the inferior alveolar canal and tooth bud regions. New bone formed by intramembranous ossification alone. The results of this experiment document the contribution of endosteal bone formation in this model of distraction osteogenesis.

Analysis of Variance↗

PubMed2004

Assessment of bone formation in a porcine mandibular distraction wound by computed tomography.

The purpose of this study was to document the progression of bone formation in a porcine mandibular distraction wound, at various distraction rates and fixation times, using three-dimensional computed tomography. Bone formation was assessed in a 0-day latency model (n=24 minipigs) using distraction rates of 1, 2, or 4 mm/day to create a 12 mm distraction gap. Animals were sacrificed at 0, 8, 16, or 24 days fixation. For experimental and control sides, three-dimensional data from computed tomographic scans were used to calculate the percent bone volume in the regions of interest. Standardized plain radiographs were used to evaluate bone formation with a semiquantitative scale: 0, 1, 2, 3. Mean percent bone volume and radiographic bone fill scores (pooled sample) increased with fixation time from 16.8% and 0.17 at 0 days, to 64% and 2.0 at 24 days fixation. Mandibles distracted at 1mm/day had higher CT values and bone fill scores than mandibles distracted at 2 or 4 mm/day. At 24 days fixation, the maximum percent bone volume (64%--1 mm/day; 24 days fixation) remained below control values (81.3%). The results of this study indicate that despite high bone fill scores on plain radiographs, the highest percent CT bone volume achieved in this model was 64%.

Animals↗

PubMed2004

Mechanical characterisation of a bone defect model filled with ceramic cements.

Ceramic bone substitute materials are often used to fill defects in comminuted articular fractures. In an in vivo study [1], calcium phosphate cements have been injected into highly loaded slot defects in the proximal tibial metaphysis. During healing, cracks were formed mostly in the proximal anterior aspect of the implanted cement and wedge-like gaps formed between the tibial plateau and the cement. Mechanical ex vivo tests were done to investigate the mechanical competence of the bone cement in such a defect situation. Entirely filled defects were loaded with up to 4.5 kN until they failed. Cyclic loading of the proximal tibiae caused micro fragmentation of the cement after 1000 cycles at 1.5-2.0 kN load. This aspect was comparable to cement fragmentation observed in vivo. Large defects in highly loaded areas should therefore additionally be stabilised with metallic implants. The ceramic cement can only be used as a filler material, which can be replaced by new bone upon resorption.

Animals↗

PubMed2003

Resorption patterns of calcium-phosphate cements in bone.

Two calcium phosphate cements, one monophasic and the other biphasic, have been used as bone void filler in a sheep model. The cements were injected into a slot defect in the proximal tibia and into a cylindrical defect in the distal femur. In this study, we focused on the resorption pattern of the two cement formulations and the subsequent biologic reaction. Bone remodeling occurred synchronously with the resorption of the implant material in a creeping substitution process. Cracks and pores in the monophasic cement were filled with osseous tissues. The biphasic cement showed faster resorption of the matrix. The more slowly resorbing granules were surrounded by newly grown bone, thus providing an inverse scaffold for cancellous bone regeneration. In highly loaded areas, the long-term support function of the fixation appears to be critical. Because cortical bridging of the defects was seen in only one case, it can be concluded that calcium-phosphate cements are preferentially suitable as cancellous bone substitute materials.

Animals↗

PubMed2003

Correlation of biomechanical stiffness with plain radiographic and ultrasound data in an experimental mandibular distraction wound.

The aim of this study was to determine the stiffness of a porcine mandibular distraction wound at the end of neutral fixation.Twenty-four Yucatan minipigs underwent unilateral mandibular distraction: zero-day latency, rates of 1, 2, and 4 mm per day, distraction gap of 12 mm. Radiographic and ultrasound bone fill scores at 0, 8, 16 and 24 days of neutral fixation were used to evaluate interval healing. At sacrifice, biomechanical stiffness was determined using an Instron machine to produce a downward force of 2 mm/min at the premolar occlusal surface. Force (kilo-Newton, kN) and displacement (mm) were recorded at a rate of 10,000 points/second. Stiffness across the distraction wound, plain radiographic and ultrasound bone fill scores all increased with duration of neutral fixation and were highest for the 1 mm per day group at all time points. At the end of fixation, even in the most clinically stable group, stiffness across the distraction wound was only 25.5% of control.Despite clinical stability and high bone fill scores by X-ray and ultrasound, the distraction wound did not achieve normal stiffness at the end of neutral fixation in this model. This may have implications for the management of patients who undergo large movements by distraction.

