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 30°–80°

� 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

� ¼ 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 gel–like 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� Pascal’s 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 tire–like 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 - 45º transverse, parallel frontal

� T spine - 60º transverse, 20º frontal

� L spine - 90º transverse, 45º 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

� Ferguson’s 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

� 35-40⁰ 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 <45 years

� Most symptoms of limited duration

� 85% of patients improve and returning to work within 1 month

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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 Nucleus Pulposus (HNP) of the

Lumbar Spine

� Displacement of the central area of the disc (nucleus) resulting in impingement on a nerve root

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Kyphosis

� Defined: abnormally increased convexity in the curvature of the thoracic spine as viewed from side

� Scheuermann’s Disease

� Hyperkyphosis that does not reverse on attempts at hyperextension

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Scoliosis

� Lateral curvature of the spine of greater than 10 degrees, usually thoracic or lumbar, associated with rotation of the vertebrae and sometimes excessive kyphosis or lordosis

� Idiopathic scoliosis

� Lateral deviation and rotation of the spine without an identifiable cause

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Low Back Pain

� Spondylolysis

� Unilateral Pars defect is the result of a fatigue fracture from repetitive hyperextension

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Low Back Pain

� Spondylolisthesis

� Bilateral Pars Interarticularis defect

� Forward slippage of one vertebra on another

� Usually L5-S1