Topic_7^J_Lecture_2_Biomechanics_of_Vetebral_Column_d3cd8487817.pdf

Biomechanics of vertebral column

1. Topic 7 – Biomechanics of
Vertebral Column
Lecture 2
PHT103

2. By the end of this lecture you should be able to
▶ Describe briefly the general structure and function of
vertebral column
▶ Explain the structure and function of cervical spine
▶ Explain the structure and function of thoracic spine
▶ Explain the structure and function of the lumbar
spine
▶ Explain the structure and function of the sacral spine
▶ Explain the structure and function of vertebral
muscles
▶ Describe the general effects of aging and Injury in
vertebral column

3. Articulations of Vertebral Column
▶2 main types of articulations
▶ Cartilaginous (Symphyses) joints: Between
the vertebral bodies
▶ Synovial joints: Between the zygapophyseal
facets
▶Hence the joints are
▶ Interbody Joints (between the vertebral
bodies)
▶Facet (apophyseal) joints (between zygapophyseal
facets)

4. Interbody Joints
▶6 degrees of freedom
▶Available movements include (think
of the planes and axis
▶ Sliding (translation)
▶ Anterior to posterior sliding (C)
▶ Medial to lateral sliding (A)
▶ Axial rotation (torsion) – (E)
▶ Compression & Distraction (B)
▶ Tilting
▶ Anterior to posterior(F)
▶ To lateral directions (D)
▶Facet joints influence the total available
motion of the interbody joints

5. Facet Joints
▶Between left and right inferior
articular facets and the
respective superior left and right
articular facets of the vertebra
immediately below.
▶Regional variations in structures
exist
▶Intra-articular accessory joint
structures present
▶ Fibroadipose meniscoids
▶ Protects the articular surfaces
that are exposed during flexion
and extension of vertebral
column

6. Ligaments and Capsules
▶6 main ligaments
▶Anterior longitudinal ligaments (ALL)
▶ Associated with interbody joints
▶Posterior longitudinal ligaments (PLL)
▶ Associated with interbody joints
▶Ligamentum flavum
▶ Thick, elastic ligament that connects lamina to lamina
▶Interspinous ligaments
▶ Connects spinous process of adjacent vertebra
▶Supraspinous ligaments
▶ Strong cordlike structure that
connects the tips of spinous
processes
▶Intertransverse ligaments
▶ Pass between transverse processes
▶Facet joint capsules
▶Assist the ligament in providing limitation to motion and stability of
vertebral column
▶Strongest in transition zones, cervicothoracic junction, or

8. posterior longitudinal ligament

15. Major ligaments of the Vertebral Column
Ligaments Function Region
Annulus fibrosus
(outer fibers)
Resists distraction, translation and rotation of
vertebral bodies
Cervical, thoracic and lumbar
Anterior
Longitudinal
Ligament
Limits extension and reinforces anterolateral
portion of annulus fibrosus and anterior
aspect of interverbal joints
C2 to sacrum, but well developed in
cervical, lower thoracic and lumbar
regions
Anterior
atlantoaxial
ligament (cont.
ALL)
Limits extension C2 to occipital bone
Posterior
longitudinal
Ligament
Limits forward flexion and reinforces
posterior portion of the annulus fibrosus
C2 to sacrum. Broad in the cervical and
thoracic regions and narrow in the lumbar
region
Tectorial membrane
(cont. PLL)
Limits forward flexion C2 to occipital bone
Ligamentum Flavum
(LF)
Limits forward flexion, particularly in the
lumbar area, where it resists separation of
the laminae
C2 to sacrum, thin, broad and long in
cervical and thoracic regions and thickest
in lumbar region

16. Major ligaments of the Vertebral Column
Ligaments Function Region
Posterior atlantoaxial
ligament (cont. LF)
Limits flexion C1 to C2
Supraspinous ligamentsLimit forward flexion Thoracic and lumbar (C7-L3/L4). Weak in
lumbar region
Ligamentum nuchae Limit forward flexion Cervical region (occipital protuberance to
C7)
Intertransverse
ligaments
Limit forward flexion Primarily in lumbar region, where they are
well developed
Intertransverse
ligaments
Limit contralateral lateral flexion Primarily in lumbar region
Alar ligaments Limit rotation of the head to the same
side and lateral flexion to the opposite
side
C1 and C2
Iliolumbar ligamentsResists anterior sliding of L5 and S1Lower lumbar regions
Facet joint capsulesResist forward flexion and axial rotationStrongest at cervicothoracic junction and
in the thoracolumbar region

