The Evolution of the Vertebral Column

8/6/2019 The Evolution of the Vertebral Column

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TheEvolutionoftheVertebralColumn:Thewhy'sandhow'sofwhat

makesusstandtall

BoyanaGrigorova

MedicalUniversity-Plovdiv

Medicine1styear

Group9

15687


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1. Introduction

Everydayourbodiesperformamazingmovements-werun,walk,climborsimply

standerect,withoutgivinganyofthesetrivialactivitiesmuchthought.Weseldom,ifever,ask ourselves,whatmakes itall possible?How andwhy dowe standtall?The

answertothesequestionslieswithintheremarkablyeffectiveandcomplexstructureofthehumanvertebral column,whichnot onlyserves toprotect the spinal cord, but toalso provide strengthand flexibility to the trunk. The extraordinary unison between

formandfunctionwithinthestructureofthehumanvertebralcolumnnotonlypermits

it to perform a variety of movements- flexion, extension, lateral movement,circumductionandrotation-butitalsofacilitateshumanbipedalism.Whatmakesthe

spinal columnevenmore remarkableis its ability towithstandmajorinternalforcesand weights far exceeding the body weight of a particular individual. The origin of

bipedalism was a turning point in hominid evolution and the importance of the

mechanical structure of the spine in this process cannot be overemphasized. The

modernanatomyofthespinehasbuiltuponstrengthsandweaknessesofabodyplan,inherited fromour ancestors, givingusanefficient and graceful gait,but alsoawide

rangeofpotentialinjuriesandpainfulproblems.It isthereforeimportanttostudyandappreciate the intricate structure and mechanics of the vertebral column,aswell as

understanditsevolution.

2. MacroscopicanatomyofthevertebraeandspineThevertebralcolumnphysicallysupportstheweightoftheheadandtrunk,allows

themovementoftheribcageforrespiration,protectsthespinalcordfrominjuriesandabsorbs stresses produced by walking, running and lifting. It also provides an

attachment for the limbs, thoracic cage andmuscles and not the least important, itenablesbipedalism.Thevertebralcolumnismadeupof33vertebrae,24ofwhicharedistinctand9arefusedtoformthesacrumandthecoccyx.Theindividualvertebrae

are attached to one another through a system of intervertebral cartilaginous discs,

ligamentsandinterlockingprocesses.Thesestructuralarrangementsallowforlimitedmovementsoftheseparatevertebrae,butgiveextensivemobilitytothespinalcolumn

asawhole.Whenviewedfromtheside,thevertebralcolumnhasfourcurvatures.Thethoracicandsacralcurvaturesdevelopduringtheembryonicandfetalperiods,whereas

thecervicalandlumbarcurvaturesdevelopafterbirth(VandeGraaff2001).Thereare

sometypicalabnormalitiesofthespinalcordcurvature,suchaskyphosis,lordosisandscoliosis.

Therearefivecategoriesofvertebrae:7cervicalvertebraeintheneck,12thoracicvertebraeinthechest,5lumbarvertebraeinthelowerback,5 sacralvertebraeatthe

baseofthespineand4 coccygealvertebrae.Atypicalvertebraconsistsofabody,andavertebralarch,whichencirclesthevertebralforamen.Collectively,allof thevertebral

foramina formthe vertebral canal, where the spinal cord issituated.The archhas apedicleand a lamina. In addition, each vertebra has a spine (processusspinalis), twotransverse processes (processus transversus), and four articular facets. Between two

neighboringvertebralpedicles,anopeningexists,calledforamenintervertebrale,wherethesegmentalspinalnervespassthrough(VandeGraaff2001).Somedifferencesexist

intheoverallstructureof thevertebrae from thefive categories.Mainly,thecervicalvertebraearethesmallestandtheyhaveuniquecharacteristics,whichallowforhead


