Rev. bras. ortop. vol.51 número4

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SOCIEDADE BRASILEIRA DE ORTOPEDIA E TRAUMATOLOGIA

w w w . r b o . o r g . b r

Original

article

Evaluation

of

body

mass

index

as

a

prognostic

factor

in

osteoarthrosis

of

the

knee

夽

Fabrício

Bolpato

Loures

a,∗

,

Rogério

Franco

de

Araújo

Góes

a

,

Pedro

José

Labronici

a

,

João

Maurício

Barretto

b

_,

_Beni

_Olej

c

a_Hospital_Santa_Teresa,_Petrópolis,_RJ,_Brazil

b_Instituto_Nacional_de_{Traumatologia}_e_Ortopedia_(Into),_Rio_de_Janeiro,_RJ,_Brazil

c_Universidade_Federal_Fluminense,_Niterói,_RJ,_Brazil

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received27July2015

Accepted31August2015

Availableonline26May2016

Keywords:

Osteoarthrosis Obesity Knee Arthroplasty

a

b

s

t

r

a

c

t

Objective:Toevaluatetherelationshipbetweenpatients’bodymassindex(BMI)andthe

degreeofradiographicseverityofkneeosteoarthrosis.

Method:117patientswithgonarthrosiswereevaluatedprospectively.Thepatients’BMIwas

calculatedandtheirkneearthrosiswasclassifiedinaccordancewiththemodifiedAhlbäck

criteria.Kruskal–Wallisanalysisofvariance(ANOVA)wasusedtoevaluatetherelationship

betweenthesetwovariables.

Results:ThegroupclassifiedasAhlbäckgradeVhadsignificantlyhigherBMIthantheothers.

Conclusion:ThereisadirectrelationshipbetweenBMIandthedegreeofradiographicseverity

ofgonarthrosis.Obesityappearstobedirectlyrelatedtotheprogressionofknee

osteoarthro-sis.

Ltda.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://

creativecommons.org/licenses/by-nc-nd/4.0/).

Avaliac¸ão

do

índice

de

massa

corporal

como

fator

prognóstico

na

osteoartrose

do

joelho

Palavras-chave:

Osteoartrose Obesidade Joelho Artroplastia

r

e

s

u

m

o

Objetivo:Avaliararelac¸ãodoíndicedemassacorporal(IMC)dopacientecomograude

gravidaderadiográficadaosteoartrosedojoelho.

Método:Foramavaliados,de formaprospectiva,117pacientesportadores degonartrose.

Ospacientestiveramseusíndicesdemassacorporalcalculadoseaartrosedojoelhofoi

classificadasegundooscritériosdeAhlbäckmodificados.Usou-seaAnovadeKruskal–Wallis

paraavaliararelac¸ãoentreessasduasvariáveis.

夽

StudyconductedatHospitalSantaTeresa,Petrópolis,RJ,Brazil.

∗ _{Corresponding}_author_.

E-mail:fbolpato@gmail.com(F.B.Loures).

http://dx.doi.org/10.1016/j.rboe.2016.05.002

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Resultados: OgrupoclassificadocomograuVdeAhlbäckapresentouumIMC

significativa-mentemaiordoqueosdemais.

Conclusão:Existerelac¸ãodiretaentreoIMCeograudegravidaderadiográficodagonartrose.

Aobesidadepareceestardiretamenterelacionadaàprogressãodaosteoartrosedojoelho.

