Biomedical subjects

G Lowet

Publications and source records attributed to G Lowet.

24 records · Page 2Linked to original sources

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

Measurement of femoral geometry in type I and type II osteoporosis: differences in hip axis length consistent with heterogeneity in the pathogenesis of osteoporotic fractures.

The epidemiologic patterns of vertebral and femoral fractures are sufficiently different to suggest that they represent distinct disorders (type I versus type II osteoporosis) although osteopenia is common in both. To determine whether differences in femoral geometry, one of the main determinants of bone quality, might contribute to the heterogeneity in osteoporotic fractures, we obtained dual energy X-ray absorptiometry scans on 210 women age 60 or older, including 105 type I fracture cases, 30 type II patients, and 75 controls. Hip axis length, measured on the scan printout, was significantly increased (p < 0.01) in hip fracture patients compared with women with postmenopausal osteoporosis, whereas femoral neck density (BMD) was equal in both groups. The best discrimination between both fracture types was obtained by a logistic regression model based on age and axis length. Adding BMD to the model did not improve the discriminative power (p = 0.67). These data provide further evidence that geometric characteristics may be implicated in hip fracture risk. Furthermore, these findings suggest that an increase in hip axis length may predispose osteopenic subjects to a femoral localization of fragility fractures, consistent with the postulated heterogeneity in the pathogenesis of osteoporotic fractures.

Absorptiometry, Photon↗

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

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↗

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↗