As the left innominate moves posteriorly/inferiorly, the left sacral base moves

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Multiple Choice

As the left innominate moves posteriorly/inferiorly, the left sacral base moves

Explanation:
Understanding how the pelvis and sacrum move together at the sacroiliac joints helps here. When the left innominate moves posteriorly and inferiorly, the sacrum on that side tends to rotate forward relative to the ilium—a movement called nutation. This nutation is an anterior and downward tilt of the sacral base. So the left sacral base moves anteriorly and inferiorly. Medial or lateral shifts aren’t the primary directions produced by this SI joint coupling, which mainly manifests as a sagittal-plane tilt (nutation) of the sacral base in response to the ilium’s posterior/inferior motion.

Understanding how the pelvis and sacrum move together at the sacroiliac joints helps here. When the left innominate moves posteriorly and inferiorly, the sacrum on that side tends to rotate forward relative to the ilium—a movement called nutation. This nutation is an anterior and downward tilt of the sacral base. So the left sacral base moves anteriorly and inferiorly. Medial or lateral shifts aren’t the primary directions produced by this SI joint coupling, which mainly manifests as a sagittal-plane tilt (nutation) of the sacral base in response to the ilium’s posterior/inferior motion.

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