Differences and Relationships Between the Physical Properties and the Microscopic Structure of Human Femoral, Tibia1 and Fibular Cortical Bone

Coefficients of correlation between certain physical properties and the histological components of the break area were calculated on an IBM 7090 computer for 56 femoral, 79 tibial and 37 fibular specimens of embalmed cortical bone of standardized size and shape. Strong positive correlations (0.01-0.02 significance level) were found between tensile strength and the percentage of interstitial lamellae in the break area; between hardness and the number of osteons/mm*; and between hardness and the percentage of osteons in the break area. Equally high negative correlations were found between tensile strength and percentage of osteons in the break area; between shearing strength and average area/osteon remnant; between elastic modulus and percentage of spaces in the break area; and an even higher correlation (0.001) between hardness and percentage of spaces in the break area. Negative correlations (a t slightly more than 0.05 significance level) were found between shearing strength and modulus and average area/osteon. Osteons tend to reduce the tensile strength and elastic modulus of bone while interstitial lamellae tend to increase them. The probable reason is the relatively greater amount of cement lines, which are sites of weakness where failure can occur, in Haversian bone as compared with lamellar bone. The predominant orientation of collagen fibers and the amount and distribution of calcium may also be involved. These factors are now being investigated. The present paper is a supplement to our previous one ('66) on the relations between statistically significant differences in the physical properties and microscopic structure of adult human femoral and fibular cortical bone. The physical properties investigated (ultimate tensile strength, single shearing strength, tensile strain, tangent modulus of elasticity, hardness, density, and the ratio of single shearing strength to ultimate tensile strength) and their relation to osteons, remnants or fragments of osteons, interstitial lamellae, and spaces are the same as in our previous investigation. Our studies relate more physical properties of bone to its microscopic structure than do the investigations of Maj and Toajari ('37), Olivo, Maj and Toajari ('37), Olivo ('37), Maj ('38), Toajari ('38, '39), Evans ('57, '58), Currey ('59, '62, '64), Dempster and Coleman ('61), and Helt et al. ('65). The majority of these investigations were on the relation of tensile strength and/or modulus of elasticity of AM. J. ANAT.. 120: 79-88 bone to the osteons or collagen fiber distribution although Currey ('64) discussed the possible relation of bone strength to the apatite crystals while He?t et al. ('65) investigated the relation of compressive strength, impact bending strength and microhardness to primary and Haversian bone. Nonhuman bone was usually used in these studies but none of them related statistically significant differences in the physical properties of the bone to its microscopic structure. MATERIALS AND METHODS The physical properties investigated in the present study were determined for 405 femoral, 193 tibial and 37 fibular specimens of cortical bone which were machined to a standardized size and shape from the proximal, the middle and the distal thirds of the shaft of the respective bones. The specimens were obtained from 1 This research was supported (in part) by Reseaxh grant AM-03865-07 from the Natlonal Institutes of Health, US. Public Health Servlce.