nutationcounternutation

Nutation and counternutation refer to reciprocal movements of the sacrum relative to the ilia, which are the two hip bones. These movements are a fundamental component of the mechanics of the pelvis and are often discussed in the context of spinal and pelvic biomechanics, particularly in fields like chiropractic and osteopathy.

Nutation is a forward and downward movement of the sacrum. Imagine the top of the sacrum tilting forward and the inferior tip moving backward. This action causes the sacral base to move anteriorly and the apex to move posteriorly. This movement also increases the anteroposterior diameter of the pelvic outlet.

Counternutation is the opposite movement, where the sacrum moves backward and upward. In this motion, the sacral base moves posteriorly and the apex moves anteriorly. This action decreases the anteroposterior diameter of the pelvic outlet and is sometimes referred to as sacral extension.

These movements are intimately linked to the ilia. During nutation, the ilia move into an anterior tilt, while during counternutation, the ilia move into a posterior tilt. This coordinated action between the sacrum and ilia contributes to the stability and mobility of the sacroiliac joints, which are crucial for weight transfer and shock absorption in the lower body.

The precise extent and interplay of nutation and counternutation can be influenced by various factors, including posture, locomotion, and even respiration. Understanding these movements is considered important for assessing and treating conditions affecting the spine and pelvis.