5. What is a motion segment?
Two adjacent vertebrae and the
associated soft tissues are considered
as the functional unit of the spine.
6. Structure of the Spine
Spinal movement is the combination
of:
Intervertebral joints
Facet joints
intervertebral joints on the anterior
side.
two gliding diarthrodial facet joints on
the posterior side
7. Intervertebral Disc:
(Composition)
composed of a nucleus pulposus (colloidal
gel with a high fluid content) surrounded by the
annulus fibrosus (a thick, fibrocartilaginous
ring that forms the disc exterior)
8. INTERVERTEBRAL DISC
Intervertebral disc make up 20-30% of the height of the
column and thickness varies from 3mm in cervical region,
5mm in thoracic region to 9 mm in the lumbar region.
Ratio between the vertebral body height and the disk height
will dictate the mobility between the vertebra –
Highest ratio in cervical region allows for motion
Lowest ratio in thoracic region limits motion
9. DISC STRUCTURE
Nucleus Pulposus (NP) is located in the center except in lumbar
where lies slightly posterior.
Gelatinous mass rich in water binding PG (proteoglycan).
Chondrotin-4 sulfate in PG molecule gives the disc a fluid maintaining capacity
(hydrophyllic) which decreases with age.
Hydration of the disc will also decrease with compressive loading - this loss of
hydration decreases its mechanical function.
10. DISC STRUCTURE
80-90% is H2O – decreases with age.
Disc volume will reduce 20% daily (reversible) which causes a loss
of 15-25 mm of height in the spinal column.
Acts as a hydrostatic unit allowing for uniform distribution of
pressure throughout the disc.
11. DISC STRUCTURE
Compressive stresses on the disc translate into tensile stresses in
the annulus fibrosis
This makes the disc stiffer which adds stability and support to the spine.
Bears weight and guides motion.
Avascular - nutrition diffusion through end-plate.
16. the thoracic and sacral curves
concave anteriorly
are present at birth
Primary spinal curves
17. Secondary Spinal Curves:
The lumbar and cervical curves
concave posteriorly
develop from supporting the body in
an upright position after young children
begin to sit and stand
19. Movements of the Spine
Movements of the spine are allowed:
The movement capabilities of the spine are
those of a ball and socket joint, including
movement in all three planes and circumduction.
Mechanically:
Annulus fibrous – acts like coiled spring
Nucleus pulposus – acts like ball bearing
20. Muscles involved in
movements of the Spine
Muscles contribute to flexion of the
spine in the cervical region:
rectus capitus anterior
rectus capitis lateralis
longus capitis
longus colli
eight pairs of hyoid muscles
24. Muscles contribute to extension of the
spine in the cervical region:
splenius capitis
splenius cervicis
assisted by:
rectus capitis posterior major and minor
obliquus capitis superior and inferior
26. Muscles contribute to the extension of the
spine in the thoracic and lumbar regions:
erector spinae - spinalis,
longissimus, iliocostalis
semispinalis - capitis, cervicis,
thoracis
deep spinal muscles - mulitifidi,
rotatores, interspinales,
intertransversarii, levatores costarum
Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/9/90/Gray389.png
27. Muscles contribute to lateral flexion of
the cervical spine:
sternocleidomastoid
levator scapulae
scalenus anterion, posterior, & medius
PLUS the cervical flexors and extensors
when developing tension unilaterally
29. Muscles contribute to lateral flexion of
the lumbar spine:
quadratus lumborum
psoas major
PLUS the lumbar flexors and extensors
when developing tension unilaterally
31. Loads on the Spine
Forces that commonly act on the spine
are:
body weight
tension in the spinal ligaments
tension in the spinal muscles
any external loads carried in the hands
32. Loads on the Spine
In normal standing position, body weight acts
anterior to the spine, creating a forward
bending load (moment) on the spine.
33. Loads on the Spine
Because the spine is
curved, body weight,
acting vertically, has
components of both
compression (Fc) and
shear (Fs) at most
motion segments.
Fc
Fs
wt
34. Loads on the Spine
During lifting, both
compression and
anterior shear act
on the spine.
Tension in the
spinal ligaments
and muscles
contributes to
compression.
Muscle
tension
Shear
reaction
force
Compression
reaction
force
Joint
center
35. Loads on the Spine
Lumbar hyperextension can create a bending
load (moment) in the posterior direction.
compression tension
36. Loads on the Spine
hyperextension
Lumbar hyperextension
produces compressive
loads at the facet joints.
37. Loads on the Spine
Spinal rotation generates shear stress in the intervertebral discs.
Superior view Lateral view
