Which statement correctly describes the PI listing's line of drive?

• A. P-A, M-L
• B. P-A, I-S
• C. P-A, S-I
• D. P-A, L-M

Answer: (B)

A PI listing means the vertebra is positioned posterior and inferior relative to the segment above. To correct it, the thrust should move the vertebra in the opposite directions: from posterior toward the front (P-A) and from inferior toward the superior (I-S). This combination—P-A, I-S—targets both components of the misalignment. Moves left-right (L-M or M-L) don’t address the posterior/inferior displacement, and direction from superior to inferior (S-I) would push the segment downward instead of upward. Therefore, the line of drive for a PI listing is P-A, I-S.