Gross Anatomy
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(Review pages 409 -422 and the lecture on The Spinal Cord)

I. Introduction

Injuries to the back are one of the most common reasons patients consult their physician. Back problems are the leading cause of lost productivity due to injuries to employees. Our bipedal form of locomotion necessitates special requirements for the back. In addition to protecting the spinal cord , the back must be able to withstand compressional forces, be mobile and provide support for the head trunk and limbs. The vertebrae enable the back to function as a flexible segmented rod. The ligaments and intervertebral discs provide support and shock absorbing capabilities. The muscles of the back facilitate movements while also acting as guy wires to help the back support the rest of the body. In this unit we will look at the anatomical basis of back function. We will also apply our knowledge about the anatomy of the back in solving common clinical problems concerning the back.

II. Anatomy of the Back ( pgs. 409 -422)

  1. Vertebral Column
    1. Comprised of vertebrae
    2. 2. Supported by ligaments and muscles
    3. 3. Curvatures
      1. Cervical
        1. Anterior convexity (lordosis)
        2. Helps balance skull on vertebral column
      2. Thoracic
        1. Posterior covexity (Kyphosis)
        2. Hump Back
        3. Exaggerated kyphotic curve
      3. Lumbar
        1. Pronounced anterior convexity (lordosis)
          1. Develops when child learns to stand upright
          2. Correlated with activity of psoas muscle
  2. Components of a Typical Vertebrae (409 - 412)
    1. 1.The student should review the following information presented in the Thorax section of the course:
      1. Bony and ligamentous anatomy of the back
      2. The parts of a vertebrae
      3. The characteristics that distinguish cervical ,thoracic and lumbar vertebrae
  3. Sacrum
    1. Usually comprised of 5 fused vertebrae
    2. 4 pair of foramina (anteriorly & posteriorly)
      1. a.exit of ventral and dorsal rami of sacral spinal nerves
    3. First sacral vertebra
      1. a.Base - superior aspect of S1 (like base of the triangle)
      2. b. Sacral promontory - anterior projecting edge of S1 (contribute to the lumbosacral angle)
    4. Median Sacral Crest (posteriorly - would have been the spinous processes)
    5. Sacral Cornu (inferior articular processes of S5)
    6. Alar / Lateral mass end in auricular surface ( articulates with similarly named surface of ilium to form sacroiliac joint
    7. Lumbarization
      1. S 1 segment is mobile and acts like a 6th. lumbar vertebrae
    8. Sacralization
      1. 5th lumbar vertebrae fuses with the 1st sacral vertebrae , becomes immobile and becomes part of sacrum
  4. Coccyx
    1. 1.Usually 4 fused vertebrae
      1. first has the cornu of the coccyx


  1. Composition
    1. Annulus Fibrosis
      1. Fibrocartilaginous layers arranged similar to rings of tree
      2. Protects against herniation
    2. Nucleus pulposus
      1. Jelly like central material
  2. Functions
    1. Shock absorption
    2. Binds vertebral bodies together
    3. Permit movement

Vertebral Joints

  1. Zygapophyseal, Apophyseal or Facet Joints
    1. Classification: Synovial, Planar
    2. Properties
      1. hyaline cartilage on joint surfaces
      2. thin, loose capsule supported by fibers of ligamentum flava
    3. Innervation
      1. Branches of dorsal rami
    4. Gliding movements
  2. Intervertebral Joint
    1. Classification: Nonsynovial, Symphysis
      1. Cartilaginous end plates of intervertebral disc anchored to vertebral bodies
      2. Supported by anterior and posterior longitudinal ligaments
    2. Properties
      1. Weight bearing
      2. Shock absorption
      3. Slight mobility in all directions


  1. A. Components
    1. 1. Auricular surface of the alar of the sacrum articulates with auricular surface of ilia
      1. a. Synovial joint
      2. b. Slight mobility
      3. c. Weight bearing
  2. B. Ligaments
    1. Sacroiliac
      1. a.Ventral
      2. b. Dorsal
      3. c. Interosseous
        1. stabilizes SIJ
      4. d.Iliolumbar
        1. Entrapment of L 5 nerve root
  3. C.Movement
    1. 1. Very slight normally
      1. a. Increases with pregnancy
    2. 2. Anterior movement of sacral promontory
      1. a. follows trunk flexion
      2. b. increases size of pelvic outlet
    3. 3. Posterior movement of sacral promontory
      1. a. follows trunk extension
      2. b. increases size of pelvic inlet


