Final answer:
The explanation for anterior torsion with a left base deeper and a right ILA being most superficial is left sacral counter-nutation. This involves the posterior movement of the left base of the sacrum, decreasing the angle between the sacrum and adjacent bones.
Step-by-step explanation:
The explanation for anterior torsion with left base deeper and right ILA most superficial is c) Left sacral counter-nutation. This involves a movement where the base of the sacrum moves backward in relation to the ilium.
During left sacral counter-nutation, the left base of the sacrum moves posteriorly, and the right ILA (inferolateral angle) appears more superficial due to this compensatory movement. Counter-nutation is the opposite of nutation; it decreases the normal sacrococcygeal curve and involves posterior movement of the sacral base, hence decreasing the angle between the sacrum and the adjacent bones.
This phenomenon occurs in relation to the sacroiliac joints, which act as the interface between the sacrum and the ilium. The sacroiliac joints are important for transferring weight and movement between the upper body and the lower extremities.