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Biomedical subjects

G Van der Perre

Publications and source records attributed to G Van der Perre.

At least 19 recordsLinked to original sources
PubMed1997

Structural and material mechanical properties of human vertebral cancellous bone.

The structural Young's modulus (i.e. that of the cancellous framework) was determined by non-destructive compressive mechanical testing in the three orthogonal axes of 48 vertebral bone cubes. In addition, the material Young's modulus (i.e. of the trabeculae themselves) was estimated using an ultrasonic technique. Apparent and true density were determined by direct physical measurements. Significant mechanical anisotropy was observed: mean structural Young's modulus varied from 165 MPa in the supero-inferior direction to 43 MPa in the lateral direction. Structural Young's modulus correlated with apparent density, with power-law regression models giving the best correlations (r2 = 0.52-0.88). Mechanical anisotropy increased as a function of decreasing apparent density (p < 0.001). Material Young's modulus was 10.0 +/- 1.3 GPa, and was negatively correlated with apparent density (p < 0.001). In multiple regression models, material Young's modulus was a significant independent predictor of structural Young's modulus only in the supero-inferior direction. The data suggest the presence of two effects in vertebral bone associated with decreasing apparent density and, by implication, bone loss in general: (a) increased mechanical anisotropy, such that there is relative conservation of stiffness in the axial direction compared with the transverse directions; and (b) increased stiffness of the trabeculae themselves.

Adult↗
PubMed1997

The use of an advanced reciprocating gait orthosis by paraplegic individuals: a follow-up study.

This article describes the results of a follow-up study of 14 paraplegic individuals who were fitted with the ARGO (Advanced Reciprocating Gait Orthosis--STEEPER) at least 1 year previously. It was found that 85% were still using the apparatus on a regular basis. The general satisfaction of the users was high, although the functional use was limited. Therapeutic reasons appeared to be the main reason for wearing the ARGO. The points that were most appreciated were the psychological and physiological benefits of standing and walking. Discussion with the users who were paraplegic provided valuable information concerning possible technical improvements to the ARGO.

Adolescent↗
PubMed1997

Prediction of vertebral strength in vitro by spinal bone densitometry and calcaneal ultrasound.

Spinal bone mineral density (BMD) measurements and calcaneal ultrasound were compared in terms of their ability to predict the strength of the third lumbar vertebral body using specimens from 62 adult cadavers (28 females, 34 males). BMD was measured using dual X-ray absorptiometry (DXA) in both vertebra and calcaneus. Quantitative computed tomography (QCT) was used to determine trabecular BMD, cortical BMD, cortical area, and total cross-sectional area (CSA) of the vertebral body. Bone velocity (BV) and broadband ultrasonic attenuation (BUA) were measured in the right calcaneus. Vertebral strength was determined by uniaxial compressive testing. Vertebral ultimate load was best correlated with DXA-determined vertebral BMD (r2 = 0.64). Of the QCT parameters, the best correlation with strength was obtained using the product of trabecular BMD and CSA (r2 = 0.61). For vertebral ultimate stress, however, the best correlation was observed with QCT-measured trabecular BMD (r2 = 0.51); the correlation with DXA-determined BMD was slightly poorer (r2 = 0.44). Calcaneal ultrasound correlated only weakly with both ultimate load and stress with correlation coefficients (r2) of 0.10-0.17, as did calcaneal BMD (r2 = 0.18). Both spinal DXA and spinal QCT were significantly (p < 0.001) better predictors of L3 ultimate load and stress than were either calcaneal ultrasound or calcaneal DXA. Multiple regression analysis revealed that calcaneal ultrasound did not significantly improve the predictive ability of either DXA or QCT for L3 ultimate load or stress. Calcaneal DXA BMD, bone velocity, and BUA correlated well with each other (r2 = 0.67-0.76), but were only modestly correlated with the DXA and QCT measurements of the vertebra. These data indicate that spinal DXA and spinal QCT provide comparable prediction of vertebral strength, but that a substantial proportion (typically 40%) of the variability in vertebral strength is unaccounted for by BMD measurements. Ultrasonic measurements at the calcaneus are poor predictors of vertebral strength in vitro, and ultrasound does not add predictive information independently of BMD. These findings contrast with emerging clinical data, suggesting that calcaneal ultrasound may be a valuable predictor of vertebral fracture risk in vivo. A possible explanation for this apparent discrepancy between in vivo and in vitro findings could be that current clinical ultrasound measurements at the calcaneus reflect factors that are related to fracture risk but not associated with bone fragility.

