Purpose] To analyze dynamic lower cervical spine kinematics under neutral head extension (Ex) and protracted head extension (Pro-Ex) using fluoroscopy. [Method] The intervertebral body angle of the lower cervical spine of 8 healthy individual was analyzed using fluoroscopy during cervical extension with the head in the neutral (Ex) and protracted (Pro-Ex) positions. [Results] At maximum cervical extension position, we noted a significanly smaller value in the Pro-Ex position than in Ex

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... During extension, the intervertebral body angle was significantly greater at C3-4 and less at C6-7 level in the Pro-Ex position compared to the Ex position in the initial phase. However, there was no significant difference in the intervertebral body angle between the two positions in final phase of extension. This shows greater extension movement C6-7 level in Pro-Ex. [Conclusion] The pro-Ex result showed less range of motion of extension. This suggests exaggerated hypermobility in the lower segments of the cervical spine, which might be implicated in early degenerative disease of the cervical spine.