Segmental proportion
Segmental proportions C7-T5 - a factor having significant impact on spinal sagittal balance.
Upper thoracic spine
A smooth distribution of segmental mobility within C7-T5 is favourable for a balanced posture and for less disability and symptoms.
If mobility C7-T3 adds up to 61.8% and T3-5 to 38.2%, these segments will be in a Golden ratio proportion, Phi (φ = 1.618).
Impact on sagittal balance
The proportion C7-T3 to T3-5 will determine the "tightness", the growth factor, of a Golden spiral. Some anatomical structures like the thoracic inlet and the length of the thoracic spine relates to the Golden spiral. These deviations will influence the spinal sagittal balance.
Thoracic inlet
A balanced mobility within C7-T5 shows a smooth spiral starting at T5 through C7-T1 and the first rib, optimizing the space for structures passing through. Deviations will influence the inclination and the space within the thoracic inlet.
Logarithmic spiral.
Thoracic spine
In the same way the spiral shows an anatomical relationship to the length of the thoracic spine, passing through C7-T1 and ending at T12. The growth factor will have an impact on the thoracic kyphosis.
This proportion is also used in algorithms assessing the geometric diameters of the thoracic cavity.