Animals↗

PubMed2003

Development of a mechanical testing system for a mandibular distraction wound.

The purpose of this study was to develop a mechanical testing system to estimate stiffness of an experimental porcine mandibular distraction osteogenesis (DO) wound. The system was designed to function without changing the morphology of the healing mandible. A customized jig was designed to allow cantilever-bending tests of the Yucatan mini-pig hemi-mandible. Experimental and control hemi-mandibles were placed in the jig and the proximal segment was secured. A material testing unit applied progressively increasing downward force on the pre-molar occlusal surface. The maximum force applied was 0.030 kN. The stiffness value for each hemi-mandible was represented by the slope of the plot of force (kN) vs displacement (mm). Radiographs were taken before and after mechanical testing to demonstrate any gross morphologic changes or identifiable fractures across the distraction wound. A total of 24 mini-pigs underwent DO of the right mandible with 0-day latency and distraction rates of 1, 2, and 4 mm per day resulting in a 12 mm gap. At the completion of 0, 8, 16, and 24 days of neutral fixation, two animals for each of three different distraction rates were sacrificed for mechanical testing. Stiffness of control hemi-mandibles ranged between 0.018 and 0.317 kN/mm (median 0.063; mean 0.099 +/- 0.080). Stiffness of experimental hemi-mandibles ranged between 0 and 0.025 kN/mm (median 0.004; mean 0.005). The subset that was tested at the end of neutral fixation had stiffness between 0.005 and 0.025 (median 0.011; mean 0.012 +/- 0.011). No morphologic changes were evident on the X-rays after testing. The results indicate that the cantilever-bending model is useful for testing stiffness of an experimental mandibular DO wound without destroying its morphology.

Animals↗

PubMed2001

[Reconstruction of the orbits with polylactate implants: animal experimental results after 12 months and clinical prospects].

In earlier experiments healing of large orbital wall defects in sheep occurred undisturbed by osteoconductive bone growth along biodegradable membranes when there was no interference with additional bone grafts or titanium miniplate osteosynthesis. In this experiment similar bilateral defects were reconstructed with poly(L/DL 80/20) lactide implants using a microporous membrane 0.5 mm thick without further support on one side, an 0.25 mm microporous membrane supported by solid polylactide buttresses and stabilized by polylactide dowels on the opposite side. After 12 months we found a symmetrical reconstruction of the normal anatomy of the orbits in CT and X-ray examinations. In contrast, histologic investigations revealed massive foreign-body reactions around degrading buttress implants and dowels especially. Milder reactions occurred in some orbits along the membranes as well, in contrast to our earlier experiments with 4-month follow-up. None of the implants had degraded completely 12 months after surgery. In our 12-month long-term survey, polylactide microporous membranes confirmed their osteoconductive potential in orbital wall reconstruction. Nevertheless, massive polylactic implants should not be considered for clinical application in the orbit because of significant late foreign-body reactions.

Animals↗

PubMed2000

An improved peel test method for measurement of adhesion to biomaterials.

Adhesion of tissues to biomaterials is desirable to prevent bacterial proliferation and for epithelial/transmucosal sealing of transcutaneous appliances, but can be counter-productive elsewhere, e.g. implants contacting tendons or maxillofacial subcutaneous tissue. It is therefore important to gauge adhesion strength of tissues to biomaterials before clinical use. Peel-testing is widely used for industrial product adhesion monitoring, but has rarely been applied biomedically. Here we describe peel-testing instrumentation designed for testing adherence of soft tissues to biomaterials. It offers the advantage that a 90 degrees angle between peel and substrate is maintained, simplifying determination of applied normal forces separating tissue layers from material surfaces. The device is portable and can be brought directly to the specimen removal site. This minimizes time delays between explantation and testing, maintaining the tissue/biomaterial interface in the freshest possible state closely approximating in vivo conditions, and so avoids measurement artifacts. So far, the instrument has been used to test adhesion of tape to a biomaterial surface (for determining the device's technical performance), assess strength of tissue adhesives, and measure adhesion of subcutaneous tissue to orthopaedic biomaterials. However, its versatility suggests additional applications for the peel-tester where adhesion of soft tissue to biomaterials is of interest.

