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Motion about an Oblique Axis
- With one hand, place one finger on the posterior superior iliac spine (PSIS) and another in the ipsilateral sacral sulcus
- The heel of your other hand goes on the contralateral inferior lateral angle (ILA)
- Press down on the ILA while feeling for posterior motion using index and middle fingers
- The deep sulcus will be more restricted with motion at the ILA, while the shallow sulcus will move more freely
- This is because the deep sulcus has rotated out of its normal position and become stuck while the shallow sulcus is still relatively free to spin on the axis of rotation
Skeletal Example
Human Example
