Anatomy · functional reading
Pelvic incidence
Pelvic incidence is an anatomical angle specific to each individual, fixed at skeletal maturity. It largely determines the sagittal organization of the pelvis and spine and does not vary with posture.
Scientific basis
Described by Legaye and Duval-Beaupère in 1998, pelvic incidence is measured on a lateral radiograph. It relates the upper endplate of the sacrum to the axis of the femoral heads.
Pelvic incidence is a morphological parameter specific to each individual. It develops during growth and becomes fixed at skeletal maturity. Unlike pelvic tilt (PT) and sacral slope, it does not vary with posture: for a given individual, the relationship pelvic incidence = pelvic tilt + sacral slope remains constant across changes of position, including between standing and sitting. Its value may, however, change slowly with aging.
Pelvic incidence determines lumbar lordosis and the latitude of pelvic orientation: the lower it is, the less pronounced the lordosis and the less latitude pelvic tilt has, particularly to compensate for an imbalance through posterior pelvic tilt (Roussouly and Pinheiro-Franco, 2011). Conversely, a high incidence goes with a more marked lordosis and greater latitude. There is no “good” or “bad” incidence, only an angle specific to each person.
Blue Portance / SBNFA™ reading
In the SBNFA™, pelvic incidence is the starting point of individualization: it is a reminder that each person has their own pelvic organization and that there is no universal sitting posture.
The hypothesis of a functional relationship close to 90° between the plane of the pelvis and the axis of the femurs, to be individualized according to pelvic incidence, belongs to the SBNFA™ reading.
Contribution to the analysis of sitting
A seat can be analyzed for its compatibility with the person’s pelvic incidence: the pelvic orientation it imposes, knee height, and whether it lets the pelvis find its own orientation.
Not to be confused with
Pelvic tilt (PT), which changes with position; sacral slope, the inclination of the sacrum; spinal profile, which describes the spinal curves as a whole.
Related terms
Sacral slope · Spinal profile · Posterior pelvic tilt · Pelvic tilt (PT)
Sources and scope
- Legaye et al. (1998): pelvic incidence, a fundamental parameter in the regulation of sagittal spinal curves (European Spine Journal)
- Le Huec et al. (2011): pelvic parameters, origin and significance (European Spine Journal)
- Roussouly and Pinheiro-Franco (2011): spino-pelvic organization and adaptation in pathology (European Spine Journal)
- Lazennec et al. (2012): standing and sitting pelvic parameters, EOS imaging (Seminars in Arthroplasty)
- Influence of age and sagittal balance on the value of pelvic incidence (European Spine Journal, 2014)
Established radiological parameter, measured in standing. Its use in adjusting a seat belongs to the SBNFA™ reading.
