Biomechanics · functional reading

Sacral nutation and counternutation

Nutation and counternutation are very small-amplitude movements of the sacrum relative to the iliac bones. In nutation, the sacral base tilts forward and downward; counternutation is the reverse movement.

Scientific basis

These movements take place at the sacroiliac joints. In nutation, the sacral promontory moves forward and downward while the sacral apex and the coccyx move backward; in counternutation, the reverse occurs. Their amplitude is on the order of 2°, around instantaneous centers of rotation that shift; they result from the movements of neighboring structures.

Amplitudes increase during pregnancy. Clinical palpation of these movements is not very reliable.

Blue Portance / SBNFA™ reading

In the SBNFA™ framework, sacroiliac micro-rotation is a micro-movement that combines nutation, counternutation and lateral tilting. These micro-movements contribute to adjustments and compensations, and then to stress redistribution. This is not a doctrine of large sacroiliac mobility.

Contribution to the analysis of sitting

Seating analysis does not observe nutation directly; it describes pelvic mobility and load distribution, within which these micro-movements take place.

Not to be confused with

Anterior and posterior pelvic tilt, movements of the whole pelvis relative to the femurs; large sacroiliac mobility: the amplitude remains on the order of a degree; “unlocking” or “realigning” the sacrum, notions with no basis in this framework; nutation in astronomy, unrelated.

Sources and scope

Viel (1989): the sacroiliac joint, a review (Annales de kinésithérapie) (in French)

Established anatomical and biomechanical notion; amplitudes are small and measurement is difficult. The micro-rotation reading is specific to the SBNFA™ framework.