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Biomedical subjects

L Claes

Publications and source records attributed to L Claes.

At least 37 records · Page 2Linked to original sources
PubMed1990

Significance of postoperative stability for bony reparation of comminuted fractures. An experimental study.

The significance of postoperative mechanical stability to bone repair of comminuted fractures was investigated in an animal experimental study comparing four commonly employed operative methods of fracture stabilization: 1. Plate osteosynthesis combined with lag screw fixation; 2. Bridging plate osteosynthesis; 3. External fixation; 4. Static interlocking intramedullary nailing. As fracture model, a triple wedge osteotomy of the right sheep tibia was used. In regard to biomechanical strength, the method which gave best postoperative stability, plate osteosynthesis in combination with interfragmentary lag screws, did not result in the best bone repair. In this experimental setup, stabilization by bridging methods, inducing bone healing by secondary intention, gave better bone regeneration in the experimental fractures.

Animals↗
PubMed1990

[The significance of postoperative stability for osseous repair of a multiple fragment fracture. Animal experiment studies].

The significance of postoperative mechanical stability for bony repair of a comminuted fracture was investigated in an animal experimental study comparing four commonly applied operative methods of stabilizing fractures: (1) flate osteosynthesis combined with lag screw fixation after reduction of the fragments; (2) bridging plate osteosynthesis; (3) external fixation; (4) static interlocking intramedullary nailing. As the fracture model, a triple-wedge osteotomy of the right sheep tibia was used. The results of in vitro testing of stiffness (N/mm) of each of the four osteosyntheses was as follows: anatomical plate: 746 N/mm; bridging plate 434 N/mm; external fixation 625 N/mm; nailing 416 N/mm. Eight weeks after the operation, the tibiae were explanted and the contralateral tibiae of six sheep were taken as a control group. The three-point bending test revealed no significant difference in bending deviation: anatomical plate 47.58 +/- 22.57 microns; bridging plate 33.93 +/- 7.67 microns; external fixation 33.83 +/- 8.02 microns; nailing 33.0 +/- 17.23 microns. However, it was noted that there was a slightly higher tendency towards stiffness of the bones after bridging plate osteosynthesis, external fixation and interlocking intramedullary nailing and that the amount of stiffness resembled that in non-operated control animals (25.56 +/- 6.66 microns). On the other hand, anatomical plate osteosynthesis showed less stiffness. To assess the tensile strength at the osteotomy area, bone samples were prepared and tested for failure on a material testing machine. The tensile strength of the bone samples showed a distinct difference in all experimental groups according to their anatomical location.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

The mechanical and morphological properties of bone beneath internal fixation plates of differing rigidity.

The internal fixation of diaphyseal fractures by bone plates is a well recognized treatment. The normal physiological stress of bone is reduced by plates that cause a negative balance of bone-remodeling processes. Many investigators have shown that the degree of stress protection is dependent on the rigidity of the plates. It was the aim of this study to quantify mechanical and morphological changes at different locations in a plated diaphyseal bone as a function of differing plate rigidity. Two types of plates with the same size but different materials were used. The stainless steel plates had a modulus of elasticity and bending stiffness 3.2 times higher than the carbon fiber reinforced carbon plates. Both types of plates were applied to the intact right and left femora of six foxhounds for 6 months. The stiffer stainless steel plates led to a significantly higher bone loss and correspondingly greater loss of mechanical properties. These effects were greatest directly beneath the plate and less with increasing distance from the plate.

Animals↗
PubMed1989

[Carbon fiber reinforced polysulfone--a new implant material].

Carbon fibre reinforced polysulfone is a composite material which contains two materials of well known biocompatibility. In comparison to metals this composite material has some advantages which makes it favourable particularly for implants in tumor surgery. The custom made arrangement of fibres in the composite allows the development of implants with special mechanical properties. The radiolucency of the material avoids problems caused by the reflection of x-rays, using metal implants. This special property allows the exact calculation of postoperative radiation doses of tumor patients. Simultaneously the structures behind the implants are not hidden. All implants can be machined during the operation to adapt them to the individual anatomical situation. Animal experimental and clinical applications of plates, screws and spinal segmental replacement implants made of this composite material have shown good results so far.

Animals↗
PubMed1989

[Carbon fiber reinforced polysulfone implants for tumor surgery of the spine].

Anterior tumor removal, cord decompression and spinal stabilization gain in significance in surgical treatment of vertebral tumors. An implant system, consisting of a basket as vertebral body replacement, plates and screws, was developed using carbon fibre reinforced polysulfone. This system allows to perform individually shaped, stable and short-distance spine fusions from an anterior approach. Moreover its radiolucence facilitates postoperative care and irradiation. Operative technique and clinical experience are demonstrated in two patients.

Bone Plates↗
PubMed1988

[Cross stabilization of the internal fixator of the spine].

