A Empirical Study On Cervical Spinal Posture And Prior Loading History Affecting Intervertebral Discs Intortion Strength

Objective: The purpose of this study is to investigate the effect of cervical spinal posture and prior loading history on intervertebral discs intortion strength, and to identify the change of cervical intervertebral disc on histopathology after the loading of the ultimate intortion strength.Method: Ten human cadaver cervical spine were harvested and dissected into 20 motion segments containing 2 vertebrace and the intervertebral discs (C_3,4 and C_5,6) and only remaining integrity the anterior longitudinal ligament, the posterior longitudinal ligament and the intervertebral discs. Intortion loads were applied on so that the effects of 2 postures (neutral trunk, flexed) and 2 loading conditions (dehydrated, hydrated) could be examined. Dissection techniques and histopathology techniques were used to determine the tissue injuries.Result: 1. Biomechanics. The cervical spinal posture and the prior loading history both affect the intervertebral discs intortion strength.Under the hydrated conditions, specimens had a lower ultimate intortion strength (P<0.01) in neutral trunk posture than in flexed posture; but under the dehydrated conditions, specimens had a higher ultimate intortion strength (P<0.01) in neutral trunk posture than in flexed postureIn both postures, hydrated specimens had a lower ultimate intortion strength than dehydrated specimens did (P<0.01).2. Morphology. After the loading of the ultimate intortion strength, all specimens was damaged, especially the end plate had fracture particularly.On histopathology, the end plate of the normal discs was integrity and combined with the fiber wreath close, the annual fibrosus arranged close and regularly, and the nucleus was integrity. But after the loading of the ultimate intortion strength, the end plate disrupted and departed partly, the annual fibrosus had fissure and harmed, but the nucleus was integrity.Conclusion: The cervical intervertebral discs may be less prone to injury in the position in which the cervical spine is straight, but more prone to injury when the discs are at highest level of hydration. After the loading of the ultimate intortion strength, the end plate and the annual fibrosus of the discs is harmed seriously.