Human vertebral cancellous bone from white males (N =19), black males (N = 16), white females (N = 12), and black females (N = 17) was examined histologically for the presence, numerical density, and morphology of in vivo microscopic cracking (microdamage). Two patterns of microcracks, linear and cross-hatched, were observed. Linear microcracks were observed in both the central portion and near surfaces of trabeculae. Those inside trabeculae were usually single microcracks approximately 50 pm in length and were found in both cement lines and in interstitial bone matrix. Linear microcracks near the trabecular surface were usually multiple parallel cracks approximately 80 μm in length. Microcracks with a cross-hatched appearance were less prevalent. They were observed primarily in vertically oriented trabeculae and were often surrounded by an area of diffuse staining. Two-way ANOVA revealed no differences in microcrack density (Cr.Dn; #/mm²) between males and females [mean (SD) 5.13 (5.02) vs. 5.41 (6.26), respectively], but whites had significantly higher microcrack density than blacks [7.00 (5.71) vs. 3.63 (4.98), respectively, p & lt; 0.05]. White males had a significantly higher microcrack density than black males [7.60 (5.56) vs. 2.21 (1.78), respectively, p & lt; 0.05]. Although not statistically significant, white females also had higher microcrack density than black females. In contrast to what has been reported in the femur, regression analysis found no statistically significant relationship between microcrack density in the spine and age for any of the four race-gender groups. However, significant power relationships were found between microcrack density and bone area fraction for all groups except for black females. The difference between axial and appendicular bone remodeling rates, and their implications for microdamage accumulation, are discussed.
Keywords: Microdamage; Cancellous bone; Human vertebra; Morphology; Microcracks; Age