18. Functions of Vertebral column
▶Kinematics
▶ Motions available for the whole vertebral
column are
▶ Flexion
▶ Extension
▶ Lateral flexion
▶ Rotation: available in each spinal region, but
varies drastically on different shapes of facet
joints
▶Coupled from individual motion segments and
variations in the regions
▶Amount of motion is determined by the size of
the IVDs
▶ Direction of motion is determined by the
orientation of facets

19. Flexion of Vertebral Column
▶Superior vertebral body above anteriorly tilts
▶Inferior facets of that vertebra slide upwardly
▶Causes separation of spinous processes
▶ Resisted by supraspinous and interspinous
ligaments
▶Widening of intervertebral foramen
▶Compression of and bulging of annulus fibrosus
anteriorly
▶Stretching of annulus posteriorly
▶ Resisting the separation of vertebral bodies
▶ Restraining the motion, along with passive tension
in facet joint capsules, ligamentum flavum, PLL
and spinal extensors

20. Extension of Vertebral Column
▶Superior vertebral body above posteriorly tilts
▶Gliding of the superior vertebra on the
contiguous(next) inferior vertebra
▶Spinous processes to approximate
▶ Bony contact of spinous processes will limit
extension
▶Narrowing of intervertebral foramen
▶Stretching of annulus fibrosus anteriorly
▶ Passive tension can limit the available motion
along with tension in the facet joint capsules and
anterior trunk muscles
▶Compression and bulging of annulus posteriorly
▶Anterior longitudinal ligament can directly limit
extension

21. Lateral Flexion of Vertebral Column
▶Superior vertebral body laterally tilts
▶Translates over the contiguous vertebra below
▶Spinous processes to approximate
▶ Bony contact of spinous processes will limit
extension
▶Contralateral widening of intervertebral foramen
to the direction of lateral flexion and narrowing
on the ipsilateral side
▶Compression of annulus fibrosus on the concavity
of the curvature
▶Stretching of the annulus fibrosus on the
convexity of the curvature
▶ Passive tension in the annulus fibers,
intertransverse ligaments and anterior and
posterior trunk muscles on the convex side limit
the lateral flexion

22. Functions of Vertebral Column
▶Kinetics
▶ Vertebral column is subjected to these
loads (forces) during normal functional
activities but also at rest
▶ Axial compression
▶ Distraction (tension)
▶ Bending
▶ Torsion
▶ Shear
▶Ability to resist these loads varies among
spinal regions and depends on
▶ Type, duration and rate of loading
▶ The person’s age and posture
▶ The condition and properties of the various
structural elements
▶ Integrity of the nervous system

23. AxialCompression
▶Force acting through the long axis of the spine at right angles to the
discs as a result of
▶ Gravity
▶ Ground reaction forces
▶ Forces produced by the ligaments and muscular contractions
▶ Any potential external load carried on the persons body
▶Discs and vertebral bodies will resist most of the compressive forces, while
some is shared by the neural arches and facet joints
▶ Most of the load is transmitted from the superior vertebral endplate to the
inferior
endplate through the trabecular bone and its cortical shell
▶ Zygapophyseal joints carry from 0-30% of the compressive load
▶ Spinous process may share some load when the spine is in hyperextension
▶The nucleus pulposus will be deformed by compressive load and force
distributed to all directions, stress created in the annulus fibrosus and central
compressive load occurs on the vertebral endplates
▶Endplates will fail(fracture) first because they are able to under the least amount of
deformation and the discs will be last to fair (rupture)

24. Bending
▶Causes both compression and tension on the structures of the spine
▶ Forward Flexion
▶ Anterior structures are subjected to compression
▶ Posterior structures are subjected to tension
▶ Resistance offered to the tensile forces by the collagen fibers in the posterior
outer annulus fibrosus, facet joint capsules, and posterior ligaments helps to
limit extremes of motion and thus provides stability in flexion
▶ Creep occurs when subjected to sustained loading
▶ Extension
▶ Posterior structures generally are either unloaded or subjected to compression
▶ Anterior structures are subjected tension
▶ Resistance to extension is provided by the anterior outer fibers of the annulus
fibrosus, the facet joint capsules and passive tension in the anterior longitudinal
ligament and by contact of the spinous processes
▶ Lateral bending
▶ Ipsilateral side of the disc is compressed
▶ Contralateral fibers of the outer annulus fibrosus and the contralateral
intertransverse ligament help to provide stability

