[A biomechanical study on cervical spinal posture and prior loading history affecting spinal compressive strength].

OBJECTIVE: The purpose of this study is to investigate the effect of cervical spinal posture and prior loading history on spinal compressive strength. METHODS: Twelve human cadaver cervical spines were harvested and dissected into 24 motion segments containing 2 vertebrae and the intervertebral discs (C3,4 and C5,6). Compressive loads were applied on so that the effects of 2 loading conditions (dehydrated, superhydrated) and 2 postures (neutral trunk, flexed) could be examined. Dissection techniques and X-rays were used to determine the tissue injuries. RESULTS: Specimens had a lower ultimate compressive strength (P <0.001) in flexed posture than in neutral trunk posture. Under the injury loading in neutral trunk posture, superhydrated specimens had a lower strength (29%, P <0.01) than dehydrated specimens did. CONCLUSION: The spine may be more prone to injury early in the morning when the discs are at highest level of hydration and the cervical spine is in fully flexed posture.