Spine

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BIOMECHANICS

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Lumbar Anatomy

5 vertebrae L1-L5

5 intervertebral discs

5 pair of exiting nerve roots

Lumbar lordosis L1-S1 ranges from 3080

The apex of lumbar lordosis L3-L4

1

2

3

4

5

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Lumbar Spine Anatomy

Typical lumbar vertebra (L2)

Body

Vertebral foramen/canal

Intervertebral foramen

Pedicle

Transverse process

Lamina

Spinous process

Facet joints

Pars interarticularis

inferior

Superior

Anterior (oblique)

A Lateral P

Posterior (oblique)

Superior

Inferiorsuperior

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Intervertebral Disc

Soft fibro-cartilaginous cushions

Between two vertebra

Allows some motion

Serve as shock absorbers

Total 23 discs

th of the spinal column's length

Avascular

Nutrients diffuse through end plates

Collagen

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Intervertebral Disc

NUCLEUS PULPOSUS

Has more water and PGs

PG are macro-molecules

Attract and retain water

Hydrophilic gellike matter Resists compression

Amount of water

Activity related

Varies throughout the day

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Intervertebral Disc

NUCLEUS PULPOSUS

Eccentrically positioned posteriorly

Young & healthy, 90% water, bound to proteoglycans

Aging> desiccation> increase viscosity> fissuring

Young nucleus> even distribution of load

Old nucleus> undue concentration on vertebral body edges

Small displacement w/ ROM, ball-bearing like

Compressive stress predominates

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Intervertebral Disc

NUCLEUS PULPOSUS Pascals law: Fluid mass within closed

container> local increase in pressure> transmit around entire side wall (annulus)

Nucleus pulpous imbibes water

Develops internal pressure

Pressure exerted in all directions

Lateral forces against annulus

Superiorly and inferiorly directed forces against end plates

Increases stiffness of end plate and annulus fibrosus

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Intervertebral Disc

ANNULUS FIBROSUS

Strong radial tirelike structure

Series of lamellae

Concentric sheets of collagen fibers

Connected to end plates

Orientated at various angles

Under compression Become horizontal

Encloses nucleus pulposus

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Intradiscal Pressure

INTRADISCAL PRESSURE

Compressive loads in vivo: 500N standing, 700N sitting

Increased to 3000 to 6000N during lifting of moderate weights, decreases with load closer to body

Estimate of P = 1.5X compressive load divided by the cross sectional area

Disk pressure is usually uniform

Pressure lowest in supine position

Disk usually does not fail, but end plates fracture

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Spinal Ligaments

Anterior Longitudinal

Posterior Longitudinal

Ligamentum Flavum

Interspinous Ligaments

Supraspinous Ligaments

Intertransverse Ligaments

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Lumbar Spine

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Lumbar Spine

Thoraco lumbar fascia

Stabilizing corset

Transmit load longitudinally to the spinous process

Ilio lumbar ligament

Stabilize 5th lumbar vertebrae from ant. Displacement

Types of motion

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Stress-Strain Curve

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The Motion Segment

Functional Spinal Unit

2 adjacent vertebrae & intervening soft tissue

Anterior

Vertebral body

Disk

ALL, PLL

Support, absorb impact, restrict vertical translation

Posterior

Neural arch & its processes

Facet joint

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STABILITY

The vertebral column subject to

Axial compression

Bending

Torsion

Shear

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STABILITY

Primary load-transmitting element, 80-90%

Bone Mineral Content, Size

Osteoporosis> loss of horizontal trabeculae

Increasing size from C to L spine

Compressive load> pressure higher in center of end plates than periphery

In vivo, filled with blood> greater strength, hydraulic shock absorber

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STABILITYPOSTERIOR ELEMENTS pedicles, lamina, facet joints,

spinous & transverse processes Bony processes> lengthen

moment arms of muscles Forces on processes>

transmitted to Lamina Forces on posterior elements>

transmitted to vertebral bodies from Pedicles

Pars Interarticularis Large bending forces;