25. Torsion & Shear
▶Torsion
▶ Forces created during axial rotation that occurs as part of the coupled
motions that take place in the spine
▶ Annulus fibrosus is the most effective in resisting torsion
▶ Particularly in lumbar region
▶ Risk of rupture of the disc fibers is increased when there is a combination of
torsion, heavy axial compression and forward bending
▶Shear
▶ Occur parallel to the disc and tend to cause each vertebra to slide on the
one below
▶ Translation anteriorly, posteriorly or laterally.
▶ Facet joins resist some of the anterior forces in lumbar region and the discs
resist the reminder
▶ When load is sustained the discs exhibit creep, and the facet joints may have
to
resist all of the shear force

26. Summary of Vertebral Function
Structure Function
Body Resists compressive forces
Transmits compressive forces to vertebral endplates
Pedicles Transmits bending forces (exerted by muscles attached to the spinous and transverse
processes) to the vertebral bodies
Laminae Resist and transmit forces (that are transmitted from spinous and zygapophyseal
articular processes) to pedicles
Serve as attachment sites for muscles and ligaments
Transverse processes Serve as attachment sites for muscles and ligaments
Spinous processes Resist compression and transmit forces to laminae
Serve as attachment sites for muscles and ligaments
Zygapophyseal facets Resist shear, compression, tensile and torsional forces
Transmit forces to laminae
Nucleus pulposus Resists compression forces to vertebral endplates and translates vertical compression
forces into circumferential tensile forces in annulus fibrosis
Annulus fibrosus Resist tensile, torsional and shear forces

27. Structure and Function of the Cervical Region
▶Cervical vertebrae must achieve many combinations of motions to
▶ Position the primary sensory organs optimally
▶ Provide stability to protect the brain stem, spinal cord, and arteries that
supply the brain
▶2 distinct regions function somewhat independently to meet the
different demands
▶ Craniovertebral segment (upper cervical region)
▶ Occipital condyles and first 2 cervical vertebrae
▶ Lower cervical region
▶ C3 to C7
▶Craniovertebral segments are able to move in opposite directions from
the lower cervical spine as needed
▶ Example: Person slouches while sitting (think of the forward head posture,
protracted position of the cervical region)
▶ Protraction: craniovertebral extension combined with lower cervical flexion
▶ Retraction: craniovertebral flexion combined with lower cervical extension

28. Structure and Function of the Thoracic Region
▶Primary goal of the structures of the thorax (including thoracic spine
and rib cage) is to
▶ Protect the vital organs and the spinal cord
▶ Preserving total trunk ROM
▶Diminished segmental mobility of the thoracic spine occurs frequently due to
prolonged sitting positions that involve slouched posture
▶Total available motion in the thoracic segments is less than that of the
cervical
and lumbar regions
▶ Loss of even small amount of thoracic motion may have a functional impact
▶Retaining functional mobility when there is reduced thoracic mobility may
place increased mobility demands on cervical or lumbar regions
▶Increase the loads on structures of these regions contributing to neck or low back
pain

29. Structure and Function of the Lumbar Region
▶Primary goal of lumbar region are to
▶ augment mobility at the hip joints to increase total mobility of the trunk
▶ effectively absorb and adjust body weight forces from head, arms, and trunk
above
▶ Effectively absorb ground reaction forces below in weight bearing
▶Flexion and extension are the predominant motion in the lumbar region
▶ Allowing us to reach our hands to the floor and overhead
▶ Adjusting to keep the line of gravity of the body over the base of support

30. Function of the Cervical Region
•The cervical spine is designed for a rela�vely large amount of mobility.
•Normally, the neck moves 600 �mes every hour whether we are awake or
asleep.
•The mo�ons of �exion and extension, lateral �exion, and rota�on are
permi�ed in the cervical region.
•These mo�ons are accompanied by transla�ons that increase in magnitude
from C2 to C7.
•the predominant transla�on occurs in the sagi�al plane during �exion and
extension.

