KinesiologyThe Spine

Spinal Column Structure

Base of support.Link between upper and lower extremities.Protects spinal cord.Stability vs. mobility

Example: cervical vs. thoracic spine

5 Regions of Vertebral Column

CervicalThoracicLumbarSacralCocygeal33 bones and 23 disks

Curvatures Viewed Laterally

Prior to birth “C-shaped”.4 distinct curves in an adult.

Cervical Lordosis

Thoracic Kyphosis

Lumbar Lordosis

Spinal Motion

Spinal movement is the combination of: Intervertebral joints Facet joints

Intervertebral Joints

Intervertebral DiscIntervertebral disk make up 20-30% of the

height of the column and thickness varies from 3mm in cervical region, 5mm in thoracic region to 9 mm in the lumbar region.

Ratio between the vertebral body height and the disk height will dictate the mobility between the vertebra – Highest ratio in cervical region allows for

motion Lowest ratio in thoracic region limits motion

Disc Structure

Nucleus Pulposus (NP) is located in the center except in lumbar lies slightly posterior. Gelatinous mass rich in water binding PG

(proteoglycan) AKA (glycoaminoglycos) GAG-protein molecule.

Chondrotin-4 sulfate in PG molecule gives the disc a fluid maintaining capacity (hydrophyllic) - decreases with age.

Hydration of the disc will also decrease with compressive loading - this loss of hydration decreases its mechanical function.

Disc Structure

80-90% is H2O – decreases with age.Disc volume will reduce 20% daily (reversible)

which causes a loss of 15-25 mm of height in the spinal column.

Acts as a hydrostatic unit allowing for uniform distribution of pressure throughout the disc.

Disc Structure

Compressive stresses on the disc translate into tensile stresses in the annulus fibrosis This makes the disc stiffer which adds stability and

support to the spine.Bears weight and guides motion.Avascular - nutrition diffusion through end-

plate.

Annulus Fibrosis

Collagen arranged in sheets called lamellae (outer layers). These lamellae are arranged in concentric rings -10-12

layers that lessen in number with age and thicken (fibrose). Enclose the nucleus and oriented in opposite directions at

an angle of 120 degrees (or 45-65 degrees). Controls the tensile loading from shear, accessory motions

in the anterior compartment and disc forces which can be up to 5x the external compression force.

Annulus FibrosisMostly avascular and lacking innervation

but the outermost layers are probably innervated (sinovertebral nerve).

Thickest anteriorly.Outermost 1/3 connects to vertebral body

via Sharpie’s fibers.Outer 2/3 connect to the end plate.

Disc Pathology - HerniationHighest incidence at C5-6, C6-7, L4-5, and

L5-S1.Disc herniation

Disc protrusion or bulge - contained• Annulus intact.• Localized – usually lateral• Diffuse – usually posterior• Prolapsed – not contained• Annular fibers disrupted – inner layers

Extrusion - migration through all layers

http://www.spinalrehab.com.au/disorders/jb2pre.jpg

Longitudinal LigamentsAnterior longitudinal

Supraspinous

Posterior longitudinal

Ligamentum flavum (elastic)

PLL diverts herniation posteriolaterally

Posterior Structures (Elements) of Motion Segment

Pedicles and lamina form the neural arch.Facet joints between the superior and

inferior articulating surfaces.Transverse and spinous processes.Interspinous and supraspinous ligaments.Ligamentum lavum.Intervertebral foramina.

Facet JointArticulation between

the superior (concave) and inferior (convex) facets.

Guide intervertebral motion through their orientation in the transverse and frontal planes.

Facet Joint CapsuleLimit motions.Strongest in thoracolumbar and

cervicothoracic regions where the curvatures change.

Resist flexion and undertake tensile loading in the superior portion with axial loading or extension.

Resists rotation in lumbar region.

Intervebral Foramina Exit for nerve root. The size is dictated by the

disc heights and the pedicle shape.

Will lose space with osteophytic formation, hypertrophy of ligaments and loss of disc height with aging – lateral stenosis.

Decreases by 20% with extension and increases 24% with flexion

Spinal Stability

The column’s ability to react to multiple forces placed on it.

Degeneration increases instability.Body reacts to restore through fibrosus and

osteophytic changes.

Types of Segmental Loading

Axial CompressionBendingTorsionShear

Axial CompressionCaused by gravity, ground reaction forces, muscle

contraction and ligaments reaction to tensile forces.

Intradiscal loads can range from 294N to 3332N depending upon position.

Most load in anterior segment, posterior can load from 0-30% depending upon segments position.

Compression at the disk causes tension at the annulus, changing the angle of the fibers and increasing the stability.

Axial Compression (cont’d)

Creep will occur in the disc, will be larger with increased force and aging.

5-11% of H2O is lost through creep.Creep is rapid 1.5-2mm in 10 min.Plateaus at 90 minutes.

BendingCombination of compression, shear and

tensile forces on the segment from translation.Bending into flexion will be resisted by

posterior annulus, PLL and the facet capsule and anterior compressive forces on the anterior structures causing disc displacement.

For extension posterior compressive forces in anterior segment and there is a tensile load in facet capsule and ALL.

TorsionCaused by axial rotation and coupled motions.Stiffness may increase due to facet

compression with certain motions i.e., flexion increases torsional stiffness at L3-4.

Annulus fibrosus resists, 1/2 fibers CW other 1/2 CCW facets may help depending upon the orientation (resists in a tensile manner).