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movements. The atlas supports the skull and has no body and no spine, but is a

componentoftheatlantooccipitaljointupward,andtheatlantoaxialjointdownwards.Theaxishasadens(atypeofprocess),whichformsthesurfacearoundwhichtheatlas

rotates.Thethoracicvertebraehavecostalfacetsthatallowthemtoarticulatewiththecorrespondingribs.Largesturdybodiesandlackofcostalfacetsdistinguishthelumbar

vertebrae.Fivefusedsacralvertebraecomposethesacrum,whichformstheposteriorpart of the pelvis and provides it with strength and stability. The four coccygealvertebraemakeupthecoccyx.Thevariouscharacteristicsofthevertebralgroupsarean

importantmanifestationoftheevolutionaryadaptationsofthespinalcolumntobipedal

locomotion.

Thevertebraeareboundtogetherbyfibrocartilaginousintervertebraldiscs,aswellasseveraldifferenttypesofligaments.Anintervertebraldiscconsistsofacentral

mucoid substance, called nucleus pulposus, and the surrounding fibrocartilaginous

lamina,orannulusfibrosus.Thediscs actasakindof cushion,which absorbsshocks,causedbywalking,jumpingorwalking.Theyalsoallowmotionbetweenthevertebrae,

sothatapersoncanbendforward,backwardorfromsidetoside.Thesurgicalremovalofanyintervertebraldiskwouldcauseadecreaseinthebodysflexibility(Mader2004).


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Ligamentum longitudinale anterius runs from the scull to the sacrum on the

anteriorsurfaceofthedisks,whileligamentumlongitudinaleposterius startsfromtheclivus and interconnects vertebrae posteriorly.

Theseligamentsreinforcethelinkingbetweenthevertebralbodies,andpreventexcessiveextension

and flexion of the vertebral column, as well asresistthegravitationalpull. Ligamentumflavumislocated between the arches of two adjacent

vertebrae, and its function is not to limit the

forwardflexionofthevertebralcolumn,butrathertoassist itsextension, thus savingmusclepower.

This ligament also function to maintain uprightposture(Baltadjievet.al.2006).

Thespinalligaments.(AdaptedfromSaveYourAchingBackandNeck:APatientsGuide).

3.Evolution of the vertebral column and bipedalism: How and why we

cametostandtall?

The transition to upright walking occurred in the early stages of hominid

evolution,whenvastgrasslandsandsavannahsreplacedtheforestsofAfrica(about4.5

million years ago) (Saladin 2003). The now flat environment demanded that earlyhominidsbeabletostandupontheirhindlegssotheycouldlookaroundforpotential

dangers. Erect posture presented these early ground-dwellers with yet one moreadvantage: free forelimbs to accomplish tasks other thanwalking. This transition to

bipedallocomotiondemandedasignificantrangeofadaptionsofthehumanskeleton:

theanatomyofthepelvis,femur,knee,greattoe,arches,spinalcolumn,skullandarmschanged,whilebrain volume increaseddramatically. Thefirst bipedalprimateswere

themembersoftheAustralopithecusgenus,whichabout2.5millionyearsagogaveriseto Homo habilis, the first representative of its genus. However, it was not until

Ligamentum nuchae can be found

betweenthemusclesontheposteriorside

oftheneck,while ligamentainterspinalia,ligamentum supraspinale and ligamentaintertransversalia connect neighboring

processes, spinal processes or transverse

processes, respectively. Ligamentumsupraspinale restricts the forward flexion

of the vertebral column, whereas

ligamenta intertransversalia its bendingfrom side to side. The articular facets

articulate vertebrae with each other,

forming flat, semi-mobile joints, whichfacilitate minor displacements.

