Chapter 6


I. Vertebral Structures

A. Vertebral body

1. kidney shaped - wider laterally than anterio posteriorly {6}
2. broader than it is high {6}

B. Large spinous process6

C. Transverse processes

1. believed to be rib vestiges {6}
2. Ll-L4 are long and thin {5}
3. L5 are longer and thicker {5}

D. Mamillary process on posterior border of superior articular processes {5}

E. Facet orientation closer to sagittal plane (vertical) {4}

1. beginning at T12 (some individual variation, T9 - Ll) {4}
2. gradual change from sagittal toward frontal plane from upper to lower segments {4}
3. anatomical design

a. limits anterior glide (translation) {20}
b. limits axial rotation {20}
c. allows considerable flexion and extension {20}
d. allows considerable sidebending {20}

F. Lumbosacral junction

1. facets of L5 more widely separated {5}
2. vertebral body of L5 is higher anteriorly than posteriorly {5}
3. sizable intervertebral disc {20}
4. more rotation and flexion/extension {20}
5. reduced sidebending {6}
6. L5 is transitional vertebra, resulting from

a. location {20}
b. unique spacial orientation of facet

c. articulation with sacrum {20}

G. Zygapophyseal joints

1. synovial joints {13}

a. articular cartilage {6, 13}
b. synovial lining {13}
c. synovial fluid {13}
d. joint capsule {13}

2. inferior facets (superior vertebra)

a. convex{6, 20}
b. face lateral and slightly anterior {6}

3. superior facets (inferior vertebra)

a. concave {6, 20}
b. face medial and slightly posterior {6}

4. not true ball—and socket {13}

a. portions of individual facet simultaneously face at least two planes {13}
b. most obvious at L4-L5 and LS, in frontal and sagittal planes {13}

H. Spinal structures having sensory innervation

1. annulus fibrosis {4, 20}
2. major ligaments {4, 20}
3. intervertebral joints {4, 20}
4. vertebral joint capsules {4, 20}
5. vertebral bodies {4, 20}
6. paraspinous muscles {4, 20}
7. all posterior osseous structures {4}
8. veins

a. epidural {4}
b. basivertebral {4}

II. Vertebral Kinematics

Flexion motion

1. inferior facets (superior vertebra) slide superior and anterior {6}
2. vertebral body tilts and glides anterior {6}
3. limited by stretching of ligaments

a. ligamentum flavum {6}
b. interspinous {6}
c. supraspinous {6}
d. posterior longitudinal {6}

B. Extension motion

1. inferior facets (superior vertebra) slide inferior and posterior (interlock) {6}
2. vertebral body tilts and glides posterior {6}
3. limited by

a. interlocking facets {6}
b. touching of spinous processes {6}
c. tension on anterior longitudinal ligament {6}

C. Sidebending motion

1. to right

a. right inferior facet (superior vertebra) slides inferior and posterior (extension) {6}
b. left inferior facet (superior vertebra) slides superior and anterior (flexion) {6}

2. to left

a. left inferior facet (superior vertebra) slides inferior and posterior (extension) {6}
b. right inferior facet (superior vertebra) slides superior and anterior (flexion) {6}
c. couples with opposite side rotation in neutral, erect (lordotic) posture {4}

D. Rotation motion

1. to right

a. right facets separate {6}
b. left facets approximate {6}

2. to left

a. left facets separate {6}
b. right facets approximate {6}

3. couples with opposite side side-bending in neutral, erect (lordotic) posture {4}

III. The Pelvis

Three bony parts

1. two innominate bones (paired and symmetrical) {6}

a. ilium {5}
b. ischium {5}
c. pubis {5}

2. sacrum {6}

B. Male and female different structurally

1. female, shorter and wider {5, 6}
2. male, longer and narrower {6}

C. Three joints

1. two sacroiliac joints between sacrum and iliac bones {6}
2. the symphysis pubis links the iliac bones anteriorly {6}

D. Bony pelvis has two lines of force

1. downward from the vertebral column {6}
2. upward ground forces {6}
3. both form a complete ring {6}

E. Pelvic Rim

1. ring of forces along the pelvic rim {6}
2. counterbalanced by the other symmetrical side {6}
3. impairment at any level of pelvic rim decreases its mechanical resistance {6}
4. complete interdependence of the various elements of the pelvic rim {6}

IV. The Sacrum

Five fused sacral vertebrae {13}

B. Four pairs of neuroforamina {13}

C. Base (SI) is superior portion

1. body of SI articulates with body of L5 {13}
a. via lumbar intervertebral disc {13}
b. facilitates transmission of weight from trunk to pelvis {13}
2. zygapophyseal joints are located posteriorly {6}

D. Apex (S5) is inferior portion {13}

E. Tightly suspended between two iliac bones by heavy ligaments {6}

F. Load bearing surface {6}

1. becomes more stable with increasing loads {6}
2. self-locking system {6}

V. The Sacroiliac Joint

Iliac surface

1. convex {3, 13}
2. lined with thin fibrocartilage {5, 13}

B. Sacral surface

1. concave {3, 6, 13}
2. lined with hyaline cartilage (1.7 to 5 times thicker than iliac fibrocartilage) {5, 13}

