- In this study, orthopedic surgeons and bioengineers investigated the kinematics of the entire head–neck complex (C0–T1) during left and right twisting motions of the head by eight women who had no anatomic abnormality or early disc degeneration
- In the upper (C0–C1) and lower (C2–T1) cervical segments, lateral bending was similar in magnitude but occurred in opposite directions, resulting in compensatory cervical lateral curvature that balances the head in the upright posture during rotation
- The upper cervical segments (C0–C1 and C1–C2) provided the main mobility needed for axial head rotation
- These and other quantitative data reported in this study enhance the understanding of the function of the healthy head–neck complex and could help improve decision-making for treatment of craniocervical diseases and injuries
Altered cervical motion can indicate injuries or diseases of the head–neck complex, such as whiplash, concussion, atlas (C1) / axis (C2) fractures, rheumatoid arthritis and cervical spine degenerative diseases. To evaluate these disorders, clinicians need to know how the head–neck complex moves in healthy individuals.
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Early research into this question was done in cadaveric specimens. More recently, imaging studies have greatly improved clinical knowledge, but most focused on the motion of either the upper or lower cervical region, measured in different groups of participants.
Runsheng Guo, MD, research fellow, and Thomas D. Cha, MD, MBA, assistant chief of the Orthopaedic Spine Center in the Department of Orthopedic Surgery at Massachusetts General Hospital, and colleagues took a different approach. They studied the kinematics of the entire head–neck complex in a single group of asymptomatic volunteers during head rotation. The most important finding, reported in the Journal of Biomechanics, is that the upper and lower cervical regions have distinct motion characteristics.
The participants were eight asymptomatic women (average age 33) who had no anatomic abnormality or early disc degeneration evident on computed tomography (CT) of the head and neck. The CT images were used to create 3D models of the skull (C0) and the cervical vertebrae from C1 to T1.
While standing, each participant rotated her head left and right while the skull and cervical spine were imaged using a dual fluoroscopic imaging system. The fluoroscopic images were paired with the 3D bone models to reproduce the positions of the skull and cervical vertebrae in 3D space.
The left and right head rotations proved to be symmetrical, and the left and right ranges of motions (ROMs) for each cervical region or individual segment were pooled. The researchers calculated maximal ROM for axial twisting (AT, the primary rotation), flexion–extension (FE) and lateral bending (LB).
Maximal LB ROMs in the upper cervical spine (C0–C2) and lower cervical spine (C2–T1) were similar, 18° and 21°. However, they occurred in opposite directions (contralateral in the upper cervical spine, ipsilateral in the lower). This resulted in a compensatory cervical lateral curvature such that the LB of the head–neck complex was only 4.6°.
At the lower cervical spine, the ratio of LB to AT was 2.4, whereas the ratio of FE to AT was 0.9.
Motion of Individual Segments
- Of the eight individual cervical segments, C0–C1 was associated with the largest FE (12°) but allowed only small AT and small LB
- C1–C2 contributed 66% of AT, as well as the largest LB (13° contralateral)
- AT, FE and LB at lower cervical segments were typically small, and there was only one significant difference between levels
This and other quantitative data included in the article could be critical for:
- Evaluating the pre- and post-operative kinematical performance of the head–neck complex
- Improving surgical and conservative treatment techniques
- Establishing rehabilitation regimens
For example, since the upper cervical segment is more mobile than the lower cervical segment, fusion of upper cervical segments could dramatically reduce the mobility of the entire head–neck complex. The emerging technique of upper cervical arthroplasty deserves more investigation as to whether it can restore head–neck function without adversely affecting the patient's quality of life.
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