CERVICAL SAGITTAL BALANCE: A BIOMECHANICAL PERSPECTIVE CAN HELP CLINICAL PRACTICE

BACKGROUND & OBJECTIVE

The objective of this study was to understand the influence of sagittal malalignment on the mechanics of the cervical spine using an ex vivo model and its implications on pathology such as radiculopathy. Cervical sagittal balance is determined by sagittal vertical alignment (SVA) and T1-Slope. SVA is measured by the anterior offset of C2 from C7 (commonly defined as forward head posture). T1-Slope measures the angle between the plane of the superior end plate of T1 and the horizontal plane. It increases with upper thoracic hyperkyphosis and strongly corelates with an increased SVA.

METHODS

Motion was tracked of 13 individual cadaver cervical vertebrae in 3-D space using 3-D CT reconstructed anatomy. These animated kinetic models allowed for precise measurements as independent adjustments of SVA and T1-Slope were observed. The occiput was fixed in a horizontal gaze as the SVA and T1-Slope were incrementally adjusted, the motions of each vertebral body and occiput were measured using an optoelectronic motion measurement system. Foramen boundary tracing was done manually for the neutral posture and then the kinematic model calculated the traced foramen boundary in all postures.

RESULTS

Increasing SVA caused C2-C7 flexion with decreased lordosis and C0-C2 extension with increased lordosis. Increasing T1-Slope while holding C2-C7 SVA constant increased C2-C7 lordosis with extension of the lower cervical segments and flexion between C0-C2 segments. T1-Slope reduction also reduced

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