The "Internal Fixator" for stabilizing the dorso-lumbar spine represents an effective and meanwhile established device to neutralize flexion-bending and sagittal shearing forces. Because of the possible movement of the Schanz' screws in the bone and within the connection clamps, this device does not withstand torsional and frontal plane shearing forces after postinjury or postlaminectomy instability. Therefore, a cross-link device, adaptable to the "Internal Fixator" has been developed. Biomechanical testing against torsion and frontal plane bending moments have shown very low stability resulting in lateral displacement of the fixation device without cross-linking. The diagonal bracing with two wire cerclages does not significantly increase the stability. The recently developed cantilever cross-link device completes the two longitudinal bars to a frame construction and increases therefore the torsional and frontal plane stability for over 70%. This supplementary device is easy to apply to the "Internal Fixator" and has been successful in clinical practise.

Biomechanical Phenomena↗
PubMed1987

Comparative study of the stability of anterior and posterior cervical spine fixation procedures.

Both posterior and anterior procedures of stabilization are used for operative immobilization of unstable functional units of the cervical spine. The primary stabilizing effect of each procedure was examined and the two were compared in an experimental study. To this end the functional units C-5 and C-6 were removed from ten fresh cervical spines, the discoligamentous structures being preserved, and C-6 was embedded in methacrylate. As a result of a tensile force in a vertical direction applied to the base of the spinous process of C-5, a flexion bending load was introduced into the unit, the main component of which was measured with the aid of one vertical- and two horizontal-displacement transducers. The respective tilting angle alpha and the translation were calculated on the basis of these values. Each individual functional unit was measured with and without the discoligamentous lesion. This posterior instability was then stabilized with an H-plate, a hook plate, sublaminar wiring, and various combinations of these. Our results lead to the following clinically relevant conclusions: With isolated posterior instability, posterior fixation with the hook plate appears to bring about exercise stability. With complete discoligamentous instability, the combined procedures certainly produce exercise stability, from a biomechanical point of view, the posterior hook, plate alone being capable of guaranteeing secure fixation. Exclusive posterior wiring with complete discoligamentous instability may, without external immobilization, result in permanent subluxation in the functional unit. Exclusive anterior H-plate fixation with complete discoligamentous instability requires additional external immobilization in the postoperative stage in order to prevent flexion.

Biomechanical Phenomena↗
PubMed1987

[Theoretical principles of the cement-free prosthetic technic].

For long-term cementless fixation of prostheses compression stress transfer between bone and prosthesis is desirable. Shear stress and relative movement between implant and bone lead to bone resorption and implant loosening. A compression stress can be achieved by a suitable force transmission, a form-closed press fit and a suitable prosthesis surface. A ripped, rough or porous surface can transfer shear and tensile stress into compression stress at the interface. A force locking anchorage of the prosthesis can produce a prestressed fixation which supports the growing of the bone into the prosthesis surface. Stiff prostheses lead to a stronger stress protection and atrophy of the bone which favors the fatigue fracture of bone trabeculae.

Biomechanical Phenomena↗
PubMed1987

The combined anterior cruciate and medial collateral ligament replacement by various materials: a comparative animal study.

On 30 sheep, a combined replacement of the anterior cruciate and medial collateral ligament of the right knee was performed with four different materials. Dacron prostheses and glutaraldehyde-preserved bovine tendon prostheses as well as braided ligament prostheses made of carbon fibers and braided resorbable polydioxanone fibers surrounded by lyophilized dura in their intra-articular part were used. Ten unoperated sheep served as a control group. After 1 year the animals were sacrificed and the knee joints were explanted and biomechanically as well as histomorphologically investigated. The gross inspection of the joints showed no ruptured medial collateral ligament replacement but did show partially and totally ruptured anterior cruciate ligament replacements. The Dacron prosthesis was broken in 50% of the cases, whereas for the other materials one ruptured ligament replacement each (12.5%) could be observed. The anterior drawer test and the determination of the tensile stiffness of the remaining ligament replacements revealed that none of the operated knees achieved the properties of the normal control knees. However, the carbon fiber implants had the best result of all prostheses tested. For all materials except the resorbable polydioxanone, abrasion particles could be found in the anterior cruciate ligament and in the synovial membrane. The tissue reaction to these particles was a mild synovitis for carbon fragments, a strong synovitis for Dacron particles, and a chronic inflammatory response to bovine tendon fragments with macrophage granulomas and fibrosis.

Animals↗
PubMed1986

Experimental studies on the influence of fibrin adhesive, factor XIII, and calcitonin on the incorporation and remodeling of autologous bone grafts.