EditoraLtda.Este ´eumartigoOpenAccesssobumalicenc¸aCCBY-NC-ND(http://

creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Osteoarthrosis(OA),osteoarthritis,orarthrosisistheleading

causeofmusculoskeletaldisabilityworldwide1_and_the_main

physicallimitingfactorintheelderlypopulation.2_This

seri-ousglobalpublichealthissue1_affects_5.2%_of_the_population

over19yearsofage(about10millionpeople).Thisnumberis

expectedtogrowto12.4millionby2015.3

Traditionally,this disease isconsidered a cartilage joint

degenerationcausedbymechanical,genetic,hormonal,bone,

andmetabolicfactors,whichresultinanimbalancebetween

thedegradationandsynthesisofarticularcartilage.4_OA_is

cur-rentlyrecognizedasadiseasethataffectsalltissuesofthe

joint.5

The pathology arises from a combination of host and

environmentalfactors.6_Obesity_is_one_of_the_main_elements

directlylinkedtokneeOApathogenesis.7_An_increase_in_the

bodymassindex(BMI)isalsoassociatedwithprogressionof

thedisease,degreeofdisability,evolutiontoarthroplasty,and

poorclinicaloutcomeaftersurgery.2

Obesityreachesitspeakincidenceinthesixthdecadeof

life,8_a_period_that_coincides_with_the_worsening_of_the

symp-tomsofdegenerative diseases.Itisanepidemicdisease in

Brazil.Thecountrynowranksfifthworldwideinthenumber

ofobeseindividuals.9

Thisstudyaimedtoassesstherelationshipofthepatient’s

BMIandthedegreeofkneeOAradiographicseverity,according

totheAhlbäckclassificationmodifiedbyKeyesetal.10

Material

and

methods

Afterapprovalofthestudyprotocolbytheethicscommittee

ofthe institution,117individualswho wouldundergototal

kneearthroplasty(TKA)betweenAugust2012andSeptember

2013wereselectedbyconvenience.Allpatientswhoagreedto

participatebysigningthefreeandinformedconsentformand

whohadaclinicalandradiographicdiagnosisofgonarthrosis

wereincluded. Patientswithhistoryoffractureorprevious

surgery in the studied knee, inflammatory diseases, bone

defectsrequiringgrafting,orvarusorvalgusdeformitygreater

than15◦_were_excluded.

Inthepre-operativeconsultation,patientshadtheirheight

and body massmeasured in amechanical anthropometric

scale, Micheletti® brand, MIC 2 model, accuracy class III,

withmass capacity of300kg and heightof 1.95m. During

thatassessment,patientsworeonlyadisposablegownand

underwear.Weightwasdocumentedinkilogramsandheight

inmeters. TheBMIwascalculatedbydividingbody weight

byheightsquared.Thisratiowasrecordedinkilogramsper

squaremeters(kg/m2_),_as_described_by_Adolphe_Quelet.11

Kneeradiographswereperformedwithloadand

monopo-dalsupportintheanteroposteriorincidence(AP)andprofile

with 30◦ _of _flexion, _with ₃₅_cm_×₄₃_cm _film _for _AP _and

24cm×30cmfilmforprofile,thepatientat110cm fromthe

lightbulb,andthebeamcenteredontheinferiorpoleofthe

patella. Super 100®X-rayequipment (Philips®, Brazil) was

used,calibratedto50kVand31mA.Thestudieswere

eval-uatedbythemaininvestigatorregardingimagequality,and

wererepeatedifnecessary.

The preoperative evaluation protocol was completed in

ordertostandardizedatacollection.Subjectswerecategorized

byBMI,asrecommendedbytheWorldHealthOrganization12

(Table1).

Knee OA was classified by the main investigator using

theAhlbäckcriteriamodifiedbyKeyesetal.10₍_Table₂_)._This

classificationwas done blindly inrelationtopatient’s BMI.

Subsequently,dataweresenttothestatistician, whomade

thegroupingaccordingtothedegreeofarthrosis.

Kruskal–Wallisanalysisofvariance(ANOVA)wasusedto

assess whetherthegroupsdifferedinageand BMI.Dunn’s

multiplecomparison(nonparametric) wasappliedat5%to

Table1–Weightclassificationperbodymassindex

(BMI).

Classification BMI(kg/m2₎

Underweight <18.5

Normalweight 18.5–24.9

Overweight 25.0–29.9

ObeseclassI 30.0–34.9

ObeseclassII 35.0–39.9

ObeseclassIII ≥40.0

Source:WHO.12

Table2–Ahlbäckclassification,modifiedbyKeyesand

Goodfellow.

