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Biomedical subjects

L E Claes

Publications and source records attributed to L E Claes.

50 records · Page 3Linked to original sources
PubMed1996

Prediction of fracture load at different skeletal sites by geometric properties of the cortical shell.

Quantitative bone assessment today is primarily based on the analysis of bone mineral density (BMD). The geometric properties of bone, which are an important parameter for skeletal strength, are generally not considered in the routine clinical assessment of osteoporosis. This study combined the geometric properties and the BMD values determined by peripheral quantitative computed tomography (pQCT) at the distal radius and at the femoral neck to predict fracture loads of the radius, femur, and lumbar vertebrae of 20 cadavers. Generalized osteopenia reduced the fracture loads at all three sites (p < 0.001). The strength of the radius and the femoral neck could best be predicted by considering either the second moment of inertia and trabecular BMD (R = 0.93) or the moment of inertia and the cortical BMD (R = 0.91). The geometric properties at the distal radius were highly correlated with the fracture load at the same skeletal site (R = 0.89) and were also used to estimate the fracture risk at the lumbar vertebrae (R = 0.75) and at the femoral neck (R = 0.87). We conclude that both geometry and density contribute substantially to the strength of the skeleton. The screening for osteoporosis and the prediction of fracture risk can be improved, therefore, by an additional consideration of the geometric properties of the cortex.

Aged↗
PubMed1996

[Intradiscal pressure forces on cervical intervertebral discs in physiologic and pathologic conditions. In vitro study].

Clinical and experimental studies concerning intradiscal pressure have mainly been carried out using the lumbar spine. It has been shown that degenerative changes in the intervertebral disc and external loads can significantly influence intradiscal pressure. To see if these findings are also relevant for cervical discs, we carried out an in vitro study using human cervical spine specimens. The specimens were tested biomechanically under various conditions with simultaneous recording of intradiscal pressure in two cervical discs. We were able to confirm in vivo measurements of intradiscal pressure reported in the literature. Simulation of muscle force led to a marked increase in intradiscal pressure. Moreover, it was demonstrated that ventral cervical fusion has a significant influence on intradiscal pressure in both adjacent segments. In general, the results improve our understanding of the basic biomechanics of the cervical spine. The experiments with fused specimens could help to explain why degeneration is accelerated in adjacent motion segments after ventral cervical fusion.

Biomechanical Phenomena↗
PubMed1996

Influence of varying muscle forces on lumbar intradiscal pressure: an in vitro study.

The purposes of this study were to determine the effect of including muscle forces in the experimental loading of the spine on the intradiscal pressure and to determine whether this effect correlates with previously established in vivo data. We modeled the spine muscles as of five distinct groups and isolated the effect of each group on the intradiscal pressure (L4-L5). Seven human lumbosacral spines were tested in pure flexion/extension, right/left lateral bending, and left/right axial rotation moments. Stimulated muscle activity strongly influenced load-pressure characteristics, especially for the multifidus. Without muscle forces active, pressure increased proportionately with increasing moment. With five pairs of symmetrical constant muscle forces active (80 N per pair) the pressure increased more than 200% in neutral position and did not increase with increasing moment. The pressure without muscle forces and without axial preload was 0.12 MPa, which is about the same found by earlier in vivo studies of anesthetized subjects in prone position. With simulated muscle forces, the pressure was 0.39 MPa and in the range found for non-anesthetized subjects. We conclude that simulating muscle forces substantially affects intradiscal pressure.

Adult↗
PubMed1996

New bioresorbable pin for the reduction of small bony fragments: design, mechanical properties and in vitro degradation.

The design, material properties, and in vivo degradation characteristics of a new resorbable pin for the reductions of small bony fragments are described. The Polypin, made of 70:30 poly (L, DL-lactide), had an initial bending strength of 155-163 MPa, as measured by a three-point bending test. Ethylene oxide (EO)- and gamma-sterilization did not substantially affect its initial mechanical properties. The initial molecular weight (Mw) of 523,000 to 600,000, however, decreased 60-75% after gamma-sterilization. Incubation of the EO-sterilized pins in 37 degrees C saline solution produced a complete loss of bending strength at 18 months. An accelerated test at 70 degrees C led to a complete loss of strength after only 96 h. Degradation of the gamma-sterilized pin at 70 degrees C was about 30% faster than that of the EO-sterilized pin. Bending strength and molecular weight were unaffected by storage at room temperature for 46 months. The relatively slow strength loss rate of the Polypin potentially extends the application of resorbable devices to slow-healing fractures. The new pin design allows application of light interfragmentary compression, thus reducing the risk of pin loosening, and an X-ray marker is provided.

Biocompatible Materials↗
PubMed1996

In vitro biocompatibility of bioresorbable polymers: poly(L, DL-lactide) and poly(L-lactide-co-glycolide).

