Miniplate osteosynthesis with four different systems in sheep.

The aim of this study was to compare a combination of a locking system with self-tapping (ST-L) or self-drilling-tapping (SDT-L) screws with a combination of conventional miniplates with self-tapping (ST) and self-forming (SF) screws. A standardized osteotomy and osteosynthesis with one of the above mentioned systems was performed in 24 sheep. Callus formation was measured with the help of CT scans assisted by a navigation system. Specimens of each osteotomy gap were taken and examined histologically. The best results were observed when self-tapping screws and the Mini-Locking-System (ST-L) were applied. The slowest healing was seen in animals treated with miniplates and SF screws. After 8 weeks an increase in bone formation could be observed in the ST, SF, SDT-L systems. The results after 8 weeks were comparable with those achieved by the ST-L system after 4 weeks. The improved stability of the osteosynthesis with the ST-L system resulted in early ossification of the osteotomy gap and the smallest amount of callus formation.

Cortical perfusion and local fat occlusion after intramedullary nailing of the ovine tibia--comparison of different surgical procedures.

UNLABELLED: The aim of this study was to determine whether reamed or unreamed nailing is more harmful to local bone perfusion and increases fat occlusion of transcortical vessels. METHODS: After creating a standard fracture of the sheep tibia, reaming was performed in the first group using an experimental optimised reaming system (RE), in the second group with the conventional AO reamer (RC). Unreamed nailing was performed in the third group (UN). UHN 7.5mm titanium was inserted in all three groups. Intramedullary pressure was measured intraoperatively. Quantitative histological analyses of the bone were performed postoperatively. RESULTS: The highest fat occlusion of transcortical vessels occurred in UN (5.7%), the lowest in RE (1.6%). The least harm to intracortical circulation was caused by RE with 28% perfused intracortical vessels compared to 17% (UN) and 18% (RC). CONCLUSION: The experimental optimised reaming system reduces circulatory disturbance and local fat occlusion compared to the existing nailing procedures.

Optimization of corticosteroid induced osteoporosis in ovariectomized sheep. A bone histomorphometric study.

During osteoporosis induction in sheep, side effects of the steroids were observed in previous studies. The aim of this study was to improve the induction regimen consisting of ovariectomy, calcium/vitamin D- restricted diet and methylprednisolone (-MP)- medication with respect to the bone metabolism and to reduce the adverse side effects. Thirty-six ewes (age 6.5 +/- 0.6 years) were divided into four MP-administration groups (n = 9) with a total dose of 1800 mg MP: group 1: 20 mg/day, group 2: 60 mg/every third day, group 3: 3 x 500 mg and 1 x 300 mg at intervals of three weeks, group 4: weekly administration, starting at 70 mg and weekly reduction by 10 mg. After double-labelling with Calcein Green and Xylenol Orange, bone biopsy specimens were taken from the iliac crest (IC) at the beginning and four weeks after the last MP injection, and additionally from the vertebral body (VB) at the end of the experiment. Bone samples were processed into stained and fluorescent sections, static and dynamic measurements were performed. There were no significant differences for static parameters between the groups initially. The bone perimeter and the bone area values were significantly higher in the VB than in the IC (Pm: 26%, p < 0.0001, Ar: 11%, p < 0.0166). A significant decrease (20%) of the bone area was observed after corticosteroid-induced osteoporosis (p < 0.0004). For the dynamic parameters, no significant difference between the groups was found. Presence of Calcein Green and Xylenol Orange labels were noted in 50% of the biopsies in the IC, 100% in the VB. Group 3 showed the lowest prevalence of adverse side effects. The bone metabolism changes were observed in all four groups, and the VB bone metabolism was higher when compared to the IC. In conclusion, when using equal amounts of steroids adverse side effects can be reduced by decreasing the number of administrations without reducing the effect regarding corticosteroid-induced osteoporosis. This information is useful to reduce the discomfort of the animals in this sheep model of corticosteroid-induced osteoporosis.

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.

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.

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.

[Evaluation of potential damage to the regenerate during callus molding after mandibular distraction osteogenesis. Experimental study using an animal model]. / Evaluation der potenziellen Regeneratschädigung bei der Kallusumformung nach Distraktionsosteogenese der Mandibula. Eine experimentelle Untersuchung am Tiermodell.

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.

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.

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.

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%.

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.

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.

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.

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.

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.

[Reconstruction of the orbits with polylactate implants: animal experimental results after 12 months and clinical prospects]. / Rekonstruktion der Orbita mit Polylaktat-Implantaten: tierexperimentelle Ergebnisse nach 12 Monaten und klinischer Ausblick.

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.

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.

[Comparative in vitro studies of self-boring and self-tapping screws. Histomorphological and physical-technical studies of bone layers]. / Vergleichende In-vitro-Untersuchungen von selbstbohrenden und selbstschneidenden Schrauben. Histomorphologische und physikalisch-technische Untersuchungen des Lagerknochens.

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.

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.