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Biomedical subjects

L E Claes

Publications and source records attributed to L E Claes.

At least 37 records · Page 2Linked to original sources
PubMed2000

Spinal biomechanics and aging are major determinants of the proteoglycan metabolism of intervertebral disc cells.

STUDY DESIGN: The proteoglycan metabolism of ovine disc nucleus pulposus and anulus fibrosus cells was investigated in relation to age, spinal level, and intrinsic spinal biomechanical properties. OBJECTIVE: To evaluate the hypothesis that with aging loss of proteoglycans from the lumbosacral disc exceeds that from upper lumbar discs because of its proximity to a rigid segment, the sacrum. SUMMARY OF BACKGROUND DATA: The proteoglycan and associated water of the disc decreases with aging. METHODS: Proteoglycans were extracted directly from the disc tissues using 4 M GuHCl and examined by composite agarose polyacrylamide gel electrophoresis. Disc cells were cultured in alginate beads, and their metabolic activity was assessed by 3H-thymidine incorporation into DNA and by bioreduction of a cell proliferation dye. Newly synthesized proteoglycans were radiolabeled with 35S, and their molecular weight distributions and ability to aggregate with hyaluronan were determined by Sephacryl S1000 gel chromatography. Resident proteoglycans extracted from disc tissues with 4 M GuHCl were similarly evaluated. A group of adult animals also were studied biomechanically to evaluate the range of spinal motion (L4/L5 to L7/S1). RESULTS: In contrast to the neonatal proteoglycan samples, the biosynthesis of proteoglycans by nucleus pulposus cells of adult discs increased progressively toward the sacrum. This correlated with increased metabolic activity. Analysis of the resident proteoglycans by composite agarose polyacrylamide gel electrophoresis indicated that although the aggrecan-1 population was present almost exclusively in the neonatal group, it was the aggrecan-2 population that predominated in the adult discs, and it became progressively more heterogeneous with aging and proximity of the disc to the sacrum. CONCLUSIONS: The proteoglycans of the lumbosacral disc of adult animals turned over faster than proteoglycans of adjacent lumbar discs. The reduced proteoglycan content and ability to aggregate, particularly in the nucleus pulposus of lumbosacral discs, indicated that proteoglycan catabolism exceeded the rate of biosynthesis. These events in the lumbosacral disc are thought to be determined mechanically by its proximity to the sacrum.

Aging↗
PubMed1999

New in vivo measurements of pressures in the intervertebral disc in daily life.

STUDY DESIGN: We conducted intradiscal pressure measurements with one volunteer performing various activities normally found in daily life, sports, and spinal therapy. OBJECTIVES: The goal of this study was to measure intradiscal pressure to complement earlier data from Nachemson with dynamic and long-term measurements over a broad range of activities. SUMMARY OF BACKGROUND DATA: Loading of the spine still is not well understood. The most important in vivo data are from pioneering intradiscal pressure measurements recorded by Nachemson during the 1960s. Since that time, there have been few data to corroborate or dispute those findings. METHODS: Under sterile surgical conditions, a pressure transducer with a diameter of 1.5 mm was implanted in the nucleus pulposus of a nondegenerated L4-L5 disc of a male volunteer 45-years-old and weighing 70 kg. Pressure was recorded with a telemetry system during a period of approximately 24 hours for various lying positions; sitting positions in a chair, in an armchair, and on a pezziball (ergonomic sitting ball); during sneezing, laughing, walking, jogging, stair climbing, load lifting during hydration over 7 hours of sleeping, and others. RESULTS: The following values and more were measured: lying prone, 0.1 MPa; lying laterally, 0.12 MPa; relaxed standing, 0.5 MPa; standing flexed forward, 1.1 MPa; sitting unsupported, 0.46 MPa; sitting with maximum flexion, 0.83 MPa; nonchalant sitting, 0.3 MPa; and lifting a 20-kg weight with round flexed back, 2.3 MPa; with flexed knees, 1.7 MPa; and close to the body, 1.1 MPa. During the night, pressure increased from 0.1 to 0.24 MPa. CONCLUSIONS: Good correlation was found with Nachemson's data during many exercises, with the exception of the comparison of standing and sitting or of the various lying positions. Notwithstanding the limitations related to the single-subject design of this study, these differences may be explained by the different transducers used. It can be cautiously concluded that the intradiscal pressure during sitting may in fact be less than that in erect standing, that muscle activity increases pressure, that constantly changing position is important to promote flow of fluid (nutrition) to the disc, and that many of the physiotherapy methods studied are valid, but a number of them should be re-evaluated.

