Biomechanics · functional reading
Posterior pelvic tilt
Posterior pelvic tilt refers to a backward tilting of the pelvis, which tends to reduce the lumbar curve. It may correspond to a person’s natural pelvic orientation or to a movement adopted depending on the position.
Scientific basis
The orientation of the pelvis is measured in particular by pelvic tilt (PT): the higher it is, the more the pelvis is retroverted and the lower the sacral slope. These two angles vary with position, whereas their sum, pelvic incidence, is fixed in adults.
Two situations must be distinguished. A person with low pelvic incidence naturally has a more vertical pelvis and a less pronounced lordosis; their pelvic tilt (PT) also has less leeway, which limits their ability to compensate through posterior pelvic tilt. Conversely, posterior pelvic tilt can be a compensation mechanism, for example when the trunk is unbalanced forward. Moving from standing to sitting is also accompanied by posterior pelvic tilt: in patients with a hip replacement, pelvic tilt (PT) increases on average by about 18° and sacral slope decreases by the same amount, while pelvic incidence remains unchanged (Lazennec et al., 2012).
Blue Portance / SBNFA™ reading
The SBNFA™ does not regard posterior pelvic tilt as a defect to be corrected. It distinguishes the natural orientation of the pelvis specific to each person from the posterior tilt imposed by a seat that does not suit them.
The idea that a posterior pelvic tilt locked in place while sitting increases certain lumbar and pelvic stresses belongs to the SBNFA™ reading.
Contribution to the analysis of sitting
A seat can be analyzed according to the pelvic orientation it favors: seat inclination, knee height, backrest shape, and the freedom it leaves the pelvis to change orientation over time.
Not to be confused with
Anterior pelvic tilt, a forward tilting; pelvic incidence, a fixed angle specific to the shape of the pelvis; pelvic tilt (PT) and sacral slope, the angles that measure this orientation; lumbar kyphosis, a rounding of the lower back that may accompany posterior pelvic tilt.
Related terms
Pelvic incidence · Spinal profile · Anterior pelvic tilt · Pelvic tilt (PT) · Sacral slope · Pelvic mobility
Sources and scope
- Legaye et al. (1998): pelvic incidence and the regulation of sagittal spinal curves (European Spine Journal)
- Barrey et al. (2013): compensatory mechanisms of sagittal balance (European Spine Journal)
- Roussouly et al. (2005): classification of sagittal profiles (Spine)
- Le Huec et al. (2011): pelvic parameters, origin and significance (European Spine Journal)
- Lazennec et al. (2012): standing and sitting pelvic parameters, EOS imaging (Seminars in Arthroplasty)
Established radiological parameters. The effects of a posterior pelvic tilt imposed in the seated position belong to the SBNFA™ reading.