  1. Cervical Region
    1. C 2 and C 7 are palpable
  2. Thoracic region
    1. Spinous processes of thoracic vertebrae point downward
      1. Tip of spine of superior vertebrae aligned with body of inferior vertebrae
      2. Palpable when back is flexed
    2. Scapula
      1. Spine at level of T 4
      2. Inferior angle = T 9
  3. Lumbar Region
    1. Short, thick spines point posteriorly
      1. Iliac crest - L4
      2. Iliac tubercles -L5
  4. Sacral Region ( Figs. 1 & 2)
    1. Anterior superior iliac spines (ASIS)
      1. a.Aligned with each other in horizontal plane
      2. b. Aligned with pubic symphysis in vertical plane
    2. 2. Posterior superior iliac spines (PSIS) -
      1. a. "Dimples" indicating SIJ at level of S2
      2. b. Assessing movement of SIJ
    3. 3. Sciatic notch


  1. Significance
    1. Proper alignment enable the back to carry out its weight bearing functions with minimal expenditure of muscle energy.
    2. Reduces chance of injury
      1. Poor alignment or "posture"places undue strain on ligaments, muscles and intervertebral discs that may result in injury to these structures.
  2. Assessment of proper posture and alignment (Fig. 3)
    1. A straight longitudinal line should pass through:
      1. Cervical, thoracic and lumbar spines
      2. Half way between dimples on each side
      3. Intergluteal fold
    2. Perpendicular lines from
      1. Superior border of scapula
      2. Inferior angle of scapula
      3. Crest of ilium
      4. Infragluteal folds
  3. Pelvic Alignment (Figs. 1 & 2)
    1. Neutral Position
      1. Depends upon interaction between opposing muscle groups
      2. ASIS and pubic tubercles aligned in vertical plane
      3. ASIS on both sides aligned in horizontal plane
      4. Iliac crests even
    2. Determinants ( See Chart "Alignment of the Pelvis")
      1. a. Posterior Back Muscles & Hip Flexors
        1. Anterior pelvic tilt & increased lumbar lordosis
      2. Anterior Abdominal Muscles and Hip Extensors
        1. Posterior pelvic tilt & decreased lumbar curve ( flat back)
      3. Ipsilateral Hip Abductors & Contralateral Lateral Abdominal Muscles
        1. Lateral pelvic tilt towards abductors side.


  1. Factors - The vertebral column is fairly mobile. The intervertebral joints permit movements in all directions. The range of motion at each joint is slight. When multiplied over an entire segment of the vertebral column ( cervical, thoracic, lumbar), these small movements can result in significant amount of movement. The cervical and lumbar regions are more mobile than the thoracic region because the cervical and lumbar vertebrae do not have ribs attached to them. Other factors that account for mobility include the size of the intervertebral discs in relation to the vertebral bodies and the shape of the discs.
  2. Types of Movements
    1. Flexion - forward bending of vertebral column
      1. larger range of motion
      2. usual cause of disc problems
    2. Extension - backward bending of vertebral column
      1. Most stable configuration
    3. Lateral Flexion ( Bending) -tilting vertebral column to one side
    4. Rotation
  3. Determinants of Movements
    1. Position of Articular facets (zygapophyseal joints)
      1. Atlantooccipital joint
        1. Condylar type
          1. permits flexion/extension ( nodding of head)
      2. Atlantoaxial
        1. Planar articular facets
        2. Pivot Joint between dens process and body of C1
        3. Rotation of atlas around dens of axis (Shaking head to say "No")
      3. Cervical region- horizontal facing joints
        1. Promote movements of flexion /extension and lateral flexion
      4. Thoracic region - frontal position promotes rotation
      5. Lumbar region - sagittal position in lumbar region
        1. Promotes lateral flexion and flexion/extension
  4. Regional Movements
    1. Cervical region
      1. a.Flexion / Extension
      2. Atlantooccipital joints
      3. b. Rotation
        1. (1) Atlantoaxial joint
      4. c. Lateral Flexion
        1. (1) Cervical zygapophyseal joints
    2. Thoracic region
      1. Respiratory
      2. Rotation
    3. Lumbar region
      1. Some flexion / extension
        1. flexion mainly due to action of abdominal muscles
        2. extension mainly due to action of erector spinae muscles
      2. Lateral flexion