When combined with flexion the amount of force required for tissue failure is decreased.

Shear

Facet joint resists especially in the lumbar area.

Annulus will undergo some tensile forces depending upon direction and the fiber orientation or angle.

Discs also resist but if creep occurs - the facet may undergo more loading.

Mobility

Amount and direct of motion in a segment is determined by: Vertebral body/disc size. Facet orientation frontal vs. sagittal.

FlexionSuperior vertebra will anterior tilt and forward

gliding will occur: Widening the intervertebral foramina 24%. Adds compressive forces on the anterior aspect of

the anterior segment moving the nucleus pulposus posteriorly.

Tensile forces placed on posterior annulus, flavum, capsule and PLL.

Central canal is widenedRationale for some of William’s flexion

exercises

Extension

Superior vertebra will tilt and glide posteriorly and the intervertebral foramina narrowed up to 20%.

The central canal is also narrowed.Nucleus pulposus moves anteriorly

Lateral Flexion

Superior vertebra will translate, tilt and rotate over inferior - direction will differ.

Concavity towards, convexity oppositeTensile forces on convexity, compressive

forces on concavityExtension in ipsilateral facet.Flexion in contralateral facet.

Rotation

Accessory motions are like lateral flexion due to same coupling in cervical and upper thoracic spine.

Exception with lower T/S and L/S in neutral coupling then opposite (in most references).

If the motion segment is flexed or extended spine (in most references) the coupling will be the same.

Regional Structural andFunctional DifferencesDifferences are apparent due to connection

requirements, sacral, upper C-spine, all junctions

Vertebral body size increases with support requirements.

Cervical, thoracic,lumbar, and sacral/cocygeal.

Cervical

CO - occipital C1 - AtlasC2 - Axis C3-6 - general basic

structure

Cervical Region FunctionMobility > Stability.Upper cervical unit –

C0-2

Lower Cervical unitC2-7

C0-1

C0 – occiput – containing the occipital condyle – convex.

C1 - no body, disk and spinous process allows for free space and a large neutral zone and cord protection - this means more motion.

Lateral facets of CO on C1 - concave C1 on convex CO - flex/ext or nodding and minimal to no lateral flexion/rotation.

C1-2

2 facets laterally and 1 medially with dens and anterior arch

transverse ligament helps control (C1 on C2 anterior displacement), stabilizes – allows nodding

also provides cartilaginous surface as does the alar ligament - limits flex/ext so right rotation requires left lateral facet to slide anterior and right lateral facet to slide posterior – so rotation is coupled with extension.

Can account for up to 50% of rotation in the neck and most of the initial ROM.

Dens

C2-7

50% wider than they are deep.Transverse process holds foramen for

vertebral artery, vein and plexus, and grove for the spinal nerve.

Facet orientation is roughly 45 degrees(35-65) in the transverse plane w/ loose capsule - allows for motion in all planes and more rotation and lateral flexion than other regions.

Thoracic Spine FunctionArticulation for the ribs Least mobility Increasing load bearingLat flex flex/Ext

Thoracic Spine Body

T1 - similar to cervical in (C7a).Normally the vertebral body equals width and depth.The ratio of disc diameter to height is highest. This

will: Decrease tensile forces Decrease possibility of disc injury

Posterior aspect becomes thicker as you go lower - ribs bigger (articulates) and more compressive forces.

End-plates become larger (higher compressive forces) as you go caudally.

Thoracic SpineLess flexible due to rib articulation, smaller disc

to body ratio, spinous process.Flavum and ALL are thicker; facet capsule less

flexible.Upper thoracic spine facet orientation

Limits flexion extension - 60/20 transv/front Allows coupled lat/rot. (rot of spinous process to the

convex side)Facets are more sagittal in T9-12 to allow flex/ext

and rot of spinous process will be toward concavity (lumbar coupling).

Thoracic SpineRib articulation consists of 2 articulations to

the thoracic vertebra – Anterior surface of the lateral process Lateral aspect of the vertebral body. Bucket handle motion of the ribs with breathing. Extension and contralateral lateral flexion ribs

separate. Flexion and lateral flexion ipsilaterally

compresses ribs.

Thoracic SpineScoliosis will cause a rib

hump.Combination of tranverse

plane rotation and frontal plane sidebend – contralateral coupling.

Convex side will occur on the ipsilateral rotated side – causing hump.

Lumbar SpineMost load bearing

structures in the skeletal system

Sagittal plane motionLargest body/disc,

lamina and pedicles short and thick for load bearing.

Lumbar Spine

L5 transitional, wedge shape of body and disc – Anterior > posterior.

L5-S1 most flexion extension.Coupling of motion - right lateral flexion will

result in right sidebend and left rotation of vertebral body (when L/S in neutral)

Spinal Musculature

Mobility vs. StabilitySlow twitch SO vs. fast twitch FOGEnergy storage

Consider the line-of-pull of all spinal muscles

SpinalMuscles

Common Theme

Rotary component

Compressive component

Small angle of insertionTherefore:

Common Theme

Rotary component

Compressive component

Small angle of insertionTherefore:

When are active vs. passive exercised indicated? When are they not?

Hip Flexors &Abdominals

General Comment Regarding Function

Contracture vs. contraction

General Comment Regarding Function

Contracture of hip flexors and effect on lumbar spine

General Comment Regarding Function

Abdominals Pelvic stability/balance Guy-support system