Sg. Roberts et al., NONINVASIVE DETERMINATION OF BONE MECHANICAL-PROPERTIES USING VIBRATION RESPONSE - A REFINED MODEL AND VALIDATION IN-VIVO, Journal of biomechanics, 29(1), 1996, pp. 91-98
Accurate non-invasive mechanical measurement of long bones is made dif
ficult by the masking effect of surrounding soft tissues. Mechanical r
esponse tissue analysis (MRTA) offers a method for separating the effe
cts of the soft tissue and bone; however, a direct validation has been
lacking. A theoretical analysis of wave propagation through the compr
essed tissue revealed a strong mass effect dependent on the relative a
ccelerations of the probe and bone. The previous mathematical model of
the bone and overlying tissue system was reconfigured to incorporate
the theoretical finding. This newer model (six-parameter) was used to
interpret results using MRTA to determine bone cross-sectional bending
stiffness, EI(MRTA). The relationship between EI(MRTA) and theoretica
l EI values for padded aluminum rods was R(2) = 0.999. A biological va
lidation followed using monkey tibias. Each bone was tested in vivo wi
th the MRTA instrument. Postmortem, the same tibias were excised and t
ested to failure in three-point bending to determine EI(3-PT) and maxi
mum load. Diaphyseal bone mineral density (BMD) measurements were also
made. The relationship between EI(3-PT) and in vivo EI(MRTA) using th
e six-parameter model is strong (R(2) = 0.947) and better than that us
ing the older model(R(2) = 0.645). EI(MRTA) and BMD are also highly co
rrelated (R(2) = 0.853). MRTA measurements in vivo and BMD ex vivo are
both good predictors of scaled maximum strength (R(2) = 0.915 and R(2
) = 0.894 respectively). This is the first biological validation of a
non-invasive mechanical measurement of bone by comparison to actual va
lues. The MRTA technique has potential clinical value for assessing lo
ng-bone mechanical properties.