Nonetheless, when all of these aresummed up, the result is an impressive

mobilityandagilityoftheentirevertebral

column.Noddingandlateralflexionoccurat the atlanto-occipital joint, whereas

rotationoftheskulloccursattheatlanto-axial joint. These two joints represent a

complexsystemofconnectionsbetweenos

occipitale cranii, the atlas (first vertebra)

andthe axis(secondvertebra).Thespineligaments contribute to the physiologicalmotions of the spine and provide

structural stability by preventing

excessivemotionsbetweenvertebraeandprotectingthespinalcordduringtrauma.


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anthropologists discovered a nearly complete Home erectus skeleton in Kenya, that

scientists saw skeletal adaptations indicating a highly efficient bipedalism. TheNariokotomeboyhadnarrowhipsandlong-neckedfemurs,whichwouldhavehelped

him maintain his balance and be a very efficient walker and runner (Walker andShipman1997).AnotherinterestingfeatureofNariokotomeboy'sanatomyishisinner

ear,whichismoredevelopedthanthatofanyearlierhominids,whohadape-likeinnerears.ThissuggeststhatHomoerectuswasamoreefficientwalkerthanhispredecessorsbecauseadevelopedinnerearisnecessarytosustainbalance(Spoor1994).However,

the spineof the Nariokotome boy still contained anextra lumbar vertebra, which is

representativeofearlierhominids,becausemodernhumansonlyhavefivevertebraeintheirlowerbacks.Takentogether,thesefeaturesofNariokotomeboy'sanatomyshow

thatHomoerectuswalkeddifferentlyfromearlierhominids,butnotexactlythesameasmodem humans. Thus,Homoerectuswere the first highly efficient bipeds, and they

show the gradual change that occurred in the evolution ofbipedalism.Homohabilis

gave rise toHomoerectusabout1.1millionyearsago,which in turn led toour own

species,Homosapiens,about300,000yearsago.Thereareafewmammalsthatcanstand,hoporwalkbrieflyontheirhindlegs,

buthumansaretheonlyspecies,whichhasadoptedbipedalismasitsexclusiveformof

locomotion.For example, chimpanzees can sit upright, standupright, and evenwalkupright, but not for long, and not very efficiently. In difference to humans, though,

chimpscannotextendtheirlegs,orlockthemstraightaswecan,andtheiruprightgait

involvestheuseofmuchmusclepower,whichcanbeverytiring(Saladin2003).Amongotheradaptationstothehumanskeleton,thoseofthehumanvertebralcolumnmade

bipedal locomotion possible. Our spines have a characteristic double curve, lumbar

curve(lordosis),whichpositionstheheadandtorsointoaverticallineaboveourfeet.

Thus,thebodycenterofgravityisshiftedtotherear,aboveandslightlybehindthehipjoint, which allows for an easily accomplished and maintained upright posture. Thesigmoid(S-)-shapedspinalcolumnallowsfortheweightofthebodytobedistributedin

such away that the feet can carry it.Also important is the fact that the spinal cord

enterstheskullthroughtheforamenmagnum,situatednearthecenterofthecranium,allowinghumanheadstobalanceeasilyatopourspinesratherthanautomaticallytilt

backwardsasitisinotherprimates.Becauseoftheseadaptations,humansneedlittlemusculareffecttokeeptheirbalance.

The lumbar spinehas been the focus ofearly adjustments tohabitual bipedallocomotion, as its anatomical structure is linked to fatigue,mobility levels, and the

effectiveness of upright walking and standing. Without the lumbar curve, our bodywouldperpetually lean forward, and muchmore effort wouldbe required for us tomaintainbipedalposture.Lumbarcolumnstudiesofgreatapesindicatethattheyhave

little flexibility totheir lower backs. Theyhavea reductionoffree lumbar column,decreased number of vertebrae with the lowest two vertebrae entrapped and thus

immobilizedbetweentheilia-allfactors,whichleadtoseverelydecreasedplasticityof

thelowerback(Lovejoy2004).Onthecontrary,thehumanvertebralcolumnexhibitssignificantmobilitycomparedtootherprimates,owingtodiverseanduniquechanges

to its anatomy. Both human and ape spines are shortened. However, our vertebral

columnstillhasagreateroverall length,and the sacrumand the iliumareshortandbroad,which eliminates anypotential contactwith the lower vertebrae, allowingfor

more flexibility. In addition, hominid lumbar vertebrae also exhibit a posteriorwideningoftheir laminaeandthespace separating theirarticularprocesses, thereby


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presumablyfacilitatinglordosis(Fig.2).

