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Di e en incidences o knee a h oplas y in he
No dic coun ies
Mika J NiemeläInen, Keijo T MäKelä, O o Robe sson, Anne e W-Dahl,
O e Fu nes, Anne M Fens ad, Alma B Pede sen, Hen ik M Sch øde , Heini
Huh ala & An i Eskelinen
To ci e his a icle: Mika J NiemeläInen, Keijo T MäKelä, O o Robe sson, Anne e W-Dahl, O e
Fu nes, Anne M Fens ad, Alma B Pede sen, Hen ik M Sch øde , Heini Huh ala & An i Eskelinen
(2017) Di e en incidences o knee a h oplas y in he No dic coun ies, Ac a O hopaedica, 88:2,
173-178, DOI: 10.1080/17453674.2016.1275200
To link o his a icle: h p://dx.doi.o g/10.1080/17453674.2016.1275200
© 2017 The Au ho (s). Published by Taylo &
F ancis on behal o he No dic O hopedic
Fede a ion.
Published online: 06 Jan 2017.
Submi you a icle o his jou nal
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Ac a O hopaedica 2017; 88 (2): 173–178 173
Di e en incidences o knee a h oplas y in he No dic coun ies
A popula ion-based s udy om he No dic A h oplas y Regis e Associa ion
Mika J NIEMELÄINEN 1, Keijo T MÄKELÄ 2, O o ROBERTSSON 3, Anne e W-DAHL 3, O e FURNES 4,5,
Anne M FENSTAD 4, Alma B PEDERSEN 6, Hen ik M SCHRØDER 7, Heini HUHTALA 8, and An i ESKELINEN 1
1 Coxa Hospi al o Join Replacemen , Tampe e; 2 Depa men o O hopaedics and T auma ology, Tu ku Uni e si y Hospi al, Tu ku, Finland;
3 The Swedish Knee A h oplas y Regis e , Depa men o O hopedics, Skåne Uni e si y Hospi al, Lund, and Depa men o Clinical Sciences,
O hopedics, Lund Uni e si y, Lund, Sweden; 4 The No wegian A h oplas y Regis e , Depa men o O hopaedic Su ge y, Haukeland Uni e si y Hospi al,
Be gen; 5 Depa men o Clinical Medicine, Uni e si y o Be gen, Haukeland Uni e si y Hospi al, Be gen, No way; 6 Depa men o Clinical Epidemiology,
Aa hus Uni e si y Hospi al, Aa hus, and he Danish Knee A h oplas y Regis y; 7 Depa men o O hopaedic Su ge y, Naes ed Hospi al, Denma k;
8 School o Heal h Sciences, Uni e si y o Tampe e, Tampe e, Finland.
Co espondence: [email p o ec ed]
Submi ed 2016-02-25. Accep ed 2016-11-07.
© 2017 The Au ho (s). Published by Taylo & F ancis on behal o he No dic O hopedic Fede a ion. This is an Open Access a icle dis ibu ed unde he e ms
o he C ea i e Commons A ibu ion-Non-Comme cial License (h ps://c ea i ecommons.o g/licenses/by-nc/3.0)
DOI 10.1080/17453674.2016.1275200
Backg ound and pu pose — The annual numbe o o al knee
a h oplas ies (TKAs) has inc eased wo ldwide in ecen yea s.
To make p ojec ions ega ding u u e needs o p ima ies and
e isions, addi ional knowledge is impo an . We analyzed and
compa ed he incidences among 4 No dic coun ies
Pa ien s and me hods — Using No dic A h oplas y Regis e
Associa ion (NARA) da a om 4 coun ies, we analyzed di e -
ences be ween age and sex g oups. We included pa ien s o e 30
yea s o age who we e ope a ed wi h TKA o unicompa men al
knee a h oplas y (UKA) du ing he pe iod 1997–2012. The nega-
i e binomial eg ession model was used o analyze changes in
gene al ends and in sex and age g oups.
Resul s — The a e age annual inc ease in he incidence o TKA
was s a is ically signi i can in all coun ies. The incidence o TKA
was highe in women han in men in all 4 coun ies. I was high-
es in Finland in pa ien s aged 65 yea s o mo e. A he end o he
s udy pe iod in 2012, Finland’s o al incidence was double ha
o No way, 1.3 imes ha o Sweden and 1.4 imes ha o Den-
ma k. The incidence was lowes in he younges age g oups (< 65
yea s) in all 4 coun ies. The p opo ional inc ease in incidence
was highes in pa ien s who we e younge han 65 yea s.