Circadian Rhythm↗
PubMed1999

Magnitudes of local stress and strain along bony surfaces predict the course and type of fracture healing.

A new quantitative tissue differentiation theory which relates the local tissue formation in a fracture gap to the local stress and strain is presented. Our hypothesis proposes that the amounts of strain and hydrostatic pressure along existing calcified surfaces in the fracture callus determine the differentiation of the callus tissue. The study compares the local strains and stresses in the callus as calculated from a finite element model with histological findings from an animal fracture model. The hypothesis predicts intramembranous bone formation for strains smaller approximately +/- 5% and hydrostatic pressures smaller than +/- 0.15 MPa. Endochondral ossification is associated with compressive pressures larger than about -0.15 MPa and strains smaller than +/- 15%. All other conditions seemed to lead to connective tissue or fibrous cartilage. The hypothesis enables a better understanding of the complex tissue differentiation seen in histological images and the mechanical conditions for healing delayed healing or nonunions.

Animals↗
PubMed1999

Multiple muscle force simulation in axial rotation of the cervical spine.

OBJECTIVE: To produce axial rotation of the cervical spine in vitro by coordinated application of eight simulated muscle forces. DESIGN: Biomechanical testing of the cervical spine by controlled pneumatics. BACKGROUND: Some muscle simulation experiments have been performed in vitro in the lumbar spine but data generally are lacking for this testing mode in the cervical spine. Thus, physiological biomechanical behavior in this region remains poorly understood. METHODS: Six human donor cervical spines were loaded by a set of computer-controlled pneumatic cylinders representing pairs of trapezius, splenius and sternocleiodmastoid muscles, plus longus and splenius colli left. Muscle functions were derived from a previously-developed mathematical optimization model. Muscle forces generally were achievable within 2 N of the intended values provided by the model. RESULTS: Rotation of the head followed fairly closely that predicted by the model. The resulting force components to produce 37 degrees were dominated by axial compression of about--100 N and the resulting moments were similar in all planes at about 2 Nm. Coupled motions were larger than primary motions in some intersegmental behavior. CONCLUSIONS: Slow, physiologic axial rotation of the head may be simulated by a complex and representative series of controlled pneumatics. Controlled rotation results in a relatively high compressive force and occurs through fairly balanced and small moments. RELEVANCE: Experimental approaches in biomechanics are generally limited to one or two simplified muscle forces whose representation of in vivo loading conditions can only be presumed. Improvements in the application of pneumatic technology are a promising approach to more thoroughly duplicating the physiological loading environment.

Aged↗
PubMed1999

Predictive value of bone mineral density and Singh index for the in vitro mechanical properties of cancellous bone in the femoral head.

