THE EFFECTS OF DENSITY AND TEST CONDITIONS ON MEASURED COMPRESSION AND SHEAR-STRENGTH OF CANCELLOUS BONE FROM THE LUMBAR VERTEBRAE OF EWES

An animal model (the ewe) was used to study mechanical parameters of c ancellous bone specimens. Compression and shear tests were conducted o n ewe vertebral trabecular bone (L1-L5) from old ewes (mean age: 9 yea rs) under two different conditions: first, at room temperature in air (''standard'' test conditions); and secondly, in a physiological salin e bath regulated at 37 degrees C. The parameters obtained under ''stan dard'' test conditions with a uniaxial compression test were the mean value of the maximum strength (sigma(max) = 22.3 (7.06) MPa), Young's modulus (E = 1510 (784) MPa), the strain at maximum strength (epsilon( sigma max) = 3.21 (0.8) percent) and the energy absorbed during the te st (W = 0.3 (0.12) MJ.M-3). No significant change was found when the t est was carried out in a saline bath at 37 degrees C (p<0.0005). An or iginal shear test ions performed to evaluate the shear strength which was found to vary from 7.5 (4.7) to 14.6 (8.53) MPa under ''standard'' test conditions depending on the method of calculation. Testing of th e specimens in a 37 degrees C physiological saline bath induced a decr ease in the shear strength from 32.5 percent (p < 0.0005) to 37.3 perc ent (p < 0.001) of those measured under ''standard'' test conditions. The non-destructive measurement of the Bone Mineral Density (BMD) to 7 3.3 percent of the maximum compressive strength sigma(max) and 61.5 pe rcent of the maximum shear strength tau(max) determined in saline solu tion at 37 similar to C. These results showed that other parameters in fluencing the mechanical properties of trabecular bone and its structu re appeared to be essential. (C) 1997 IPEM. Published by Elsevier Scie nce Ltd.