1. AXIAL SKELETON OSTEOLOGY AND ARTHROLOGY
Dr. Michael P. Gillespie

2. HUMAN SKELETON: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-1A.   Human skeleton. A, Anterior view. B, Posterior view. The axial skeleton is highlighted in blue. (From Thibodeau GA, Patton KT: Structure and function of the body, ed 13, St Louis, 2008, Mosby.)

3. HUMAN SKELETON: POSTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-1A.   Human skeleton. A, Anterior view. B, Posterior view. The axial skeleton is highlighted in blue. (From Thibodeau GA, Patton KT: Structure and function of the body, ed 13, St Louis, 2008, Mosby.)

4. RELATIVE LOCATION OR REGION WITHIN THE AXIAL SKELETON
Term
Synonym
Definition
Posterior
Dorsal
Back of the body
Anterior
Ventral
Front of the body
Medial
None
Midline of the body
Lateral
Away from the midline of the body
Superior
Cranial
Head or top of the body
Inferior
Caudal
Tail, or the bottom of the body
Dr. Michael P. Gillespie
The definitions assume a person is in the anatomic position.

5. COMPONENTS OF THE AXIAL SKELETON
Cranium
Vertebrae
Ribs
Sternum
Dr. Michael P. Gillespie

6. CRANIUM The cranium encases and protects the brain.
It houses several sensory organs.
Eyes, ears, nose and vestibular system.
Only the temporal and occipital bones are relevant to our study of kinesiology.
Dr. Michael P. Gillespie

7. OSTEOLOGIC FEATURES OF THE CRANIUM
Temporal Bone
Mastoid process
Occipital Bone
External occipital protruberance
Superior nuchal line
Inferior nuchal line
Foramen magnum
Occipital condyles
Basilar part
Dr. Michael P. Gillespie

8. TEMPORAL BONES
The two temporal bones form part of the lateral external surface of the skull immediately surrounding and including the external acoustic meatus.
The mastoid process is just posterior to the ear and serves as an attachment point to many muscles (i.e. sternocleidomastoid and longissimus).
Dr. Michael P. Gillespie

9. OCCIPITAL BONE
The occipital bone forms the posterior base of the skull.
The external occipital protruberance (EOP) is a palpable midline point. It is an attachment point for the ligamentum nuchae and the medial part of the upper trapezius muscle.
The superior nuchal line extends laterally from the EOP to the base of the mastoid process of the temporal bone. This line serves as the attachment point for several muscles of the neck (i.e. trapezius and splenius capitis).
The inferior nuchal line marks the anterior edge of the attachment of the semispinalis muscle capitis muscle.
The foramen magnum is a large circular hole at the base of the occipital bone. It serves as a passageway for the spinal cord.
Occipital condyles project from the anterior-lateral margins of the foramen magnum forming the convex component of the atlanto-occipital joint.
The basilar part of the occipital bone lies just anterior to the anterior rim of the foramen magnum.
Dr. Michael P. Gillespie

10. LATERAL VIEW OF THE SKULL
Dr. Michael P. Gillespie
FIGURE 9-2.   Lateral view of the skull.

11. INFERIOR VIEW OF THE OCCIPITAL AND TEMPORAL BONES
Dr. Michael P. Gillespie
FIGURE 9-3.   Inferior view of the occipital and temporal bones. The lambdoidal sutures separate the occipital bone medially, from the temporal bones laterally. Distal muscle attachments are indicated in gray, and proximal attachments are indicated in red.

12. VERTEBRAE
The vertebrae provide stability throughout the trunk and neck. They protect the spinal cord, ventral and dorsal roots, and exiting spinal nerve roots.
3 sections of the vertebra
Vertebral body (anterior)
Transverse and spinous processes (posterior) – posterior elements (neural arch, vertebral arch)
Pedicles – bridges that connect the body with the posterior elements – transfer muscle forces applied to the posterior elements forward across the vertebral body and intervertebral discs.
Dr. Michael P. Gillespie

13. Dr. Michael P. Gillespie
FIGURE 9-4.   A cross-section of a spinal cord is shown. Note the relationship among the neural tissues, components of the cervical vertebra, and the vertebral artery. (Modified with permission from Magee DL: Orthopedic physical assessment, ed 3, Philadelphia, 1997, Saunders.)

14. MAJOR PARTS OF A MIDTHORACIC VERTEBRA
Table 9-2
Major parts of a Midthoracic Vertebra
Chapter 9 Page 311
Dr. Michael P. Gillespie

15. ESSENTIAL CHARACTERISTICS OF A VERTEBRA
Dr. Michael P. Gillespie
FIGURE 9-5A.   The essential characteristics of a vertebra. A, Lateral view of the sixth and seventh vertebrae (T6 and T7). B, Superior view of the sixth vertebra with right rib.

16. ESSENTIAL CHARACTERISTICS OF A VERTEBRA
Dr. Michael P. Gillespie
FIGURE 9-5B.   The essential characteristics of a vertebra. A, Lateral view of the sixth and seventh vertebrae (T6 and T7). B, Superior view of the sixth vertebra with right rib.

17. RIBS
Twelve pairs of ribs enclose the thoracic cavity forming a protective cage for the cardiopulmonary organs.
The rib head and tubercle articulate with the thoracic vertebrae forming two synovial joints:
Costocorporeal (costovertebral)
Costotransverse
These joints anchor the posterior end of a rib to its corresponding vertebra.
The anterior end of a rib consists of flattened hyaline cartilage.
Dr. Michael P. Gillespie

18. TYPICAL RIB Dr. Michael P. Gillespie
FIGURE 9-6A.   A typical right rib. A, Inferior view. B, Posterior view.

19. STERNUM
Three parts
Manubrium (Latin – handle)
Body
Xiphoid process (Greek – sword)
The manubrium fuses with the body of the sternum at the manubriosternal joint (a cartilaginous joint that often ossifies later in life).
The xiphoid process is connected to the sternum by fibrocartilage at the xiphisternal joint that often fuses by 40 years of age.
Sternoclavicular joints.
Sternocostal joints.
Dr. Michael P. Gillespie

20. OSTEOLOGIC FEATURES OF THE STERNUM
Manubrium
Jugular notch
Clavicular facets for sternoclavicular joints
Body
Costal facets for sternocostal joints
Xiphoid process
Intrasternal Joints
Manubriosternal joint
Xiphosternal joint
Dr. Michael P. Gillespie

21. STERNUM Dr. Michael P. Gillespie
FIGURE 9-7.   Anterior view of the sternum, part of the right clavicle, and the first seven ribs. The following articulations are seen: (1) intrasternal joints (manubriosternal and xiphisternal), (2) sternocostal joints, and (3) sternoclavicular joints. The attachment of the sternocleidomastoid muscle is indicated in red. The attachments of the rectus abdominis and linea alba are shown in gray.