Absorptiometry, Photon↗
PubMed1996

Effect of salmon calcitonin on femoral bone quality in adult ovariectomized ewes.

The aim of this study was to evaluate the effect of intermittent calcitonin on femoral bone quality in adult ewes from the time of ovariectomy. Six months after the start of the experiment, bone density measurements and mechanical testing (torsion and resonant frequency analysis of the diaphysis and compression of an excised trabecular bone cylinder from the femoral neck) were performed in sham-control and ovariectomized (OVX) ewes treated with placebo or salmon calcitonin (50 or 100 units, 3 times/week). Crystallinity of bone was evaluated by measuring X-ray diffraction line broadening. After OVX, a nonsignificant bone loss was found at all measured sites in the femur (-3 to -9%) together with a decreased biomechanical competence in the trabecular bone (compressive strain -28%, P < 0.05). Treatment with salmon calcitonin, 50 or 100 IU subcutaneously three times a week from the time of ovariectomy, resulted in a significant dose-dependent preservation of bone strength in the trabecular bone of the femoral neck compared with OVX. No adverse effects of calcitonin were observed on bone crystal composition as assessed by diffractiometry. We conclude that in adult ewes intermittent calcitonin treatment from the time of OVX was associated with a significant preservation of cancellous bone strength and strain in trabecular bone of the femoral neck, without affecting crystalline properties of bone.

Animals↗
PubMed1996

Study of the vibrational behaviour of a healing tibia using finite element modelling.

Two finite element models of a fractured tibia with healing callus were developed. In the first model, the callus was modelled at the middle of the diaphysis, while in the second one the callus was located at two-thirds of the length, distal from the knee. From these two models the static torsional stiffness as well as the resonant frequencies and mode shapes of the first four vibration modes were calculated for a series of increasing values of Young's modulus of the callus. Two situations were considered. In the first situation, the geometry of the callus was kept constant, while in the second, the dimensions of the callus were reduced while its Young's modulus was increased. The resonant frequencies were found to increase with increasing stiffness of the callus. The single bending modes were found to be more sensitive when the callus was at the middle of the diaphysis, whereas the double bending modes were more sensitive when the callus was situated distally. Mode shapes were similar to those for the intact tibia when the stiffness of the callus was 5% of the stiffness of the intact bone or higher. A basically linear relation was found between the torsional stiffness and the resonant frequencies. A theoretical relation between resonant frequencies and torsional stiffness was evaluated and found to be valid if the Young's modulus of the callus was equal to or greater than 5% of the Young's modulus of the intact bone. The present results support the quantitative interpretation of vibration analysis measurements for the assessment of tibial fracture healing.

Bony Callus↗
PubMed1996

Ultrasound velocity measurement in long bones: measurement method and simulation of ultrasound wave propagation.

A new method for the measurement of ultrasound velocity in long bones is presented. The method can be applied in vitro as well as in vivo. It automatically corrects for the influence of soft tissue, such that the real velocity in bone is obtained. In a series of simulation experiments, hypotheses on the followed wave path were verified. A very good agreement was found between the measurement obtained in the experimental set-up and the values calculated for the hypothesised wave path in the experimental structure. These simulations revealed the feasibility of the technique to determine the velocity in a local site of the structure. Clinical applications of this technique include the monitoring of callus consolidation after fracture and the detection of bone degenerative diseases such as osteoporosis.