In addition to changes in the vertebral column, numerous other adaptations

occurredinthehumanskeletomuscularsysteminordertoallowforhabitualbipedal

locomotion.Anatomicallythepelvisevolvedfromalong,narrowstructure,suitedforquadrupedmotion,totheshort,broadversionofthemodernhuman.Thecurvediliac

bladesofthecurrentpelvisprovidefarmorestabilityandsupportfortheweightoftheupperbody,thusfacilitatinguprightwalking.Therewerealsomanychangesinthelegs

toallowhumanstowalkbipedally.Humanshavestraighttoesthatarenone-opposable

tohelppropulsionwhilewalking.Thehumancalcaneus,whichbearstheweightofthebody,isverylarge.Apesareflat-footed,buthumanshaveanarchtotheirfeet,which

actslikeaspringthatabsorbsshockwhilethebodyismoving.Also,humanshavefully

extendablelegsduetoalockablekneejoint,andanaturalknock-kneedstance,whichdiffersfromthechimpanzeebow-leggedstance(Nickels2003).Additionally,thehuman

femurattachesataninwardangletothepelvis,whichmakesthekneeslieunderneath

thebody (Tattersall andSchwartz2001). Asa result of this orientation, humans canstanduprightforhourswithoutmuchenergyexpenditure.

Thus,theevolutionofbipedallocomotionhasledtoadeterminatemorphology

ofthehumanvertebralcolumnandskeleton.Thisincludeslordosisofthelumbarspine,bigger and sturdier lumbar vertebrae, amedulla spinalis,which enters the cranium

morevertically,broadenedsacrumandilium,thelossofatail,thecomingaboutofa

lumbarbalancealongthehip-knee-ankle-footaxis,andstronghipmusclestoenhancestability.

3. ClinicalfeaturesofthespineBipedalismismarkedbyseveralskeletalchanges,manyofwhichwereadaptive

compromises,meaningtheycameatcertaincoststothehominidsthatevolvedthem.

Theseincludelowerbackproblemsduetopressuresonthespine,persistentchronic

painanddebilitatinginjuries.InthesectionbelowIseektoexploresomeofthemorecommonafflictionofthespinalcolumn,theirsymptomsandpotentialtreatments.

Abnormalspinal curvature can result from improperposture,paralysis of theupper-body muscles, or other diseases. Most common in the thoracic region is the

developmentofscoliosis,whichresultswhenthebodyandarchofaparticularvertebrafail to develop properly. This leads to lateral tilting of the body. If caught in early

childhooditmaybepossibletocorrectitwithabackbrace.


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Increased thoracic curvature or kyphosis could result from osteoporosis,

spondylomalacia, spinal tuberculosis orwhen a particular individual participates insportssuchasweightlifting.Scheurmannsdiseaseoccurswhenthefrontpartsofthe

thoracicvertebraedonotgrowasfastasthebackparts,leadingto kyphosis.Kyphosis(roundingoftheback,orahunchbackposture)canresultfromPottsdiseaseaswell.In

thiscondition,calledalsotuberculosisofthespineorvertebra,thereisasofteningandcollapse of the vertebrae,which may result inparaplegia, back pain, swelling, fever,cough and weight loss. On the otherhand, an exaggerated lumbar curvature is also

called lordosis. Itmaybe caused by the same reasons as kyphosis, orwhen thebody

weightissignificantlyincreasedcomparedtonormal(Saladin2004).