22. VERTEBRAL COLUMN 33 vertebral bony segments divided into five regions.
Cervical
Thoracic
Lumbar
Sacral
Coccygeal
Dr. Michael P. Gillespie

23. CURVATURES WITHIN THE VERTEBRAL COLUMN
When viewed from the side, the vertebral column shows four slight bends called normal curves.
Relative to the anterior aspect of the body, the cervical and lumbar curves are convex (bulging out), whereas the thoracic and sacral curves are concave (cupping in).
The curves in the vertebral column increases its strength, help maintain balance in the upright position, absorb shocks during walking, and help to protect the vertebrae from fracture.
Various conditions may exaggerate the normal curves of the vertebral column, or the column may acquire a lateral bend, resulting in abnormal curves.
The abnormal curves are kyphosis, lordosis, and scoliosis.
Dr. Michael P. Gillespie

24. VERTEBRAL COLUMN
Dr. Michael P. Gillespie

25. INCORRECT LABELING OF THE NORMAL CURVES
Dr. Michael P. Gillespie
FIGURE 9-8A.   A side view shows the normal sagittal plane curvatures of the vertebral column. A, The neutral position while one is standing. B, Full extension of the vertebral column increases the cervical and lumbar lordosis but reduces (straightens) the thoracic kyphosis. C, Flexion of the vertebral column decreases the cervical and lumbar lordosis but increases the thoracic kyphosis.
The terms lordosis and kyphosis should be reserved for pathology. The curves depicted in the picture above are in fact the normal curves of the spinal column and should be identified as such.

26. EXTENSION AND FLEXION OF THE VERTEBRAL COLUMN
Dr. Michael P. Gillespie
FIGURE 9-8B,C.   A side view shows the normal sagittal plane curvatures of the vertebral column. A, The neutral position while one is standing. B, Full extension of the vertebral column increases the cervical and lumbar lordosis but reduces (straightens) the thoracic kyphosis. C, Flexion of the vertebral column decreases the cervical and lumbar lordosis but increases the thoracic kyphosis.

27. LINE OF GRAVITY
The line of gravity acting on a person with ideal posture passes near the mastoid process of the temporal bone, anterior to the second sacral vertebra, just posterior to the hip, and anterior to the knee and ankle.
In the vertebral column, the line of gravity typically falls just to the concave side of the apex of each region’s curvature.
Ideal posture allows gravity to produce a torque that helps maintain the optimal shape of the spinal curvatures.
The external torque attributed to gravity is the greatest at the apex of each region: C4 and C5, T6, and L3.
Dr. Michael P. Gillespie

28. LINE OF GRAVITY Dr. Michael P. Gillespie
FIGURE 9-9.   An illustration showing the line of gravity passing through the body of a person standing with ideal posture. (Modified from Neumann DA: Arthrokinesiologic considerations for the aged adult. In Guccione AA, ed: Geriatric physical therapy, ed 2, Chicago, 2000, Mosby.)

29. COMMON POSTURAL DEVIATIONS
Dr. Michael P. Gillespie
FIGURE 9-10.   A drawing showing common postural deviations of the vertebral column and pelvis within the sagittal plane. All subjects in the figure are considered normal, from a neuromuscular perspective. The red line at each iliac crest indicates the varying degree of pelvic tilt (or lumbar lordosis). (Modified from McMorris RO: Faulty postures, Pediatr Clin North Am 8:217, 1961.)

30. LIGAMENTOUS SUPPORT OF THE VERTEBRAL COLUMN
The vertebral column has extensive ligament support.
These ligaments limit motion, help maintain natural spinal curvatures, stabilize the spine, and protect the spinal cord and nerve roots.
Dr. Michael P. Gillespie

31. LIGAMENTS: LATERAL VIEW
Dr. Michael P. Gillespie
FIGURE 9-11A.   Primary ligaments that stabilize the vertebral column. A, Lateral overview of the first three lumbar vertebrae (L1 to L3). B, Anterior view of L1 to L3 vertebrae with the bodies of L1 and L2 removed by cutting through the pedicles. C, Posterior view of L1 to L3 vertebrae with the posterior elements of L1 and L2 removed by cutting through the pedicles. In B and C, the neural tissues have been removed from the vertebral canal.

32. LIGAMENTS: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-11B.   Primary ligaments that stabilize the vertebral column. A, Lateral overview of the first three lumbar vertebrae (L1 to L3). B, Anterior view of L1 to L3 vertebrae with the bodies of L1 and L2 removed by cutting through the pedicles. C, Posterior view of L1 to L3 vertebrae with the posterior elements of L1 and L2 removed by cutting through the pedicles. In B and C, the neural tissues have been removed from the vertebral canal.

33. LIGAMENTS: POSTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-11C.   Primary ligaments that stabilize the vertebral column. A, Lateral overview of the first three lumbar vertebrae (L1 to L3). B, Anterior view of L1 to L3 vertebrae with the bodies of L1 and L2 removed by cutting through the pedicles. C, Posterior view of L1 to L3 vertebrae with the posterior elements of L1 and L2 removed by cutting through the pedicles. In B and C, the neural tissues have been removed from the vertebral canal.