31. Function of the Cervical Region
•The atlanto-occipital joints allow for primarily nodding movements between the head and the atlas
•The combined range of mo�on for �exion-extension reportedly ranges from 10° to30°.
•In �exion, the occipital condyles roll forward and slide backward (Fig. 4–31A).
•In extension, the occipital condyles roll backward and slide forward (Fig. 4–31B).
•few degrees of rota�on and lateral �exion available.

35. Function of the Cervical Region
•Mo�ons at the atlantoaxial joint include rota�on, lateral �exion, �exion, and extension.
•Approximately 55% to 58% of the total rota�on of the cervical region occurs at the atlantoaxialjoints (Fig. 4–32).
•The atlas pivots about 45° to either side, or a total of about 90°.
•The alar ligaments limit rota�on at the atlantoaxial joints.

36. Function of the Cervical Region
•Lateral �exion and rota�on are coupled mo�ons.
•In the upper cervical segments, lateral �exion is coupled with contralateral rota�on and rota�on is coupled with
contralateral lateral �exion.

37. Function of the Cervical Region
•Flexion of these segments must include anterior �lt of the cranial vertebral body coupled with anterior transla�on.
•Extension includes posterior �lt of the cranial vertebral body coupled with posterior transla�on.

38. Function of the Cervical Region
•Lateral �exion is coupled with ipsilateral rota�on, and rota�on is coupled with ipsilateral lateral
�exion.
•The disc at C5/C6 is subject to a greater amount of stress than other discs because C5/C6 has the
greatest range of �exion-extension and is the area where the mechanical strain is greatest.

39. Function of the Cervical Region
Kinetics
•weight of the head (compressive load) must be transferred
through atlanto-occipital joint to the articular facets of the
axis then transferred through the pedicles and laminae of
the axis to the inferior surface of the body and to the two
inferior zygapophyseal articular processes.
•Subsequently, the forces are transferred to the adjacent
inferior disc.

40. Function of the Cervical Region
Kinetics
•In the cervical region from C3 to C7, compressive forces are transmi�ed by three
parallel columns: a single anterocentral column formed by the vertebral bodies and
discs and two rodlike posterolateral columns composed of the le� and right
zygapophyseal joints.
•The compressive forces are transmi�ed mainly by the bodies and discs, with a li�le
over one-third transmi�ed by the two posterolateral columns.
•Compressive loads are rela�vely low during erect stance and si�ng postures and high
during the end ranges of �exion and extension.

41. Function of the Cervical Region
•The cervical spine has approximately 45% of the compressive strength of the lumbar spine
but only 20% of the bending strength.
•There is greater bending strength in extension compared to �exion.

44. Function of the Thoracic Region
Kinematics
•All mo�ons are possible in the thoracic region, but the range of
�exion and extension is extremely limited in the upper thoracic
region (T1 to T6) because of the rigidity of the rib cage and because
of the zygapophyseal facet orienta�on in the frontal plane.

•In the lower part of the thoracic region (T9 to T12), the
zygapophyseal facets lie closer to the sagi�al plane, allowing an
increased amount of �exion and extension.
•In the upper part of the thoracic region, lateral �exion and rota�on
are coupled in the same direc�on, while rota�on in the lower region
may be accompanied by lateral �exion in the opposite direc�on

45. Function of the Thoracic Region
Kinetics
•The thoracic region is subjected to increased compression forces in comparison with the
cervical region because of the greater amount of body weight that needs to be
supported and the region’s kypho�c shape.
•The line of gravity falls anterior to the thoracic spine. This produces a �exionmoment on
the thoracic spine that is counteracted by the posterior ligaments and the spinal
extensors.

46. Function of the Lumbar Region
•The lumbar region is capable of movement in �exion, extension, lateral �exion, and
rota�on.
•The lumbar zygapophyseal facets favor �exion and extension because of the
predominant sagi�al plane orienta�on
•Most of the flexion takes place at the lumbosacral joint

47. Function of the Lumbar Region
•Lateral �exion and rota�on are most free in the upper lumbar region
and progressively diminish in the lower region.
•The largest lateral �exion range of mo�on and axial rota�on occurs
between L2 and L3.
•When the medial orienta�on of the zygapophyseal joint surfaces is
greater, the resistance to axial rota�on is greater.
•The total amount of lumbar mo�on from a neutral lordo�c posi�on is
reported to be as follows:
•�exion: 52°
•extension: 19°
•lateral �exion: 30° to each side and
•rota�on: 32° to each side (+/–12°)

48. Function of the Lumbar Region
Kinetics
Compression
•One of the primary func�ons of the lumbar region is to provide support for the weight of the upper
part of the body in sta�c as well as dynamic situa�ons.
•The increased size of the lumbar vertebral bodies and helps the lumbar structures support the
addi�onal weight.
•Lumbar region must also withstand the tremendous compressive loads produced by
muscle contraction.
•lumbar interbody joints shared 80% of the load and the zygapophyseal facet joints in axial
compression shared 20% of the total load.
•With increased extension or lordosis, the zygapophyseal joints will assume more of the compressive
load.

