THE BIOMECHANICS OF SPINAL ELEMENTS (LIGAMENTS, VERTEBRAL BODY, DISC)
Despite the continuing research effort, data regarding the material properties and biomechanical parameters of spinal elements, particularly the ligaments, remains sparse. The ligaments, discs, and vertebrae of the human spinal column were tested for their biomechanical strength. 65 samples of human vertebrae were tested in direct axial compression to failure in an M.T.S. testing machine. Average values of force at failure ranged from 2587N in the cervical spine to 4590N in the lumbar spine. Average values of stress at failure decreased from 7.9N/mm('2) in the cervical spine to 2.8N/mm('2) in the lumbar spine. Mean values of engineering strain at failure ranged from 24.4% to 33.9%. Overall, 33 samples of the human intervertebral disc were tested in direct axial tension to failure. Average values of force at failure ranged from 592N in the cervical spine to 1254N in the lumbar spine. Deformations to failure ranged from 8.9mm to 11.1mm. Mean values of stiffness of the disc increased from 64.2N/mm in the cervical spine to 213.2N/mm in the lumbar spine. Determining the strength parameters of human spinal ligaments was of principle importance in this investigation due to the paucity of information in the literature. Information was obtained from 402 samples of the various spinal ligaments from 41 human cadavers. Each ligament was isolated in situ and tested in direct axial tension to failure in an electro-hydraulic testing system. The six major spinal ligaments: anterior longitudinal (ALL), posterior longitudinal ligament (PLL), joint capsules (JC), ligamentum flavum (LF), interspinous ligament (ISL), and supraspinous ligament (SSL), were evaluated at all spinal levels from the head to the sacrum. Mean values of force at failure, deformation at failure, energy to failure, and stiffness were found for each ligament at all spinal levels. Mean values of engineering stress at failure, engineering strain at failure, and elastic modulus were found for each ligament at lumbar spinal levels. A representative force-deformation curve of a ligament was modeled using a simple lumped parameter system. Histological evaluation of the ligaments was completed to provide internal verification of results. An auxiliary investigation of 250 samples of monkey spinal ligaments was completed to find a ratio between strength parameters of the monkey and human spinal ligaments.
FRANK ANTON PINTAR,
"THE BIOMECHANICS OF SPINAL ELEMENTS (LIGAMENTS, VERTEBRAL BODY, DISC)"
(January 1, 1986).
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