Bone and Bones↗
PubMed1996

Interactive simulation of cranial surgery in a computer aided design environment.

Accurate pre-surgical planning is a prerequisite for successful craniofacial surgery. This paper introduces a simulation system developed in a computer aided design (CAD) environment, where a 3-D mathematical model of the skull is entered. The architecture of the program yields a flexible and easy-to-use system that allows the simulation of surgery on the wire frame image of the model. Possible actions simulated are osteotomy, bending, rotation, translation and removal. Numerical values for anatomical distances and the intracranial volume are easily calculated. Information on the techniques used and the numerical data resulting from the simulation can be stored. Plots of intermediate steps of the simulation or of contours of separate pieces permit feed-back to the operating theatre.

Computer Simulation↗
PubMed1996

A comparison of time-domain and frequency-domain approaches to ultrasonic velocity measurement in trabecular bone.

Different methods for ultrasonic velocity determination using broad-band pulse transmission have been investigated in 70 human calcanae in vitro. The work took place within the context of the EC BIOMED1 concerted action Assessment of Quality of Bone in Osteoporosis. Ultrasonic velocities were determined using three different transit time definitions: first arrival (TTV1), thresholding (TTV2), and first zero crossing (TTV3). Phase velocity (PV) was determined over a range of frequencies from 200 to 800 kHz using a new phase spectral analysis technique. The different velocity measurements were compared in terms of their magnitudes and their inter-correlations. There were significant differences of up to 260 m s-1 between different transit time velocities (p < 0.0001), indicating the sensitivity of the measurement to the arrival criteria used. Phase velocities were lower than all of the transit time velocities (p < 0.0001) and decreased with increasing frequency (p < 0.005). A strong correlation (r2 = 0.968) was observed between PV at 400 kHz (PV400) and TTV3, with much weaker correlations between PV and the other transit time velocities. Reproducibility for transit time velocity measurement was optimal for TTV3 (coefficient of variation, cv = 0.41%), and for PV it was optimal at 600 kHz (cv = 0.34%). These data indicate that transit time measurements may be subject to errors due to the modification of the pulse shape during propagation through bone by attenuation and dispersion. Velocity measurement by phase spectral analysis appears to offer advantages over the transit time approach, and should be the method of choice for velocity measurement in trabecular bone. Where transit time velocity measurements are made, the first-zero-crossing criterion appears to be have some advantages over other arrival criteria. We also note that PV measurements provide new information on dispersion which could prove to be relevant to the structural and mechanical characterization of trabecular bone.

Adult↗
PubMed1996

The effect of fracture and fracture fixation on ultrasonic velocity and attenuation.

Measurement of the velocity of propagation and attenuation of ultrasound (200 kHz) is believed to be a useful non-invasive technique for assessing the mechanical properties of bone. A new method for the determination of ultrasound velocity and attenuation of longitudinal waves in cortical bone was used in vivo and in situ on intact and fractured human tibiae. The measured ultrasound attenuation and velocity were found to be unaffected by the soft tissue between transducers and bone. The ultrasound velocity in vivo on control tibiae was 3614 +/- 32 m s-1 and the attenuation was 5.52 +/- 0.43 dB MHz-1 cm-1. The ultrasound velocity in fractured tibiae was considerably lower 1 week after fracture (2375 +/- 82 m s-1), but had significantly increased after 3 weeks (to 2882 +/- 90 m s-1). A higher attenuation was measured 1 week after fracture (17.81 +/- 3.91 dB MHz-1 cm-1), but it had decreased again 3 weeks after fracture (10.42 +/- 3.56 dB MHz-1 cm-1). In situ studies under well-defined conditions confirmed the in vivo results. The effects of internal plate fixation and gradually cutting through the cortex on the ultrasound velocity and attenuation were studied in situ. These results demonstrate the clinical potential of this technique for the non-invasive assessment of bone fracture healing.

