Correlation Between Tensile Properties Of Annulus Fibrosus And Magnetic Resonance Image Findings Of Lumbar Spine

Background As one of the major conjunction between adjacent vertebrae, intervertebral discs always bear different motive situations as compression, stress or rotation. In certain processes, annulus fibrosus keeps the structure of the whole intact intervertebral disc with its unique fiber arrangement. Tensile properties is one of the most important characters of annulus fibrosus. Magnetic resonance image plays an important role in clinical diagnosis of intervertebral disease, with Pfirrmann grade and Modic changes widely accepted by surgeons. Nowadays, most researches of annulus fibrosus focused on tensile properties of different biochemical situations and histological status, while there is no research on the correlation between tensile properties and magnetic resonance image findings.Objective To investigate the tensile properties of annulus fibrosus (AF), and to access its correlation with MRI findings (Pfirrmann grade and Modic changes).Methods27human cadaveric lumber spines were harvested (16male,11female, mean age44.3years, range31-57). All spines underwent MRI examination. Then all intervertebral discs were removed from adjacent motion segments, divided into parts as nucleus pulposus, anterior AF, anterolateral AF, lateral AF and posterolateral AF, and further divided into three subgroups averagely:inner, middle and outer parts. Specimens were made for each of the regions, and tensile test were performed with testing machine (Zwick/Roell Z2.5). Linear fitting was performed to analyze the relationship between age, gender and tensile properties. ANOVA and LSD were used to analyze the tensile properties with different Pfirrmann grades. T-test was used to analyze the tensile properties with different Modic change situations.Results1738specimens from158discs,27cadavers were tested. All degeneration and MCs visible by MRI were seen in L4-L5and L5-S1. The mean tensile module of all tested specimens is4.80±1.96MPa,8.25±2.73MPa and13.20±3.19MPa, for inner, middle and outer AF, respectively. The overall UTS are1.1±0.54MPa,1.73±0.87MPa and3.37±1.30MPa, respectively. No significant age-or gender-related changes can be found. Tensile module and UTS all increased from the inner to outer annulus, with elongation decreased. Tensile module and UTS all decreased with the severity of degeneration increases, except the UTS of middle annulus. When MCs presents, inner annulus showed significantly lower module with MCs, while this difference did not appear in middle and outer annulus. The UTS presented decreased significantly in all inner to outer region when MCs appears.Conclusion The tensile properties decrease with higher Pfirrmann grade of MRI. When MCs presents, AF showed lower tensile module, especially the inner region.