34. MAJOR LIGAMENTS OF THE VERTEBRAL COLUMN
Name
Attachments
Function
Comment
Ligamentum Flavum
Between the anterior surface of one lamina and the posterior surface of the lamina below.
Limits flexion
High in elastin
Posterior to the spinal cord
Supraspinous and interspinous ligaments
Between adjacent spinous processes from C7 to sacrum
Ligamentum nuchae is the cervical and cranial extension of the supraspinous ligaments
Intertransverse ligaments
Between adjacent transverse processes
Limits contralateral flexion and forward flexion
Few fibers in cervical and thoracic, thin in lumbar
Dr. Michael P. Gillespie

35. MAJOR LIGAMENTS OF THE VERTEBRAL COLUMN
Name
Attachments
Function
Comment
Anterior longitudinal ligaments
Between occipital bone and anterior vertebral bodies including sacrum
Limits extension
Reinforces anterior aspect of IVDs
Most developed in lumbar spine
Twice the tensile strength of PLL
Posterior longitudinal ligaments
Posterior surfaces of all vertebral bodies between C2 and sacrum
Limits flexion
Reinforces posterior sides of IVDs
Lies within vertebral canal just anterior to spinal cord
Capsules of the apophyseal joints
Margin of each apophyseal joint
Strengthen the apophyseal joint
Loose in the neutral position, but become taut in the extremes of other positions
Dr. Michael P. Gillespie

36. STRESS STRAIN CURVE LIGAMENTUM FLAVUM
Dr. Michael P. Gillespie
FIGURE 9-12.   The stress-strain relationship of the ligamentum flavum is shown between full extension and the point of tissue failure beyond full normal-range flexion. Note that the ligament fails at a point 70% beyond its fully slackened length. (Data from Nachemson A, Evans J: Some mechanical properties of the third lumbar interlaminar ligament, J Biomech 1:211, 1968.)

37. PROMINENT LIGAMENTUM FLAVUM
Dr. Michael P. Gillespie
FIGURE 9-13.   A prominent ligamentum nuchae in a thin healthy woman.

38. CERVICAL REGION
Smallest and most mobile of the vertebrae, which facilitates the large range of motion of the head.
Transverse foramina are located in the transverse processes of the cervical spine through which the vertebral artery travels.
Dr. Michael P. Gillespie

39. CERVICAL VERTEBRA: SUPERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-14.   A superior view of seven cervical vertebrae.

40. CERVICAL VERTEBRA: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-15.   An anterior view of the cervical vertebral column.

41. TYPICAL CERVICAL VERTEBRAE (C3 TO C6)
Small rectangular bodies.
The superior surfaces are concave side to side, with raised lateral hooks called uncinate processes (uncus means “hook”).
These form the uncovertebral joints (a.k.a. “joints of Luschka”).
Osteophytes can form around the margins of these joints which can reduce the size of the intervertebral foramen (IVF) and impinge upon exiting nerve roots.
Superior articular facets face posterior and superior, whereas the inferior articular facets face anterior and inferior.
Dr. Michael P. Gillespie

42. CERVICAL VERTEBRA: POSTERIOR-LATERAL VIEW
Dr. Michael P. Gillespie
FIGURE 9-17.   A posterior-lateral view of the fourth cervical vertebra.

43. CERVICAL VERTEBRAL COLUMN: LATERAL VIEW
Dr. Michael P. Gillespie
FIGURE 9-18.   A lateral view of the cervical vertebral column.

44. ATYPICAL CERVICAL VERTEBRAE (C1, C2, & C7)
Atlas (C1)
Axis (C2)
“Vertebra Prominens” (C7)
Dr. Michael P. Gillespie

45. ATLAS (C1) The primary function is to support the head.
The atlas has large, palpable transverse processes, usually the most prominent of the cervical vertebrae.
The transverse processes serve as attachment points for muscles that move the cranium.
Dr. Michael P. Gillespie

46. ATLAS
Dr. Michael P. Gillespie

47. ATLAS (C1) Dr. Michael P. Gillespie
FIGURE 9-19A, B.   The atlas. A, Superior view. B, Anterior view.

48. AXIS (C2)
The axis has an upwardly projecting dens (odontoid process) which provides a vertical axis of rotation for the atlas and head.
Dr. Michael P. Gillespie

49. AXIS (C2) Dr. Michael P. Gillespie
FIGURE 9-20A.   The axis. A, Anterior view. B, Superior view.

50. AXIS (C2) Dr. Michael P. Gillespie
FIGURE 9-20B.   The axis. A, Anterior view. B, Superior view.

51. ATLANTO-AXIAL ARTICULATION
Dr. Michael P. Gillespie
FIGURE 9-21.   A superior view of the median atlanto-axial articulation.

52. “VERTEBRA PROMINENS” (C7)
C7 is the largest of all cervical vertebrae and has many characteristics of thoracic vertebrae.
This vertebra has a large spinous process, characteristic of thoracic vertebrae.
The hypertrophic anterior tubercle may sprout an extra cervical rib, which may impinge on the brachial plexus.
Dr. Michael P. Gillespie

53. THORACIC REGION Typical Thoracic Vertebrae (T2 to T9)
The heads of ribs 2 – 9 typically articulate with a pair of costal demifacets.
Atypical Thoracic Vertebrae (T1 and T10 to T12)
T1 has a full costal facet the accepts the entire head of the first rib.
The spinous process of T1 is elongated and often as prominent as C7.
The bodies of T10 – T12 may have a single full costal facet. These segments usually lack costotransverse joints.
Dr. Michael P. Gillespie

54. TYPICAL THORACIC VERTEBRAE
Dr. Michael P. Gillespie
FIGURE 9-22.   A lateral view of the sixth through eighth thoracic vertebrae.

55. LUMBAR REGION
Massive wide bodies for supporting the entire superimposed weight of the head, trunk, and arms.
The spinous processes are broad and rectangular projecting horizontally (as opposed to the slant n the thoracic region).
Short mammillary processes project from the posterior surface of each superior articular facet for attachment of the multifidi muscles.
Dr. Michael P. Gillespie

56. LUMBAR VERTEBRAE: SUPERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-23.   A superior view of the five lumbar vertebrae.

57. LUMBAR VERTEBRA: LATERAL-POSTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-24.   A lateral and slightly posterior view of the first lumbar vertebra.

58. SACRUM
Triangular bone with the base facing superiorly and apex inferiorly.
Transmits weight of the vertebral column to the pelvis.
In childhood, each of the five separate sacral vertebrae is joined by a cartilaginous membrane.
By adulthood they fuse into a single bone.
Four paired ventral (pelvic) sacral foramina transmit the ventral rami of spinal nerve roots that form the sacral plexus.
Four paired dorsal sacral foramina transmit the dorsal rami of sacral spinal nerve roots.
The sacral canal houses and protects the cauda equina.
A large auricular surface articulates with the ilium, forming the sacroiliac joint.
The apex articulates with the coccyx.
Dr. Michael P. Gillespie

59. LUMBOSACRAL REGION: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-26.   An anterior view of the lumbosacral region. Attachments of the piriformis, iliacus, and psoas major are indicated in red. Attachments of the quadratus lumborum are indicated in gray.