In an experimental study on sheep the effects of fibrin adhesive system (FAS), plasma factor XIII (FXIII), and calcitonin on autologous cancellous bone grafts were studied. Drill holes in the tibia were filled with transplant bone, either untreated or locally treated with fibrin adhesive, with or without plasma factor XIII. We used 24 sheep, divided into three groups. Plasma factor XIII and calcitonin were administered parenterally; the third group received no treatment. For evaluation we carried out quantitative bone and fluorescence morphometry and microangiography. We found that local fibrin adhesive significantly decreased the remodeling and growth of the transplanted cancellous bone. Plasma factor XIII, given parenterally, increased the amount of bone in the transplant site; calcitonin showed no visible effect.

Animals↗
PubMed1986

The stabilizing effect of various implants on the torn acromioclavicular joint. A biomechanical study.

A biomechanical in vitro test was performed to determine the stabilizing effect of various implants for the surgical treatment of the torn acromioclavicular joint. In a specially designed testing device, plastic and cadaver specimens of the shoulder girdle were stressed in various ways. Different dislocations between the acromion and the clavicle and between the clavicle and the coracoid were determined, as well as the stiffness of the implants. A convenient stabilizing effect combined with less rigid fixation to secure the newly treated AC joint was provided by K-wire fixation with cerclage. Interfering shear and bending stresses could be avoided with this method, while the other implants showed various disadvantages. From a biomechanical point of view, a carbon-fiber ligament replacement provides sufficient stability in cases of chronic acromioclavicular separation.

Acromioclavicular Joint↗
PubMed1986

[Resorbable implants for refixation of osteochondral fragments in joint surfaces].

Resorbable pins made of solid polydioxanone (PDS) were tested for refixation of osteochondral fragments. In both medial femoral condyles of sheep osteochondral fragments were chiselled and refixed by 3 PDS pins. After 3 months the sheep were sacrificed and healing of the fragments investigated histologically and biomechanically. Fragment dislocation was not seen in any of the cases and the cartilage surface could be described as normal. The strength of the bone healing zone reached 80% of the strength of the normal bone. The contact surface between fragment and subchondral bone showed complete bony healing. Only the border of the cartilage flake was still visible. The PDS pins had not been completely biodegraded after 3 months.

Animals↗
PubMed1985

Bone healing stimulated by plasma factor XIII. Osteotomy experiments in sheep.

Sheep had their right metatarsals osteotomized midshaft and stabilized by plate and screws. One group was injected with 1250 units of Factor Thirteen for 9 days postoperatively, and a control group received placebo injections. After 8 weeks, the bones were evaluated biomechanically, histomorphologically and by densitometry. The bones of the treated group had a significantly higher tensile strength than the bones of the control animals. The correlation of biomechanical and morphological results demonstrated that the tensile strength increased with an increasing number of osteons crossing the osteotomy gap. The hydroxyapatite content of the bone healing zone was 7.3 per cent higher for the treated bones than for the control bones.

Animals↗
PubMed1985

In vivo and in vitro investigation of the long-term behavior and fatigue strength of carbon fiber ligament replacement.

The long-term behavior of carbon fiber ligament replacements was evaluated in sheep. In vitro assessments of both isolated carbon fiber prostheses and resected animal ligaments were performed. The right knee in 45 sheep was reconstructed. In 30 animals, only the medical collateral ligaments were replaced, but with different systems of anchorage to bone. In 15 animals, a combined replacement of medial collateral ligament and anterior cruciate ligament was performed. In the first group the animals were sacrificed three months postoperation, while in the latter group evaluation was performed one year after surgery. After one year the strength of the medial collateral ligament complex was higher than that of the normal sheep ligaments. The elasticity and extensibility were similar to those of the normal ligaments. No case of partial rupture or rupture of the medial collateral ligament replacements was seen, but four of 12 anterior cruciate replacements showed signs of partial rupture. In vitro testing showed that rupture is more likely to occur where movement occurs around a small radius of bending, and this may be a factor in these cases where the anterior cruciate ligament enters a bony tunnel at an acute angle. Histologic assessment showed good biocompatibility, similar to that reported by other authors. With an operative technique designed to increase the radius of bending where the carbon fiber enters bone, these ligament replacements have a fatigue strength and elasticity adequate for long-term survival.

Animals↗
PubMed1983

The influence of various carbon fibre braiding techniques and methods of fixation on the extensibility of ligament prostheses.

An alloplastic ligament prosthesis with carbon fibres should not only be biocompatible but should also restore the biomechanical function of a natural system, which includes restoring its elasticity. Tests with new types of braided carbon fibre strands showed their elastic extensibility to increase with increasing number of filament tows and increasing braid angle. The best results were obtained with 32 tows and a 43 degrees braid angle. This strand type was tested in vitro as a medial collateral ligament prosthesis with two methods of fixation in human knees and, in like manner, in vivo in sheep knees. Biomechanical tests in vitro using human cadaver knees and sheep knees after 12 weeks' implantation showed an elasticity similar to that of normal natural ligaments.

Animals↗