Risk factors and clinical significance of posterior slip of the proximal vertebral body after lower lumbar fusion

Figure 1 Pelvic and spinal parameters and retrograde distance of cranial adjacent segments. A: Pelvic incidence: The angle between the line perpendicular to the sacral plate at its midpoint and the line connecting this point to the axis of the femoral heads; Pelvic tilt: The angle between the line connecting the midpoint of the sacral plate to the femoral head axis and the vertical axis; Sacral slope: The angle between the superior plate of S1 and a horizontal line; B: Lumbar lordosis (LL): The angle between the superior endplate of the L1 vertebra and the superior endplate of the S1; Lower LL: The angle between the superior endplate of the L4 vertebra and the superior endplate of the S1; C: Retrograde distance of cranial adjacent segments: The distance between point A and point B; point A: The dorsal edges of the cranial endplate of the inferior vertebral, point B: The intersection point between the line crossing the dorsal edges of the caudal endplate of the superior vertebral and perpendicular to the cranial endplate of the inferior vertebral. PI: Pelvic incidence; PT: Pelvic tilt; LL: Lumbar lordosis; lLL: Lower LL; SS: Sacral slope.