Sacral slope

Scientific basis

Together with pelvic tilt (PT), it satisfies the relationship pelvic incidence = pelvic tilt + sacral slope: since incidence is fixed, the two positional parameters vary in opposite directions. Sacral slope is closely linked to lumbar lordosis, and Roussouly’s classification of spinal profiles is based on it.

When moving from standing to sitting, sacral slope usually decreases by 20 to 30°. In French, it is called pente sacrée.

Blue Portance / SBNFA™ reading

In the SBNFA™ reading, sacral slope, together with pelvic tilt (PT), describes the sagittal orientation of the pelvis and its relationship to the spinal profile. Its range of variation is determined by pelvic incidence: each person has their own margin, with no common ideal value.

Contribution to the analysis of sitting

Seating analysis does not measure sacral slope, which is a radiological parameter. It observes the orientation of the pelvis and how it varies over time.

Not to be confused with

Pelvic incidence, a fixed morphological parameter; pelvic tilt (PT), which varies in the opposite direction; lumbar lordosis, a spinal curve closely linked to sacral slope without being identical to it; nutation, a movement of the sacrum relative to the iliac bones, on the order of 2°.

Related terms

Anterior pelvic tilt · Pelvic incidence · Sacral nutation and counternutation · Spinal profile · Posterior pelvic tilt · Pelvic tilt (PT)

Sources and scope

• Le Huec et al. (2011): pelvic parameters, origin and significance (European Spine Journal)
• Kouyoumdjian (2023): involvement of the hip-spine relationship in hip arthroplasty surgery (Revue de chirurgie orthopédique et traumatologique) (in French)