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J Timonen

Publications and source records attributed to J Timonen.

35 records · Page 2Linked to original sources
PubMed1995

Estimation of structural and geometrical properties of cortical bone by computerized tomography in 78-year-old women.

The structural and geometrical properties of the tibia shaft were investigated at two sections by means of computerized tomography (CT) in 78-year-old women with high (n = 19) and low (n = 17) calcaneal bone mineral density (BMD, g/cm3) previously measured by 125I-photon absorption. The high BMD group had a 20-21% higher tibial BMD and 9-12% higher bone cross-sectional area than was observed in the low BMD group. The distribution of bone mass indicated that the low BMD group had lost bone mainly from the endosteal surface, especially in the anterior part of the tibia. However, both groups had a similar basic pattern of mass distribution at the measured sections. The high BMD group had higher moments of inertia at the upper section than the low BMD group. The differences between the groups were more pronounced when only the high density areas were included. At the lower section, the differences between the groups also appeared significant at the high density levels. There were no group differences in the area moments of inertia. The results suggest that the true distribution of bone mass should be taken into account in determining the moments of inertia. In the tibia, determination of the cross-sectional mass distribution of bone combined with BMD should have a better discriminatory capability than BMD only in studying bone strength and fracture risk.

Absorptiometry, Photon↗
PubMed1995

Elastic wave propagation in bone in vivo: methodology.

The purpose of this study was to investigate the usefulness of elastic wave propagation (EWP) in estimating the mechanical properties (elasticity) of human tibia. The test group was composed of 78-yr-old women assigned to high (n = 19) and low (n = 17) bone mineral density (BMD) groups as measured at the calcaneus by the 125I-photon absorption method. The EWP apparatus consisted of an impact-producing hammer with a force strain gauge and two accelerometers positioned on the bone. Results for nylon and acrylic were used to calibrate the apparatus. Polyvinyl chloride (PVC) solid rods and tubes of various diameters were used to evaluate the relationship between the elastic wave velocity and cross-sectional area. The density and the cross-sectional area of tibia were measured by the computerized tomographic (CT) method at the same intersection points as velocity recordings. The velocities in tibia of bending waves produced by the mechanical hammer were found to depend on the density, area moment of inertia, and density-dependent elastic constants of bone. It is important to account for the changes of these quantities along the bone. It is suggested that the velocity of elastic waves and various indices derived there from provide inexpensive ways of evaluating the elastic properties of bone.

Acceleration↗