The pelvic index is used to assess which type of deformity?

The pelvic index is used to assess which type of deformity?

• A. Sagittal plane decompensation
• B. Coronal plane deformity
• C. Global kyphosis
• D. Temporal bone alignment

Answer: (A)

This item tests sagittal balance and how the pelvis compensates for sagittal misalignment. When there is forward or backward imbalance in the spine, the body shifts to maintain an upright posture, and the pelvis tilts as a primary compensatory mechanism. The pelvic index is a radiographic measure that captures this sagittal-plane decompensation, reflecting how far the pelvis has rotated to restore balance. It does not directly measure coronal-plane deformities (like lateral curve), global kyphosis magnitude, or unrelated structures such as temporal bone alignment. Therefore, the pelvic index best reflects sagittal plane decompensation.

This item tests sagittal balance and how the pelvis compensates for sagittal misalignment. When there is forward or backward imbalance in the spine, the body shifts to maintain an upright posture, and the pelvis tilts as a primary compensatory mechanism. The pelvic index is a radiographic measure that captures this sagittal-plane decompensation, reflecting how far the pelvis has rotated to restore balance. It does not directly measure coronal-plane deformities (like lateral curve), global kyphosis magnitude, or unrelated structures such as temporal bone alignment. Therefore, the pelvic index best reflects sagittal plane decompensation.