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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

At least 19 recordsLinked to original sources
PubMed1996

Evaluation of soft tissue reactions at the interface of titanium limited contact dynamic compression plate implants with different surface treatments: an experimental sheep study.

Five types of limited contact dynamic compression plates (LC-DCPs) of pure titanium with different surface treatments and an electropolished stainless steel LC-DCP were tested. The surface roughness parameters and chemical surface conditions were determined and checked for probable surface contamination. After an implantation period of 3 months on long bones of sheep, the soft tissue adjacent to the plates was evaluated histomorphometrically. The difference in roughness parameters was statistically significant for most surface conditions. A correlation was found between the surface roughness of the implants and the thickness of the adjacent soft tissue layer. The thinnest soft tissue reaction layer with a good adhesion to the implant surface was observed for the titanium anodized plates with coarse surface. Smooth implants, in particular the electropolished stainless steel plates, induced statistically significant thicker soft tissue layers. Profilometer roughness measurements combined with scanning electron microscopy techniques were useful methods to characterize the surface morphology.

Animals↗
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

Influence of materials for fixation implants on local infection. An experimental study of steel versus titanium DCP in rabbits.

Resistance to infection may be influenced by foreign bodies such as devices for fracture fixation. It is known that stainless steel and commercially-pure titanium have different biocompatibilities. We have investigated susceptibility to infection after a local bacterial challenge using standard 2.0 dynamic compression plates of either stainless steel or titanium in rabbit tibiae. After the wounds had been closed, various concentrations of a strain of Staphylococcus aureus were inoculated percutaneously. Under otherwise identical experimental conditions the rate of infection for steel plates (75%) was significantly higher than that for titanium plates (35%) (p < 0.05).

Animals↗
PubMed1995

Intramedullary nailing and pulmonary embolism: does unreamed nailing prevent embolization? An in vivo study in rabbits.

Pulmonary embolism in reamed femoral nailing has been reported and discussed over recent years. Does an unreamed nailing technique with a solid nail prevent this rare but serious complication of intramedullary fixation? In an animal model in rabbits, we studied the pathophysiologic impact on pulmonary function and the impact on hemostasis of reamed and unreamed nailing of intact femora and tibiae, and of femoral fracture in relation to intramedullary pressure. No statistical difference of PaO2, PaCO2, and PCO2et was found in the femur whether a reamed or unreamed procedure was performed. Two of six animals with unreamed femoral nailing, one of six animal with reamed femoral nailing, and one of five animals with a femoral fracture fulfilled four of four or three of four criteria for embolization (increase of the difference of PaCO2 and PCO2et, decrease of PaO2, increase of blast cells in central-venous blood and bone marrow/fat in histologic section of the lungs and bone). Tibial nailing did not alter pulmonary function in either group. Intramedullary pressure was increased in all animals with perioperative impairment of pulmonary function (375 to 676 mbar). Analysis of the hemostatic results showed a significant difference of platelet activation in reamed versus unreamed nailing of the femur 1 hour after nailing (p < 0.01) and a significant decrease of fibrinogen and antithrombin III (p < 0.001/p < 0.01) in reamed femoral nailing. We conclude that unreamed nailing of the femur with a solid rod may also cause bone marrow embolization with alteration of pulmonary function as long as an important increase of the intramedullary pressure is generated during the nailing procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Influence of reaming versus nonreaming in intramedullary nailing on local infection rate: experimental investigation in rabbits.

The question of whether the impairment of the endosteal blood supply, which is induced by nailing with reaming of the medullary cavity, increases the risk of a postoperative infection cannot be conclusively answered by studying existing literature. The aim of this study was to investigate the effect of medullary reaming on the occurrence of local infection based on an infection model in the rabbit tibia (n = 44). An infection rate of 50% was found after unreamed nailing, as opposed to an infection rate of 64% after medullary reaming. The number of bacteria observed after reaming was significantly higher than after nail insertion without previous reaming. The differing susceptibilities to infection as observed in this model are statistically significant (p < or = 0.05).

