Influence of crack length and anatomical location on the fracture toughness of annulus fibrosus.

Fracture toughness (J) of a soft biological tissue is an important mechanical property that characterizes its resistance to crack or tear extension. To date, no information is available on fracture toughness of annulus fibrosus (AF); therefore, its defect tolerance is not known. The present study modified a previously introduced method to determine J of ovine AF. Then, the effect of the notch length on the failure pattern and J was investigated. Also, the test samples of anterior and lateral regions were collected to determine the effect of the location on J. Results showed that for a notch length of less than 45% of total width, no crack extension occurred, but for a notch length above 45% of the width, crack propagation and ultimately the failure of the AF were observed. However, statistical analysis indicated no significant difference on J (p = 0.5) for the initial notch length of 50% and 70% of total width. The fracture toughness was significantly higher for the samples extracted from the lateral site than those from the anterior site (p < 0.05). Dissimilar failure patterns were observed for different initial notch lengths. Among the parameters studied, the defect tolerance of AF was dependent on the initial tear size.