  1. Mechanical ( Absence of radiating pain)
    1. Lumbosacral Strain ( Low back pain)
      1. Involves muscles &/or ligaments
      2. Localized pain- usually does not radiate
        1. exacerbated by some movements( flexion) ; lessened by others
        2. point tenderness
        3. patient lists to affected side
      3. Increased lumbar lordosis
      4. Straight Leg raise (Laseague's sign) - negative
    2. Inflammation
      1. Ankylosing spondylitis - inflammation of articular processes
        1. constant pain unaffected by position
        2. loss of lumbar lordosis
        3. reduction in range of all motions
        4. point tenderness
  2. Spinal Cord Trauma
    1. Results from fracture of 1 or more vertebrae
    2. Symptoms depend upon severity of trauma and vertebrae involved
      1. cervical - can cause death or tetraplegia
      2. thoracic - lower limb paraplegia
      3. lumbar ( cauda equina) loss of lower limb function without total paraplegia
    3. Localization - See Chart Spinal Cord Lesions
  3. Herniated Intervertebral Disc
    1. Cause
      1. Bulging of disc
        1. annulus weakens and nucleus causes portion of disc to bulge
      2. Herniation of nucleus pulposus
        1. annulus degenerates leading to protrusion of nucleus
        2. posterior lateral protrusion of nucleus
      3. Piece of disc breaks free
    2. Factors
      1. Moveable regions meet stable regions
        1. Lower cervical meet upper thoracic
        2. Lower lumbar meet sacral
      2. Age
        1. Degeneration of annulus fibrous
    3. Localization of Herniation Site
      1. Cervical Region
        1. Spinal nerves exit above corresponding vertebrae
        2. Herniated disc impinges upon exiting above it (see " Chart on Herniated Discs")
      2. Lumbar Region
        1. Spinal nerves exit below corresponding vertebrae
      3. Large intervertebral foramina
      4. Pass around pedicle
      5. Enters intervertebral foramen above corresponding disc
      6. Herniated disc impinges upon nerve above before it exits intervertebral foramen
        1. see " Chart on Herniated Discs"
    4. Neurological Testing
      1. Sensation
        1. pain felt along involved dermatome(s)
      2. Muscle weakness
        1. weakness in muscles supplied by affected spinal nerve
      3. Positive straight leg test






Lumbar Spine Alignment
Posterior Back:

Erector Spinae

Posteriorly & Upward Anterior pelvic tilt Increased lordosis
Anterior Abdominal:

Rectus Abdominis

Ext. Oblique

Anteriorly & Upward Posterior pelvic


Decreased lordosis - Flat back
Hip Extensors:

Gluteus Maximus


Posteriorly & Downward Posterior pelvic


Decreased lordosis - Flat back
Hip Flexors:

Iliacus, Psoas, Tensor Fascia Lata, Rectus Femoris

Anteriorly &


Anterior pelvic tilt Increased lordosis
Hip Abductors:

Gluteus Medius

Gluteus Minimus

Laterally &

downward on same side

Ipsilateral tilt downward
Lateral Abdominal:

Internal Oblique

Transversus Abdominis

Medially and upward on same side Contralateral tilt



Spinal Level Motor Involvement Sensory


Motor Reflexes
C- 2 Tetraplegia ; can not breath unassisted No sensation below upper region of neck None
C - 6 Shoulder function, elbow flexion, wrist extension intact. No lower limb function Neck, posterior lateral arm, radial forearm unaffected Biceps, Brachioradialis
Thoracic Spinal Cord Complete use of neck and upper limb. Lower limb paraplegia Neck, upper limb intact. Lower limb anesthesia. Thorax & Abdomen- depends on level injured Biceps, Brachioradialis, Triceps
L - 2 Hip Flexion & some adduction possible Portion of anterior & medial thigh intact. No sensation in remainder of limb No lower limb reflexes.