The acute toxicity of two degradable polymers, a 70:30 poly (L-D, L-lactide) (PLDLA) and a 90:10 poly(L-lactide-co-glycolide) (PLGA), was evaluated by the agar diffusion test and the filter test with L929 mouse fibroblasts. Extracts of the materials prepared in phosphate-buffered saline at 37 and 70 degrees C were assessed for mitochondrial succinate dehydrogenase activity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT assay) and the incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA of BALB 3T3 cells. Both materials revealed no signs of cytotoxicity during the agar diffusions and filter tests. In the MTT and BrdU assays PLDLA and PLGA showed similar results. Cells treated with extracts prepared at 37 degrees C caused slight stimulation of mitochondrial activity. In contrast, cells incubated with the 70 degrees C media revealed a concentration-dependent decrease of mitochondrial activity. DNA synthesis was significantly decreased by the 37 degrees C extracts. As in the MTT assay, the effect of the extracts prepared at 70 degrees C was significantly greater. From these in vitro results it is suggested that PLDLA and PLGA have satisfactory biocompatibility. High concentrations of the degradation products, however, had a toxic influence on the cell culture systems used.

3T3 Cells↗
PubMed1996

Formalin fixation strongly influences biomechanical properties of the spine.

As fresh human cadaveric spine specimens for in vitro testing are hard to obtain and carry a potential risk of infection, the possibility of using embalmed spine specimens has been considered. The cross-linking effect of formalin fixation, however, raises uncertainties regarding the biomechanical likeness of preserved specimens. They have been reported to be stiffer, but no quantitative data exist. The purpose of this study was to determine the biomechanical differences between fresh and formalin-fixed spine specimens, using L1-2 motion segments from six 16-week-old calf spines. The range of motion and neutral zone were determined in flexion-/extension, left/right axial rotation, and right/left lateral bleeding. The range of motion decreased in the formalin fixed specimens by as much as 80%, and the neutral zone by as much as 96%. The results of this study therefore imply that, for biomechanical testing, formalin-fixed specimens are not representative of the in vivo conditions.

Animals↗
PubMed1995

Stability increase of the lumbar spine with different muscle groups. A biomechanical in vitro study.

STUDY DESIGN: This study investigated the influence of five different muscle groups on the monosegmental motion (L4-L5) during pure flexion/extension, lateral bending, and axial rotation moments. OBJECTIVES: The results showed and compared the effect of different muscle groups acting in different directions on the stability of a single motion segment to find loading conditions for in vitro experiments that simulate more physiologically reasonable loads. SUMMARY OF BACKGROUND DATA: In spine biomechanics research, most in vitro experiments have been carried out without applying muscle forces, even though these forces stabilize the spinal column in vivo. METHODS: Seven human lumbosacral spines were tested in a spine tester that allows simulation of up to five symmetrical muscle forces. Changing pure flexion/extension, lateral bending, and axial rotation moments up to +/- 3.75 Nm were applied without muscle forces, with different muscle groups and combinations. The three-dimensional monosegmental motion was determined using an instrumented spatial linkage system. RESULTS: Simulated muscle forces were found to strongly influence load-deformation characteristics. Muscle action generally decreased the range of motion and the neutral zone of the motion segments. This was most evident for flexion and extension. After five pairs of symmetrical, constant muscle forces were applied (80 N per pair), the range of motion decreased about 93% in flexion and 85% in extension. The total neutral zone for flexion and extension was decreased by 83% muscle action. The multifidus muscle group had the strongest influence. CONCLUSION: This experiment showed the importance of including at least some of the most important muscle groups in in vitro experiments on lumbar spine specimens.

Adult↗
PubMed1995

Biological response to ligament wear particles.

In ligament replacement cases where the artificial ligament has worn and partially or totally ruptured, the released wear particles have been associated with a chronic synovitis that inhibits integration of the ligament and contributes to the ultimate failure of the device. In this study, the biological response to ligament wear particles from nine different artificial ligaments was quantitatively evaluated in vivo. Wear particles, the majority of which were < 7 microns, were generated in vitro. These particles were injected into rabbit knee joints, and the biological response as well as the systemic migration of the particles were evaluated histologically after 4 weeks. The extent of the inflammatory reaction to the ligament wear particles was found to be significantly (p < 0.05) influenced by the type of material implanted. No particles were found in the regional lymph nodes or in the spleen, liver, kidney, or lung.

Animals↗
PubMed1995

Osteonal structure better predicts tensile strength of healing bone than volume fraction.

