Intraoperative Alignment in Adult Spinal Deformity Surgery

Primary outcomes

1. Change in Pelvic incidence (PI)

   Time frame: Pre-operative, 6 weeks post-operative

   Pelvic incidence (PI) is a fixed anatomical parameter measuring the sagittal orientation of the sacrum relative to the hip joints (femoral heads), calculated as the angle between a line perpendicular to the midpoint of the sacral plate and a line connecting that midpoint to the axis of the femoral heads. The average PI angle in adults is generally between 40° and 55°.

2. Change in Pelvic incidence (PI)

   Time frame: Pre-operative, 3 months post-operative

   Pelvic incidence (PI) is a fixed anatomical parameter measuring the sagittal orientation of the sacrum relative to the hip joints (femoral heads), calculated as the angle between a line perpendicular to the midpoint of the sacral plate and a line connecting that midpoint to the axis of the femoral heads. The average PI angle in adults is generally between 40° and 55°.

3. Change in Pelvic incidence (PI)

   Time frame: Pre-operative, 6 months post-operative

   Pelvic incidence (PI) is a fixed anatomical parameter measuring the sagittal orientation of the sacrum relative to the hip joints (femoral heads), calculated as the angle between a line perpendicular to the midpoint of the sacral plate and a line connecting that midpoint to the axis of the femoral heads. The average PI angle in adults is generally between 40° and 55°.

4. Change in Lumbar lordosis (LL)

   Time frame: Pre-operative, Intra-operative (up to 1 hour)

   Lumbar lordosis (LL) measures the degree of inward, anteriorly convex curvature of the lower spine, usually quantified as an angle on lateral radiographs or imaging, often ranging between 30° and 80°

5. Change in PI-LL mismatch

   Time frame: Pre-operative, Intra-operative (up to 1 hour)

   Pelvic incidence-lumbar lordosis (PI-LL) mismatch measures the difference between a fixed pelvic parameter (PI) and the functional lumbar curve (LL). A mismatch >10 degrees (specifically PI minus LL) signifies sagittal malalignment.

6. Change in sagittal Vertical Axis (SVA)

   Time frame: Pre-operative, Intra-operative (up to 1 hour)

   Distance from the C7 plumb line to the posterior-superior corner of S1; optimal is < 5 cm.

7. Change in T1-Pelvic Angle (TPA)

   Time frame: Pre-operative, Intra-operative (up to 1 hour)

   Angle between the center of the T1 vertebral body, the femoral heads, and the sacral endplate, representing both SVA and pelvic tilt.

8. Change in T10-pelivc angle (PA)

   Time frame: Pre-operative, Intra-operative (up to 1 hour)

   The angle between the center of the T10 vertebra, the hip center, and the midpoint of the S1 upper endplate.

9. Change in L1-pelivc angle (PA)

   Time frame: Pre-operative, Intra-operative (up to 1 hour)

   The angle between a line from the L1 vertebra center to the femoral head axis, and a line from the S1 superior endplate to the femoral head axis.

10. Intraclass correlation coefficient (ICC)

    Time frame: End of study (up to 24 months)

    ICCs will be used to assess for consistency and reproducibility of the radiographic measurements made by the various observers. ICCs will be assessed using the following ranges: excellent (0.75-1.0), good (0.60-0.74), fair (0.40-0.59), and poor (< 0.40).