ELSEVIER 1350-4533(95)00064-X Orthogonal relationships between ultrasonic velocity and material properties of bovine cancellous bone C. F. Njeh, R. Hodgskinson*, J. D. Currey* and C. M. Langtont Health Research Institute, Sheffield Hallam University, Sheffield, UK *Department o f Biology, University of York, York, UK iAcademic Department of Medical Physics, University of Hull, Hull, UK Rrc-eived 2 Fehruq 1995, accepted 24 May 1995 ABSIXACT Osteoporotic frartures follow a period of asymptomatic bone loss and hence bone strength, predominantly in cancellous bone. An effective management of osteoporosis require,? an understanding of the mechaniral behauiour of cnncelhs bone including the anisotropic dependence. Ultraso~und velority (V) and elasticity (Young’s modulus, E) awe mear- ured in the three orIhogona1 dirertions in 20 mm cubes of bovine cancellous bone. Student paired t-test analysis showed si~gnz$cant variations in velot-ity and elasticity for the three orthogonal directions, the highest s@zifirance bping between proximal-distal (PD) and an&&posterior (At’) directions with t = 5.63 and 4.09 for velocity and elasticity respectively, the lowest significance between mediolateral (ML) and anter@flostpn’or dirertions. Elastirity Jollowed a power law relationship with appawnt density (p) as reported in the literature, the exponent (b) being direction dependent (b = 1.98 + 0.2 1 for PD, 2.42 + 0.24 for AP and 2.03 z!z 0.17 Jtir ML). The adjusted R’ va1ue.T between elasticity and apparent density were highly signijcant (79.9% for PD, 81.9% Jar AP and 85.7% Jor ML). The relationship between velocity and apparent density is less signzjirant in terms of the amount ofvariance explained (483% for PD, 63.3% for AP and 64.4% for ML). R” values relating elasticity and velocity were again high!? signifirant (79.4% ,for PD, 82.9% for AP an.d 80.5y/o for ML) and the roej$cients, determined 67 reCgre.Gin analysis, independent oJ direction. Analysis of velocity. rlastirity and density data for a range oJref&renre materials demonstrated that experimentally measured long-itudinal wave velocity could be reliably substituted into the bar wave equation (v = mp) This imp&T that a combination of velocity and apparent density may be an improved indicator oJbonr fkg+lit? than density alone. Copyright 0 1996 Hseuier Science Ltd for IPEMB. Keywords: Cancellous bone, ultrasound velocity, Young’s modulus, compressive strength Med. Eng. Phys., 1996, Vol. 18, 373-381, .July INTRODUCTION important consequence is an increase of fractures, Cancellous bone plays a major role in maintaining the structural integrity of the skeletal system; at the femoral neck for example, cancellous bone accounts for an estimated 70% of the compressive strength’. There is an important need, therefore, to understand the mechanical behaviour of can- cellous bone, particularly the anisotropy in elas- ticity. This knowledge could be utilized in a wide range of applications, including orthopaedic implants (particularly total knee replacements which are primarily fixed in cancellous bone), arthoplasty and the diagnosis and management of osteoporosis. Osteoporosis results from a period of asympto- matic bone loss and reduced bone strength, pre- dominantly in cancellous bone. The most which may occu> either spontaneously or after minimal trauma, when loss of bone is sufficient to cause mechanical weakness’. The increase in prevalence of osteoporosis has resulted in an upsurge in studies into the pathogenesis, diag- nosis and treatment”. No effective treatment of established osteoporosis is currently available’, therefore prevention of bone loss and fragility remains the only practical approach to its manage- ment. This necessitates the development of non- invasive techniques to detect incipient fragility, to determine the risk of fracture and to monitor the effectiveness of therapy. Several methods have evolved for measuring bone mineral density&“. These include single photon absorptiometry (SPA), dual photon absorptiometry @PA) > dual energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). H owever, fracture risk for