OBJECTIVE: The purpose of this study was to assess the validity of two methodically different radiological parameters, bone mineral density and Singh Index, for the prediction of mechanical properties in femoral cancellous bone. DESIGN: Coherence between in vitro evaluation of mechanical properties and bone mineral density on a femoral bone slice, combined with clinical determination of Singh Index on ordinary X-rays. BACKGROUND: It is accepted that bone densitometry yields excellent prediction of mechanical bone quality, but is considered to be an expensive and not widely available method for routine diagnostics in clinical practice. In contrast, determination of Singh Index is an inexpensive and simple technique, but its predictive value for bone mechanics is still controversially discussed. METHODS: We used cortically confined bone slices from 33 femoral heads. Bone mineral density was measured using quantitative computed tomography. Strength and elastic modulus were assessed by mechanical testing in up to 39 circular positions on each slice. Singh Index was evaluated on ordinary X-rays of the hip by two independent readers. RESULTS: Bone mineral density showed strong correlations with strength (r=0.86) and good correlations with elastic modulus (r=0.68). Singh Index correlated well with strength (r=0.70), but only moderately with elastic modulus (r=0.52). CONCLUSIONS: The strong validity of bone mineral density in predicting mechanical bone quality was confirmed. Singh Index assessment permits a rough estimation of mechanical strength in particular and can therefore be used for first estimations of mechanical bone quality, provided that readings were performed by experienced clinicians. RELEVANCE: Reduced mechanical bone quality induces an increase in fracture risk. Whenever performed, bone mineral density measurement allows an excellent evaluation of the mechanical properties of cancellous bone in the hip and can be recommended for screening evaluations. The assessment of Singh Index on ordinary X-rays of the hip is an inexpensive and simple method, and allows a rough estimation of the mechanical quality of the femur. However, due to its subjective character, its predictive value for the mechanical quality of bone in individual patients remains uncertain.

Aged↗
PubMed1999

Intradiscal pressure recordings in the cervical spine.

OBJECTIVE: Experimental investigations analyzing the biomechanics of the cervical spine are less common than similar studies of other regions of the spine. There are no reports on cervical intradiscal pressure (PID) measurements in vitro. We therefore wanted to establish normal values for PID under physiological conditions by simultaneous muscle force simulation. Moreover, the impact of ventral cervical fusion should be elucidated, because in clinical studies, it is a well-known phenomenon that the adjacent segments often show increased degenerative changes. We present a pilot study. METHODS: Seven human cervical spine specimens were tested biomechanically in a specially developed spine tester. Only pure moments were used for flexion/extension, axial rotation, and lateral bending (maximal moment +/- 0.5 Nm). PID was measured simultaneously in C3-C4 and C5-C6. The specimens were tested as intact specimens and after discectomy and fusion in C4-C5. Both test situations were repeated with simulation of muscle forces. RESULTS: We found characteristic load-pressure curves for each of the three motion axes. In neutral position, PID correlated well with former published data from in vivo measurements. After fusion of C4-C5, there was a marked increase of PID in both adjacent segments (e.g., < or = 180% for axial rotation). With muscle force simulation, the increase was even higher (e.g., < or = 400% for axial rotation). CONCLUSION: For the first time, PID could be measured in the cervical spine in an experimental setting. The results obtained using normal specimens under physiological conditions confirmed those reported in two clinical studies. After cervical fusion, a marked increase in PID could be found in both adjacent segments. Presuming that an increase in PID had a negative effect on metabolism of the intervertebral disc, our results may help to explain why progressive degeneration occurs in these segments.

Adult↗
PubMed1998

Importance of the intersegmental trunk muscles for the stability of the lumbar spine. A biomechanical study in vitro.

STUDY DESIGN: A biomechanical study was performed to determine the consequences of a simulation of muscle forces on the loads imposed on the functional spinal units. OBJECTIVES: No biomechanical study has investigated the effect of incorporation of agonist and antagonist muscle forces on the loading of functional spinal units. SUMMARY OF BACKGROUND DATA: Spinal disorders and low back pain are increasingly becoming a worldwide problem. Traditional conservative therapies are intended to strengthen the muscles of the trunk using a judicious regimen of physical exercises. METHODS: Eighteen whole, fresh-frozen human cadaveric lumbar spine specimens (L2-S2; average age, 53.4 years) were tested in a spine tester using pure flexion-extension, lateral bending, and axial moments. The effects of coactivation of psoas and multifidus muscles on L4-L5 mobility were simulated in vitro by applying two pairs of corresponding force vectors to L4. The segmental stability was defined by the correlation of an applied moment to the resultant deformation as shown in load-displacement curves, and the range of motion was defined as the angular deformation at maximum load. RESULTS: The coactivation of muscles was accompanied by a 20% decrease in the range of motion (i.e., a significant increase in stability) during lateral bending and axial moments. Application of flexion-extension moments and muscle coactivation resulted in a 13% increase in the sagittal range of motion. CONCLUSIONS: The action of the intersegmental agonist and antagonist muscles biomechanically increases the overall stiffness (stability) of the intervertebral joints in axial torque and lateral bending, whereas it may destabilize the segment in flexion.