49. Function of the Lumbar Region
Shear
•In the upright standing posi�on, the lumbar segments are subjected to anterior shear forces
caused by the lordo�c posi�on, the body weight, and ground reac�on forces.
•This anterior shear or transla�on of the vertebra is resisted by the direct impact of the inferior
zygapophyseal facets of the cranial vertebra against the superior zygapophyseal facets of the
subjacent (caudal)vertebra.

52. Function of the Sacral Region
Kinematics
•Nutation is the term commonly used to refer to movement of the sacrum
whereby the sacral promontory moves anteriorly and inferiorly while the
sacral apex moves posteriorly and superiorly (Fig. 4–52A).
•During the closed chain task of forward bending from a standing position,
for example, the sacrum will nutate on the two innominate bones
immediately following flexion of the lumbosacral junction.
•Counternutation refers to the opposite movement, in which the sacral
promontory moves posteriorly and superiorly while the sacral apex moves
anteriorly

54. Function of the Sacral Region
Kinetics
•Stability of the sacroiliac joints is extremely important because these joints must
support a large portion of the body weight.
•In normal erect posture, the weight of the head, arms, and trunk is transmitted
through the fifth lumbar vertebra and lumbosacral disc to the first sacral
segment.
•The force of the body weight creates a nutation torque on the sacrum.
Concomitantly, the ground reaction force creates a posterior tilt of the
innominates.
•The countertorques of nutation of the sacrum and posterior tilt of the
innominates are supported by the ligamentous tension and fibrous expansions
from adjacent muscles, which reinforce the joint capsules and blend with the
ligaments.

55. MUSCLES OF THE VERTEBRAL COLUMN
The Craniocervical/Upper Thoracic Regions
Two primary roles:
•To hold the head upright against gravity and
•To in�nitely posi�on the head in space in order to op�mally position the sensory organs.

56. MUSCLES OF THE VERTEBRAL COLUMN
The muscles of the cervicothoracic region also serve two primary roles:
•To position the head and neck in space, and
•To stabilize the head and neck to allow and produce movement of the scapula.

58. MUSCLES OF THE VERTEBRAL COLUMN
Posterior Muscles

59. MUSCLES OF THE
VERTEBRAL COLUMN
Posterior Muscles
•trapezius muscle is the most
superficial of the posterior.
•when the upper extremi�es are �xated, the
trapezius can produce extension of the head
and neck.
•Ac�ng unilaterally, the upper trapezius can
produce ipsilateral lateral �exion and
contralateral rota�on of the head and neck.

60. MUSCLES OF THE VERTEBRAL
COLUMN
•The levator scapula lies deep to the trapezius.
•If the upper extremity is stabilized, it will produce
ipsilateral lateral �exion and rota�on of the cervical
spine.
•Levator scapula is optimally aligned to produce
a posterior shear force on the cervical spine

63. MUSCLES OF THE VERTEBRAL
COLUMN
•The splenius capitis and splenius cervicis muscles lie
deeper than the levator scapulae.
•These muscles serve as prime movers of the head and neck.
• They produce extension when working bilaterally and ipsilateral
rota�on when working unilaterally.

66. The semispinalis capi�s and semispinalis cervicis
muscles are deeper than the splenius group.
These muscles have the most op�mal line of pull
and a large moment arm to produce extension of
the head and neck and an increase in the
cervical lordosis.

