INTERNAL MEDICINE
SERIES
OMM LECTURE
Sacrum and Innominates
Julia Faller, D.O., PGY1
ANATOMY
Innominate: 3 bones; ilium, ischium and pubis
Sacrum: 5 fused vertebrae
Sacral base: top part of the sacrum
Sacral promontory: anterior portion of 1st segment
Sacral apex: bottom part of the sacrum
Sacral sulci: superior lateral part of sacrum
Inferior lateral angles (ILA’s): inferior lateral part
of sacrum
ANATOMY
ANATOMY
LIGAMENTS
True pelvic ligaments: sacroiliac ligaments
that surround and help stabilize the SI joint
Anterior
 Posterior
 Interosseous

LIGAMENTS
Accessory pelvic ligaments
Sacrotuberous—originates at ILA and attaches
to ischial tuberosity
 Sacrospinous—originates at sacrum and
attaches to ischial spines
 Iliolumbar—originates from transverse
processes of L4 and L5 and attaches to medial
side of iliac crest

LIGAMENTS
LIGAMENTS
Board Points
The sacrospinous ligament divides the
greater and lesser sciatic foramen
The iliolumbar ligament is often the first
ligament to become painful in lumbosacral
decompensation
MUSCLES
Primary pelvic muscles: levator ani and
coccygeus (pelvic diaphragm)
Secondary: muscles that have partial
attachment to the true pelvis
Iliopsoas
 Obturator internus
 Piriformis

Clinical Point
Approximately 11% of the population will
have the entire peroneal portion of the
sciatic nerve running through the belly of
the piriformis.
Piriformis hypertonicity can cause buttock
pain that radiates down the thigh, but not
usually below the knee.
MECHANICS
Innominates: rotate about an inferior
transverse axis of the sacrum during the
walking cycle.
Sacrum: four types of motion
Respiratory
 Craniosacral
 Postural
 Dynamic

AXIS
RESPIRATORY AXIS
Respiratory motion occurs about the
superior transverse axis of the sacrum.
Located at S2
During inhalation the sacral base moves
posterior.
During exhalation the sacral base moves
anterior
RESPIRATORY AXIS
CRANIOSACRAL AXIS
Motion occurs about the superior transverse
axis of the sacrum
AKA inherent motion
During craniosacral flexion the sacral base
rotates posteriorly, counernutation
During craniosacral extension the sacral
base rotates anteriorly, nutation
CRANIOSACRAL AXIS
POSTURAL AXIS
Motion occurs about the middle transverse
axis of the sacrum.
As a person begins to bend forward, the
sacral base moves anteriorly.
At terminal flexion the sacrotuberous
ligaments become taut and the sacral base
will move posteriorly.
POSTURAL AXIS
OBLIQUE AXIS
Motion that occurs during ambulation.
Dynamic motion
As weight bearing shifts from one side to
the other while walking, the sacrum engages
two sacral oblique axes.
Stepping forward with the right leg will
cause a left sacral axis to be engaged.
OBLIQUE AXIS
INNOMINATE DYSFUNCTION
The side of the positive standing flexion test
is the side of the dysfunction.
Types:
Anterior/posterior rotation
 Superior/inferior innominate shear
 Superior/inferior pubic shear
 Inflare/outflare

INNOMINATE DYSFUNCTION
Anterior innominate rotation: one
innominate will rotate anteriorly
Inferior transverse axis
Tight quadriceps
ASIS inferior/PSIS superior
Longer leg ipsilaterally
ASIS restricted to compression
ANTERIOR INNOMINATE
INNOMINATE DYSFUNCTION
Posterior innominate rotation: one
innominate will rotate posteriorly
Inferior transverse axis
Tight hamstrings
ASIS superior/PSIS inferior
Shorter leg ipsilaterally
ASIS restricted to compression
POSTERIOR INNOMINATE
INNOMINATE DYSFUNCTION
Superior innominate shear: one
innominate will slip superiorly
ASIS and PSIS superior
Pubic rami superior
Short leg ipsilaterally
ASIS restricted to compression
SUPERIOR INNOMINATE SHEAR
INNOMINATE DYSFUNCTION
Inferior innominate shear: one
innominate will slip inferiorly
ASIS and PSIS inferior
Pubic rami inferior
Long leg ipsilaterally
ASIS restricted to compression
INFERIOR INNOMINATE SHEAR
INNOMINATE DYSFUNCTION
Superior pubic shear: one pubic bone is
displaced superiorly compared to the other
Trauma or tight rectus abdominus
ASIS/PSIS level
Pubic bones superior ipsilaterally
ASIS restricted to compression
SUPERIOR PUBIC SHEAR
INNOMINATE DYSFUNCTION
Inferior pubic shear: one pubic bone is
displaced inferiorly compared to the other
Trauma or tight abductors
ASIS/PSIS level
Pubic bones inferior ipsilaterally
ASIS restricted to compression
INFERIOR PUBIC SHEAR
INNOMINATE DYSFUNCTION
Innominate inflare: innominate rotates
laterally
ASIS more lateral ipsilaterally therefore the
distance between the ASIS and umbilicus is
greater on the affected side
Ischial tuberosity more medial ipsilaterally
ASIS restricted to compression ipsilaterally
INNOMINATE DYSFUNCTION
Innominate outflare: innominate rotates
medially
ASIS more medial ipsilaterally therefore the
distance between the ASIS and umbilicus is
less on the affected side
Ischial tuberosity more lateral ipsilaterally
ASIS restricted to compression ipsilaterally
SACRAL DYSFUNCTION
Three types of dysfunction
Sacral torsion on an oblique axis
 Sacral shear (unilateral sacral
flexion/extension)
 Bilateral sacral flexion/extension