Journal Article↗

PubMed2000

Effect of mechanical load on articular cartilage collagen structure: a scanning electron-microscopic study.

Little is known about the morphological effect of a mechanical load upon articular cartilage. The objective of this study was to describe and quantify the deformation of the articular cartilage collagen structure of the tibial plateau under static loading. Whole intact rabbit knee joints were loaded in vitro by simulating a quadriceps force of 3x, 1x or 0.5x body weight (high, medium, low) over durations of 30 or 5 min (long, short). Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. Under high force and long duration loading the collagen fibers exhibited high deformation with an increased thickness of the layer of collagen fibers oriented almost parallel to the surface and a cartilage thickness reduced to 54%. Collagen fiber deformation occurred mostly in the transitional and upper radial zone. The area of tibial indentation and the cartilage thickness reduction increased with magnitude and duration of load. The collagen matrix did show a bulging edge at the border of the meniscus and exhibited remarkable deformation under the meniscus.

Animals↗

PubMed1998

[Experimental reconstruction of the sheep orbit with biodegradable implants].

In a complex animal model in sheep, polydioxanone (PDS) and polylactic membranes were used for the reconstruction of large orbital-wall defects. In a long-term experiment over 1 year, polylactic implants alone showed the best performance as compared with combinations involving autogenous bone grafts and titanium miniplate fixation. As soon as these polylactic implants are approved for human surgery, they will be used to solve the still challenging problem of anatomical reconstruction of large comminuted fractures of more than one orbital wall.

Animals↗

PubMed1997

Long-term in vivo degradation and bone reaction to various polylactides. 1. One-year results.

Injection-moulded pins from poly(L-lactide), poly(L/DL-lactide) (95/5%) were implanted in the cortex of the tibiae of sheep. The bone-implant interface was evaluated to observe whether there is any bone resorption caused by the implants. The molecular weight and crystallinity changes upon implantation were also measured. There was no net bone loss around the implants or sterile cyst formation in any of the animals implanted with polylactides up to 1 year. The new bone formed around the poly(L-lactide) and poly(L/D-lactide) pins was separated from the implants with a thin layer of connective tissue. For the implants from poly(L/DL-lactide), there was direct apposition of bone on the polymeric material. At 1 year of implantation, the implants were not completely resorbed, although the molecular weight of polylactides was reduced from 40,000-50,000 to 500-300. The crystallinity at 1 year was about 45% for poly(L/DL-lactide) and poly(L/DL-lactide) and 65% for poly(L-lactide), respectively, indicating the presence in the degraded material of thermodynamically stable crystals.

Animals↗

PubMed1997

One- or two-plate fixation of mandibular angle fractures?

Standard treatment of mandibular angle fractures with miniplates, according to the recommendations of Champy et al. (1976), consists of fixation with one plate at the superior border of the mandible ventral to the external oblique line. In certain constellations, a second miniplate at the lower mandibular margin may provide additional stability. In contrast, extremely high complication rates following two-plate fixation of mandibular angle fractures were reported by Ellis and Walker (1994). In a prospective randomized study, 31 consecutive patients were treated with 2.0 mm (mini) plates (Synthes Co., Switzerland). One group was treated with one plate, the other one with two plates. In none of the patients was intermaxillary immobilization used. Follow-up was performed 6 months postoperatively, consisting of clinical and radiographic examination. No significant differences (P = 0.74 for infection, and P = 1.0 for occlusal and postoperative sensory disturbance) in postoperative short- or long-term complications were found between the two groups. The results are compared with our experimental investigations presented at the annual congress of the Germany Society of Oral and Maxillofacial Surgery, 1995. Two-plate fixation may not offer advantages over single-plate fixation in general. However, individual fracture constellations may benefit from variation in plate(s) localization. Factors contributing to complications in mandibular angle fractures are discussed.

Adult↗

PubMed1996

Bone regeneration with resorbable polymeric membranes: treatment of diaphyseal bone defects in the rabbit radius with poly(L-lactide) membrane. A pilot study.

