Intraoperative Alignment in Adult Spinal Deformity Surgery

Change in Pelvic incidence (PI)

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°.

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

Change in Pelvic incidence (PI)

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°.

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

Change in Pelvic incidence (PI)

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°.

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

Change in Lumbar lordosis (LL)

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°

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

Change in PI-LL mismatch

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.