Lumbar and sacral Biomechanics

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Transcript of Lumbar and sacral Biomechanics

  • Spine

  • Sreeraj S R

    BIOMECHANICS

  • Sreeraj S R

    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