In e p e a ion — The incidence o knee a h oplas y s eadily
inc eased in he 4 coun ies o e he s udy pe iod. The di e ences
be ween he coun ies we e conside able, wi h he highes inci-
dence in Finland. Pa ien s aged 65 yea s o mo e con ibu ed o
mos o he o al incidence o knee a h oplas y.
■
To al knee a h oplas y (TKA) o se e e os eoa h i is (OA)
has good long- e m ou comes, and gi es g ea e pain elie
and be e unc ional imp o emen han non-su gical ea -
men (Ca e al. 2012, Skou e al. 2015). Good long- e m
implan su i o ship has esul ed in TKA also becoming a
ea men o se e e knee OA in younge pa ien s, al hough
ou comes and implan su i o ship ha e been epo ed o be
wo se han in elde ly pa ien s (Lonne e al. 2000, Rand e al.
2003, P ice e al. 2010, Julin e al. 2010).
Repo ed inc eases in he a e o TKA and es ima es o
u u e demand p edic a subs an ial inc ease in he incidence
o TKA in many coun ies (Jain e al. 2005, Ku z e al. 2007,
Kim e al. 2008, Culli o d e al. 2010, W-Dahl e al. 2010a,
Nemes e al. 2015). Bo h he b oadening o indica ions o
younge pa ien s and he inc ease in o al incidence o TKA
ha e aised conce ns o a possible inc ease in e ision bu den
in he long e m (Ku z e al. 2007, Gioe e al. 2007). Di -
e ences be ween geog aphic loca ions and age g oups ha e
been no ed in he incidences o TKA (Ka z e al. 1996, Wells
e al. 2002). The majo inc ease in he incidence o TKA has
been ound in people bo n in he pe iod 1946–1964 ( he baby-
boome gene a ion) (Leskinen e al. 2012).
The aim o his s udy was o analyze ends in he incidence
o TKA and unicompa men al knee a h oplas y (UKA) using
No dic A h oplas y Regis e Associa ion (NARA) da a om
be ween 1997 and 2012, o iden i y any changes o di e ences
in (o be ween) age g oups, he sexes, and coun ies.
10097 Niemela inen D.indd 17310097 Niemela inen D.indd 173 3/16/2017 11:17:21 AM3/16/2017 11:17:21 AM
174 Ac a O hopaedica 2017; 88 (2): 173–178
Pa ien s and me hods
The NARA compiles da a on 4 No dic coun ies ha ha e sim-
ila o ganiza ion o heal hca e and compa able pa ien cha ac-
e is ics (Table 1). The NARA has in o ma ion on he TKAs
and UKAs pe o med in Denma k, No way, and Sweden om
1997 h ough 2012 and in Finland om 2000 h ough 2012.
The knee a h oplas y egis ies o Sweden (SKAR) and
Denma k (DKR) and he a h oplas y egis ies o No way
(NAR) and Finland (FAR) pa icipa ed in he p esen s udy.
All 4 egis ies ha e used indi idual-based egis a ion o
ope a ions and pa ien s. A minimal NARA da ase was c e-
a ed o con ain da a ha all 4 egis ies could deli e , bu o
adminis a i e easons he Finnish A h oplas y Regis e has
been able o p o ide Finnish da a acco ding o he NARA da a
de i ni ions om he beginning o 2000. A pilo s udy ca ied
ou om NARA da a did no include FAR da a and i did no
ha e an age cu o (Robe sson e al. 2010). The NARA da a-
base includes da a on he pa ien s ha enable TKA and UKA
incidence analyses, i.e. pa ien -le el da a on bo h demog aph-
ics and implan ypes.
Selec ion and ans o ma ion o he espec i e da ase s and
de-iden i i ca ion o he pa ien s, which included dele ion o
he na ional ci il egis a ion numbe s, we e pe o med wi hin
each na ional egis e . The anonymous da a we e hen me ged
in o a common da abase. Because o he small numbe o
pa ien s aged 30 yea s o less who we e ope a ed, in he p es-
en s udy we only included pa ien s aged 30 yea s o mo e
who had unde gone a TKA o UKA su gical p ocedu e due o
p ima y os eoa h i is o he knee.
