In the erect posture, the pelvis is tilted forward. The plane of the inlet makes an angle of about 55° with the horizontal & is called 'angle of incination'.
When the angle of inclination is increased due to sacralisation of 5 th lumbar vertebra, it is called as High inclination.
Obstetric significance of high inclination -
1. It may cause delay in engagement because the uterine axis fails to coincide with that of the inlet.
2. It favours occipitoposterior position
3. There may be difficulty in descent of the head due to long birth canal & flat sacrum interfering with internal rotation.
(Low inclinaton due to lumbarisation of first sacral vertebra facilitates early engagement)
Read :
Anatomy of pelvis with diagrams
Anatomy of pelvis - summary
African women have greater angle of inclination than caucasians, possibly causing higher rates of CPD.
(Why racial difference? - Related to malnutrition & possible genetic factors. see this pdf
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