excessive extension Thicker than rest of lamina Common site of

stress/fatigue fractures> weakens motion segment> spondylolithesis

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STABILITY

Facet Joints Major role in controlling motion

Resist torsion & shear, role in compression

Lumbar FSU facets 40% torque resistance, 40% disk, 20% ligaments

Load sharing varies with flexion & extension Seated position> decreased lumbar lordosis> increased

intradiscal pressure & decreased load-bearing of the facets

Orientation of facets C spine - 45 transverse, parallel frontal

T spine - 60 transverse, 20 frontal

L spine - 90 transverse, 45 frontal

Capsules lax> allow gliding

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MOBILITY

Flexion-Extension

large, due to sizable disks & lack of facet restraint

posterior half of disk, moves w/ flex-ext

Lateral bending

Axial rotation

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MOBILITY

Lumbo pelvic rhythm

Coordinated simultaneous activity of lumbar flexion and tilting of pelvis

LPR can increase the range of forward flexion, anterior pelvic tilt and flexion of lumbar spine

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Lumbo sacral angle

Fergusons angle

Is formed by the fifth lumbar vertebra and first sacral segment

The first sacral segment , which inclined anteriorly and inferiorly forms an angle with the horizontal

35-40 considered normal

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Sacral Anatomy

The sacrum is a series of 3, 4, or 5 fused coccygeal vertebrae

The coccyx articulates with the inferior aspect of the sacrum1

234C

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SACROILIAC JOINT

A joint that connects the spinal column with the pelvis. The V-shaped sacrum near the base of the spine fits like a wedge between the wide wings of the ilium (hipbone).

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SACROILIAC JOINT

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MOBILITY AND STABILITY

Poorly understood

Permits a small amount of motion

Stiff, coarse interdigitating articular surfaces

Complete ankylosis in up to 76% over age of 50

Nutation, as described by Kapandji, is the anterior inferior motion of the sacral base.

counter- nutation as the movement of the sacral base posteriorly and superiorly.

This nutation and counter- nutation motion of the sacrum is a pivoting type of motion, so that when the base moves forward, the sacral apex (inferior part of the sacrum) moves posteriorly.

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Muscles

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Iliocostalis Lumborum

O Common tendon origin in

sacrum, iliac crest, lumber vertebrae

I Lower borders ribs 6-12

N Dorsal rami of spinal nerves

F Bilateral

Spinal extension Maintenance of erect posture Stabilization of spine during

flexion

Unilateral Lateral flexion Ipsilateral rotation

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Longissimus Thoracis

O Common tendon origin

in sacrum, iliac crest, lumber vertebrae

I T1-12 transverse

processes

N Dorsal rami of spinal

nerves

F Same as above

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Spinalis Thoracis

O Common tendon origin

in sacrum, iliac crest, lumber vertebrae

I T3-8 spinous processes

N Dorsal rami of spinal

nerves

F Same as above

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Multifidus O

Transverse processes C4-L5

Sacrum

PSIS

I Spinous process of vert above

origin

N Spinal nerve roots

F Extend and lateral flexion of

vertebral column

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Quadratus Lumborum O

Iliolumbar Ligament Iliac crest

I Lower border 12th rib L1-L4 transverse processes

N ventral branches of T12 and L1 to

L4.

F Pelvis elevation Trunk extension Trunk lateral flexion Pulls down rib 12 to fix origin of

diaphragm

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Rotatores O

Transverse processes from axis to sacrum

I Laminae of vert above

N Direct branches over spinal

nerve roots

F Spine extension

Rotation to opposite side

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Disorders Of The Back/Spine

Back Strain/Sprain

Ankylosing Spondylitis

Cauda Equina

Herniated Nucleus Pulposus (HNP)

Spinal Stenosis

Kyphosis/Scoliosis

Low Back Pain (LBP): Spondylolysis, Spondylolisthesis

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Back Strain/Sprain

LBP is the most frequent cause of lost work time and disability in adults

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Ankylosing Spondylitis

Progressive spinal flexion deformities (may progress to a chin-on-chest deformity)

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Cauda Equina symdrome

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Herniated Nucle