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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). 

 CTR Graph 
The  red line in the graph represents the measured distribution of segmental mobility C7-T5. The two surrounding black lines, represents  50% of the variation,  upper and lower quartiles, (Q1-Q3). Values within Q1-Q3 are defined as normal pretension, values below Q1 as compression and values above Q3 as tension. Read more
PERFECT DISTRIBUTION OF SEGMENTAL MOBILITY.

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.

GOLDEN RATIO RELATIONSHIP TO THE THORACIC INLET

Logarithmic spiral.

LOGARITHMIC SPIRAL POLAR EQUATION radius = ae^bxtheta

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.

GOLDEN RATIO OF THE THORACIC KYPHOSIS.