Fractures of the spine are most common at L1, L2 and T12. This injury iscommonwhenalargeweightfalseonthebodyorwhenlandingonyourfeetfroma

considerable height. In such an instance a vertebra may displace from it proper

position,moving forward fromits neighbor. Inthis casetheremay beabreakinthearticular facets of one or more vertebra, or rupture of the supporting ligaments.

Spondylolisthesisistheforwarddisplacementofonevertebratotheonebelow,commonbetweenthebodyofL5andthesacrum,andoftenduetounderdevelopedpedicleofthevertebra that got displaced (Fig. 3). Such an injury may press on the spinal nerve,

resultinginsciaticaorlowbackache(ChungandChung2004).Spondylitis,ontheotherhand,isachronicinflammationofthejointsbetweenthevertebraeandthesacroiliac

region.Itcausespain,stiffness,swellingandlimitedmotion.

One in every 1000 babies is born with spina bifida- a condition, in whichvertebrae fail toformacompletearchandenclosethe spinal cord(Fig.4).Thereare


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twotypesofthiscondition spinabifidaoccultaandspinabifidacystica.Ofthetwo,the

firstoneislessserious,asitssymptomissimplyatuftofhairabovetheaffectedspot.However,spinabifidacysticacanbeveryserious,asanexternalsacisformedoutsideof

thebody,inwhichmeninges,cerebralfluidandpartsofthespinalcordandnervescanbecontained.

Ababywithspinabifidashouldbedeliveredbycesareansection,asthesaccouldburstduringpassagethroughthebirthcanal,anditscontentcanbedamaged.Pregnant

womencansignificantlyreducetheirriskofcarryingababywith spinabifidabytaking

folicacidsupplementsearlyduringpregnancy(Saladin2004).

Themostcommonabnormalconditionoftheintervertebraldiscsisaherniateddisk.This isaprotrusionofthenucleuspulposus throughtheannulusfibrosus,which

mayruptureduetoitsthinnerposteriorpart, intotheintervertebralforamenorinto

thevertebralcanal.Thenerverootisoftencompressed,whichmayleadtochronicpain,whichradiatesintothebuttockandlowerlimb(sciatica).Itmostlyaffectsthelumbar

region, where the nucleus pulposus is not supported by ligamentum longitudinalis

posterior. Lumbar spondylosis is another degenerative jointdisease associatedwithadisplacementoftheintervertebraldisksortheoccurrenceofbonyoutgrowths,which

pressuponthespinalnervesandcausesciatica.


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4. Mechanicalandkineticpropertiesofthespine

Theevolutionofthespinalcolumnfromthetimeofourearliestancestorstothe

modern human has led to not only a progressively more complex morphologicalstructure,butalsotothedevelopmentofintricatemotionpatternsassociatedwithit.

Understandingthefundamentalbiomechanicalprinciplesthatguidespinalmovementsis extremely crucialwhen aiming to perform a surgical correction of various spinaldisorders,whichareeitherduetocongenitaloracquired pathologies. Surgeons,who

havedeepunderstandingoftheseprinciples,aremorelikelytounderstandtheforces

thatcreatespecificdeformitiesanddeviseasuccessfulschemefortheirmanagement.Suchmedicalproceduresarevitaltopatientswithspinalabnormalitiesastheycanbe

usedsuccessfullyforcurvaturecorrection,preventionoffurtherdeformity,restorationof balance and improvement of neurological function (Schlenk et.al. 2003). The

mechanicalandkineticpropertiesofthespinearecomplex,astheforcesthatactupon

itscomponentsandonitasawhole,affectitonmultiplelevels.Theforces,appliedto

the spine, can be generally broken down into multiple vectors (a vector is a forcedirectedtowardsafixedpointinspace);howevertheireffectsacrossthedistinctspinal

regionsmostly follow a common pattern.Namely,when a load is impressed uponasinglevertebraoraunitofvertebrae,theyrespondbyfirstdisplacingthemselvesfrom

theirnormalpositionuntil resistance isencountered.There isan initiallaxregiontothesemotionsanditistermedaneutralzone(NZ)(FromSpinebiomechanics;alsosee