60. LUMBOSACRAL REGION: POSTERIOR-LATERAL VIEW
Dr. Michael P. Gillespie
FIGURE 9-27.   A posterior-lateral view of the lumbosacral region. Attachments of the multifidi, erector spinae, and gluteus maximus are indicated in red.

61. SACRUM: SUPERIOR VIEW Dr. Michael P. Gillespie
FIGURE 9-28.   A superior view of the sacrum. Attachments of the iliacus muscles are indicated in red.

62. COCCYX Small triangular bone consisting of four fused vertebrae.
Base of coccyx joins the apex of the sacrum at the sacrococcygeal joint (which usually fuses late in life).
The joint has a fibrocartilaginous disc.
Dr. Michael P. Gillespie

63. CAUDA EQUINA
At birth the spinal cord and vertebral column are nearly the same length.
The vertebral column grows slightly faster than the spinal cord.
The spinal cord terminates at around the level of L1 or L2.
The lumbosacral spinal nerve roots must travel a great distance caudally before reaching their corresponding intervertebral foramina.
The elongated nerves represent a horse’s tail, hence the term cauda equina.
Severe fracture or trauma to the lumbosacral region can damage the cauda equina but spare the spinal cord.
Damage to the cauda equina can result in muscle paralysis, atrophy, altered sensation, and reduced reflexes.
Dr. Michael P. Gillespie

64. TYPICAL INTERVERTEBRAL JUNCTION
Three functional components:
1. Transverse and spinous processes
Levers that increase the mechanical leverage of muscles and ligaments.
2. Apophyseal joints
Guiding intervertebral motion (like railroad tracks for a train).
3. Interbody joints
Connect an intervertebral disc with a pair of vertebral bodies.
Dr. Michael P. Gillespie

65. TYPICAL INTERVERTEBRAL JUNCTION
Dr. Michael P. Gillespie
FIGURE 9-29.   A model highlights the three functional components of a typical intervertebral junction: transverse and spinous processes, apophyseal joints, and interbody joint, including the intervertebral disc. The L1-L2 junction is shown flexing, guided by the sliding between the articular facet surfaces of the apophyseal joints (black, thicker arrow). The medial-lateral axis of rotation is shown through the interbody joint. The interspinous and supraspinous ligaments are shown stretched. Note the compression of the front of the intervertebral disc. Also note that the spinal cord terminates near the L1 vertebra and then forms the cauda equina.

66. MOVEMENT IN THE VERTEBRAL COLUMN
With a few exceptions, movement within any given intervertebral joint is relatively small.
When added across the entire vertebral column, however, these small movements can yield considerable angular rotation.
Dr. Michael P. Gillespie

67. TERMINOLOGY DESCRIBING MOVEMENT
Osteokinematics
Rotations within the three cardinal planes.
Each plane, or degree of freedom, is associated with one axis of rotation.
Movement is described in a cranial-to-caudal fashion.
Arthrokinematics
Describes the relative movement between articular facet surfaces within the apophyseal joints.
Dr. Michael P. Gillespie

68. OSTEOKINEMATICS OF THE VERTEBRAL COLUMN
Dr. Michael P. Gillespie
FIGURE 9-30.   Terminology describing the osteokinematics of the vertebral column; illustrated for a typical lumbar intervertebral junction.

69. APOPHYSEAL JOINTS 24 pairs of apophyseal joints.
Each apophyseal joint is formed between opposing articular facet surfaces.
Lined with articular cartilage and enclosed by a synovial-lined, well innervated capsule.
The articular surfaces of most apophyseal joints are flat.
Apophysis means “outgrowth” which emphasizes the protruding nature of the articular process.
The facets act as barricades. They permit certain movements, but block other movements.
The near vertical orientation of the apophyseal joints in the lower thoracic, lumbar, and lumbosacral regions block excessive anterior translation of one vertebra on another.
Dr. Michael P. Gillespie

70. ARTHROKINEMATICS APOPHYSEAL JOINTS
Terminology
Definition
Functional Example
Approximation of joint surfaces
An articular facet surface tends to move closer to its partner facet. Usually caused by a compression force.
Axial rotation between L1 and L2 causes approximation (compression) of the contralateral apophyseal joint.
Separation (gapping) between joint surfaces
An articular facet tends to move away from its partner facet. Usually caused by a distraction force.
Therapeutic traction is a way to decompress or separate the apophyseal joints.
Sliding (gliding) between joint surfaces
An articular facet translates in a linear or curvilinear direction relative to another articular facet. Sliding between joint surfaces is caused by a force directed tangential to the joint surfaces.
Flexion-extension of the mid to lower cervical spine.
Dr. Michael P. Gillespie

71. APOPHYSEAL JOINT (OPENED)
Dr. Michael P. Gillespie
FIGURE 9-31.   A posterior view of the second and third lumbar vertebrae. The capsule and associated ligaments of the right apophyseal joint are removed to show the vertical alignment of the joint surfaces. The top vertebra is rotated to the right to maximally expose the articular surfaces of the right apophyseal joint. Note the slight gapping within the right apophyseal joint.

72. INTERBODY JOINTS
From C2-3 to L5-S1, 23 interbody joints are present in the spinal column.
Each interbody joint contains an intervertebral disc, vertebral endplates, and adjacent vertebral bodies.
The joint is a cartilaginous synarthrosis.
Dr. Michael P. Gillespie

73. INTERVERTEBRAL DISCS
Central nucleus pulposus surrounded by an annulus fibrosus.
The nucleus pulposus is a pulplike gel in the mid to posterior part of the disc.
In youth, the lumbar discs consist of 70% - 90% water.
The discs act as a hydraulic shock absorption system, dissipating and transferring loads across vertebrae.
The annulus fibrosus consists of 15 to 25 concentric layers or rings of collagen fibers.
Abundant elastin protein is also interspersed conferring circumferential elasticity to the annulus fibrosus.
If the disc is dehydrated and thin, a disproportionate amount of compressive force is placed on the apophyseal joints.
Dr. Michael P. Gillespie

74. INTERVERTEBRAL DISC Dr. Michael P. Gillespie
FIGURE 9-33.   The intervertebral disc is shown lifted away from the underlying vertebral endplate. (Modified from Kapandji IA: The physiology of joints, vol 3, New York, 1974, Churchill Livingstone.)

