Walking Cycle Clinical observation of the normal walking cycle (Click here to view an interactive animation of the walking cycle) demonstrates that sacral sidebending and rotation couple to opposite sides. In the normal walking cycle, the sacrum appears to move with left torsion on the left oblique axis, return to neutral, rotate in right torsion on the right oblique axis, and then return to neutral. With left torsion on the left oblique axis, the sacrum rotates left and sidebends right, with the right sacral base moving into anterior nutation. In right torsional movement on the right oblique axis, the sacrum rotates right and sidebends left, with the left sacral base moving into anterior nutational movement. Because the nutational component of this normal walking movement is anterior in direction, left torsion on the left oblique axis (L on L) and right torsion on the right oblique axis (R on R) are described as anterior torsional movements.

For descriptive purposes, this complex, polyaxial, torsional movement is considered to occur around an oblique axis. By convention, the left oblique axis runs from the upper extremity of the left sacroiliac joint to the lower end of the right sacroiliac joint, and the right oblique axis runs from the upper end of the right sacroiliac joint to the lower extremity of the left sacroiliac joint. Although the exact biomechanics of the torsional movements of the sacrum are unknown, the hypothetical left and right oblique axes are useful for descriptive purposes.

The nutational movement in normal walking is anterior on one side, return to neutral, and anterior to the opposite side, and return to neutral. Posterior nutational movement does not appear past neutral in the normal walking cycle. Because much of the activity of the musculoskeletal system involves the walking cycle, maintenance of normal L-on-L and R-on-R sacral torsion is an important therapeutic objective.

1. At right heel strike, the right innominate has rotated in a posterior direction and the left innominate has rotated in a anterior direction. The anterior surface of the sacrum is rotated to the left and the superior surface is level (Click here to visualize this position).

2. At right leg midstance, the right leg is straight and the innominate is rotating anteriorly. The sacrum has rotated right and side-bent left (Click here to visualize this position).

3. At left heel strike, the left innominate begins to rotate anteriorly; after toe-off, the right innominate begins to rotate posteriorly. The sacrun is level, rotated right (Click here to visualize this position).

4. At left leg midstance, the left innominate is high and the left leg is straight. The sacrum has rotated to the left and is side-bent right (Click here to visualize this position).

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