Sacral torsions and sacral diagnosis: name any sacrum in four steps

9 min read. Updated October 9, 2026.

A sacral torsion is the sacrum rotated around one of its two oblique axes and stuck there. The name gives the rotation first and the axis second: left on left means rotated left on the left oblique axis, and left on right means rotated left on the right oblique axis. Five findings name every torsion, and the same five findings separate torsions from unilateral sacral flexion and extension.

The axes

Oblique axes are named for their upper end. The left oblique axis runs from the top of the left sacroiliac joint down to the bottom of the right one; the right oblique axis is its mirror image. Torsions happen around these.
The middle transverse axis carries sacral flexion and extension between the ilia: the postural axis.
The superior transverse axis sits at S2. It is the respiratory and cranial axis.
The inferior transverse axis is where the innominates rotate on the sacrum.

Two words come up constantly. Nutation (sacral flexion) moves the base forward and down and the apex back. Counternutation (sacral extension) moves the base back and up and the apex forward.

The landmarks

Sacral sulcus: the dip beside each PSIS at the top of the sacrum. A deep sulcus means that side of the base is forward; a shallow sulcus means it is back.
Inferior lateral angle (ILA): the bottom corners of the sacrum. In a torsion, one ILA is posterior (and usually a little inferior).

When the sacrum rotates left, its right base swings forward and its left ILA swings back. So the deep sulcus sits on the side opposite the rotation, and the posterior ILA sits on the rotation side.

The tests

Seated flexion test

The patient sits and bends forward while you follow both PSISs. The side that rides up earlier or farther is positive. Sitting locks out the legs, so this test isolates sacral motion between the ilia.

In a torsion, the positive side is opposite the axis.
In unilateral flexion or extension, the positive side is the involved side.

Spring test

Press on the lumbosacral junction. If the base springs forward, the test is negative: the base is free to move forward (forward torsions, flexions). If it will not spring, the test is positive: the base is stuck back (backward torsions, extensions).

Sphinx test (lumbar extension)

The patient props up on the elbows, which drives the sacral base forward. If one side of the base is already stuck forward, the free side catches up and the sulci even out. If one side is stuck back, the free side moves forward alone and the asymmetry gets worse.

The table

Every row below comes from the rulebook our cases are generated from.

Diagnosis	Seated flexion	Sulcus	ILA	Spring	Sphinx
Left on leftForward torsion	Right	Right deep	Left posterior	Negative	Evens out
Right on rightForward torsion	Left	Left deep	Right posterior	Negative	Evens out
Left on rightBackward torsion	Left	Right deep	Left posterior	Positive	Gets worse
Right on leftBackward torsion	Right	Left deep	Right posterior	Positive	Gets worse
Left unilateral sacral flexionBase stuck forward	Left	Left deep	Left posterior and inferior	Negative	Evens out
Left unilateral sacral extensionBase stuck back	Left	Left shallow	Left anterior and superior	Positive	Gets worse
Right unilateral sacral flexionBase stuck forward	Right	Right deep	Right posterior and inferior	Negative	Evens out
Right unilateral sacral extensionBase stuck back	Right	Right shallow	Right anterior and superior	Positive	Gets worse

Built from the same rulebook as the cases. Seated flexion is positive on the side opposite the axis in torsions and on the involved side in unilateral patterns.

Two bilateral patterns round out the set. They have no clear seated flexion side.

Diagnosis	Sulci	ILAs	Spring
Bilateral flexion	Both deep	Both posterior	Negative
Bilateral extension	Both shallow	Both anterior	Positive

Name any sacrum in four steps

Compare the deep sulcus and the posterior ILA. Opposite sides: a torsion. Deep sulcus with an inferior, posterior ILA on the same side: unilateral flexion on that side. Shallow sulcus with a superior, anterior ILA on the same side: unilateral extension on that side.
Torsion? Rotation is the side of the posterior ILA (the side opposite the deep sulcus).
The axis is opposite the positive seated flexion test.
Matching names are forward, mismatched are backward. Then check the spring and sphinx: forward torsions spring (negative) and even out in sphinx; backward torsions do not spring (positive) and get worse.

Worked example 1

Seated flexion positive on the left. Deep left sulcus. Posterior right ILA. Spring negative. Sulci even out in sphinx.

Deep sulcus left, posterior ILA right: opposite sides, so a torsion. Rotation is right (the posterior ILA). The axis is opposite the left seated flexion: the right axis. Right on right is a forward torsion, and the negative spring and leveling sphinx agree. Right on right.

Worked example 2

Seated flexion positive on the left. Deep right sulcus. Posterior left ILA. Spring positive. Asymmetry worse in sphinx.

Opposite sides again, so a torsion rotated left. Axis opposite the left seated flexion: right. Left on right is backward, and the positive spring and worsening sphinx agree. Left on right.