The da a we e ea ed wi h ull con i den iali y, acco ding
o he egula ions o he espec i e coun ies. This included
es ic ed access o he common da abase, which was limi ed
o he au ho s o he p esen pape . The quali y o da a in he
No dic egis ies is high, and he egis ies ha e bo h na ional
co e age and a high deg ee o comple eness (annual epo s
2015: Danish Knee A h oplas y Regis e , No wegian A h o-
plas y Regis e , Swedish Knee A h oplas y Regis e , Finnish
A h oplas y Regis e ) (A hu sson e al. 2005, Espehaug e
al. 2006).
o TKAs and UKAs in Denma k, No way, and Sweden om
1997 o 2012 and in Finland om 2000 o 2012. The inci-
dence was calcula ed as incidence densi y, which is de i ned
as he numbe o new cases in a popula ion du ing a gi en
ime pe iod ela i e o he sum o he pe son- ime alues o
he a - isk popula ion. Nega i e binomial eg ession was used
o es ima e he incidence a e a ios (IRRs) and he 95% con-
i dence in e als (CIs) o UKAs and TKAs o each coun y
because o e idence o o e dispe sion o da a. IRR epo s
he es ima ed a e age annual inc ease o incidence. Analyses
we e s a i i ed by sex and age g oup. The s a is ical analyses
we e conduc ed wi h SPSS 22.0 and S a a 8.2 so wa e.
Resul s
Pa ien cha ac e is ics
385,310 p ima y knee a h oplas ies we e egis e ed in he
4 coun ies du ing he s udy pe iod. Du ing his pe iod, we
obse ed an inc ease in OA om 84% o 90% and simul ane-
ously a decline in heuma oid a h i is om 10% o 4% as
indica ion o knee a h oplas y. O hese ope a ions, 317,008
TKAs and 27,687 UKAs we e pe o med o knee OA in
pa ien s aged 30 yea s o mo e. Female pa ien s ep esen ed
202,940 (64%) o he TKA cases and 15,778 (57%) o he
UKA cases. The mean age o he pa ien s was 70 yea s (SD
9.0) in he TKA g oup and 65 yea s (SD 9.4) in he UKA
g oup (Table 1).
Incidence o knee a h oplas y (TKA and UKA)
In all 4 coun ies, he incidences o knee a h oplas y inc eased
du ing he s udy pe iod (Figu e 1). A he beginning o he
s udy, he incidences we e 3.4 in Denma k, 3.6 in No way, 9.0
in Sweden, and 13 in Finland pe 10,000 popula ion. A he
end o he s udy, he incidences we e 21 in Denma k, 14 in
No way, 21 in Sweden, and 28 in Finland pe 10,000 popula-
ion. The ela i e change in incidence o knee a h oplas y was
6.0- old in Denma k, 3.9- old in No way, 2.3- old in Sweden,
and 2.1- old in Finland om he s a o he s udy o he end.
Table 1. Pa ien cha ac e is ics. Mean age applies o bo h TKA and UKA. The numbe o
ope a ions has been di ided in o age g oups. S udy pe iod 1997–2012, excep o Finland
(2000–2012)
Denma k No way Sweden Finland To al
Mean age (SD) 69.0 (9.5) 69.7 (9.2) 69.8 (9.0) 69.0 (9.0)
Females, % 63 66 60 68
UKA (n) 5,395 5,054 12,956 4,282
Age g oups, n (%)
30–64 21,624 (33) 12,872 (31) 42,084 (30) 30,264 (31) 106,844
65–74 24,577 (38) 15,751 (37) 53,492 (39) 38,305 (39) 132,125
75+ 18,587 (29) 13,412 (32) 43,403 (31) 30,324 (31) 105,726
To al 64,788 42,035 138,979 98,893 344,695
E hics
E hical app o al o he s udy was
ob ained h ough he e hical app o al
p ocess o each na ional egis y.
S a is ics
We desc ibed pa ien cha ac e is ics, ca -
ego ized in o sex and age g oups, using
desc ip i e s a is ics p esen ed as mean
and s anda d de ia ion (SD). Incidences
a e p esen ed as he numbe o ope a-
ions pe o med pe 104 o popula ion.