Refractures and secondary fractures occur after removal of internal fixation devices even when the X-rays show well-mineralized bony unions. This indicates the unreliability of bone density as the only parameter to estimate the strength of healing bone. The aim of this study was to show that the strength of healing bone is more influenced by microstructural parameters than by bone density. A drill hole defect in the sheep tibia was used to investigate bone healing under stable conditions. After 4, 6, 9, 12, 24 and 104-week healing periods, bone specimens were taken from the healing zone and tested mechanically as well as histo-morphologically. The bone volume fraction in the defect increased at the beginning faster than the strength. In the later phase (> 24 weeks) the bone remodeling process dominated with little increase in bone volume fraction but an increase in strength. The increase in strength was linearly correlated to the orientation of the bone lamellae. Orientation of the bone lamellae which cannot be well visualized in a clinical X-ray, relates to strength more than density. Because only density and not microstructure can be well demonstrated in a clinical X-ray, a radiographically 'healed' defect may not reflect structural restoration for many years.

Animals↗
PubMed1995

Effect of dynamization on gap healing of diaphyseal fractures under external fixation.

We asked whether dynamization of externally fixed diaphyseal fractures could improve bone healing in comparison to rigid fixation of fractures having similar remaining gap sizes. To answer this question we evaluated metatarsal osteotomies in 12 sheep. The osteotomy with a 0.6-mm gap was stabilized with a specially designed high bending and torsional stiffness external ring fixator. Osteotomies in six sheep were stabilized rigidly (axial movement < 0.06 mm) or dynamically (axial movement 0.15-0.34 mm). The cyclical axial interfragmentary movement was caused by the load-bearing of the operated limb. With increasing healing time, the initially allowed movement was decreased by callus formation around the osteotomy. The reduction in interfragmentary movement was measured and monitored by a linear variable displacement transducer at the external fixator and a telemetry system. After 9 weeks the sheep were sacrificed and the healed bones were investigated biomechanically and histomorphologically. Compared to the rigidly fixed osteotomies, the dynamized osteotomies showed significantly (P < 0.05) greater (+41%) callus formation and 45% greater tensile strength of the newly formed bone in the cortical osteotomy gap. Histological analysis indicated that the effect of dynamization occurred mainly after the 5th week. RELEVANCE: From these results we conclude that dynamic fixation of diaphyseal gaps is advantageous in comparison to stable external fixation.

Journal Article↗
PubMed1994

Comparative investigation on the biomechanical properties of ligament replacement in the sheep knee using six different ligament prostheses.

Six different ligament prostheses were implanted in 40 sheep to replace the anterior cruciate and medial collateral ligament of the right knee. After one year the explanted knee joints were tested for stability by measurement of the anterior drawer. Tensile tests on the ligament replacements were performed to determine the stiffness and rupture force of the replacement. Gross inspection of the knee joint showed abrasion and partial ruptures for all types of prostheses after one year. Depending on the type of prosthesis total rupture rates between 0 and 66% of all implants could be seen. The anterior drawer for the operated knee was 3-4 times higher than for the non-operated contralateral side. Neither the stiffness nor the rupture strength of the replacements reached the biomechanical properties of the normal ligaments.

Animals↗
PubMed1992

Mechanical characterization of biodegradable implants.

The mechanical properties of degradable implant materials are low in comparison to metals used in orthopaedic surgery. There are possibilities to improve the strength of degradable implants by self-fibre-reinforcement, high molecular weight or special manufacturing processes. However, the moduli of the materials cannot be increased significantly by these techniques. Comparison of the mechanical properties of the most important materials are shown. Creep and relaxation are characteristic properties of degradable materials and limit the use of load-carrying implants. The rate of degradation in vitro and in vivo shows larger differences between the various materials and range from a few weeks up to 3 years.

Biodegradation, Environmental↗
PubMedDate not supplied

[Functional sequelae of surgical decompression of the lumbar spine--a biomechanical study in vitro].

PURPOSE: Dorsal decompression has become accepted as the standard surgical treatment for spinal stenosis. However, no consensus has been reached to date concerning the extent of resectioning required or the ensuing functional impairment of the segment. As a result, a discussion is now underway on the necessity of employing various additional methods for instrumented stabilisation. The aim of this biomechanical in vitro study is to objectify the functional impact of various defined decompression techniques. METHODS: With the aid of a universal spine tester, the increasing defect situations following left hemifacetectomy, bilateral hemifacetectomy, left hemilaminotomy and laminectomy of the functional spinal unit L4/5 were assessed. A three-dimensional motion analysis was performed on six human lumbar spine specimens under the loading conditions flexion/extension, left/right bending and right/left rotation. RESULTS: The results showed an increase in both the neutral zone and the range of motion under all the loading components. No significant differences were observed in coupled motions following decompression. CONCLUSIONS: Laminectomy leads to a distinct instability and the question arises of how much additive stability achieved by instrumented stabilization will be adequate.

Adult↗