68. MUSCLES OF THE VERTEBRAL COLUMN
•The longissimus capi�s and longissimus cervicis are deeper than
and lateral to the semispinalis group.
•Their deep posi�on places them close to the axis of rota�on for
�exion and extension, They produce compression of the cervical
segments.
•The lateral posi�on allows them to produce ipsilateral lateral
�exion when working unilaterally
•when working bilaterally, they serve as frontal plane stabilizers of
the cervical spine

70. MUSCLES OF THE VERTEBRAL COLUMN
•The suboccipital muscles are the deepest posterior
muscles and consist of the rectus capitis posterior minor
and major, inferior oblique, and superior oblique muscles.
•Together, they produce occipital extension.
•Working alone, they produce ipsilateral rotation and lateral
flexion.
•They may serve primarily a proprioceptive role and
produce small movements in order to fine-tune motion.

71. Lateral Muscles

72. MUSCLES OF THE VERTEBRAL COLUMN
Lateral Muscles
•Scalene muscles are located on the lateral aspect of the cervical spine and
serve as frontal plane stabilizers

73. MUSCLES OF THE VERTEBRAL COLUMN
•The anterior scalene muscles, when working bilaterally, will
�ex the cervical spine and produce an anterior shear.
•Unilaterally, the anterior scalene muscles will produce
ipsilateral lateral �exion and contralateral rota�on to the
cervical spine.

75. MUSCLES OF THE VERTEBRAL COLUMN
The middle scalene muscles are more laterally
placed than are the anterior scalene
muscles, and their line of pull makes them
excellent frontal plane stabilizers.
The posterior scalene muscles predominantly
laterally �ex the neck.

77. MUSCLES OF THE VERTEBRAL COLUMN
It is unique in that, because of this orienta�on, it lies anterior to the axis
of rota�on in the lower cervical spine, producing �exion
when ac�ng bilaterally but posterior to the axis at the
skull, producing extension of the head on the neck.
Ac�ng unilaterally, the sternocleidomastoid muscle will produce
ipsilateral lateral �exion and contralateral rota�on of the
head and neck.

78. Anterior Muscles

80. MUSCLES OF THE VERTEBRAL COLUMN
Anterior Muscles
•longus capitis and longus colli
•Although they do have sufficient moment arm to
produce flexion, they also produce a fair amount of
compression.

81. MUSCLES OF THE VERTEBRAL
COLUMN
The longus capi�s and longus colli work in
synergy with the trapezius to stabilize the head and neck
in order to allow the trapezius to upwardly rotate the
Scapula.

82. MUSCLES OF THE VERTEBRAL COLUMN
The rectus capi�s anterior and rectus capi�s lateralis
are able to produce �exion as a result of their line of pull.

83. MUSCLES OF THE VERTEBRAL COLUMN
Lower Thoracic/Lumbopelvic Regions
Muscles of the lower spine regions produce and control
movement of the trunk and stabilize the trunk for mo�on of
the lower extremi�es.

84. MUSCLES OF THE VERTEBRAL COLUMN
Posterior Muscles

85. MUSCLES OF THE VERTEBRAL COLUMN
The erector spinae consist of the longissimus and
iliocostalis muscle groups. In general, these muscles are
iden��ed as extensors of the trunk.

86. MUSCLES OF THE
VERTEBRAL COLUMN
The erector spinae act eccentrically un�l approximately
two-thirds of maximal �exion has been a�ained,
at which point they become electrically silent. This is
called the �exion-relaxa�on phenomenon.

88. MUSCLES OF THE VERTEBRAL
COLUMN
Mul��dus line of pull is ver�cally oriented, and they are distant from
the axis of rota�on and therefore have an e�ec�ve moment
arm for extension by increasing the lumbar lordosis.

89. MUSCLES OF THE VERTEBRAL
COLUMN
The quadratus lumborum is deeper than the
erector spinae
and multifidus muscles.
The quadratus lumborum, when acting bilaterally,
serves as an important frontal plane stabilizer.
When acting unilaterally,
the quadratus lumborum can laterally flex the spine

90. MUSCLES OF THE
VERTEBRAL COLUMN
Anterior Muscles
The rectus abdominis is the prime flexor of the trunk.
Tension on this abdominal fascial system will provide stability, similar to that provided by a corset,
around
the trunk.

91. MUSCLES OF THE VERTEBRAL
COLUMN
The abdominal wall consists of the external oblique, the
internal oblique, and the transversus abdominis
muscles.
These muscles together form what McGill called the
“hoop” around the entire abdomen, with the abdominal
wall
as the anterior aspect and the thoracolumbar fascia
and its
muscle attachments as the posterior aspect.
This hoop plays an important role in stability of the
lumbopelvic region.

92. Aging