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In vivo flexion-extension and axial rotation magnetic resonance imaging (MRI) studies of the cervical spine were performed inside a positioning device.To determine the functional changes of neuroforaminal size that occur during flexion-extension and axial rotation of the cervical spine in healthy persons.Kinematic MRI studies of the cervical spine were performed to obtain detailed information about the functional changes that occur in neuroforaminal size during flexion-extention and axial rotation. The results were compared with published data of in vitro functional flexion-extension and axial rotation studies of the cervical spine.Inside a positioning device, the cervical spines of 30 healthy persons were examined in a whole-body magnetic resonance scanner from 40° of flexion to 30° of extension at nine different angle positions. In addition, axial rotation was performed at neutral position (0°) and at 20° and 40° of axial rotation to both sides. The images were analyzed with respect to the neuroforaminal size at each position using a reformatted 3D-FISP sequence.At flexion, widening of the neuroforaminal size of up to 31% (compared with neutral position, 0°) was observed. Conversely, at extension a decrease in the size of the neuroforamen of up to 20% was recognized. At 20° and 40° of ipsilateral rotation of the head, a reduction in the neuroforaminal size of up to 15% and 23%, respectively, compared with the neutral position was noted. In contrast, a widening of the foraminal size was recognized on the contralateral side of 9% and 20% at 20° and 40° rotation. Statistically significant differences (p ≦ 0.05) were found in the neuroforaminal size between different degrees of flexion and extension and in addition for axial rotation compared to neutral position (0°).Compared with the results of previous biomechanical studies of human cadaver cervical spines, kinematic MRI provides additional noninvasive data concerning the physiological changes of the neuroforaminal size during flexion-extension and axial rotation in healthy individuals.