Age was ca ego ized in o 3 g oups: < 65
yea s, 65–74 yea s and ≥ 75 yea s. We
analyzed ends in he gene al incidence
10097 Niemela inen D.indd 17410097 Niemela inen D.indd 174 3/16/2017 11:17:21 AM3/16/2017 11:17:21 AM
Ac a O hopaedica 2017; 88 (2): 173–178 175
The ela i e change in incidence o UKA was 10- old in
Denma k, 1.5- old in Finland, 7.1- old in No way, and 0.5-
old in Sweden om he s a o he s udy o he end.
Du ing he s udy pe iod, he es ima ed a e age annual
inc ease in he incidence o TKA by age g oups and sex was
s a is ically signi i can in all coun ies, wi h he excep ion
o Finnish emales aged 65–74 yea s (IRR = 1.02, 95% CI:
1.00–1.03) (Table 2). IRR was highes in he younges age
g oup in bo h sexes and a dec easing end was de ec ed as
age inc eased. Females had lowe IRRs, excep in Denma k in
pa ien s aged 65–74 yea s. A s a is ically signi i can dec ease
in UKAs was de ec ed in Sweden in pa ien s who we e 65
yea s o mo e, whe eas in Denma k and in No way he e was
a signi i can ly highe annual incidence o UKA in all age
g oups—excep o UKAs in women aged 75 yea s o mo e in
No way. The e was no signi i can change in he annual inci-
dence o UKA o e he s udy pe iod in Finland, in men o
women o any age g oup (Table 2).
Incidence by sex
The incidences o TKA acco ding o sex a e shown in Fig-
u es 2 and 3. The incidence was highe in women han in men
in all 4 coun ies. A he end o he s udy pe iod, he inci-
dences o TKA we e 9.1 in Denma k, 11.0 in No way, 18.2
in Sweden, and 20.9 in Finland pe 10,000 men—gi ing a
ela i e change o 4.2- old in Denma k, 5.9- old in No way,
2.8- old in Sweden, and 2.7- old in Finland om he s a o
he s udy o he end. In women, he incidences o TKA we e
22.6 in Denma k, 15.7 in No way, 22.5 in Sweden, and 32.8
in Finland pe 10,000 women a he end o he s udy, and he
ela i e change was 5.2- old in Denma k, 3.1- old in No way,
2.4- old in Sweden, and 1.9- old in Finland om he s a o
he s udy o he end.
The incidence o UKA was highe in Sweden in bo h men
and women a he s a o he s udy han a he end o he s udy,
whe eas in he o he 3 coun ies he incidence o UKA was
highe a he end o he s udy han a he s a o he s udy
(Figu es 4 and 5).
20122010200820062004200220001998
Denma k
No way
Sweden
Finland
40
35
30
25
20
15
10
5
0
Incidence o TKA + UKA pe 10,000 inhabi an s
Yea o ope a ion
20122010200820062004200220001998
Denma k
No way
Sweden
Finland
40
35
30
25
20
15
10
5
0
Incidence o TKA in men pe 10,000 inhabi an s
Yea o ope a ion
20122010200820062004200220001998
Denma k
No way
Sweden
Finland
40
35
30
25
20
15
10
5
0
Incidence o TKA in women pe 10,000 inhabi an s
Yea o ope a ion
Figu e 1. To al incidence o TKA and UKA by
yea o ope a ion in pa ien s aged 30 yea s o
mo e. Incidences a e shown pe 10,000 inhab-
i an s. The incidence in Denma k is es ima ed
o include 10–15% unde es ima ion be ween
1997 and 2007 due o lowe comple eness.
Figu e 2. Incidence o TKA in males aged
30 yea s o mo e. Incidences a e shown pe
10,000 inhabi an s.
Figu e 3. Incidence o TKA in emales aged
30 yea s o mo e. Incidences a e shown pe
10,000 inhabi an s.