75. ANNULUS FIBROSIS Dr. Michael P. Gillespie
FIGURE 9-34.   The detailed organization of the annulus fibrosus shown with the nucleus pulposus removed. Collagen fibers are arranged in multiple concentric layers, with fibers in every other layer running in identical directions. The orientation of each collagen fiber (depicted as θ) is about 65 degrees from the vertical. (Modified from Bogduk N: Clinical anatomy of the lumbar spine, ed 4, New York, 2005, Churchill Livingstone.)

76. VERTEBRAL ENDPLATES
The vertebral endplates are relatively thin cartilaginous caps of connective tissue that cover most of the superior and inferior surfaces of the vertebral bodies.
At birth they are thick, accounting for approximately 50% of the height of each intervertebral space.
During childhood, the endplates function as growth plates for the vertebrae.
Dr. Michael P. Gillespie

77. VERTEBRAL ENDPLATE Dr. Michael P. Gillespie
FIGURE 9-35.   A vertical slice through the interbody joint shows the relative position of the vertebral endplates. (Modified from Bogduk N: Clinical anatomy of the lumbar spine, ed 4, New York, 2005, Churchill Livingstone.)

78. INTERVERTEBRAL DISC AS A HYDROSTATIC PRESSURE DISTRIBUTER
The intervertebral discs act as shock absorbers to protect the bone from excessive pressure.
Compressive forces push the endplates inward and toward the nucleus pulposus.
The nucleus pulposus deforms radially and outwardly against the annulus fibrosus.
When the compressive force is removed from the endplates, the stretched elastin and collagen fibers return to their original preload length.
Dr. Michael P. Gillespie

79. FORCE TRANSMISSION THROUGH DISC
Dr. Michael P. Gillespie
FIGURE 9-36.   The mechanism of force transmission through an intervertebral disc. A, Compression force from body weight and muscle contraction (straight arrows) raises the hydrostatic pressure in the nucleus pulposus. In turn, the increased pressure elevates the tension in the annular fibrosus (curved arrows). B, The increased tension in the annulus inhibits radial expansion of the nucleus. The rising nuclear pressure is also exerted upward and downward against the vertebral endplates. C, The pressure within the disc is evenly redistributed to several tissues as it is transmitted across the endplates to the adjacent vertebra. (Modified from Bogduk N: Clinical anatomy of the lumbar spine, ed 4, New York, 2005, Churchill Livingstone.)

80. INTRADISCAL PRESSURE DURING COMMON POSTURES AND ACTIVITIES
Dr. Michael P. Gillespie
FIGURE 9-37.   A comparison between data from two intradiscal pressure studies. Each study measured in vivo pressures from a lumbar nucleus pulposus in a 70-kg subject during common postures and activities. The pressures are normalized to standing. (Modified from Wilke H-J, Neef P, Caimi M, et al: New in vivo measurements of pressures in the intervertebral disc in daily life, Spine 24:755, 1999.)

81. DIURNAL FLUCTUATIONS IN WATER CONTENT WITHIN THE INTERVERTEBRAL DISCS
When a healthy spine is unloaded (i.e. bed rest) the pressure within the nucleus pulposus is relatively low.
This low pressure attracts water to the disc and the disc swells slightly while sleeping.
When we are awake and upright, weight bearing produces compressive forces that push water out of the disc.
The water retaining capacity of the disc declines with age.
With less water and a lower hydrostatic pressure, the disc can bulge outward when compressed (like a flat tire).
Dr. Michael P. Gillespie

82. SPINAL COUPLING
Movement performed within any given plane throughout the vertebral column is coupled with automatic and usually imperceptible movement in another plane.
This is referred to as spinal coupling.
Dr. Michael P. Gillespie

83. NORMAL SAGITTAL PLANE CURVATURES ACROSS REGIONS OF THE SPINAL COLUMN
Dr. Michael P. Gillespie
FIGURE 9-39.   The normal sagittal plane curvatures across the regions of the vertebral column. The curvatures define the neutral position for each region, often referred to as “ideal” posture while standing.

84. CONNECTIVE TISSUES THAT MAY LIMIT MOTIONS OF THE VERTEBRAL COLUMN
Motion of the Vertebral Column
Connective Tissues
Flexion
Ligamentum nuchae
Interspinous and supraspinous ligaments
Ligamentum flava
Apophyseal joints
Posterior annulus fibrosis
Posterior longitudinal ligament
Beyond neutral extension
Cervical viscera (esophagus and trachea)
Anterior annulus fibrosis
Anterior longitudinal ligament
Dr. Michael P. Gillespie

85. CONNECTIVE TISSUES THAT MAY LIMIT MOTIONS OF THE VERTEBRAL COLUMN
Motion of the Vertebral Column
Connective Tissues
Axial rotation
Annulus fibrosis
Apophyseal joints
Alar ligaments
Lateral flexion
Intertransverse ligaments
Contralateral annulus fibrosus
Dr. Michael P. Gillespie

86. CRANIOCERVICAL REGION
“Craniocervical region” and “neck” are used interchangeably.
Three articulations
Atlanto-occipital joint
Atlanto-axial joint complex
Intracervical apophyseal joints (C2 to C7)
Dr. Michael P. Gillespie

87. ATLANTO-OCCIPITAL JOINTS
The atlanto-occipital joints provide independent movement of the cranium relative to the atlas.
Dr. Michael P. Gillespie

88. ATLANTO-OCCIPITAL JOINTS: POSTERIOR - EXPOSED
Dr. Michael P. Gillespie
FIGURE 9-40.   A posterior view of exposed atlanto-occipital joints. The cranium is rotated forward to expose the articular surfaces of the joints. Note the tectorial membrane as it crosses between the atlas and the cranium.

89. ATLANTO-OCCIPITAL JOINTS: ANTERIOR
Dr. Michael P. Gillespie
FIGURE 9-41.   An anterior view illustrates the connective tissues associated with the atlanto-occipital joint and the atlanto-axial joint complex. The right side of the atlanto-occipital membrane is removed to show the capsule of the atlanto-occipital joint. The capsule of the right atlanto-axial (apophyseal) joint is also removed to expose its articular surfaces. The spinal cord and the bodies of C3 and C4 are removed to show the orientation of the posterior longitudinal ligament.

