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Biomedical subjects

L Claes

Publications and source records attributed to L Claes.

At least 19 recordsLinked to original sources
PubMed1992

Comparative experimental biomechanical study of different types of stabilization methods of the lower cervical spine.

In a comparative experimental biodynamic study using thirty-two human cervical spines of cadavers the primary stabilization effect of different types of spondylodesis was examined. Whereas in flexion stress all methods showed a sufficient stability, the rotation tests proved, that in case of a dorsal instability of the lower cervical spine, posterior interlaminar wiring or anterior plate stabilization showed no reliable stabilization effect. However, the compression clamps by ROOSEN and TRAUSCHEL as well as the hook-plates by MAGERL are suitable dorsal stabilization methods with excellent rotation stability. In case of dorsal instability of the lower cervical spine a posterior spondylodesis is necessary and sufficient.

Biomechanical Phenomena↗
PubMed1992

[A method for in vivo measurements of implants used in the reconstruction of spinal fractures].

Little is known about the forces and moments acting on the spinal column during various movements and activities, and thus about the loading of implants used in the treatment of spinal fractures. A measuring method using an external fixation device was developed to determine the in vivo loading of spinal implants. On the basis of these data the forces acting on the spine can be calculated. The present paper describes this measuring method as applied to the fixation device, and initial experience with this device in a first application is presented.

Biomechanical Phenomena↗
PubMed1991

Biomechanics of fixation systems to the cervical spine.

The biomechanical evaluation of a cervical spine implant must include flexural and torsional testing if it is used for stabilizing a traumatic unstable motion segment. A cadaveric model is presented that allows flexural and torsional testing of a cervical spine motion segment, measuring the tilting angle, the translation, and the torsional angle. After measuring the intact segments, in the first series, a so-called posterior instability was created and stabilized posteriorly with the hook-plate and sublaminar wiring; anteriorly with the H-plate; and with combinations of these implants. In a second series, their stabilizing effect after complete discoligamentous instability was tested. With isolated posterior instability, it was found that the flexural stability is preserved, whereas torsional stability is markedly reduced. In cases of isolated posterior instability, only hook plating alone or its combination with anterior H-plating seemed to bring about a higher torsional stability than the intact specimen. In cases of complete discoligamentous instability, only anterior H-plate and posterior hook plate procedures combined or the hook plate alone was able to guarantee both torsional and flexural stability higher than the intact spine. Exclusive posterior wiring without postoperative external immobilization in complete discoligamentous instability may result in permanent subluxation of the functional unit. Exclusive anterior H-plate fixation in complete discoligamentous instability requires additional external immobilization in the postoperative phase to prevent flexion and torsion.

Biomechanical Phenomena↗
PubMed1991

[Non-contact measuring of small translations and rotations in all degrees of displacement].

The investigation of biomechanical problems often makes it necessary to measure displacements and rotations in space. An easy-to-handle optical measuring system has been developed that permits non-contact simultaneous determination of small translations and rotations in all degrees of freedom. Three two-dimensional light-sensitive sensors (PSD [position sensing detector] elements) were arranged spatially to form a measuring sensor. After processing in a computer, the signals definitively determine relative shift and rotation. Thus it is possible, for example, to measure the relative movement between two adjacent spinal vertebrae under different loads.

Biomechanical Phenomena↗
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

[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↗
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↗
PubMed1979

Total "internal" hemipelvectomy.

Several authors have described resections of tumorbearing parts of the pelvis including reconstructive plastic surgery. With extensive tumor growth present mutilating hemipelvectomies often have been the last resort. Even the most sophisticated prostheses hardly ever enabled the patients to walk again. We have therefore performed total "internal" hemipelvectomies in three cases. The necessary substitute consisted of half a pelvis made of polyacetal resin produced from a given model. The model's measures and shape was established by computer tomograms thus resulting in an individually shaped pelvis half. The operative procedure aims at the maintenance of osseous muscular insertions and origins and their reconstruction. Utmost care has to be taken in avoiding damage to nerves and vessels. Fixation of the implant is performed by screws aiming through the sacroiliac joint into ala and corpus of the sacrum and corticocancellous grafts incorporated in the implant. The symphyses are united by means of plate fixation. The hip joint is substituted by a total prosthesis. With the procedure described we have managed three cases of extensive malignant tumors of the pelvis. One patient suffered a nerve lesion and skin necrosis with infection. The two remaining patients are capable of weight-bearing and standing on the inflicted leg alone.