Table 2. Nega i e binomial eg ession analysis. Incidence a e a ios
(IRRs) wi h 95% con i dence in e als
A h oplas y Male Female
Age, yea s IRR 95% CI IRR 95% CI
Denma k
TKA 30–64 1.17 1.14–1.19 1.15 1.13–1.17
UKA 30–64 1.26 1.20–1.32 1.24 1.17–1.30
TKA 65–74 1.08 1.04–1.13 1.12 1.10–1.13
UKA 65–74 1.25 1.18–1.31 1.20 1.16–1.24
TKA 75+ 1.12 1.10–1.13 1.10 1.08–1.12
UKA 75+ 1.20 1.14–1.26 1.14 1.11–1.17
No way
TKA 30–64 1.16 1.14–1.18 1.13 1.12–1.15
UKA 30–64 1.13 1.07–1.19 1.11 1.05–1.18
TKA 65–74 1.11 1.10–1.13 1.08 1.07–1.09
UKA 65–74 1.12 1.08–1.16 1.07 1.01–1.13
TKA 75+ 1.09 1.08–1.10 1.06 1.04–1.07
UKA 75+ 1.09 1.05–1.14 1.02 0.96–1.06
Sweden
TKA 30–64 1.15 1.13–1.16 1.13 1.11–1.14
UKA 30–64 1.02 0.99–1.05 1.00 0.98–1.02
TKA 65–74 1.07 1.06–1.09 1.05 1.04–1.07
UKA 65–74 0.93 0.92–0.94 0.91 0.90–0.92
TKA 75+ 1.07 1.06–1.08 1.05 1.04–1.05
UKA 75+ 0.90 0.89–0.91 0.88 0.87–0.89
Finland
TKA 30–64 1.13 1.11–1.16 1.11 1.09–1.14
UKA 30–64 10.5 0.99–1.11 1.02 0.95–1.09
TKA 65–74 1.04 1.02–1.06 1.02 1.00–1.04
UKA 65–74 0.99 0.91–1.06 0.96 0.92–1.00
TKA 75+ 1.04 1.03–1.06 1.03 1.01–1.05
UKA 75+ 0.99 0.92–1.06 0.95 0.90–1.00
10097 Niemela inen D.indd 17510097 Niemela inen D.indd 175 3/16/2017 11:17:21 AM3/16/2017 11:17:21 AM
176 Ac a O hopaedica 2017; 88 (2): 173–178
Incidence by age g oup
The incidence o TKA was highes in Finland in pa ien s aged
65 yea s o mo e. The o al incidence was lowes in he young-
es age g oup in all coun ies. The incidence was highe a he
s a o he s udy han a he end in all age g oups (Figu e 6).
Discussion
We ound ha he o al incidence, comp ising bo h TKAs and
UKAs, inc eased in all coun ies and he ends o inc ease
we e compa able be ween coun ies. The inc ease in su gical
p ocedu es in Finland om 2004 o 2006 may be explained by
he coming in o o ce o a new social and heal hca e egula ion
ha ins uc ed hospi als o sho en pa ien wai ing imes o
su ge y. Despi e ha ing compa able socioeconomic si ua ions
and heal hca e sys ems, di e ences in he incidence o knee
a h oplas y be ween coun ies we e no able. A pilo s udy
om he NARA da a es ed a common da ase and epo ed
esul s om he pe iod 1997–2007 (Robe sson e al. 2010).
The p esen s udy con inued o analyze changes in he inci-
dence o a h oplas y un il 2012, based on expe ience gained
om he pilo s udy.
The o al inc ease in he numbe o a h oplas ies in all
coun ies was mainly caused by an inc eased incidence o
TKA. In Sweden, he e was a signi i can dec ease in he inci-
dence o UKA in pa ien s aged 65 yea s o mo e. In 3 o he
coun ies, a ia ions in incidences o UKA be ween g oups
we e mo e he e ogeneous (Table 2, Figu es 4 and 5). The ea-
sons o he changes in incidence o UKA a e mul i ac o ial.
P e ious s udies om na ional egis ies ha e a ec ed UKA
incidences, as mos egis ies show highe o e all e ision
a es o UKAs han o TKAs (Fu nes e al. 2007, Koskinen e
al. 2008, W-Dahl e al. 2010b). Howe e , he e ha e also been
s udies claiming be e clinical ou come om UKA and also
mo e cos -e ec i eness (Slo e e al. 2006, Lyg e e al. 2010).