Biomechanical Phenomena↗
PubMed1998

Spinal segment range of motion as a function of in vitro test conditions: effects of exposure period, accumulated cycles, angular-deformation rate, and moisture condition.

BACKGROUND: The purpose of this study was to thoroughly evaluate the relationship of possible mechanical and environmental conditions in the testing of spinal joint segments, including ambient-temperature exposure, accumulated test cycles, angular-deformation rate, and moisture condition on the motion characteristics of joints, with the example of isolated spinal segments. METHODS: In one test, controlled loading was applied to six motion segments every 8 hours in each of the primary anatomical directions while moisture was held constant. In a second test, 18 specimens were divided equally into moisture-static, air-exposed, and slowly irrigated groups and loaded to 500 cycles. In a third test, a similar sample was tested over a range of angular-deformation rates (0.6-5.1 degrees/second). RESULTS: Range of motion (ROM) increased steadily with ambient-temperature exposure time, resulting in a 10% change at about 20 hours but was most stable in the moisture-static group over both accumulated load cycles and loading rate changes. CONCLUSIONS: The most critical factor for functional testing of spinal segments appears to be length of exposure.

Animals↗
PubMed1998

Effects of mechanical factors on the fracture healing process.

An interdisciplinary study based on animal experiments, cell culture studies, and finite element models is presented. In a sheep model, the influence of the osteotomy gap size and interfragmentary motion on the healing success was investigated. Increasing gap sizes delayed the healing process. Increasing movement stimulated callus formation but not tissue quality. Typical distributions of intramembranous bone, endochondral ossification, and connective tissue in the fracture gap are quantified. The comparison of the mechanical data determined by a finite element model with the histologic images allowed the attribution of certain mechanical conditions to the type of tissue differentiation. Intramembranous bone formation was found for strains smaller than approximately 5% and small hydrostatic pressure (< 0.15 MPa). Strains less than 15% and hydrostatic pressure more than 0.15 MPa stimulated endochondral ossification. Larger strains led to connective tissue. Cell culture studies on the influence of strain on osteoblasts supported these findings. Proliferation and transforming growth factor beta production was increased for strains up to 5% but decreased for larger strains. Osteoblasts under larger strains (> 4%) turned away from the principal strain axis and avoided larger deformations. It is hypothesized that gap size and the amount of strain and hydrostatic pressure along the calcified surface in the fracture gap are the fundamental mechanical factors involved in bone healing.

Animals↗
PubMed1998

Tenodeses destroy the kinematic coupling of the ankle joint complex. A three-dimensional in vitro analysis of joint movement.

To study the effect of ligament injuries and surgical repair we investigated the three-dimensional kinematics of the ankle joint complex and the talocrural and the subtalar joints in seven fresh-frozen lower legs before and after sectioning and reconstruction of the ligaments. A foot movement simulator produced controlled torque in one plane of movement while allowing unconstrained movement in the remainder. After testing the intact joint the measurements were repeated after simulation of ligament injuries by cutting the anterior talofibular and calcaneofibular ligaments. The tests were repeated after the Evans, Watson-Jones and Chrisman-Snook tenodeses. The range of movement (ROM) was measured using two goniometer systems which determined the relative movement between the tibia and talus (talocrural ROM) and between the talus and calcaneus (subtalar ROM). Ligament lesions led to increased inversion and internal rotation, predominantly in the talocrural joint. The reconstruction procedures reduced the movement in the ankle joint complex by reducing subtalar movement to a non-physiological level but did not correct the instability of the talocrural joint.

Aged↗
PubMed1997

Are sheep spines a valid biomechanical model for human spines?

