Kinematic analysis of the lower cervical spine in the protracted and retracted neck flexion positions.

[Purpose] The aim of this study was to analyze lower cervical spine kinematics in protracted and retracted neck flexion positions in healthy people. [Subjects and Methods] The craniovertebral angle (CVA) and intervertebral body angles of the lower cervical spine of 10 healthy individuals were analyzed using fluoroscopy in a neutral sitting with the head in the neutral (N), protracted (Pro), and retracted (Ret) positions and with the neck in full flexion with the head in the neutral (N-fx), protracted (Pro-fx), and retracted (Ret-fx) positions. [Results] There were significant differences in the CVA and intervertebral body angle at the C3-4 level, and the Ret position showed the highest values followed by the N and Pro positions. Regarding the intervertebral body angle at the C4-5 level, the Pro position showed a higher value than the N and Ret positions. At the C6-7 level, the Pro position showed the lowest value compared with the N and Ret positions. In the CVA, the Ret-fx position showed a higher value than the N-fx and Ret-fx positions. [Conclusion] The results suggest that in the neutral sitting position, protraction is an ineffective posture due to overstress of the C6-7 segment, which is placed in a hyperflexed position at this level. Instead, retraction is the recommend posture for the patient with C6-7 degeneration, which makes for a more flexed position in the upper cervical spine and a less flexed position in the lower cervical spine.