L - 4 Hip flexion , adduction & Knee flexion normal. Anterior, medial thigh; medial leg and foot normal Patellar


S - 1 Hip, knee & ankle dorsiflexors normal.

Ankle plantar flexors intrinsic muscles of foot weak

Perineum lack sensation; most of lower limb has sensation Patellar; Achilles


    Level of spinal cord injury is indicated by the highest level that remains intact. For example, a C3 lesion means that the dermatormes and myotomes associated with C- to C3 are intact. All those below C3 are affected. Likewise, an L4 lesion means that all dermatomes and myotomes located at L4 and above are intact. Those below L4 ( L5 through S4) are not.


Root Disc Sensory Motor Reflex
C 5 C 4-5 Lateral & Anterior Arm

(Axillary nerve)

Deltoid, Rotator cuff Biceps
C 6 C 5-6 Radial Forearm


Dorsum of Hand

(Superficial Radial)

Biceps, Extensor carpi radialis longus & brevis,


C 7 C 6-7 3rd. digit (Median & radial) Triceps, Extensor digitorum, Flexor carpi radialis Triceps
C 8 C 7 -T1 Ulnar side of forearm, hand & 4 & 5th digits

Med. Antebrachial cutaneous, Ulnar)

Flexor digitorum superficialis & profundus
T 1 T1-2 Medial side of arm

Medial Brachial Cutaneous)

Interossei, Lumbricals,


L 3 L 2-3 Anterior & Medial Thigh (femoral) Quadriceps


L 4 L 3-4 Medial leg (saphenous br. of femoral n.) Tibialis anterior

Tibialis posterior

L 5 L 4-5 Lateral leg & dorsum of foot ( common peroneal ) Extensor Digitorum Longus; Gluteus medius & minimus
S 1 L 5-S1 Lateral & plantar surface of foot ( sural; tibial) Peroneus longus & brevis; triceps surae,

gluteus maximus


Figure 1 Alignment

Figure 2 Pelvic Alignment
Proper Pelvic Alignment involves:

1. The iliac crests should be at the same level (A-B)

2. The ASIS on both sides should be parallel to each other

3. The ASIS and Pubic tubercles on both sides should be parallel in the frontal plane

Improper Pelvic Alignment:

1. Lateral tilt - Iliac crests are not parallel. One is either higher or lower than the other

2. Anterior tilt - ASIS rotated forward of the pubic tubercles increasing lumbar lordosis

3. Posterior tilt - Pubic tubercles rotated forward of the ASIS decreasing lumbar lordosis

Figure 3
Back Posture
Proper back posture is achieved when the superior ( A - A) and inferior (B - B) angels of the scapula are parallel to each other as are the iliac crests (C - C) . A straight line should pass equidistant between these structures on both sides and also between both PSIS.


  1. Know and be able to recognize the parts of a vertebra and the sacrum.
    1. Be able to distinguish between cervical , thoracic and lumbar vertebrae
    2. Know which bony structures are palpable
  2. Understand the structure and function(s) of the following joints :
    1. Articular facets (zygapophyseal), Intervertebral,Sacroiliac
    2. Know the ligaments that support each joint and the function(s) of these ligaments
  3. Be able to demonstrate how to asses the movements that take place at the various joints of the vertebral column
    1. Understand how the shape of the articular processes determine the types of movements that can take place
  4. Be able to asses the normal alignment of the lumbar spine, sacroiliac joint and pelvis
    1. Know the muscles that are responsible for normal posture and alignment
    2. Be able to determine the types of postural faults that could result from various muscle lesions
  5. Be able to distinguish between mechanical and non-mechanical causes of back pain
  6. Know how to localize the site of spinal cord trauma resulting from a fractured vertebrae
    1. Be able to localize the site of spinal cord trauma resulting from vertebral fracture
  7. Know the causes of a herniated intervertebral disc
    1. Understand the relationship between disc herniation and spinal root involvement in the cervical and lumbar regions of the vertebral column
    2. Be able to localize the site of a herniated disc from the symptoms presented
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