Fig.5).Thepresenceofsuchaneutralzoneisresponsibleforthespinescapabilityto

performrelatively largemotionswithoutemploying muchmuscular force. FollowingtheNZ, themotion reaches its limit, termed the elasticzone(EZ).Themagnitude, to

whichaspinalunitcandisplaceundermaximumload,iscalledarangeofmotion(ROM).Mainly these three parameters characterize the displacement movements of the

vertebrae.


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Other kinematic terms that can be employed to describe spinal motions are

flexion,extension,axialrotationandlateralbending.Upontheemploymentoftargetedforcetowardsthevertebralcolumn,itscomponentsnotonlybegintodisplace,butthey

also tend to rotate around an axis, called the IAR or instantaneous axis of rotation(Schlenket.al. 2003). The IAR is the focal pointaroundwhich flexion and extension

transpire.SixfundamentalmovementsofthespinalcolumnaroundtheIRAcanoccur:1)rotationortranslationaroundthelongaxis(A);2)rotationortranslationaroundthecoronalaxis(B);3)rotationortranslationaroundthesagittalaxis(C)(Fig.6A-C).The

IRA for any of thesetypesofmotion isconfined toa relativelysmallareawithin the

spinal unit; if this area isenlarged, thatmay bea symptom for a spinal disorder. Incomparison,apevertebral columnsareconsiderably lessflexible,as their spines lack

the extensive morphological changes that permit humans to perform such acomprehensiverangeofvertebralmovements.Upontheapplicationofanexternalforce,

thespinalcolumnundergoesarotationaldeformationatanangleinrelationtoeither

thecoronal,sagittalorlongaxis.

Whenthereistranslationaldeformation,itcanoccuralonganyaxis.Changesin

thenormalmotionpatternsofthespineunderexternalorinternalstressesmaybealso

anindicationofabnormality.Spinaldeformitiescanbeseparatedintothreecategories:1) coronal plane 2) sagittal plane 3) axial plane (Schlenk et.al. 2003). Usually, the

applicationofexcessiveforceorotherstressorsuponanalreadydamagedspine,leadstoabnormalities.Variousactivitiesofdailyliving,whichput invivoloadsonthespine,

canbethecauseofspinaldeformitiesaswell,becausesomebehaviorsmayputasmuch

as2,270Nofforceuponaspinalunit,

whichamazinglycanexceed50timesthebodypartweightabovethejoint

ofinterest(FromSpinebiomechanics).Spinal deformities can be corrected

surgically by means of variousimplants such as stabilizing

constructs, the cross-rod technique

forcorrectionoflumbarandthoracickyphotic deformities, a crossed-

screw fixation technique to fix

sagittal and coronal plane

abnormalities, in vivo implantcontouring to alter segmental


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relationships, spinal derotation to alter a scoliotic to kyphotic curve, etc. (Fig. 7).

Naturally, the above-mentioned surgical procedures comprise only a few of theestablishedtechniques,currentlyemployedforthecorrectionofvertebraldeformities.

Thesemethodscanbevarieduponasseennecessarybythesurgeon,inordertoadaptthemtothespecificitiesofthevariousspinalregions,whichhaveuniqueanatomical

andbiomechanicalproperties.