90. ATLANTO-OCCIPITAL JOINTS: POSTERIOR
Dr. Michael P. Gillespie
FIGURE 9-42.   A posterior view illustrates the connective tissues associated with the atlanto-occipital joint and atlanto-axial joint complex. The left side of the posterior atlanto-occipital membrane and the underlying capsule of the atlanto-occipital joint are removed. The laminae and spinous processes of C2 and C3, the spinal cord, and the posterior longitudinal ligament and tectorial membrane are also removed to expose the posterior sides of the vertebral bodies and the dens.

91. ATLANTO-AXIAL JOINT COMPLEX
The atlanto-axial joint complex has two articular components: a median joint and a pair of laterally positioned apophyseal joints.
The median joint is formed by the dens of the axis (C2) projecting through an osseous-ligamentous ring created by the anterior arch of the atlas and the transverse ligament.
The transverse ligament of the atlas stabilizes the atlanto-axial articulation and prevents anterior slippage.
The two apophyseal joints are formed by the articulation of the inferior areticular facets of the atlast with the superior articular facets of the axis.
Two degrees of freedom are allowed by this joint complex: horizontal plane rotation and flexion- extension.
Dr. Michael P. Gillespie

92. ATLANTO-AXIAL JOINT COMPLEX: SUPERIOR
Dr. Michael P. Gillespie
FIGURE 9-43.   A superior view of the dens and its structural relationship to the median atlanto-axial joint. The spinal cord is removed and the tectorial membrane is cut. Synovial membranes are in blue.

93. ATLANTO-AXIAL JOINT COMPLEX: POSTERIOR
Dr. Michael P. Gillespie
FIGURE 9-44.   A posterior view of the atlanto-axial joint complex. The posterior arch of the atlas, tectorial membrane, and transverse ligament of the atlas are cut to expose the posterior side of the dens and the alar ligaments. The dashed lines indicate the removed segment of the transverse ligament of the atlas.

94. INTRACERVICAL APOPHYSEAL JOINTS (C2 TO C7)
The facet surfaces within the apophyseal joints of C2 to C7 are oriented like shingles on a 45-degree sloped roof.
This orientation enhances the freedom of movement in all three planes.
Dr. Michael P. Gillespie

95. APPROXIMATE ROM FOR THE THREE PLANES OF MOVEMENT CRANIOCERVICAL
Joint or Region
Flexion & Extension (Sagittal Plane, Degrees)
Axial Rotation (Horizontal Plane, Degrees)
Lateral Flexion (Frontal Plane, Degrees)
Atlanto-occipital joint
Flexion: 5
Extension: 10
Total: 15
Negligible
About 5
Atlanto-axial joint complex
35-40
Intracervical region (C2-C7)
Flexion:
Extension:
Total:
30-35
Total across craniocervical region
Flexion:
Extension:
Total:
65-70
Dr. Michael P. Gillespie

96. KINEMATICS OF CRANIOCERVICAL EXTENSION
Dr. Michael P. Gillespie
FIGURE 9-45.   Kinematics of craniocervical extension. A, Atlanto-occipital joint. B, Atlanto-axial joint complex. C, Intracervical region (C2 to C7). Elongated and taut tissues are indicated by thin black arrows.

97. KINEMATICS OF CRANIOCERVICAL FLEXION
Dr. Michael P. Gillespie
FIGURE 9-46.   Kinematics of craniocervical flexion. A, Atlanto-occipital joint. B, Atlanto-axial joint complex. C, Intracervical region (C2 to C7). Note in C that flexion slackens the anterior longitudinal ligament and increases the space between the adjacent laminae and spinous processes. Elongated and taut tissues are indicated by thin black arrows; slackened tissue is indicated by a wavy black arrow.

98. PROTRACTION AND RETRACTION OF THE CRANIUM
Dr. Michael P. Gillespie
FIGURE 9-47A.   Protraction and retraction of the cranium. A, During protraction of the cranium, the lower-to-mid cervical spine flexes as the upper craniocervical region extends. B, During retraction of the cranium, in contrast, the lower-to-mid cervical spine extends as the upper craniocervical region flexes. Note the change in distance between the C1 and C2 spinous processes during the two movements.
FIGURE 9-47B.   Protraction and retraction of the cranium. A, During protraction of the cranium, the lower-to-mid cervical spine flexes as the upper craniocervical region extends. B, During retraction of the cranium, in contrast, the lower-to-mid cervical spine extends as the upper craniocervical region flexes. Note the change in distance between the C1 and C2 spinous processes during the two movements.

99. KINEMATICS OF CRANIOCERVICAL AXIAL ROTATION
Dr. Michael P. Gillespie
FIGURE 9-48.   Kinematics of craniocervical axial rotation. A, Atlanto-axial joint complex. B, Intracervical region (C2 to C7).

100. KINEMATICS OF CRANIOCERVICAL LATERAL FLEXION
Dr. Michael P. Gillespie
FIGURE 9-49.   Kinematics of craniocervical lateral flexion. A, Atlanto-occipital joint. The rectus capitis lateralis is shown laterally flexing the joint. B, Intracervical region (C2 to C7). Note the ipsilateral coupling pattern between axial rotation and lateral flexion. Elongated and taut tissue is indicated by thin black arrows.

101. THORACIC REGION
The thorax consists of a relatively rigid rib cage, formed by ribs, thoracic vertebrae, and sternum.
The rigidity provides a stable base for muscles to control the craniocervical region, protection for intrathoracic organs, and a mechanical bellows for breathing.
Dr. Michael P. Gillespie

102. COSTOTRANSVERSE & COSTOCORPOREAL JOINTS: SUPERIOR-LATERAL VIEW
Dr. Michael P. Gillespie
FIGURE 9-51A.   The costotransverse and costocorporeal joints of the midthoracic region. A, Superior-lateral view highlights the structure and connective tissues of the costotransverse and costocorporeal joints associated with the sixth through the eighth thoracic vertebrae. The eighth rib is removed to expose the costal facets of the associated costocorporeal and costotransverse joints. B, Superior view shows the capsule of the left costocorporeal and costotransverse joints cut to expose joint surfaces. Note the spatial relationships among the nucleus pulposus, annulus fibrosus, and spinal cord.

