1. Biomechanics of Human Spine
ENT 214 Biomechanics
Biomechanics of Human Spine

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3. 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

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5. Structure of the Spine What is a motion segment?
two adjacent vertebrae and the associated soft tissues
considered the functional unit of the spine

6. Interspinous ligament Posterior longitudinal ligament
Structure of the Spine
Supraspinous ligament
Intervertebral joint and facet
Spinous process
Ligamentum flavum
Interspinous ligament
Transverse process
Anterior longitudinal ligament
Cartilaginous end-plate
Intervertebral disc
Intervertebral foramen with nerve root
Posterior
Anterior
Vertebral canal
Posterior longitudinal ligament
Vertebral body
Two adjacent vertebrae and the associated tissues comprise the motion segment.

7. 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

8. 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

9. 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)

10. Cervical Vertebra Picture retrieved from
Cervical
Vertebra

11. Structure of the Spine What are the primary spinal curves?
the thoracic and sacral curves
concave anteriorly
are present at birth

12. Thoracic Vertebra Picture retrieved from

13. 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

14. Cervical Vertebra Picture retrieved from
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15. Lumbar Vertebra Picture retrieved from
Lumbar
Vertebra
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16. Structure of the Spine Lordosis - exaggerated lumbar curve
Vertical alignment
Lordosis
Kyphosis
Scoliosis
Lordosis - exaggerated lumbar curve
Kyphosis - exaggerated thoracic curve
Scoliosis - lateral spinal curvature

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19. 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

20. 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

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22. Movements of the Spine
What muscles contribute to flexion of the spine in the abdominal region?
rectus abdominis
internal obliques
external obliques

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24. 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

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26. 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
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27. 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

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29. 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

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31. 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

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 Fc Fs wt
Because the spine is curved, body weight, acting vertically, has components of both compression (Fc) and shear (Fs) at most motion segments.

34. Compression reaction force
Loads on the Spine
Muscle tension
Shear reaction force
Compression reaction force
Joint center
During lifting, both compression and anterior shear act on the spine. Tension in the spinal ligaments and muscles contributes to compression.

35. 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

36. Loads on the Spine
compression
tension
Lumbar hyperextension can create a bending load (moment) in the posterior direction.

37. Loads on the Spine
hyperextension
Lumbar hyperextension produces compressive loads at the facet joints.

38. Loads on the Spine Superior view Lateral view
Spinal rotation generates shear stress in the intervertebral discs.

40. Human Posture When Lifting

41. Common Injuries Low back pain Soft tissue Injuries Acute fractures
Stress Fracture – spondylolysis (fracture in vertebral neural arch)
Disc herniation