Thebiomechanicalpropertiesof themodernhumanspine aredeterminednot

onlybythespecificmorphologicalcharacteristicsofthevertebrae,butbytheunique

featuresofthespineligamentsandtheintervertebraldiscsaswell.Thediscsnormallyhaveaveryhighwatercontent-upto90%oftheirvolume-andthisiswhatlargely

guidestheirbiomechanicalproperties(fromSpineBiomechanics).Asforceisappliedtoadisc,thewaterwithinstartstodiffuseslowlythroughoutthedisclayers,affectingits

relaxation times (the time it takes the disc to return to its initial state after a

disturbance).Lossofmoisturecausesdiscdegeneration,thus increasingitsrelaxationtimeandreducingthemobilityofthespine. Itisalsoimportanttonotethatoneofthe

reasons thehumanspine losesmuchofitselasticitywithage isthatthespinaldiscswatercontentdecreasesto74%andlessoftheirtotalvolume.dIngeneral,theinnerportion of the disc, the nucleus puposus, is made up of collagen type II, while the

concentricannulusfibrosusiscomprisedexclusivelyoftypeIcollagen.Withage,theseproportionschangeandcollagentypeIIIappears,alsocausingthediscstolosesomeof

theirflexibilityandsturdiness.

5. Conclusion

Theexactperiodwhenourancestorsstartedwalkingontwofeetisstilllargely

debatable, but it is universally accepted that bipedalism evolved relatively early inhuman history, presumably about 3.5 - 4 million years ago. One of the earlieststructurestoadapttoahabituallyuprightposturewasthehumanspine.Someofthe

vertebralcolumnchangesincludedalengtheningofthelumbarspine,theappearanceof

auniquelyhumanspinalcurvature,thepositioningoftheforamenmagnumbelowtheskull,whichissupportedbythespine,thelargersurfaceareaofthevertebrae,which

consequentlyacquiredmoreweightbearingcapacitythanthoseofourancestors,etc.Bipedal stance must have provided early hominids with certain benefits, or else it

would not have evolved. What these benefits were, remains largely a mystery, but

amongthemfreeingofthehandstocarryfooditems,moreefficientwalkingoverlongdistances or spottingpredators have beenconsidered.Most importantly, though, the

evolutionofbipedalismandallthevariousskeletaladaptationsassociatedwithitsetthe stage for advanced tool use and increased brain size in humans. Today, theadaptationsofthehumanspinehaveallowedustoforeverseparateourselvesfromour

primatecousins;nonetheless,deformitiesofthespinecanbethecurseofmanypeoplesexistence.Itisthereforeessentialtostudyandunderstandtheevolutionofthespine,

andtocomeupwithapproachestouseitsuniqueadaptationssolelytoourbenefit.


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Bibliography

BaltadjievG.,AtanasovaP.,KoevaI.,SivkovS.(2006).Humananatomy,thirdedition.

Raikov-MedicalPublishingHouse.ChungK.andChungH.Grossanatomy,sixthedition.WolterKluwer:Lippinctott,

WilliamsandWilkins.

LovejoyC.O.(2005).ThenaturalhistoryofhumangaitandposturePart1.Spineand

pelvis.GaitandPosture21:95-112.

Mader,S.S.(2004).Understandinghumananatomyandphysiology,sixthedition.The

McGraw-HillCompanies.

Nickels,M.(2003).HumansandChimpanzeesCompared.IllinoisWesleyanUniversity,

Bloomington,IL.

Saladin.(2003).Anatomyandphysiology:Theunityofformandfunction,thirdedition.

TheMcGraw-HillCompanies.

SchlenkR.,KowalskiR.,BenzelC.E.(2003).Biomechanicsofspinaldeformity:Spinal

deformities.NeurosurgeryFocus14:1.

Schwartz,J.&Tattersall,I.(2001).Extincthumans.Colorado:WestviewPress.

Spoor,F.,Wood,8.,andF.Zonneveld.(1994).Implicationsofearlyhominid

labyrinthinemorphologyforevolutionofhumanbipedallocomotion,Nature,369,

645-648.

VanDeGraaff,MP.(2001).Humananatomy,sixthedition.TheMcGraw-HillCompanies.

Walker,A.andShipman,P.(1997).Thewisdomofthebones.NewYork:Vintage.

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