Which listing uses inferior lateral PSIS SCP?

• A. PIIN
• B. PIEX
• C. PI
• D. IN

Answer: (B)

The listing system encodes three directional components of a subluxation: sagittal (posterior or anterior), vertical (inferior or superior), and transverse (internal or external, i.e., medial or lateral). For the PSIS contact point, describing an inferior lateral location means you want a posterior orientation, an inferior level, and a lateral (external) position. That combination is Posterior–Inferior–External, which is written as PIEX. So the correct listing uses the inferior lateral PSIS SCP.

Why the others don’t fit: specifying only posterior and inferior wouldn’t capture the lateral aspect, so a code like PI is incomplete. An internal (IN) component would imply a medial orientation rather than lateral, which doesn’t describe the inferior lateral PSIS SCP. And an inferior-only code (IN or PIIN) would omit the necessary third directional component to pin down the exact SCP on the PSIS. PIEX uniquely conveys posterior, inferior, and external (lateral) positioning.