GradeI Jointspacenarrowing GradeII Jointspaceobliteration

GradeIII AP=tibialplateauattrition<5mm

Profile=posteriorpartofthetibialplateauintact GradeIV AP=5–10mmtibialplateauattrition

Profile=extensiveattritiontheposteriorpartofthe tibialplateau

GradeV AP=Severesubluxationofthetibia Profile=anteriortibialsubluxation>10mm

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identifythosegradesthatdifferedsignificantlyamong them-selves.

Theage ofthe groups was analyzed by calculating the

mean, median, minimum, and maximum; Kruskall–Wallis

ANOVAwasusedtoassessthehomogeneityofthegroups.

Results

Theanthropometriccharacteristicsofthesample,suchasage,

bodyweight,height,andBMI,weredescribedandareshown

inTable3.

Afterclassificationofeachkneeaccordingtothemodified

Ahlbäckcriteria,patientsweredividedintogroupsandtheir

BMIswereusedtocalculatethemean,median,standard

devi-ation,minimum,andmaximumofeachgroup.Kruskal–Wallis

ANOVAshowedasignificantdifferenceinBMIamonggroups

(p=0.047).ThesevaluesareshowninTable4.

Inordertodeterminewhichgroupsweredifferent,Dunn’s

multiple comparisons test at the level of 5% was used,

revealingthat thegroup classifiedas AhlbäckgradeVhad

significantlyhigherBMIthangradesIIIandIV(p=0.047),as

showninFig.1.ThegroupclassifiedasAhlbäckgradeIIhad

asmallnumberofpatients(n=10),whichreducesreliability

forinclusionintheanalysis.Nostatisticallysignificant

differ-encesatthelevelof5%wereobservedamongtheotherpairs

ofgroups.

The age of the groups was also compared with

Kruskal–WallisANOVA.Themeanvalues,median,standard

deviation,maximum,andminimumofeachgroupareshown

inTable5. Statisticalanalysisshowedthatthe samplewas

homogeneous regardingage, and the differences were not

significant(p=0.20).

Amongpatientswho hadarthrosis classifiedasAhlbäck

gradeV,61%(11)hadaBMIgreaterthan30kg/m2_and_were

classifiedasobese.Thisnumberwasloweringroupsdegrees

ofarthrosisIIIandIV,42% and27%(25andeightpatients),

respectively.Amongthe117operatedpatients,only20(17.1%)

Table3–Anthropometriccharacteristics.

Variable Mean SD Median Minimum Maximum

Age(years) 68.9 7.1 68.5 53 84

Weight 77.3 13.4 77 53 120

Height(m) 1.6 0.1 1.62 1.4 1.9

BMI(kg/m2₎ _29.3 _4.5 _28.7 _20.3 _43.4

Source:Datafromtheinstitution.

SD,standarddeviation;BMI,bodymassindex

Table4–ComparisonofBMIgroupsafterdivisionby

Ahlbäckclassification.

Grade Number Mean SD Median Minimum Maximum p-Valuea

II 10 29.3 5.3 29.5 21.8 36.0 0.047

III 59 29.2 4.6 28.9 20.3 43.4

IV 30 28.2 3.6 28.0 23.3 37.4

V 18 31.9 4.3 32.8 24.0 38.3

Source:Datafromtheinstitution.

a _{Kruskal–Wallis}_ANOVA.

44

42

40

38

36

34

32

30

28

BMI (kg/m2)

26

24

22

20

II III IV

Ahlbäck grade

V

Fig.1–ComparisonamongAhlbäckgroups.

Table5–Comparisonofagegroupsafterdivisionby

Ahlbäckclassification.

Grade Number Mean SD Median Minimum Maximum p-Valuea

II 10 65.0 7.0 64.5 55 74 0.20

III 59 69.0 6.8 68.5 55 82

IV 30 68.8 6.0 68 58 79

V 18 70.7 9.2 73 53 84

Source:Datafromtheinstitution.

a _{Kruskal–Wallis}_ANOVA.

hadnormalweight,accordingtoWorldHealthOrganization

standards.

