The LOD is P-A, L-M only. What listing does this indicate?

• A. PI
• B. IN
• C. EX
• D. AS

Answer: (C)

In this system, a vertebral listing is read from the two directional components of the line of drive: sagittal (front-to-back) and transverse (left-to-midline). When the line of drive is only P-A (posterior-to-anterior) and L-M (left-to-midline), you have a specific two-axis vector. The code that matches this exact combination is EX. So the LOD being P-A, L-M only points to an EX listing.

The other options would involve different directional components beyond P-A and L-M, which isn’t the case here, so they don’t fit this LOD.