12 Questions
What are nutation and counternutation?
Terms used to describe movements limited to the near sagittal plane
Which motion is considered nutation?
The anterior tilt of the base of the sacrum relative to the ilium
Which motion is considered counternutation?
The posterior tilt of the base of the sacrum relative to the ilium
What creates the primary stabilizing forces at the sacroiliac joint?
All of the above
What is the close-packed position of the sacroiliac joint?
Full nutation
Which forces increase articular stability at the sacroiliac joint?
Both compression and shear forces
Which of the following is a vulnerable position for the sacroiliac joint?
Full nutation
Which of the following motions can cause nutation and counternutation?
Both sacral-on-iliac and iliac-on-sacral rotation
What is the natural position of the sacroiliac joint when unloaded?
Full counternutation
Which of the following is not a primary stabilizing force at the sacroiliac joint?
None of the above
Which plane are the articular surfaces of the sacroiliac joint largely in?
Sagittal plane
Which motion increases compression and shear forces between joint surfaces?
Nutation
Study Notes
- The sacroiliac joint has complex rotational and translational movements.
- Nutation and counternutation are terms used to describe movements limited to the near sagittal plane.
- Nutation is the anterior tilt of the base of the sacrum relative to the ilium, while counternutation is the reverse motion.
- Nutation and counternutation can occur by sacral-on-iliac rotation, iliac-on-sacral rotation, or both motions performed simultaneously.
- Nutation increases compression and shear forces between joint surfaces, thereby increasing articular stability.
- The close-packed position of the sacroiliac joint is considered full nutation.
- Forces that create a nutation torque are considered the primary stabilizing forces at the sacroiliac joint.
- The stabilizing torque is created by gravity, stretched ligaments, and muscle activation.
- When unloaded, the sacroiliac joints naturally return to a less stable, or counternutated, position.
- The plane of the articular surfaces of the sacroiliac joint is largely vertical, making it vulnerable to vertical slipping, especially when subjected to large forces.
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