Animals↗
PubMed1995

[Biomechanical reaction of the bones to intra- and extramedullary load bearers: the significance of implant contact].

Bone reacts very differently to changes in the environment relating to implant surgery. Since the advantages and disadvantages of implants have to be set against each other, the functions of implants and the demands made upon them will be considered first. The contact area between the bone and the implant will then be discussed. The contact surfaces and their induction of necrosis are at present in the forefront of our research in the area of biomechanics. The essential issues are: the avoidance of early temporary porosity, the possibilities of providing best conditions for "accelerated" bone healing, the reduction of refracture risks, and the improvement of infection resistance. Considerable opportunities for improvement of the most recent insights into the biology and biomechanics of the contact zones.

Bone Resorption↗
PubMed1995

[Standards, guidelines and principles for clinical trials: medical products].

In addition to existing legislation there have been valid european and international Good Clinical Practice (GCP) guidelines and standards for the planning management and evaluation of clinical research projects and of clinical investigation of medical products since the 1990's. GCP regulates patient protection, the responsibilities of the sponsors, information management, data processing and quality assurance. The Draft International Standard (ISO/DIS 14155) and the European Standard (CEN/EN 540) stipulate the prerequisites and conditions for the clinical testing of medical products and devices. The essential documents for any research or investigative project include the trial protocol and the investigator's brochure. Observation of the guidelines and standards must be emphasized chiefly for reasons of publication suitability and the international recognition of the research and development findings.

Clinical Trials as Topic↗
PubMed1995

[Healing of spiral fractures in the sheep tibia comparing different methods--osteosynthesis with internal fixation, interlocking nailing and dynamic compression plate].

The healing process of spiral fractures of the sheep tibia was investigated in an experiment with simulated clinical conditions. The effects of conventional internal fixation techniques with the DCP and the intramedullary nail are compared with those of internal fixation with the spine fixator. The internal fixation techniques are described in terms of their bending stiffness when mounted on the fractured bone. The in vivo investigation was documented clinically and radiographically and the post mortem specimens were evaluated histologically. The bending stiffness of the healed bone was assessed in relation to the contralateral side. After application of the DCP, primary healing took place and extensive transcortical necrosis occurred in the implant bed. Intramedullary nailing led to secondary healing and to necrosis of the inner cortex close to the endosteum. After internal fixation with the spine fixator, gap healing took place and no cortical necrosis was observed. The clinical course was generally good after all procedures. The histological evaluation shows that damage to the vascularity of the bone can only be avoided by using the spine fixator. This principle seems to be appropriate for the purposes of biological internal fixation.

Animals↗
PubMed1994

Three-dimensional dynamic AO external fixation of distal radial fractures--a preliminary report.

External fixation of unstable and intra-articular distal radial fractures has become increasingly popular. Dynamic external fixation, allowing movement of the wrist during the fixation period, is a relatively new approach which may further improve functional end results. To permit early functional treatment, the small AO external fixator was supplemented by a joint allowing all three degrees of rotational freedom. The centre of rotation is located at a point outside the device and lies approximately in the head of the capitate. With the natural centre of wrist rotation coincident with that of the fixator, admissable movements of the wrist include both flexion-extension and radio-ulnar deviation, without threatening fracture reduction. In vitro testing and initial clinical experience with a prototype are encouraging. Several improvements of the original design have been made and a multicentric clinical study is scheduled for further evaluation of the new dynamic external fixator.

Adult↗
PubMed1994

Evaluation of the soft tissue interface at titanium implants with different surface treatments: experimental study on rabbits.

