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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
PubMed1994

A universal spine tester for in vitro experiments with muscle force simulation.

We report a new apparatus to determine the quasistatic, three-dimensional, load-displacement characteristics of spines including muscle forces. The loading frame can be adapted to mono- and polysegmental specimens from the lumbar or cervical spine as well as to entire spines. Three force and three moment components can be applied in either direction individually or in combination with no constraint on the resulting motion; the loads can be applied at user-chosen rates of application and release with continuous recording of displacements, so as to study either creep or relaxation. The loads and displacement-measuring devices are computer-controlled. Thus, this testing device provides a tool for many kinds of stability tests and for basic research of spine biomechanics. A first experiment shows that the application of muscle forces significantly affects the load-deformation characteristics and intradiscal pressure.

Biomechanical Phenomena↗
PubMed1994

Gait pattern analysis after ankle ligament reconstruction (modified Evans procedure).

We followed 38 patients with chronic ankle instability treated by a modified Evans procedure. Evaluation at an average of 68 months follow-up included a standard clinical questionnaire and examination, radiological procedures, and gait analysis. Plantar pressure distribution measurements were recorded during walking and were compared with data from a group of normal subjects (N = 100). The subjective patient questionnaire revealed 87% good or excellent results, but residual pain was reported by 40% of the patients. The gait analysis indicated a significant increase in midfoot loading (22%) consistent with an observed restriction of inversion after surgery. However, the plantar pressure changes were not associated with poor clinical outcome. We cannot say whether these increased pressures will be associated with long-term outcome.

Adult↗
PubMed1994

[A three-dimensional goniometer linkage system for the analysis of movement with six degrees of freedom].

A measuring system for the determination of the six degrees of freedom of three-dimensional movements is described. The main advantages of this goniometer linkage system are ease of handling and good cost-quality relationship. For small movements it has an accuracy of about 0.1 mm and 0.1 degree. Six potentiometers are rod-linked in such a way that the system can follow any movement, unconstrained. From the rotation of the potentiometers, the spatial movement of two solid bodies can be calculated by a computer. The reliability of the system has been demonstrated in several in vitro and in vivo applications.

Biomechanical Phenomena↗
PubMed1994

[Report of the Biodegradable Implants Study Group].

There is a group for the development and testing of biodegradable implants within the German Section of AO/ASIF-International. After in-vitro screening of various polylactide materials and copolymers a L/DL-polylactide 70/30 was selected. In animal experiments it showed long durability over a period of 9 months and expected degradation afterwards. In clinical experience over more than three years the biodegradable pins with x-ray opaque markers (Polypin) applied for fixation of osteochondral lesions yielded good results and no infections. A multicenter clinical study now includes 57 patients. Polypin is the first biodegradable implant of the AO/ASIF-group.

Animals↗
PubMed1993

Stress diagnostics of the sprained ankle: evaluation of the anterior drawer test with and without anesthesia.

This study investigated the effect of anesthesia of the peroneal communis nerve on stress diagnostics in acute ankle ligament rupture. Using a special holding device, the anterior drawer sign was measured under loading of 4 to 15 kg with and without a peroneal nerve block. In 65 patients, we found a highly significant difference between these two conditions. In a total of 110 patients, the measurement of anterior drawer sign was correlated to other diagnostic procedures. Absolute values of mechanical anterior drawer sign had a correlation of 0.479, whereas the difference of the measurements in injured and noninjured feet correlated with 0.582. We suggest anesthesia in stress diagnostics to increase accuracy. The anterior drawer sign alone, even under anesthesia, is not reliable to detect the full extent of the ligament damage.

Adult↗
PubMed1993

[Impaired gait after base fractures of the 5th metatarsal bone].

Between 1982 and 1990, twenty fractures of the base of the fifth metatarsal were treated operatively and followed up for a mean of 4.5 years (range: 1-9 years). All patients were evaluated clinically, roentgenographically and with kinetic gait analysis. A scoring system was used to record and evaluate the clinical and radiological data. Nine patients had an excellent result and nine a good result; one patient had a fair and one a poor result. Examination by kinetic gait analysis showed a gait asymmetry in eleven of the twenty patients, with decreased load on the formerly injured areas of the involved foot and increased load on the corresponding areas of the contralateral foot. However, only three patients had a clinically visible gait disorder. We believe that the gait disorder described is an automatically adopted movement pattern. Its cause lies in the initial pain after the trauma and during the postoperative care and sometimes continues even after the cessation of pain. Kinetic gait analysis allows quantification of asymmetry of gait and clinically non-visible load disorder. Therefore, pain and established gait asymmetry are clinically relevant in such patients because they can be treated specifically.

Adolescent↗
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

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↗