STUDY DESIGN: Range of motion, neutral zone, and stiffness parameters of the complete cervical, thoracic, and lumbar sheep spine were determined in flexion and extension, axial left/right rotation, and right/left lateral bending. OBJECTIVES: To determine quantitative biomechanical properties of the sheep spine and compare them with those from the human spine. SUMMARY OF BACKGROUND DATA: Sheep spines often serve as a model for experimental in vivo and in vitro studies in spine research, but few quantitative biomechanical data from sheep spines for comparison with human specimens are available. METHODS: Complete spines were sectioned into single-joint segments and tested in a spine tester under pure moments in the three main anatomic planes. RESULTS: The craniocaudal variation in range of motion in all load directions was qualitatively similar between sheep spines and values reported in the literature for human specimens. CONCLUSIONS: Based on the biomechanical similarities of sheep and human spines demonstrated in this study, it appears that the use of the sheep spine, which already includes evaluation of surgical techniques and bone healing processes, might be extended to spinal implants.

Animals↗
PubMed1997

Anatomy of the sheep spine and its comparison to the human spine.

BACKGROUND: The sheep spine is often used as a model for the human spine, although the degree to which these spines are anatomically comparable has yet to be categorically established. The purpose of this study was to investigate the characteristic anatomical dimensions of the sheep spine and to compare these with existing human data. METHODS: Five complete spines were measured to determine 21 dimensions from the pedicles, spinal canal, transverse and spinous processes, facets, endplates, and disc. RESULTS: The results showed that sheep and human vertebrae are most similar in the thoracic and lumbar regions, although they show substantial differences in certain dimensions. Morphological variations as a function of spine level typically were well matched in the two species. CONCLUSIONS: Sheep spine may be a useful model for experiments related to the gross structure of the thoracic or lumbar spine, with certain limitations for the cervical spine. A thorough database has been provided for deciding the appropriateness of using the sheep spine as a model for the human spine.

Animals↗
PubMed1997

Load-displacement properties of the thoracolumbar calf spine: experimental results and comparison to known human data.

The availability of human cadaveric spine specimens for in vitro tests is limited and the risk of infection is now of vital concern. As an alternative or supplement, calf spines have been used as models for human spines, in particular to evaluate spinal implants. However, neither qualitative nor quantitative biomechanical data on calf spines are available for comparison with data on human specimens. The purpose of this study was to determine the fundamental biomechanical properties of calf spines and to compare them with existing data from human specimens. Range of motion, neutral zone, and stiffness properties of thoracolumbar calf spines (T6-L6) were determined under pure moment loading in flexion and extension, axial left/right rotation and right/left lateral bending. Biomechanical similarities were observed between the calf and reported human data, most notably in axial rotation and lateral bending. Range of motion in the lumbar spine in flexion and extension was somewhat less in the calf than that typically reported for the human, though still within the range. These results suggest that the calf spine can be considered on a limited basis as a model for the human spine in certain in vitro tests.

Animals↗
PubMed1997

NOVEL Award 1996: 2nd prize Tenodeses do not fully restore ankle joint loading characteristics: a biomechanical in vitro investigation in the hind foot.

OBJECTIVE: In order to understand the biomechanical consequences of ligament injuries and surgical reconstruction procedures, their effects on intra-articular loading in the ankle joint complex and Chopart joint line and on the plantar pressure patterns were investigated in vitro. METHODS: Twelve fresh-frozen lower leg specimens were freed of soft tissue down to the malleoli and prepared for accessing the talocrural, subtalar, talonavicular and calcaneocuboid joints. The specimens were fixed in a loading simulator and axially loaded with 600 N in six experimental conditions: intact; after cutting the anterior talofibular ligament; after additionally cutting the calcaneofibular ligament; after performing three common types of tenodeses, the Evans, Watson-Jones and Chrisman-Snook procedures. The intra-articular loading characteristics were determined with pressure sensitive film. Plantar loading patterns were measured with a capacitive EMED pressure distribution platform. RESULTS: Average intra-articular pressures were increased and were related either to decreased contact areas or to increased contact forces found in all joints after ligament resections and tenodeses. Plantar loading was increased under the medial aspect of the foot and decreased under the midfoot region. CONCLUSIONS: The results indicate that ankle ligament injuries, as well as surgical reconstructions by tenodeses, affect joint loading characteristics and may exacerbate joint degeneration. RELEVANCE: Excessive laxity of the ankle joint is considered a pre-arthrotic condition and is treated with various surgical procedures. Some of these procedures that utilize the tendon of the peroneus brevis have been shown to change joint kinematics. The aim was to evaluate joint loading characteristics and the potential danger of developing arthritis as a consequence of various tenodeses techniques. For this purpose, in vitro investigations are needed to directly determine intra-articular pressure measurements.

