ORTHOGONAL RELATIONSHIPS BETWEEN ULTRASONIC VELOCITY AND MATERIAL PROPERTIES OF BOVINE CANCELLOUS BONE

Osteoporotic fractures follow a period of asymptomatic bone loss and h ence bone strength, predominantly in cancellous bone. An effective man agement of osteoporosis requires an understanding of the mechanical be haviour of cancellous bone including the anisotropic dependence. Ultra sound velocity (V) and elasticity (Young's modulus, E) were measured I n the three orthogonal directions in 20 mm cubes of bovine cancellous bone. Student paired t-test analysis showed significant variations in velocity and elasticity for the three orthogonal directions, the highe st significance being between proximal-distal (PD) and antero-posterio r (AP) directions with t = 5.63 and 4.09 for velocity and elasticity r espectively, the lowest significance between medio-lateral (ML) and an tero-posterior directions. Elasticity followed a power law relationshi p with apparent density (rho) as reported in the literature, the expon ent (b) being direction dependent (b = 1.98 +/- 0.21 for PD, 2.42 +/- 0.24 for AP and 2.03 +/- 0.17 for ML). The adjusted R(2) values betwee n elasticity and apparent density were highly significant (79.9% for P D, 81.9% for AP and 85.7% for ML). The relationship between velocity a nd apparent density is less significant in terms of the amount of vari ance explained (48.5% for PD, 63.3% for AP and 64.4% for ML). R(2) val ues relating elasticity and velocity were again highly significant (79 .4% for PD, 82.9% for AP and 80.5% for ML) and the coefficients, deter mined by regression analysis, independent of direction. Analysis of ve locity, elasticity and density data for a range of reference materials demonstrated that experimentally measured longitudinal wave velocity could be reliably substituted into the bar wave equation (v = root E/r ho). This implies that a combination of velocity and apparent density may be an improved indicator of bone fragility than density alone. Cop yright (C) 1996 Elsevier Science Ltd for IPEMB.