C. Synovial joint {3, 15}

D. Stiff articular capsule {20}

E. Articular surface

1. L — or auricular (ear) - shaped when viewed from side” {3, 13, 20}
2. Multi—elevations and depressions viewed from anterior—posterior {6, 13, 20}

F. Ligaments

1. intrinsic (within the joint)

a. interosseous ligament {13}

(1) thick, fibrous {13}
(2) fills large portion of the joint cavity {13}
(3) attaches to both sacrum and ilium {13}
(4) controls trunk and ground forces as they converge {13}

(a) provides stability {13}
(b) allows small, deforming, translation of each bone on the other {13}

(5) one of the strongest ligaments in the body {13, 20}

b. anterior sacroiliac ligament thickens anteior and inferior aspects of joint capsule {13}
c. posterior sacroiliac ligament

(1) dorsal rand of sacral spinal nerves between posterior and interosseous ligaments {13}

2. extrinsic (outside the joint)

a. anterior — iliolumbar ligament {13}

(1) attaches from L5 transverse process to crest of ilium and anterior aspect of sacrum and SI joint {5, 13}
(2) stabilizes anterior joint {6, 13}
(3) stabilizes L5—Sl {13}
(a) against forward shear {13}
(b) in rotation {13}
(c) in sidebending to opposite side {6}
b. posterior ligaments
(1) extremely thick {13}
(2) stronger than anterior {13}
(3) sacrotuberous and sacrospinous
(a) function in weight bearing {13}
(b) limit nutation of sacrum as trunk forces converge on sacrum {13}
(c) help limit posterior rotation of an ilium on the sacrum {13}
(d) divide the sciatic notch into two openings {6}
i) greater sciatic foramen superiorly, allows exit of piriformis muscle {6}
ii) lesser sciatic foramen inferiorly, transmits tendon of obturator internus {6}

G. Cartilage

1. deformation occurs with compression of joint {13}
2. as trunk and ground forces converge to joint, deformation reduces force {13}

H. Muscles

1. some of the strongest in the body surround joint {21}
2. none have primary function of moving joint {21}

I. Movement

1. no voluntary movement {21}
2. occur by other movements of body {21}

a. weight bearing change {21}
b. postural influences

J. Should be in state of equilibrium {6, 13, 21}

VI. Sacroiliac Kinematics

A. Subject of much debate in literature

B. All agree there is limited mobility

C. Kapandji {6}

1. Describes theories of Farbeuf, Bonnaire, and Weisel for nutation and its axis of rotation
2. Classical theory of nutation and counternutation

a. axis of rotation posterior to joint surface (axial ligament)
b. nutation (sacral flexion)

(1) sacral promontory (base) moves inferior and anterior
(2) apex moves superior and posterior
(3) iliac bones approximate
(4) ischial tuberosities separate

c. counternutation (sacral extension)

(1) sacral (promontory) base moves superior and posterior
(2) apex moves inferior and anterior
(3) iliac bones separate
(4) ischial tuberosities approximate

D. Mitchell et al’

1. distinguish between iliosacral and sacroiliac motions

a. forces transmitted from lower extremities are iliosacral
b. forces transmitted from the spine are sacroiliac

2. three horizontal innominate (ilial) axes
3. three horizontal sacral axes
4. diagonal sacral axes

a. right and left oblique axes
b. created by contraction of one piriformis muscle (sacral torsions)

E. Porterfield’3

1. suggests two distinct axes (dynamic) of rotation

a. junction between cranial and caudal aspects of sacroiliac joint surface (horizontal axes)

(1) anterior rotation of ilium - ASIS and iliac crest move downward and forward
(2) posterior rotation of ilium - PSIS and iliac crest move downward and backward
(3) sacral nutation (flexion)
(4) sacral counternutation (extension)

b. just posterior to the pubic symphysis (horizontal axis)

(1) upward translation of ilium on sacrum (upslip)
(2) downward translation of ilium on sacrum (downs lip)

VII. The Pubic Symphysis

Articulation of two pubic bones {5}

B. Joint surface lined with thin layer of cartilage {5, 6, 13}

C. Joint surfaces separated by thick intrapubic fibrocartilaginous disc {5, 6, 13}

D. Suprapubic ligament covers superior aspect of joint {5, 6, 13}

E. Anterior pubic ligament blends with aponeurosis of Rectus Abdominis muscle {5, 13} and External Oblique muscle {5}

F. Posterior pubic ligament joins with the inner abdominal fascia of Transverse Abdominis muscle {13}

G. Arcuate ligament (thick, inferior ligament) stabilizes joint from different forces {13}

1. compression
2. tensile
3. rotary

H. Structural differences between sexes

1. fibrocartilaginous disc wider in females {13}
2. symphysis longer (vertical) in males {13}

I. Symphysis used to determine skeletal age {13}

1. undergoes variety of changes with

a. age {13}
b. function {13}
c. in females, hormonal influences of pregnancy {13}
d. in females, mechanical trauma of parturition {13}

J. Pubic bones transfer and absorb ground and trunk forces {13}

K. Pubic bone is attachment for many muscles which affect forces to this area, especially medial thigh group (adductors) {13}

L. Little movement at this joint {6, 13}

  Next: Chapter 7