Worked example 3

Seated flexion positive on the right. Deep right sulcus. Right ILA inferior and posterior. Spring negative. Sulci even out in sphinx.

Deep sulcus and inferior, posterior ILA on the same side: a unilateral pattern, and the base is forward. Right unilateral sacral flexion.

Try it yourself

Pick a diagnosis to see its findings, or switch to quiz mode and name the sacrum from the findings alone.

Forward torsions

Backward torsions

Unilateral

Left on left

Forward torsion, on the left oblique axis

Seated flexion: Positive on the right
Sulcus: Right deep
ILA: Left posterior
Spring test: Negative (base springs)
Sphinx: Asymmetry evens out
L5 (compensated): Neutral, sidebent left, rotated right
Muscle energy: Left side, chest down (lateral Sims)

Posterior view, as you stand behind the patient. Dashed line: the oblique axis in use.

L5 and the sacrum

L5 and the sacrum move as a pair, and the teaching model links them with two rules:

L5 sidebending engages the oblique axis on the same side. L5 sidebent left sets up the left oblique axis.
L5 rotates opposite to the sacrum in a compensated pattern.

Forward torsions pair with a neutral (Type I) L5; backward torsions pair with a non-neutral (Type II) L5.

Torsion	Expected L5
Left on left	Neutral, sidebent left, rotated right
Right on right	Neutral, sidebent right, rotated left
Left on right	Non-neutral, sidebent right, rotated right
Right on left	Non-neutral, sidebent left, rotated left

Muscle energy for torsions

The patient lies on the side of the axis. For forward torsions the chest is turned down toward the table (lateral Sims, "hugging the table"); for backward torsions the chest faces up (lateral recumbent).

Torsion	Patient position
Left on left	Left side, chest down
Right on right	Right side, chest down
Left on right	Right side, chest up
Right on left	Left side, chest up

Position the patient and localize the motion to the lumbosacral junction by rotating the trunk and positioning the legs. In the usual forward setup the hips are flexed past 90 degrees; in the backward setup the bottom leg is straighter, the hips are flexed less, and the top leg becomes the lever.
Lower the legs off the table to take up the sidebending barrier.
The patient gently lifts the legs toward the ceiling (in the backward setup, the top knee) against your equal resistance for 3 to 5 seconds.
The patient relaxes completely; you take up the new slack.
Repeat 3 to 5 times, then recheck.

The exact leg lever (one leg or both) and side-lying variant differ between schools; the position rule above is the part boards test.

Unilateral flexion and extension: treatment

Unilateral flexion (base forward): patient prone. Press forward and up on the inferior, posterior ILA of that side to carry the base back. The patient breathes in deeply and holds while you hold the gain, and you resist as they breathe out.
Unilateral extension (base back): patient prone or propped in sphinx. Press forward and down on the shallow base. Here exhalation helps, and you resist the return on inhalation.

Abducting and internally rotating the hip on the involved side can loosen the sacroiliac joint. Bilateral flexion and extension are treated the same way with pressure on both ILAs or both bases.

Common traps

Seated versus standing flexion. Seated isolates the sacrum; standing tests the innominate (see innominate and pubic dysfunctions).
The sphinx label. Read what the sulci do, not whether the chart calls it positive.
Depth versus height of the ILA. Posterior describes depth; inferior describes height. Torsions give a posterior ILA; unilateral flexion gives one that is both posterior and inferior.
Incomplete findings. If the findings contradict each other or a test is missing, do not force a diagnosis; a real exam stem will give you enough to decide.
Landmarks are soft. Overlying tissue and innominate position change how deep a sulcus feels, and agreement between examiners is limited. That is a reason to test motion, not just position.

Practice

The free trainer gives you 10 sacral torsion cases a day: tap the landmarks, name the torsion, pick the muscle energy position. Try it now.

Frequently asked

What does left on left mean?

The sacrum is rotated left on the left oblique axis. It is a forward torsion: the deep sulcus is on the right, the left ILA is posterior, the seated flexion test is positive on the right and the spring test is negative.

How do you tell a forward from a backward torsion?

Forward torsions have matching names (left on left, right on right), a negative spring test and sulci that even out in the sphinx position. Backward torsions have mismatched names (left on right, right on left), a positive spring test and an asymmetry that gets worse in sphinx.

Which side is the seated flexion test positive in a sacral torsion?

On the side opposite the oblique axis. In left on left or right on left (both on the left axis), it is positive on the right.

What position do you use for muscle energy on a left on left torsion?

The patient lies on the left side, the side of the axis, chest down toward the table (lateral Sims). Backward torsions use the axis side too, but chest up.

What is the difference between a sacral torsion and a unilateral sacral flexion?

In a torsion the deep sulcus and the posterior ILA are on opposite sides and the seated flexion test is positive opposite the axis. In unilateral flexion the deep sulcus and an inferior, posterior ILA are on the same side, and the seated flexion test is positive on that side.