Lumbosacral Motion
Normal Neutral Mechanics
In the biomechanical model, anterior nutation is called sacral flexion and posterior nutation is called sacral extension. During anterior nutation, there is an inferior translatory movement of the sacrum. During posterior nutation, there is a superior translatory movement.
Bilateral symmetry of anterior/posterior nutation depends on the symmetry of the two sacroiliac joints. With asymmetry of a patient's two sacroiliac joints being so common, asymmetry of anterior/posterior nutation is also quite common.
With the lumbar spine in the neutral position, lumbar vertebrae and the sacrum will move in opposite directions. For example:
- When lumbar flexion occurs (forward bending), the sacrum nutates posteriorly (the sacral base tilts backward) as L5 flexes.
- When lumbar extension occurs (backward bending), the sacrum nutates anteriorly (the sacral base tilts forward) as L5 extends.
The axis around which this anterior-posterior nutation occurs has been described differently by various investigators but appears to be related to the upper and lower limbs of the sacroiliac joint and their junction somewhere around S2. Click here to visualize the effects of lumbar flexion/extension from an oblique view.
- If the sacrum rotates to the right and side bends to the left, the lumbar vertebrae will rotate to the left and side bend to the right (Click to view an interactive animation of neutral lumbosacral mechanics from a
top view
back view
front view
- If the sacrum rotates to the left and side bends to the right, the lumbar vertebrae will rotate to the right and side bend to the left (Click to view an interactive animation of neutral lumbosacral mechanics from a
top view
back view
front view
Click here to join Dr. Philip E. Greenman, D.O., F.A.A.O., as he describes normal neutral mechanics.
In the biomechanical model, anterior nutation is called sacral flexion and posterior nutation is called sacral extension. During anterior nutation, there is an inferior translatory movement of the sacrum. During posterior nutation, there is a superior translatory movement.
Bilateral symmetry of anterior/posterior nutation depends on the symmetry of the two sacroiliac joints. With asymmetry of a patient's two sacroiliac joints being so common, asymmetry of anterior/posterior nutation is also quite common.
With the lumbar spine in the neutral position, lumbar vertebrae and the sacrum will move in opposite directions. For example:
- When lumbar flexion occurs (forward bending), the sacrum nutates posteriorly (the sacral base tilts backward) as L5 flexes.
- When lumbar extension occurs (backward bending), the sacrum nutates anteriorly (the sacral base tilts forward) as L5 extends.
- If the sacrum rotates to the right and side bends to the left, the lumbar vertebrae will rotate to the left and side bend to the right (Click to view an interactive animation of neutral lumbosacral mechanics from a top view back view front view
- If the sacrum rotates to the left and side bends to the right, the lumbar vertebrae will rotate to the right and side bend to the left (Click to view an interactive animation of neutral lumbosacral mechanics from a top view back view front view
Click here to join Dr. Philip E. Greenman, D.O., F.A.A.O., as he describes normal neutral mechanics.