a curved stack of 33 vertebrae structurally divided into five regions

1. BIOMECHANICS
OF HUMAN SPINE

2. Picture retrieved from
http://en.wikipedia.org/wiki/Image:Spinal_column_curvature.png

3. Structure of the Spine
 a curved stack of 33 vertebrae
structurally divided into five regions:
 cervical region - 7 vertebrae
 thoracic region - 12 vertebrae
 lumbar region - 5 vertebrae
 sacrum - 5 fused vertebrae
 coccyx - 4 fused vertebrae

4. Picture retrieved from
http://www.becomehealthynow.com/images/organs/spine/ant_lat.jpg

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.

12. Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/e/e9/ACDF_oblique_annotated_english.png
Cervical
Vertebra

13. Thoracic
Vertebra
Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/d/d2/Gray90.png

14. .
.
Lumbar Vertebra
Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/b/b2/Gray430.png

15. Spinal curves:

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

18. Structure of the Spine
Lordosis - exaggerated lumbar curve
Kyphosis - exaggerated thoracic curve
Scoliosis - lateral spinal curvature
Vertical
alignment
Lordosis Kyphosis Scoliosis

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

21. Picture retrieved from
http://upload.wikimedia.org/
wikipedia/en/6/6f/Rectus_c
apitis_anterior_muscle.PN
G

22. Muscles contribute to flexion of the
spine in the abdominal region:
 rectus abdominis
 internal obliques
 external obliques

23. Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/3/32/Illu_trunk_muscles.jpg

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

25. Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/5/51/Splenius.png

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

28. Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/1/1a/Sternocleidomastoideus.png

29. Muscles contribute to lateral flexion of
the lumbar spine:
 quadratus lumborum
 psoas major
 PLUS the lumbar flexors and extensors
when developing tension unilaterally

30. Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/8/8d/Quadratuslumborum.png

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

39. Human Posture When Lifting

40. COMMON INJURIES
Low back pain
Soft tissue Injuries
Acute fractures
Stress Fracture – spondylolysis (fracture
in vertebral neural arch)
Disc herniation