Discussion

Thefirstepidemiologicalstudythatdescribedtherelationship

ofobesitywithkneeOAwastheFraminghanstudy,7_which,

after40yearsoffollowup,definedobesityasaprecedent

con-ditiontoosteoarthrosis. Otherrisk factorsdescribed inthe

study were female sex, aging,and geneticinheritance, but

theseareimmutable.

Obesityisacontemporarydiseasethatisepidemicinthe

UnitedStates:themajorityofadultsinthatcountryare

over-weightorobese,accordingtotheWorldHealthOrganization

standards.InBrazil,thenumberofoverweightindividualshas

tripledinthelast30years:62.5%ofmenand64.9%ofwomen

areoverweightorobese.13_This_places_the_country_as_fifth_in

theworldrankingofobesity.9

BMIhasan excellentcorrelation withthepercentageof

bodyfatinmostofthepopulation14_and_acts_as_a_predictor

ofobesity,althoughitiscontroversialinobviouslyextreme

cases. Itisa simpleand reliablemeasurement thatcanbe

usedforriskassessmentofkneeosteoarthrosis.15

Bodyweighthasbeenshowntobeanimportantrisk

fac-torinthegenesisofosteoarthrosis,8_and_the_main_affected

joint istheknee.16 _There_are_numerous_theories_to_explain

thecausalrelationshipbetweenobesityandkneeOA,ranging

frommechanicaltometabolicfactors.6_The_incidence_of_OA

inobese individuals istwicethatfoundinthose with

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patientshavea38%increaseinOAprevalence.Obese

individ-ualshavea200%higherchance,whileinthemorbidlyobese

grouptheprevalenceis400%higher.

Knowing the naturalhistory and the factors that

influ-encetheevolutionofthedisease iscrucialtoitstreatment

andprognosis.18 _The_association_between_BMI_and

progres-sionofkneeosteoarthrosisisnotclearyet.Fewstudieshave

triedtodifferentiate the factors involvedin thegenesis of

thedisease from those relatedto itsprogression; although

preventingitsprogressionmay bemoreeffectiveasa

pub-lic health strategy than trying to inhibit its emergence.19

Cooper et al.,19 _after _a _five-year _follow-up _of ₃₅₄ _patients

withameanof75.8years,observedthatobesityisarisk

fac-torforboth incidenceand radiographicprogression ofOA,

althoughits greatestinfluenceisonthegenesisofthe

dis-ease.Sharmaetal.20_studied₂₉₂_knees_with_OA₁₅₄_with_varus

and115withvalgusalignment.Theyfoundadirect

relation-shipbetweenBMIandradiographicseverityofthediseasein

patientswithvarusalignment,butnotinpatientswith

val-gusknee,highlightingthatobesitymustbeassociatedwith

otherfactorstodeterminetheevolutionofthedisease.After

asystematicreviewoftheliterature,Beloetal.21_concluded

thattheassociationbetweenBMIandOAprogressionis

uncer-tain.

Thepresent studyshowedadirectrelationshipbetween

thepatient’sBMIandradiographicseverityofkneeOA,which

is in agreement with findings in the literature.18–20,22 _The

meanageofthegroupscouldbeaconfoundingfactor,asthe

diseaseisprogressiveandolderpatientstendtohavehigher

jointwear.22,23_Statistical_tests_revealed_that_the_groups_were

homogeneousregardingage,showingthatthisfactordidnot

influencetheassociationobserved.