Recently, a dominant influence of the surface roughness parameters for the soft tissue reaction at the implant tissue interface was found in an experimental study on sheep. The purpose of the present study is to correlate the surface roughness parameters of different experimental bone plates to the results of the histomorphometric analyses of the adjacent soft tissues. Pure titanium plates (35 x 5 x 1 mm) with six different surface treatments and electropolished stainless steel plates were tested. Prior to implantation the surface roughness parameters were determined using a profilometer and a scanning electron microscope. The tibia of adult rabbits served as test sites. At least four plates of each type were implanted. Three months postoperatively the implants were harvested with an intact tissue envelope and were left in situ for the histological preparation. The difference in the roughness parameters is statistically significant for most surface conditions and has an effect on the soft tissue reaction. The histological evaluation shows a significant higher number of blood vessels for steel plates in comparison to titanium plates with handground and blasted surface conditions. For the rough type of anodized titanium surfaces a significantly thinner soft tissue capsule is found, compared to electropolished steel plates. For the steel plates a fluid film was found between the implant and the adjacent tissue layer. The material and the surface roughness of the implant, determine the tissue reaction at the interface. The rough type of anodized titanium implants seems to be preferable.

Animals↗
PubMed1994

Influence of type of medullary nail on the development of local infection. An experimental study of solid and slotted nails in rabbits.

Any operation involving the implantation of a foreign body increases the risk of infection. The implant material and its surface, the dead space, and any necrosis or vascular changes play a significant role in susceptibility to infection. We investigated the effect of the dead space in an intramedullary nail on the rate of local infection. We inoculated the intramedullary cavities of rabbit tibiae with various concentrations of a human pathogen, of Staphylococcus aureus strain, and then inserted either a solid or a hollow slotted stainless-steel nail. We found a significantly higher rate of infection after use of the slotted nail (59%) than after the solid nail (27%) (p < 0.05).

Animals↗
PubMed1994

[Intramedullary pressure in intramedullary nailing of the femur and tibia].

Intramedullary nailing of shaft fractures of the femur and tibia is a recognized operative procedure and its use has even been enlarged by the introduction of the so-called interlocking technique. In recent years case reports have been published describing peroperative pulmonary embolism during reamed femoral nailing, suggesting either an unfavorable effect of the reaming or the pressure increase in the medullary cavity while reaming and nailing. In an in vitro study on explanted human femora and tibiae we investigated the intramedullary pressure increase in reamed and unreamed nailing procedures of both bones. A lower pressure increase was noted in unreamed nailing compared to reamed nailing in the femur (289/496 mm Hg) and in the tibia (128/>833 mm Hg). The unreamed tibial nailing displayed significantly less pressure increase than the unreamed femoral nailing (p = 0.01). Opening of the medullary cavity with the so-called cheese cutter (cannulated cutter over a centering pin) showed significantly greater pressure increase in the femur than in the tibia (p = 0.01). Pressure increase seems to be dependent of the mode of insertion of the unreamed nail (ram-blows versus manual insertion), although the difference in the tibial unreamed nailing is statistically not significant.

Biomechanical Phenomena↗
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↗
PubMed1994

Force required for bone segment transport in the treatment of large bone defects using medullary nail fixation.

In distraction osteogenesis, different factors influence quality and quantity of bone formation. These factors are rigidity of fixation, frequency, and velocity of transport; and integrity of periosteum, endosteum, and intramedullary vascularization. Little data are available on forces related to distraction osteogenesis and limb lengthening, and no data on forces related to bone segment transport. This experiment investigates the correlation of the bone regeneration process with transport forces. Bone segment transport over an intramedullary nail provides an excellent model for measurement of external forces during distraction osteogenesis because soft-tissue and muscle resistance is reduced as compared with limb lengthening. In an animal experiment (sheep), tibial shaft defects of 20 mm and 45 mm were treated. External transport forces were measured daily during bilateral wire transport of a bone segment over an intramedullary nail. Forces increased during transport. Overall transport forces for large defects were slightly higher than those for small defects, reaching 350 N by the end of transport. For large defects, transport forces leveled off during bone transport and rose again at the end. Correspondingly, for large defects, stress relaxation within the tissues increased during the third and the sixth week of transport. This plateau may be interpreted as a reduction of internal forces within the repair tissues at the distraction site, implying a spreading of the healing phases during the bone regeneration process or geometrically different shapes of the regenerate.