Di e en UKA implan models wi h a longe lea ning cu e
compa ed o TKA, indica ions o p ima y UKA su ge y, and
a highe e ision isk han wi h TKA may explain he di e -
ences in he incidence compa ed o TKA. The inc ease in he
incidence o UKA in pa ien s less han 65 yea s o age may
be explained by he inc ease in minimally in asi e su ge y
(MIS), which enables a sho e pos ope a i e s ay in hospi al.
The 4 coun ies had compa able popula ions wi h ega d o
age and sex, and he e o e ins ead o age-s anda dized da a we
analyzed incidence be ween age g oups. O he 3 age g oups,
pa ien s less han 65 yea s o age had he lowes incidence o
TKA. Howe e , he ela i e inc ease in incidence was highe
in ha age g oup han in he o he age g oups. In ecen yea s,
i appea s ha he indica ions ha e widened o include younge
pa ien s, which has esul ed in a p opo ionally highe inc ease
in incidence in pa ien s less han 65 yea s o age, compa ed o
pa ien s aged 65 yea s o less (Robe sson e al. 2010, Leski-
nen e al. 2012). Be o e his, knee a h oplas y su ge y was
ini ially ese ed o elde ly pa ien s and hose wi h se e e
disease (Robe sson e al. 2014), and younge pa ien s wi h
heuma oid a h i is. The easons o inc easing incidence
in younge TKA pa ien s may be mul i ac o ial. Inc easing
obesi y in young people (Kau iainen 2005, Lohmande e al.
2009), pa icipa ion in con ac spo s (D iban e al. 2015), and
he in oduc ion o as - ack su ge y (which sui s younge
pa ien s well) a e p obable easons.
The p esen s udy had some s eng hs and limi a ions. The
majo s eng h was he unique collabo a ion o 4 na ional eg-
is ies in he c ea ion o a mul ina ional da abase co e ing a
la ge numbe o pa ien s, which enabled in e na ional com-
pa isons o e eal possible di e ences and which migh help
o es ima e u u e demands. Fu he mo e, he comple eness
20122010200820062004200220001998
Denma k
No way
Sweden
Finland
4
3
2
1
0
Incidence o UKA in men pe 10,000 inhabi an s
Yea o ope a ion
20122010200820062004200220001998
80
60
40
20
70
50
30
10
0
Incidence o TKA by age pe 10,000 inhabi an s
Yea o ope a ion
Denma k
No way
Sweden
Finland
Age 30–64
Age 65–74
Age 75–
Figu e 4. Incidence o UKA in males aged
30 yea s o mo e. Incidences a e shown pe
10,000 inhabi an s.
Figu e 5. Incidence o UKA in emales aged
30 yea s o mo e. Incidences a e shown pe
10,000 inhabi an s.
Figu e 6. Incidence o TKA acco ding o age
g oup. Incidences a e shown pe 10,000
inhabi an s.
20122010200820062004200220001998
Denma k
No way
Sweden
Finland
4
3
2
1
0
Incidence o UKA in women pe 10,000 inhabi an s
Yea o ope a ion
10097 Niemela inen D.indd 17610097 Niemela inen D.indd 176 3/16/2017 11:17:25 AM3/16/2017 11:17:25 AM

Ac a O hopaedica 2017; 88 (2): 173–178 177
and alidi y o da a we e high in he No dic coun ies a he
end o he s udy pe iod (comple eness, NAR: 95%; SKAR:
97%; DKR: 97%; FAR: 96%) (annual epo s 2015: Danish
Knee A h oplas y Regis e , No wegian A h oplas y Regis-
e , Swedish Knee A h oplas y Regis e , Finnish A h oplas y
Regis e ). Comple eness in he DKR was epo ed o be 89%
in 2007 (Robe sson e al. 2010), which may ha e caused
10–15% unde es ima ion o incidence in Denma k o e he
pe iod 1997–2007. To al ela i e change in incidence was
highes in Denma k, and ha may ha e been due o he in l u-
ence o a lowe comple eness o he DKR in he ea ly yea s
o he s udy pe iod (Table 3). The lack o da a on BMI and
o he subg oups could also be conside ed a limi a ion o he
p esen s udy.
