Knowledge of the biomechanics of the spine following injury is essential to the surgeon in his management of patients. However, there is not much information available on the alterations of the biomechanics after injury. This experiment was performed to collect basic information, with the purpose of establishing thresholds of stability of the cervical spine under normal physiologic loads. Seventeen motion segments of the human cervical spine were studied. (A motion segment consists of two adjacent vertebrae and the interconnecting soft tissues.) A constant load of 25 per cent of the body weight was applied to the upper vertebra while the lower vertebra was fixed. Various ligaments, the intervertebral disc, and facet joints of the motion segment, here referred to as components, were dissected in two predetermined patterns: anterior to posterior or posterior to anterior. The load was applied to simulate flexion or extension. Motion was measured in the sagittal plane at each stage of the component transection.
Results were plotted for rotation and horizontal translation of the upper vertebra—as function of transection of the components. In general, the elastic deformation was small, even when a majority of the components were sectioned. Failure was sudden and there was no consistent pre-failure phase.
These in vitro studies have provided accurate information, which is clinically useful in predicting stability of the motion segments as a function of ligament, disc and facet transection.