Adult↗
PubMed1995

The influence of geometrical distortions of three-dimensional finite elements, used to model proximal femoral bone.

A realistic three-dimensional finite element model of the proximal femur requires the use of irregularly shaped elements to represent this geometry, unless the geometry is considerably simplified. The authors have investigated the influence of different types of element distortions upon the accuracy of two stresses which are relevant in the proximal femur: the bending stress and the tangential (hoop) stress. While most angular and geometric distortions did not influence the bending stress significantly, the position of the middle node on the edge of a quadratic element was very critical, as were some types of element skewness. The hoop stresses can only be calculated accurately if the geometry is modelled as well as possible by a cylinder, and not by a cone.

Femur↗
PubMed1994

Physical meaning of bone mineral content parameters and their relation to mechanical properties.

The relations between parameters obtained by clinical absorptiometric techniques, such as SPA, DPA, DXA and QCT, and geometrical and material parameters of bone structures are investigated. Two types of bone are considered: the diaphysis of a long bone, modelled as a hollow cylindrical structure consisting of compact bone, and secondly a cylindrical body consisting of trabecular bone. The latter is a model for the vertebral body and for the femoral neck. Parameters investigated are BMD (as gr/cm2) and BMC (as gr/cm). The modeling predicts good agreements between BMD and the wall thickness in the diaphysis of the bone, between BMC and the area of cross section of a long bone and between BMC and the effective area in a body of trabecular bone.

Absorptiometry, Photon↗
PubMed1994

The effect of osteoporosis on the mechanical properties of bone structures.

Since experimental data on the mode of failure of the lumbar vertebral body and the femoral neck scarce, a model predicting their fracture mechanisms under a representative loading is needed. This model should be ask to describe the inference of osteoporosis on the mechanical strength, and should use BMC-measurement date as an input. A simple mechanical model for both structures, composed of a thin-walled cylindrical cortual shell, filled with a trabecular bone core is used. We find that the BMC evaluated as the mineral content in a 1 cm thick section (expressed in g/cm) is a good predictor for the strength of the vertebral body, while for the femoral neck, additional information on the cortical wall thickness is needed.

Absorptiometry, Photon↗
PubMed1994

Vibration, sonic and ultrasonic wave propagation analysis for the detection of osteoporosis.

The feasibility of vibration analysis and wave propagation analysis for the detection of osteoporosis is discussed. The relationship between the resonant frequencies, obtained by vibration analysis, and geometrical and material properties of long bones is found using a simple beam model. This relationship was verified experimentally on 142 excised bones. In vitro measurements for the detection of osteoporosis were performed on excised bones. Using a specific protocol for vibration and ultrasound measurements, a population of osteoporotic patients and age-matched controls were measured. From these measurements was concluded that the bending rigidity, calculated for the resonant frequencies, in osteoporotic patients had decreased as compared to the control group. Also the ultrasound velocity in the tibial cortex was lower in the osteoporotic group.

Adolescent↗
PubMed1993

The relation between resonant frequencies and torsional stiffness of long bones in vitro. Validation of a simple beam model.

The results of vibration analysis experiments and impact torsion tests performed on excised animal long bones were used to validate a simple beam model for the prediction of torsional stiffness from resonant frequencies. Resonant frequency data on two mutually perpendicular bending vibration modes of 142 excised long bones were evaluated. Torsional stiffness of the same bones had been determined by an impact torsion test. Using a simple beam model, a theoretical relation between resonant frequencies and torsional stiffness was derived. If total bone mass and bone length are known, the formula thus derived allows one to calculate torsional stiffness from resonant frequencies. Linear regression analysis shows a strong correlation between the measured and the calculated torsional stiffness for sheep femora (r2 = 0.63, n = 24), dog femora (r2 = 0.94, n = 34), dog tibiae (r2 = 0.79, n = 18) and monkey radii (r2 = 0.77, n = 66). It was found that this linear relation was valid not within one bone type alone. Linear regression analysis on the combined data of all bones demonstrated that all bones obeyed the same global linear relation between measured and the calculated torsional stiffness (r2 = 0.98, n = 142). This implies that one and the same beam model is valid for the different bone types investigated. The calculation of stiffness from resonant frequencies, however, requires total bone mass, m, and length to be known. In view of in vivo applications, the feasibility of using total bone mineral content (TBMC) as a measure for m was investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The development of a physiological hip prosthesis: evaluation of the strains after implantation of a prototype of hip implant: experiment in a dry femur.