Journal Article↗
PubMed1997

A mechanical model of human spinal motion segments.

A modular mechanical model of the spine was developed which can be adapted to approximate the mechanical properties of various spinal levels and pathologic conditions in single- or multi-segmental forms. The characteristics of the model were compared with those of human L4-5 specimens in flexion and extension, axial rotation and lateral bending. The model showed comparable ranges of motion to those of human specimens in all directions and likewise was characterized by increasing stiffness with increasing load as well as hysteresis. This model can be used as a standard for the comparison of different spine testers. As a substitute for cadaveric specimens in implant testing, these models provide the advantages of availability, consistent properties, and adaptability, and avoid the risks associated with handling human tissue.

Adult↗
PubMed1996

In situ rigidity of a new sliding rod for management of the growing spine in Duchenne muscular dystrophy.

STUDY DESIGN: This biomechanical, in vitro laboratory study determined the static stiffness of a new telescoping rod and the axial motion of this implant during various loading conditions. OBJECTIVES: To compare the stability of the new telescoping rod with the classic Luque instrumentation, and to determine whether the sliding rod elongates or contracts during spine motion. SUMMARY OF BACKGROUND DATA: A new telescoping rod was developed to stabilize the spine in children with Duchenne muscular dystrophy and to provide capacity for spinal growth. METHODS: The stability of 11 instrumented calf spines was determined in flexion, extension, lateral bending, and torsion to determine the stiffnesses of the spines instrumented with these two implants. The telescoping motion in the left and right rod was measured in the new rod system. RESULTS: In flexion, the spines with the telescoping rods were stiffer than those with the Luque implant. However, no significant differences in the stiffness coefficients were found for extension, lateral bending, or torsion. The restoring force of the telescoping system was greater than that of the Luque system in all directions. All modes of loading produced an accommodating change of length in the construct. CONCLUSIONS: The dynamic telescoping system provides stiffness comparable with that of established systems while allowing elongation during growth of the young patient.

Animals↗
PubMed1996

Identification and distribution of synthetic ligament wear particles in sheep.

After one year, wear of medial collateral ligament replacements in sheep resulted in the presence of large numbers of wear particles and fibers in the joint space. This study examined the frequency of transport of these particles to the regional lymph nodes and to the liver and spleen. Inguinal, iliac, and paraaortic nodes were examined with regular and polarized light for the presence of particles presumably originating from polyethylene, aramid, polytetrafluoroethylene, polyesterterephthalate, polylacticacid, and carbon ligaments. Lymph nodes from sheep that had received tendon autograft replacements were also evaluated. Particles were observed in 33% of all nodes and in at least one node in 84% of all sheep. Particles were found in contralateral nodes, but not in the spleen or liver. Particles were observed usually as intracellular in foamy histiocytes, although extracellular carbon fibers and extracellular aramid fibers were also seen. Giant cells were occasionally detected in the polytetrafluoroethylene, polyethylene, and aramid nodes. In the polytetrafluoroethylene nodes and in the autograft nodes particles containing Mg, Si, and Fe were identified by elemental analysis. The morphological similarities between various birefringent particles and the particles indirectly identified as talc have led us to question the identification of wear debris solely on the basis of birefringence.

Animals↗