SACRAL TORSION
Sacral rotation about an oblique axis along
with somatic dysfunction at L5
The axis is named for the side of the
superior pole it runs through
SACRAL TORSION RULES
When L5 is sidebent, a sacral oblique axis is
engaged on the same side as the
sidebending
When L5 is rotated, the sacrum rotates the
opposite way on an oblique axis
The seated flexion test is positive on the
opposite side of the oblique axis
Board Points
Know the rules of L5 on the sacrum
MOTION OF TORSIONS
Motion present over the part of the sacrum
that moved anteriorly
Motion restricted over the part of the
sacrum that moved posteriorly
Motion restricted over the poles that make
up the oblique axis
SACRAL TORSION
Forward sacral torsion AKA anterior sacral
torsion.
Rotation is on the same side of the axis.
Left on left/right on right
Negative lumbosacral spring test
SACRAL TORSION: L on L
Left on left
Right sulcus deeper
Left ILA posterior and inferior
Lumbar curve convex to the right
Motion at right base only
SACRAL TORSION: R on R
Right on right
Left sulcus deeper
Right ILA posterior and inferior
Lumbar curve convex to the left
Motion at left base only
SACRAL TORSION
Backward sacral torsion AKA posterior
sacral torsion
Rotation is on the opposite side of the axis
Right on left/left on right
Positive lumbosacral spring test
Positive backward bending test
L5 will be non-neutral
SACRAL TORSION: R on L
Right superior sulcus moves posterior and
the left ILA moves anterior
Right sulcus shallow
Left ILA anterior and superior
Lumbar curve convex to the right
Motion at left ILA only
SACRAL TORSION: L on R
Left superior sulcus moves posterior and the
right ILA moves anterior
Left sulcus shallow
Right ILA anterior and superior
Lumbar curve convex to the left
Motion at right ILA only
BILATERAL SACRUM
Bilateral flexion and extension
The entire sacral base moves anterior or
posterior about a middle transverse axis
Common in the postpartum female
BILATERAL SACRAL FLEXION
Right and left sulci deep
ILA’s shallow bilaterally
Increased lumbar curve
False negative seated flexion test
Motion at base
Negative spring test
BILATERAL SACRAL EXTENSION
Right and left sulci shallow
ILA’s deep bilaterally
Decreased lumbar curve
False negative seated flexion test
Motion at both ILA’s
Positive spring test
SACRAL SHEARS
AKA unilateral sacral flexion/extension
The sacrum will shift anteriorly or
posteriorly around a transverse axis
UNILATERAL SACRAL FLEXION
Ipsilateral deep sulcus
Ipsilateral inferior ILA
Ipsilateral ILA posterior
Ipsilateral positive seated flexion test
Ipsilateral motion at sulcus
Ipsilateral restriction at ILA
Negative lumbosacral spring test
UNILATERAL SACRAL EXTENSION
Ipsilateral shallow sulcus
Ipsilateral superior ILA
Ipsilateral ILA anterior
Ipsilateral positive seated flexion test
Ipsilateral motion at ILA
Ipsilateral restriction at sulcus
Positive lumbosacral spring test
Question 1
Which structure divides the greater and
lesser sciatic foramen?
a. Sacrotuberous ligament
b. Sacrospinous ligament
c. Sacroiliac ligament
d. Tendon of the obturator internus
e. Tendon of the piriformis
Question 1
Which structure divides the greater and
lesser sciatic foramen?
a. Sacrotuberous ligament
b. Sacrospinous ligament
c. Sacroiliac ligament
d. Tendon of the obturator internus
e. Tendon of the piriformis
Question 2
Which of the following movements will
cause the sacral base to move anterior?
a. Cranial extension
b. Counternutation
c. Exhalation
d. Weight bearing on right leg
e. Weight bearing on left leg
Question 2
Which of the following movements will
cause the sacral base to move anterior?
a. Cranial extension
b. Counternutation
c. Exhalation
d. Weight bearing on right leg
e. Weight bearing on left leg
Question 3
Which of the following findings is present
in a left innominate anterior rotation?
a. PSIS inferior on left
b. PSIS superior on right
c. PSIS superior on left
d. ASIS superior on left
e. PSIS and ASIS posterior on left
Question 3
Which of the following findings is present
in a left innominate anterior rotation?
a. PSIS inferior on left
b. PSIS superior on right
c. PSIS superior on left
d. ASIS superior on left
e. PSIS and ASIS posterior on left