Adolescent↗
PubMed1979

[Plastic replacement of the abdominal wall by uncoated carbon cloth. An animal experiment on the rabbit (author's transl)].

Carbon cloth is a new biomaterial which is suitable for the replacement of ligaments and connective tissues, because of its biological and physical properties. In 30 rabbits a defect was cut into the abdominal wall. In 20 the defect was covered by an implanted carbon cloth. The other 10 animals were used as controls. After implantation wound healing was excellent. No herniation could be observed in the group with the implants. After 3 months histological examinations revealed the ingrowth of collagen fibres into the carbon cloth. It had become a strong and resilient abdominal wall replacement. A physical-strength test showed stability of the newly formed abdominal wall with good anchorage to normal tissue.

Abdominal Muscles↗
PubMed1979

[Studies on the modification of wound healing by a lack of essential fatty acids].

A fat-free diet produces a deficiency of essential fatty acids in Wistar rats. This is associated with disturbances of wound healing in the colon and skin due to an impaired collagen metabolism, since hydroxyproline content in the wound area is decreased. The results are of clinical significance with regard to total parenteral nutrition in surgical patients.

Animals↗
PubMed1979

[Experimental studies on the biomechanics of the lateral ligaments of the knee joint].

Measurements of absolute strain and stress on collateral ligaments of human knees were made with two new measuring cells. The medial collateral ligament was found to have three functional different parts, the most important of which was the ventral. During motion of the knee, tensile forces amounted to about 20 N when the lateral ligament was in extension and the medial ligament in full flexion. Moments of abduction and adduction increased strain and stress manyfold.

Biomechanical Phenomena↗
PubMed1979

[Studies on the intra-osseous fastening of alloplastic ligament substitutes in sheep using carbon fibers].

The alloplastic replacement of the medial collateral ligament of the knee of sheep by carbon fibers gave a strength comparable with the natural ligament. Coating of the fibers, e.g., with epoxy resin, leads to a reduced integration of the implant into the tissues. Physical and histologic results together with the intraosseus anchorage show that pure carbon fibers are a suitable material for alloplastic ligament replacement.

Animals↗
PubMed1978

[Biomechanical efficiency and biocompatibility of lubricating sprays PTFE or graphite (author's transl)].

The screws and plates used in operative treatment of fractures cause moments of friction between the bone screw head and the bone plate hole during the tightening of the screws. This results in hidden damage to the grinding metal surfaces, with the danger of erosion corrosion and in a reduction in the screw force. By covering the screw heads with the lubricating sprays PTFE or graphite friction was significantly reduced, the screw force increased by 40% and extensive damage to the surfaces avoided. Lubricating sprays or their extracts, in fetal calf serum or in dimethylsulfoxide, were added to fibroblast cultures. Toxicity was manifest as changes in the synthesis of DNA, as measured by autoradiography. Sprays or spray extracts in fetal calf serum did not inhibit cell proliferation. In vivo experiments in rats reflected the in vitro results, there being no evidence that toxic substances were released from the sprays by physiological solvents: There was a lack of histopathological changes in the inner organs and a local encapsulation of implants which was essentially like that in a teflon control group.

Aerosols↗
PubMed1978

[Stability after obtaining cancellous bone from the greater trochanter].

To test the endangered stability after obtaining cancellous bone from the greater trochanter, the ultimate breaking force of 40 human femura was measured with a material testing machine (Instron 1115). 1. 10 Femura after removing bone from the greater trochanter as a routine clinical procedure showed a significantly reduced trochanteric stability (p less than 0.05), 4 subtrochanteric and 3 pertrochanteric fractures, compared to 10 intact opposite femura with vertical shear fractures of femural neck and head without damage to the trochanteric region. 2. The number of fractures crossing the window was reduced by half, p less than 0.05 when a round cortical window compared to when a square window of the same area was cut. As the reduced stability caused by the remove of cancellous bone can not be avoided, we can clearly reduce the danger of stress concentration in the notches by cutting a round corticalis window. Cancellous bone from the greater trochanter should only used, if it cannot be taken from the brim or posterior iliac spine of the pelvis.

Biomechanical Phenomena↗