There is an increasing need to accurately define the soft tissue components of the human cervical spine in order to develop and exercise mathematical analogs such as the finite element model. Currently, a paucity of data exists in the literature and researchers have constantly underscored the need to obtain accurate data on cervical spine ligaments. Consequently, the objective of the study was to determine the geometrical and biomechanical properties of these ligaments from the axis to the first thoracic level. A total of thirty-three human cadavers were used in the study. Geometrical data included the length and cross-sectional area measurements; and the biomechanical properties included the force, deflection, stiffness, energy, stress, strain, and Young's modulus of elasticity data.
Data were obtained for the following ligaments: anterior and posterior longitudinal ligaments, joint capsules, ligamentum flavum, and interspinous ligament. Cryomicrotomy techniques were used to determine the geometrical characteristic. The length data were obtained using sagittal images and area data were determined using axial images. The biomechanical tests involved conducting failure tensile tests at a quasistatic rate of 10 mm/sec using in situ principles (ligaments were not tested in isolation) and the data were analyzed and synthesized as follows. The force-deformation relationships for each ligament type and at each spinal level were normalized. The mean force-deformation curves were obtained and grouped into clinically relevant mid and lower cervical regions.
The anterior and posterior longitudinal ligaments responded with the highest length measurements in both regions of the spine. In contrast, the ligamentum flavum and joint capsules exhibited the highest area of cross-section. All ligaments demonstrated increasing cross-sectional areas in the lower cervical group compared to the mid-cervical group. Detailed force-deflection characteristics are provided for all the five types of ligaments in both groups. The stiffness parameters were higher in the mid-cervical region than in the lower cervical region for the anterior longitudinal ligament, interspinous ligament, and ligamentum flavum, while the reverse was true for the other ligaments. The energy was higher in the lower cervical region than in the mid-cervical region for the joint capsules, ligamentum flavum, interspinous ligament, and anterior longitudinal ligament. The lowest values of energy to failure were observed for the interspinous ligament followed by the posterior longitudinal ligament, ligamentum flavum, anterior longitudinal ligament, and joint capsules in both regions. The anterior and posterior longitudinal ligaments responded with the highest stress followed by the joint capsules, interspinous ligament, and ligamentum flavum. While the joint capsules and ligamentum flavum demonstrated large strain to failure, the anterior and posterior longitudinal ligaments responded with the least percentage of strain to failure. The Young's modulus of elasticity based on a bilinear fit for each ligament type at each of the two regions is given. These studies provide important fundamental data on the properties of human cervical spine ligaments.