Fig. 4.

Average length for all types of microcrack. (i) Did not hit an osteon. (ii) Hit an osteon and stopped. (iii) Hit an osteon and was deflected. (iv) Hit an osteon and penetrated the cement line. (v) Hit an osteon at both ends. (vi) Osteonal. (vii) Pre-existing. Error bars in the figure represent standard deviation. Sample size for category (i) microcracks n = 312, similarly n (ii) = 53, n (iii) = 47, n (iv) = 69, n (v) = 35, n (vi) = 54, n (vii) = 7. Statistical analysis indicated that crack length at the time of encountering an osteon significantly affected its ability to propagate. Statistical analysis showed that microcracks that penetrated the cement line were significantly longer (P < 0.05) than those of other groups. All the individual groups showed statistically significant difference (P < 0.05) except category (v) vs. (ii, vi and vii), and category (vi) vs. (vii).