Master of Kinesiology (MKin)
Kinesiology and Physical Education
Faculty of Science
Dr. Diane Gregory
Introduction: Intervertebral disc (IVD) herniation is characterized by an expulsion of nucleus pulposus (NP) material through the annulus fibrosus (AF). The AF contains two major adhesive structures, the intralamellar matrix and the interlamellar matrix, which act to maintain the strength of the AF and prevent NP material migration. As a herniation occurs, clefts form within the intralamellar matrix, pushing the NP between adjacent collagen fibres; meanwhile, delamination of the interlamellar matrix causes the NP to pool between layers of the AF. Further, herniation more readily occurs in a combined loading scenario of both compression and flexion. Flexion, and in particular end range flexion, induces tissue creep, where the elongation of fibres within the AF reduces its capacity for tensile resistance, thereby providing a potential mechanism for why flexion is needed to induce herniation. While previous research has examined the effect of combined flexion and compression on the mechanical properties of the AF, the isolated effect of flexion has not been ascertained.
Aims: The purpose of the current work is to observe the effect of static flexion, in combination with compression, on the intralamellar and interlamellar adhesive properties of the AF.
Methodology: For this study, the C3/C4 cervical functional spinal units (FSU) of porcine specimens were selected due to their anatomical and biomechanical similarity to human spines. All specimens were loaded under 1200N axial compression and one of the following posture conditions: neutral or static end range flexion for 2-hours. Following loading, six AF samples were dissected from each IVD: four single-layer samples and two multilayer samples. The multi-layer samples underwent peel tests to determine the mechanical properties of the interlamellar matrix while the single-layer samples underwent tensile tests to determine the mechanical properties of the intralamellar matrix. Comparisons between mechanical properties were performed to determine if there was a difference between extraction location (anterior vs posterior), extraction depth (inner vs outer AF) and postural condition. Mechanical properties obtained from these tests were statistically compared across conditions.
Results: The results demonstrated that flexion had an influence on the mechanical properties of the adhesive matrices of the AF. Regarding the interlamellar matrix, flexion elicited a significant decrease in lamellar adhesive strength when compared to a neutral posture. In consideration to the intralamellar matrix, flexion elicited a decrease in failure point strain when compared to neutral. Furthermore, flexion resulted in a significant increase in stiffness of the inner region of the AF compared to the outer region of the AF in flexion and the inner region of the AF in a neutral posture. Flexion also resulted in a significant decrease in toe region strain for the inner region of the AF when compared to the inner region of the AF in a neutral posture. The inner region of the AF was also seen to have a significant increase in stress at 30% strain when compared to the outer region of the AF when undergoing flexion.
Discussion/Conclusion: The current findings suggest that the mechanical properties of the interlamellar and intralamellar matrices are sensitive to flexion, creating an environment that promotes an increased potential for herniations to occur.
Briar, Keaton, "THE IMPACT OF COMBINED FLEXION AND COMPRESSION ON THE MECHANICAL INTEGRITY OF THE ANNULUS FIBROSUS" (2021). Theses and Dissertations (Comprehensive). 2386.
Available for download on Saturday, August 06, 2022