Agoodratingsystemshouldbesimple,reproducible,and

abletogroupdifferentstagesofaninjuryinhomogeneous

subgroups, allowing for comparisonsand indicating

treat-mentandprognosis.Ratingsthatassessthereductioninjoint

spacearebetterforevaluatingtheprogressionofa

degener-ativekneedisease.18,24_The_authors_believe_that_the_Ahlbäck

classification,modifiedbyKeyesetal.,10_meets_these

prereq-uisites.Albuquerque et al.24 _observed_a _poor_{interobserver}

correlationforthemodifiedAhlbäckclassification;however,

Gallietal.25_have_reported_that_physicians_experienced_in_knee

surgerycansafelyusethisclassification.Themain

investiga-torisamemberoftheBrazilianSocietyofOrthopedicsand

Traumatology(SociedadeBrasileiradeOrtopedia e

Trauma-tologia[SBOT]), amember ofthe Brazilian Society ofKnee

Surgery(SociedadeBrasileiradeCirurgiadoJoelho[SBCJ])and

holdsaMaster’sdegreeinthearea,consideredexperiencedin

kneesurgeryandthereforeabletomaketheclassifications.

Petersonet al.26 _reported _a _good _correlation _in_this

classi-fication, both interobserver and in relationto the Kellgren

and Lawrenceclassification.27 _The_prevalence_of_joint _pain

isstronglyrelated tothe radiographicclassification.19 _Most

patientsinthepresentstudywereclassifiedasAhlbäckgrade

III,astageinwhichclinicaltreatmentusuallyceasestobe

effectiveandsurgerybecomesanoption.

IntheUnitedStates,approximately450,000knee

arthro-plasties were performed in 2005. Projections indicate that,

according to the aging population and the growth of

obe-sity,thesenumbersareexpectedtoreach3.5millionTKAsby

2030.28_There_are_no_official_statistics_for_Brazil,_but_it_is

esti-matedthatover70,000totalkneeprosthesesareperformed

peryear.29_The_country_now_ranks_fifth_in_the_world_ranking

ofobesity;projectionsoftheBrazilianInstituteofGeography

and Statistics(InstitutoBrasileiro deGeografia eEstatística

[IBGE])indicatethat,by2030,thecountrywillhavethesixth

largest elderlypopulationworldwide.30 _The_combination_of

thesetwofactorsallowsforthepredictionthattherewillbean

exponentialgrowthofosteoarthrosisinBrazil.Understanding

whysomepatientsdevelopneedforarthroplasty,while

oth-ersremainwithstablediseaseforlongperiods,maybethe

solutiontocontrolthismajorpublichealthproblem.

Besidesbeinganimportantfactorinthegenesisand

sever-ity ofknee osteoarthritis,1,7 _as_shown _in_the _present_study,

Guiaetal.16_have_shown_that_overweight_individuals_are_1.5

timesmorelikelyandthatobeseindividualsarethreetimes

morelikelytoundergoarthroplastywhencomparedwiththeir

normalweight peers.Theassociation betweenobesity and

outcome aftersurgeryisambiguous. Bakeret al.31

demon-strated that outcome after TKA was satisfactory in obese

patients, but therateofsurgicalwoundcomplicationswas

higherinthisgroup.Samsonetal.,32_after_a_literature_review,

showed thatthecomplicationrateinpatientswithmorbid

obesitywas 10–30%higherthan inthecontrolgroup.Deep

infection was threeto nine times morefrequent. Kremers

etal.,33_after_studying₈₁₂₉_patients_undergoing_primary_TKA

(6475)orTKArevision(1654),demonstratedthatthefinal

hos-pitalcostsinpatientswithaBMIabove30kg/m2_was_250–300

dollarshigherinprimaryarthroplastiesand600–650dollars

higherinrevisionarthroplasty.

The present study had some limitations. The modified

Ahlbäckclassificationisthemostpopularamongsurgeons,

but its usehinderedcomparisonwithother studies,which

mostlyusedtheKellgreenandLawrenceclassification.27_The

verticalstudydesigndidnotallowforafollow-upofthe

tem-poralevolutionofthepatients.

Conclusion

There is a direct relationship between BMI of the patient

andtheradiographicseverityofkneeosteoarthrosis.Obesity

appearstobeassociatedwiththeprogressionofthisdisease.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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