Tubular poly(L-lactide) membranes with a pore size of 5-15 microns and a molecular weight of 70,000 Daltons were implanted into 24 New Zealand skeletally mature rabbits to cover 10-mm mid-diaphyseal defects of the radius of the forelimb. An identical defect on the contralateral limb was not treated with the membrane and served as a control. The animals were killed at 1, 2, 4, 8, 12, 24, 36, and 64 weeks after implantation, and radiographic and microscopic studies were conducted. The canals of the polymeric tubes were initially filled with blood. At 2 weeks, there was direct woven bone formation within the polymeric tube in continuity with the fragment cortices and its medullary canal. The formation of woven bone across the defect progressed until reconstruction of the defect had occurred at 6-8 weeks. The bone continued to remodel throughout the observation period of 64 weeks. By 12 weeks, bone within the lumen of the implant consisted of cancellous bone and cortical bone lining the membrane walls. At 24, 36, and 64 weeks, the implants were filled with cancellous bone and cortical bone in direct apposition to the polymer membrane. For one implant, the newly formed woven bone had only incompletely filled the defect at 8 weeks. This resulted in a nonunion with a residual gap of 0.5 mm and the appearance of mature bone. There was extensive bone formation along the intraosseous membrane in both control and implanted defects, although the untreated defects were rapidly filled with overlying muscle and soft tissues. The osseous activity of the untreated defects appeared confined to the bone ends by the interposed muscle and fibrous soft-tissue margins. The untreated defects resulted in radial-ulnar synostosis along the intraosseous membrane with cortical bone caps at the bone ends. The poly(L-lactide) membrane remained intact throughout the 64-week period without evidence of significant degradation. The membranes were encapsulated in a thin fibrous tissue. There was no histological evidence of acute or chronic inflammation associated with the implants.

Animals↗

PubMed1996

[Experimental studies of the biomechanical stability of different miniplate configurations for the mandibular angle].

Miniplate fixation of mandibular fractures has become the treatment of choice in most cases. In fractures of the mandibular angle one 4- or 6-hole miniplate is applied ventral to the oblique line of the buccal cortex of the mandible. Not in every case adequate stabilization is being accomplished by one plate. In order to find out if stability might be increased by a two miniplate fixation technique in which a second plate is applied at the inferior border of the mandibular angle 16 polyurethane and 16 humane mandibles were used and standardized osteotomies were performed at the right mandibular angle. These two groups were divided in 4 sub-groups of four mandibles each and plate fixation of the sub-groups was performed as follows: 6-hole plate on the buccal side of the oblique line, 6-hole plate as before and an additional 2-hole plate at the inferior margin of the mandible, 2-hole plate at the oblique line and 6-hole at the inferior margin and finally two 4-hole plates at the same position. The stability of fixation was measured according to Kroon's method (Kroon et al. 1988), based on a three-dimensional in-vitro model in which muscle forces during mastication acting on the mandible were simulated. Axial loading forces close to the fracture site produced significantly inferior splaying and lingual compression in single miniplated angle fractures. Application of a second miniplate at the inferior border provided significantly higher resistance to loading forces close to the fracture line where two 4-hole miniplates showed superior results. We conclude that two miniplates are an effective method of treating mandibular angle fractures with minor fracture surfaces by establishing a second line of osteosynthesis to neutralize rotational forces.

Biomechanical Phenomena↗

PubMed1996

[Development of a resorbable implant: experimental reconstruction of the orbits with polylactate membranes. Animal model and preliminary results].

In a complex animal model in five sheep, PDS or polylactic biodegradable membranes were used for reconstruction of large orbital defects in combination with autogenous bone grafts and stable internal fixation with titanium miniplates and screws. Because of anatomical similarities, animal model and human clinical findings are comparable. After eight weeks, in four sheep all reconstructions were separated from the maxillary and frontal sinus by a continuous mucosal layer. The bone grafts were integrated into the bony frame of the orbit. Foreign body reactions were milder with polylactic membranes compared to PDS, probably due to the slow degradation of polylactide. These preliminary results will lead to a further study with a larger series to compare the two biodegradable materials and to prepare the way for clinical use of polylactic membranes in orbital reconstruction.

Animals↗