Based upon previous research on the relation between hip prosthesis designs and strain distributions in a proximal femur model, a prototype of a "physiological" hip prosthesis was designed and manufactured. Strain gauge measurements on a dry femur before and after implantation of this prosthesis were made in different loading conditions simulating one-legged stance with and without torsional loading and two-legged stance. The strains in the outer cortex were within 10% of the physiological values along the whole medial side in all measurement conditions.

Biomechanical Phenomena↗
PubMed1992

Longitudinal effect of tiludronate on bone mineral density, resonant frequency, and strength in monkeys.

The effect of Tiludronate on bone was studied in 72 growing monkeys (Papio papio), 36 males and 36 females, aged 4-7 years. They were randomly allocated into four groups (18 animals per group, 9 males and 9 females): group I, controls; group II, 10 mg/kg/day; group III, 20 mg/kg/day; and group IV, 40 mg/kg/day of Tiludronate. A total of 12 animals (6 males and 6 females) in each group were sacrificed at the end of treatment (1 year) and 6 animals (3 males and 3 females) per group 1 year later. Bone mineral density (BMD) was measured by dual-photon absorptiometry. Biomechanical properties were evaluated by an impact torsion test and by resonant frequency analysis. Bone mineral measurements indicated that at the end of 1 year of treatment BMD was significantly higher, especially at the distal epiphysis of the radius, than in controls. No significant differences between groups were found in BMD 1 year after stopping treatment. Biomechanical analyses indicated that torsional stiffness increased after treatment. No differences between groups were found 1 year after stopping treatment. Results of resonant frequencies indicated an increased calculated transversal stiffness after treatment and 1 year later and an increased buckling strength 1 year after stopping treatment. In conclusion, the results on the effect of Tiludronate in growing monkeys indicate a profound effect of this drug on bone density and biomechanical properties. The biomechanical results indicate that this drug is safe, with conservation of bone strength despite a change in intrinsic mechanical properties of the bone.

Animals↗
PubMed1992

Development of an above-knee prosthesis equipped with a microcomputer-controlled knee joint: first test results.

The shortcomings of conventional above-knee prostheses are due to their lack of adaptive control. Implementation of a microcomputer controlling the knee joint in a passive way has been suggested to enhance the patient's gait comfort, safety and cosmesis. This approach was used in the design of a new prosthetic system for the above-knee amputee, and tested on one patient. The knee joint of a conventional, modular prosthesis was replaced by a knee joint mechanism, equipped with a controllable brake on the knee joint axis. Sensors and a microcomputer were added, keeping the system self-contained. The modularity of the design permits the use of an alternative, external, PC-based control unit, emulating the self-contained one, and offering extended data monitoring and storage facilities. For both units an operating environment was written, including sensor/actuator interfacing and the implementation of a real-time interrupt, executing the control algorithm. A double finite state approach was used in the design of the control algorithm. On a higher level, the mode identification algorithm reveals the patient's intent. Within a specific mode (lower level), the relevant mode control algorithm looks for the current phase within the gait cycle. Within a particular phase, a specific simple control action with the brake replaces normal knee muscle activity. Tests were carried out with one prosthetic patient using a basic control algorithm for level walking, allowing controlled knee flexion during stance phase. The technical feasibility of such a concept is illustrated by the test results, even though only flexion during early stance phase was controlled during the trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Artificial Limbs↗