The incidence o TKA s eadily inc eased in all pa icipa -
ing coun ies in his s udy, which is in line wi h i ndings om
o he s udies (Ku z e al. 2007, W-Dahl e al. 2010a, Leskinen
e al. 2012). The incidence o knee a h oplas y in emales was
ound o be g ea e han ha in males in ou s udy, bu he
esul s o p e ious s udies ha e also shown ha he p opo -
ion o emale pa ien s has dec eased wi h ime (Nemes e al.
2015). Mo eo e , he sex dis ibu ion may also a y be ween
na ions (Pax on e al. 2011, Nemes e al. 2015). One s udy
deli e ed p ojec ions o p ima y and e ision hip and knee
a h oplas y in he Uni ed S a es om 2005 o 2030 (Ku z
e al. 2007). In ha s udy, he au ho s p edic ed ha i he
numbe o o al knee a h oplas ies pe o med con inues a he
cu en a e, he demand o p ima y TKA would be p ojec ed
o g ow by a ac o o 7 by 2030. In ano he p e ious s udy
om he Finnish A h oplas y Regis y, he annual cumula i e
incidence o UKA and TKA inc eased apidly be ween 1980
and 2006, especially in pa ien s aged 50–59 yea s, he so-
called baby-boome gene a ion (Leskinen e al. 2012). In ou
s udy, he inc ease in incidence was mainly due o he inc ease
in incidence o TKAs. This i nding is consis en wi h a s udy
by W-Dahl e al. (2010a) om he Swedish Knee A h oplas y
Regis e , which showed ha al hough he incidence o TKA
has inc eased in pa ien s unde 55 yea s o age, he incidence
o UKA and high ibial os eo omy (HTO) has dec eased. Obe-
si y is also a g owing bu den in many coun ies and, as his has
been shown o be a ce ain isk ac o o knee os eoa h i is,
especially in young pa ien s, i may con ibu e o he inc eas-
ing demand o TKAs in u u e (Apold e al. 2014a, b, Sil e -
wood e al. 2015).
A p e ious s udy has aised conce ns abou he long- e m
ou come o TKAs and he possibili y o an inc easing e ision
bu den, because younge age has been associa ed wi h a highe
isk o ea ly pe ip os he ic join in ec ion and asep ic mechan-
ical ailu e a e TKA (Meehan e al. 2014). In ano he s udy,
young age was ound o impai he p ognosis o TKA and was
associa ed wi h inc eased e ision a es o non-in ec ious ea-
sons (Julin e al. 2010). A compa ison s udy unde aken by he
No wegian Knee A h oplas y Regis e and a Uni ed S a es
a h oplas y egis y showed an inc eased isk o e ision in
pa ien s less han 65 yea s o age compa ed o pa ien s aged
65 yea s o olde (Pax on e al. 2011). In ou s udy, he p o-
po ional g ow h o TKAs du ing he s udy pe iod was highes
in pa ien s who we e younge han 65 yea s. Despi e his, he
incidence o knee a h oplas y in he younges age g oup was
lowe han in pa ien s aged 65 yea s o mo e. Based on his
i nding, he majo i y o knee a h oplas ies will p obably be
pe o med on elde ly pa ien s in he u u e also. E en hough
pa ien s less han 65 yea s old ep esen ed a lowe incidence
le el han pa ien s who we e 65 o olde in ou s udy, hese
wo king-age pa ien s should be conside ed o be an impo an
subg oup because o hei highe physical ac i i y and highe
demands o su ge y, and he mul i ac o ial easons behind he
success o TKA (Keeney e al. 2014, Kli e al. 2014, Pa izi
e al. 2014). An e ec on he e ision bu den can he e o e be
an icipa ed in u u e.
In summa y, he incidence o knee a h oplas y has s eadily
inc eased in he 4 No dic coun ies. This inc ease was caused
by an inc ease in he incidence o TKA, whe eas he incidence
o UKA a ied be ween coun ies. The p opo ional inc ease
in incidence was highes in pa ien s aged less han 65 yea s.
Howe e , pa ien s who a e 65 yea s o mo e s ill comp ise he
majo i y o hose who unde go knee a h oplas y, and hey a e
he main con ibu o y ac o o he inc ease in he o al numbe
o TKA ope a ions.
S udy design: MN and AE. Analysis o da a and s a is ics: HH and MN.
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AE.
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