Three-dimensional movements of the upper cervical spine

Area of Science:

• Orthopedics
• Biomechanics
• Anatomy

Background:

• Understanding normal occipito-atlanto-axial joint complex motion is crucial for diagnosing instability.
• Quantitative data on 3D joint movements aids in clinical evaluation.

Purpose of the Study:

• To quantitatively determine the three-dimensional movements of the occiput-C1 and C1-C2 joints.
• To establish baseline normal motion parameters for these critical upper cervical segments.

Main Methods:

• In vitro study using ten fresh cadaveric cervical spine specimens (occiput to C7).
• Application of incremental pure moments (up to 1.5 N-m) to simulate physiological loading.
• Stereophotogrammetry used to record 3D bone movements during flexion, extension, lateral bending, and axial rotation.

Main Results:

• Calculated neutral zone, elastic zone, and range of motion for occiput-C1 and C1-C2 joints.
• Occiput-C1 neutral zones: 1.1° (flex/ext), 1.5° (lat bend), 1.6° (axial rot).
• C1-C2 neutral zones: 3.2° (flex/ext), 1.2° (lat bend), 29.6° (axial rot).
• Occiput-C1 ranges of motion: 3.5° (flex), 21.0° (ext), 5.5° (lat bend), 7.2° (axial rot).
• C1-C2 ranges of motion: 11.5° (flex), 10.9° (ext), 6.7° (lat bend), 38.9° (axial rot).
• Greatest intervertebral motion occurred at C1-C2 axial rotation (38.9°), with its neutral zone comprising 75% of this motion.

Conclusions:

• The C1-C2 joint demonstrates significantly greater motion, especially in axial rotation, compared to the occiput-C1 joint.
• A substantial neutral zone in C1-C2 axial rotation suggests a potential for instability within this segment.
• These quantitative 3D motion data provide essential biomechanical insights into upper cervical spine function.