103. COSTOTRANSVERSE & COSTOCORPOREAL JOINTS: SUPERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-51B.   The costotransverse and costocorporeal joints of the midthoracic region. A, Superior-lateral view highlights the structure and connective tissues of the costotransverse and costocorporeal joints associated with the sixth through the eighth thoracic vertebrae. The eighth rib is removed to expose the costal facets of the associated costocorporeal and costotransverse joints. B, Superior view shows the capsule of the left costocorporeal and costotransverse joints cut to expose joint surfaces. Note the spatial relationships among the nucleus pulposus, annulus fibrosus, and spinal cord.

104. APPROXIMATE ROM FOR THE THREE PLANES OF MOVEMENT THORACIC REGION
Flexion & Extension (Sagittal Plane, Degrees)
Axial Rotation (Horizontal Plane, Degrees)
Lateral Flexion (Frontal Plane, Degrees)
Flexion:
Extension:
Total:
30-35
25-30
Dr. Michael P. Gillespie

105. KINEMATICS OF THORACOLUMBAR FLEXION
Dr. Michael P. Gillespie
FIGURE 9-52.   The kinematics of thoracolumbar flexion are shown through an 85-degree arc: in this subject, the sum of 35 degrees of thoracic flexion and 50 degrees of lumbar flexion. A, Kinematics at the thoracic region. B, Kinematics at the lumbar region. Elongated and taut tissues are indicated by thin black arrows.

106. KINEMATICS OF THORACOLUMBAR EXTENSION
Dr. Michael P. Gillespie
FIGURE 9-53.   The kinematics of thoracolumbar extension are shown through an arc of 35 to 40 degrees: the sum of 20 to 25 degrees of thoracic extension and 15 degrees of lumbar extension. A, Kinematics at the thoracic region. B, Kinematics at the lumbar region. Elongated and taut tissue is indicated by thin black arrows.

107. KINEMATICS OF THORACOLUMBAR AXIAL ROTATION
Dr. Michael P. Gillespie
FIGURE 9-54.   The kinematics of thoracolumbar axial rotation is depicted as the subject rotates her face 120 degrees to the right. The thoracolumbar axial rotation is shown through an approximate 40-degree arc: the sum of about 35 degrees of thoracic rotation and 5 degrees of lumbar rotation. A, Kinematics at the thoracic region. B, Kinematics at the lumbar region.

108. KINEMATICS OF THORACOLUMBAR LATERAL FLEXION
Dr. Michael P. Gillespie
FIGURE 9-55.   The kinematics of thoracolumbar lateral flexion are shown through an approximate 45-degree arc: the sum of 25 degrees of thoracic lateral flexion and 20 degrees of lumbar lateral flexion. A, Kinematics at the thoracic region. B, Kinematics at the lumbar region. Elongated and taut tissue is indicated by a thin black arrow.

109. LUMBAR REGION
L1 to L4
The facet surfaces of most lumar apophyseal joints are oriented nearly vertically.
This orientation favors sagittal plane motion at the expense of rotation in the horizontal plane.
L5-S1
The facet surfaces of the L5-S1 apophyseal joints are usually oriented in a more frontal plane than those of other lumbar regions.
Dr. Michael P. Gillespie

110. APPROXIMATE ROM FOR THE THREE PLANES OF MOVEMENT LUMBAR REGION
Flexion & Extension (Sagittal Plane, Degrees)
Axial Rotation (Horizontal Plane, Degrees)
Lateral Flexion (Frontal Plane, Degrees)
Flexion:
Extension:
Total:
5-7 20
Dr. Michael P. Gillespie

111. SPONDYLOLISTHESIS Dr. Michael P. Gillespie
FIGURE 9-59.   Severe anterior spondylolisthesis at the L5-S1 junction, after a fracture of the pars articularis. (Modified from Canale ST, Beaty JH: Campbell’s operative orthopedics, ed 11, St Louis, 2008, Mosby.)

112. HERNIATED NUCLEUS PULPOSUS
Dr. Michael P. Gillespie
FIGURE 9-60.   Two views of a full herniated nucleus pulposus in the lumbar region. (From Standring S: Gray’s anatomy, ed 40, New York, 2009, Churchill Livingstone.)

113. LUMBOPELVIC RHYTHM DURING TRUNK FLEXION
Dr. Michael P. Gillespie
FIGURE 9-61.   Three different lumbopelvic rhythms used to flex the trunk forward and toward the floor with knees held straight. A, A normal kinematic strategy used to flex the trunk from a standing position, incorporating a near simultaneous 40 degrees of flexion of the lumbar spine and 70 degrees of hip (pelvic-on-femoral) flexion. B, With limited flexion in the hips (for example, from tight hamstrings), greater flexion is required of the lumbar and lower thoracic spine. C, With limited lumbar mobility, greater flexion is required of the hip joints. In B and C, the red shaded circles and red arrows indicate regions of restricted mobility.

114. LUMBOPELVIC RHYTHM DURING TRUNK EXTENSION
Dr. Michael P. Gillespie
FIGURE 9-62.   A typical lumbopelvic rhythm is shown in three phases while the trunk is extended from a forward bent position. The motion is conveniently divided into three chronologic phases (A to C). In each phase the axis of rotation for the trunk extension is arbitrarily placed through the body of L3. A, In the early phase, trunk extension occurs to a greater extent through extension of the hips (pelvis on femurs), under strong activation of hip extensor muscles (gluteus maximus and hamstrings). B, In the middle phase, trunk extension occurs to a greater degree by extension of the lumbar spine, requiring increased activation from lumbar extensor muscles. C, At the completion of the event, muscle activity typically ceases once the line of force from body weight falls posterior to the hips. The external moment arm used by body weight is depicted as a solid black line. The greater intensity of red indicates relatively greater intensity of muscle activation.

115. ANTERIOR PELVIC TILT Dr. Michael P. Gillespie
FIGURE 9-63A.   Anterior and posterior tilting of the pelvis and its effect on the kinematics of the lumbar spine. A and C, Anterior pelvic tilt extends the lumbar spine and increases the lordosis. This action tends to shift the nucleus pulposus anteriorly and reduces the diameter of the intervertebral foramen. B and D, Posterior pelvic tilt flexes the lumbar spine and decreases the lordosis. This action tends to shift the nucleus pulposus posteriorly and increases the diameter of the intervertebral foramen. Muscle activity is shown in red.
FIGURE 9-63C.   Anterior and posterior tilting of the pelvis and its effect on the kinematics of the lumbar spine. A and C, Anterior pelvic tilt extends the lumbar spine and increases the lordosis. This action tends to shift the nucleus pulposus anteriorly and reduces the diameter of the intervertebral foramen. B and D, Posterior pelvic tilt flexes the lumbar spine and decreases the lordosis. This action tends to shift the nucleus pulposus posteriorly and increases the diameter of the intervertebral foramen. Muscle activity is shown in red.