Animals↗
PubMed1994

[Histologic studies of replacement of the anterior cruciate ligament with PDS-augmented patellar tendon transplants].

The bone-patellar tendon-bone graft is currently the best substitute for the anterior cruciate ligament (ACL). To improve the results we compared a modified Jones procedure with an additional PDS augmentation. In 25 sheep the ACL was reconstructed in the left knee after total resection. The only resection of the ACL was done in all right knees. One year postoperative 21 sheep remained in the experiment and came to evaluation. There were 10 modified Jones procedures and 11 PDS augmentations. In both groups, the central one-third of the patellar tendon was implanted through a femoral and tibial drill hole for reconstruction of the anterior cruciate ligament. The transplants were fixed on both ends with a 1-mm cord of polydioxanon (PDS), a soft preload of 50 N was given with a spring balance and the ends of the cords were fixed with a screw and a washer. In the second group we did an additional augmentation with a doubled cord of 2 mm PDS. Early mobilization and weight-bearing was allowed. Throughout the observation period all animals were labelled for fluorescence microscopy. One year after resection of the ACL without reconstruction there were totally destroyed joints. Histology showed damaged menisci and joint surfaces without any cartilage as a sign of severe arthrosis. The macroscopic aspect of the transplants showed strong ligaments coated totally by a synovial membrane with good vascularization. Only little signs of degeneration were to be seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Tissue response and in vivo degradation of selected polyhydroxyacids: polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA).

The tissue response and in vivo molecular stability of injection-molded polyhydroxyacids--polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA, 5-22% VA content)--were studied. Polymers were implanted subcutaneously in mice and extirpated at 1, 3, and 6 months in order to study tissue response and polymer degradation. All polymers were well tolerated by the tissue. No acute inflammation, abscess formation, or tissue necrosis was observed in tissues adjacent to the implanted materials. Furthermore, no tissue reactivity or cellular mobilization was evident remote from the implant site. Mononuclear macrophages, proliferating fibroblasts, and mature vascularized fibrous capsules were typical of the tissue response. Degradation of the polymers was accompanied by an increase in collagen deposition. For the polylactide series, the inflammatory response after 1 month of implantation was less for materials containing the D-unit in the polymer chain, whereas in the case of the polyhydroxybutyrate/valerates, the number of inflammatory cells increased with increasing content of the valerate unit in the polymer chain. Between 1-3 months, there was slightly more tissue response to the PHB and PHB/VA polymers than to PLA. This response is attributed to the presence of leachable impurities and a low molecular weight soluble component in the polyhydroxybutyrate/valerates. At 6 months, the extent of tissue reaction was similar for both types of polymers. All polylactides degraded significantly (56-99%) by 6 months. For a poly(L-lactide) series, degradation rate in vivo decreased with increasing initial molecular weight of the injection-molded polymer. Several samples showed pronounced bimodal molecular weight distributions (MWD), which may be due to differences in degradation rate, resulting from variability in distribution of crystalline and amorphous regions within the samples. This may also be the result of two different mechanisms, i.e., nonenzymatic and enzymatic, which are involved in the degradation process, the latter being more extensive at the later stage of partially hydrolyzed polymer. The PHB and PHB/VA polymers degraded less (15-43%) than the polylactides following 6 months of implantation. Generally, the polymer with higher valerate content (19%, 22%) degraded most. The decrease in molecular weight was accompanied by a narrowing of the MWD for PHB and copolymers; there was no evidence of a bimodal MWD, possibly indicating that the critical molecular weight that would permit enzyme/polymer interaction had not been reached. Weight loss during implantation ranged from 0-50% for the polylactides, whereas for the PHB polymers weight loss ranged from 0-1.6%.

Absorption↗