Thoracolumbar rotation ROM: which of the following is true about the stationary arm?

• A. It is aligned with the midline of the spine
• B. It is parallel to the floor
• C. It is aligned with the pelvis
• D. It is perpendicular to the floor

Answer: (B)

Thoracolumbar rotation occurs in the horizontal plane around a vertical axis through the trunk, so you need a stable, horizontal reference to quantify how far the trunk turns. Keeping the stationary arm parallel to the floor provides that fixed baseline, allowing the moving arm to reflect true axial rotation without being shifted by pelvic tilt or spinal posture. Aligning the stationary arm with the midline of the spine or with the pelvis would introduce movement into the reference itself, confounding the measurement, and making the baseline vertical (perpendicular to the floor) would measure a different orientation rather than the horizontal rotation you’re assessing.