116. POSTERIOR PELVIC TILT Dr. Michael P. Gillespie
FIGURE 9-63B.   Anterior and posterior tilting of the pelvis and its effect on the kinematics of the lumbar spine. A and C, Anterior pelvic tilt extends the lumbar spine and increases the lordosis. This action tends to shift the nucleus pulposus anteriorly and reduces the diameter of the intervertebral foramen. B and D, Posterior pelvic tilt flexes the lumbar spine and decreases the lordosis. This action tends to shift the nucleus pulposus posteriorly and increases the diameter of the intervertebral foramen. Muscle activity is shown in red.
FIGURE 9-63D.   Anterior and posterior tilting of the pelvis and its effect on the kinematics of the lumbar spine. A and C, Anterior pelvic tilt extends the lumbar spine and increases the lordosis. This action tends to shift the nucleus pulposus anteriorly and reduces the diameter of the intervertebral foramen. B and D, Posterior pelvic tilt flexes the lumbar spine and decreases the lordosis. This action tends to shift the nucleus pulposus posteriorly and increases the diameter of the intervertebral foramen. Muscle activity is shown in red.

117. KINESIOLOGIC EFFECTS OF LUMBAR FLEXION & EXTENSION
Structure
Effect of Flexion
Effect of Extension
Nucleus Pulposus
Deformed or pushed posteriorly
Deformed or pushed anteriorly
Annulus Fibrosus
Posterior side stretched
Anterior side stretched
Apophyseal Joint
Capsule stretched
Articular loading decreased
Capsule slackened
Articular loading increased
Intervertebral Foramen
Widened
narrowed
Posterior longitudinal ligament
Increased tension (elongated)
Decreased tension (slackened)
Dr. Michael P. Gillespie

118. KINESIOLOGIC EFFECTS OF LUMBAR FLEXION & EXTENSION
Structure
Effect of Flexion
Effect of Extension
Ligamentum flavum
Increased tension (elongated)
Decreased tension (slackened)
Interspinous ligament
Supraspinous ligament
Anterior longitudinal ligament
Spinal cord
Dr. Michael P. Gillespie

119. SITTING POSTURE & EFFECTS ON ALIGNMENT
Dr. Michael P. Gillespie
FIGURE 9-65A.   Sitting posture and its effects on the alignment of the lumbar and craniocervical regions. A, With a slouched sitting posture, the lumbar spine flexes, which reduces its normal lordosis. As a consequence, the head tends to assume a forward (protracted) posture. B, With an ideal sitting posture, possibly aided with a low-back cushion, the lumbar spine assumes a more normal lordosis, which facilitates a more desirable “chin-in” (retracted) position of the head. The line of gravity resulting from body weight is shown in red.
FIGURE 9-65B.   Sitting posture and its effects on the alignment of the lumbar and craniocervical regions. A, With a slouched sitting posture, the lumbar spine flexes, which reduces its normal lordosis. As a consequence, the head tends to assume a forward (protracted) posture. B, With an ideal sitting posture, possibly aided with a low-back cushion, the lumbar spine assumes a more normal lordosis, which facilitates a more desirable “chin-in” (retracted) position of the head. The line of gravity resulting from body weight is shown in red.

120. SACROILIAC JOINTS
The sacroiliac joints mark the transition between the caudal end of the axial skeleton and the lower appendicular skeleton.
The tight fitting SI joint is designed for stability, ensuring effective transfer of potentially large loads between the vertebral column, the lower extremities, and ultimately the ground.
Dr. Michael P. Gillespie

121. SACROILIAC JOINTS: EXPOSED SURFACES
Dr. Michael P. Gillespie
FIGURE 9-68A, B.   The exposed auricular surfaces of the right sacroiliac joint are shown. A, Iliac surface. B, Sacral surface. (Modified from Kapandji IA: The physiology of joints, vol 3, New York, 1974, Churchill Livingstone.)

122. LIGAMENTS OF THE SACROILIAC JOINT
Primary
Anterior sacroiliac
Iliolumbar
Interosseous
Short and long posterior sacroiliac
Secondary
Sacrotuberous
Sacrospinous
Dr. Michael P. Gillespie

123. LUMBOSACRAL REGION: ANTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-70.   An anterior view of the lumbosacral region and pelvis shows the major ligaments in the region, especially those of the sacroiliac joint. On the specimen’s left side, part of the sacrum, superficial parts of the iliolumbar ligament, and the anterior sa­croiliac ligament are removed to expose the auricular surface of the ilium and deeper interosseous ligament.

124. LUMBOSACRAL REGION: POSTERIOR VIEW
Dr. Michael P. Gillespie
FIGURE 9-71.   A posterior view of the right lumbosacral region and pelvis shows the major ligaments that reinforce the sacroiliac joint.

125. NUTATION & COUNTERNUTATION
Nutation means to nod.
Nutation is the anterior tilt of the base (top) of the sacrum relative to the ilum.
Counternutation
Counternutation is a reverse motion defined as the relative posterior tilt of the base of the sacrum relative to the ilium.
Dr. Michael P. Gillespie

126. KINEMATICS OF THE SACROILIAC JOINTS
Dr. Michael P. Gillespie
FIGURE 9-73A, B.   The kinematics at the sacroiliac joints. A, Nutation. B, Counternutation. Sacral rotations are indicated by darker shade of tan, iliac rotations are indicated by the lighter shade of tan. The axis of rotation for sagittal plane movement is indicated by the small green circle.

127. FUNCTIONS OF THE SACROILIAC JOINTS
Stress relief mechanism within the pelvic ring.
A stable means of load transfer between the axial skeleton and lower limbs.
Dr. Michael P. Gillespie

128. MUSCLES THAT REINFORCE AND STABILIZE THE SACROILIAC JOINT
Erector Spinae
Lumbar multifidi
Abdominal muscles
Rectus abdominis
Obliquus abdomninis internus and externus
Transversus abdominis
Hip extensor muscles
Latissimus dorsi
Iliacus and piriformis
Dr. Michael P. Gillespie