Hresko et al reported a simple equation that can divide high-grade spondylolisthesis into categories based on pelvic orientation. The authors are from Children Hospital Boston, Hospital Sainte-Justine (Montreal), Centre des Massues and Groupe de Biomecanigue Clinique in Lyons, France.
Patient selection: high-gradespondylolisthesis (> 50% translation of L5 on S1)
Examination: lateral pelvic X-ray with the patient standing straight
Parameters (Figure 1, page 2209):
(1) pelvic tilt in degrees (PT), the angle between the vertical reference line and a line running between (a) the center of a line running along the superior surface of the sacrum and (b) the center of the hip axis
(2) sacral slope in degrees (SS), the angle between (a) the line running along the superior surface of the sacrum and (b) a horizontal line running through the anterosuperior sacrum
delineation line for sacral slope in degrees =
= (0.844835 * (pelvic tilt)) + 25.021
Pelvic Tilt
Sacral Slope
Location
Pelvis
high
low
below line
unbalanced
low
high
above line
balanced
In an unbalanced pelvis the pelvis is retroverted and the sacrum vertical.
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