Transcript Biomechanics of the Human Spine

ENT 214
Biomechanics
Biomechanics of Human Spine
Picture retrieved from
http://en.wikipedia.org/wiki/Image:Spinal_column_curvature.png
Structure of the Spine
What is the vertebral column?
 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
Picture retrieved from
http://www.becomehealthynow.com/images/organs/spine/ant_lat.jpg
Structure of the Spine
What is a motion segment?
 two adjacent vertebrae and the
associated soft tissues
 considered the functional unit of the
spine
Structure of the Spine
Transverse
process Posterior
Interspinous
longitudinal
ligament
ligament
Supraspinous
ligament
Vertebral
body
Intervertebral
joint and facet
Spinous
process
Ligamentum
Vertebral
flavum
canal
Posterior
Anterior
Anterior
longitudinal
ligament
Cartilaginous
end-plate
Intervertebral
disc
Intervertebral
foramen with
nerve root
Two adjacent vertebrae and the associated
tissues comprise the motion segment.
Structure of the Spine
What are the joints between adjacent
vertebrae?
 intervertebral symphysis joints on the
anterior side
 two gliding diarthrodial facet joints on
the posterior side
Structure of the Spine
What is the function of the facet joints?
 to channel and limit the range of
motion in the different regions of the
spine
 to assist in load bearing, sustaining
up to 30% of the compressive load on
the spine, particularly when the spine is
in hyperextension
Structure of the Spine
What are the intervertebral discs?
 fibrocartilaginous discs that cushion the
anterior spinal symphysis joints
 composed of a nucleus pulposus (colloidal
gel with a high fluid content) surrounded by the
annulus fibrosus (a thick, fibrocartilaginous
ring that forms the disk exterior)
Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/e/e9/ACDF_oblique_annotated_english.png
Cervical
Vertebra
Structure of the Spine
What are the primary spinal curves?
 the thoracic and sacral curves
 concave anteriorly
 are present at birth
Thoracic
Vertebra
Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/d/d2/Gray90.png
Structure of the Spine
What are the 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
Cervical
Vertebra
Picture retrieved from
http://en.wikipedia.org/w
iki/Image:Gray85.png
Picture retrieved from
http://en.wikipedia.org/wiki/Image:Cervical_vertebra_english.png
Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/6/62/Gray94.png
Lumbar
Vertebra
Picture retrieved from
http://upload.wikimedia.org/wikipedia/commons/b/b2/Gray430.png
Structure of the Spine
Vertical
alignment
Lordosis
Kyphosis
Scoliosis
Lordosis - exaggerated lumbar curve
Kyphosis - exaggerated thoracic curve
Scoliosis - lateral spinal curvature
Picture retrieved from
http://www.childsdoc.org/spring2002/scoliosis2.jpg
Movements of the Spine
What 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
Movements of the Spine
What 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
Picture retrieved from
http://upload.wikimedia.org/
wikipedia/en/6/6f/Rectus_c
apitis_anterior_muscle.PN
G
Movements of the Spine
What muscles contribute to flexion of
the spine in the abdominal region?
 rectus abdominis
 internal obliques
 external obliques
Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/3/32/Illu_trunk_muscles.jpg
Movements of the Spine
What 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
Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/5/51/Splenius.png
Movements of the Spine
What muscles contribute to 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
Movements of the Spine
What 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
Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/1/1a/Sternocleidomastoideus.png
Movements of the Spine
What muscles contribute to lateral
flexion of the lumbar spine?
 quadratus lumborum
 psoas major
 PLUS the lumbar flexors and extensors
when developing tension unilaterally
Picture retrieved from
http://upload.wikimedia.org/wikipedia/common
s/8/8d/Quadratuslumborum.png
Loads on the Spine
What forces commonly act on the spine?
 body weight
 tension in the spinal ligaments
 tension in the spinal muscles
 any external loads carried in the hands
Loads on the Spine
In normal standing position, body weight acts
anterior to the spine, creating a forward
bending load (moment) on the spine.
Loads on the Spine
Fs
Fc
wt
Because the spine is
curved, body weight,
acting vertically, has
components of both
compression (Fc) and
shear (Fs) at most
motion segments.
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
Joint
center
Compression
reaction
force
Sample Problem 1
How much tension
must be developed by
the erector spinae
with a moment arm of
6cm from L5-S1 joint
center to maintain the
body in the position
shows on your right?
Given that
Head : 58 N
Arms : 81 N
Trunk : 328 N
Box : 111 N
Loads on the Spine
compression
tension
Lumbar hyperextension can create a bending
load (moment) in the posterior direction.
Loads on the Spine
Lumbar hyperextension
produces compressive
loads at the facet joints.
hyperextension
Loads on the Spine
Superior view
Lateral view
Spinal rotation generates shear stress in the intervertebral discs.
Human Posture When Lifting
Common Injuries




Low back pain
Soft tissue Injuries
Acute fractures
Stress Fracture – spondylolysis (fracture in
vertebral neural arch)

Disc herniation