Incidence and risk factors of exercise-related knee disorders in young adult men

RESEARCH ARTICLE Open Access Incidence and isk ac o s o exe cise- ela ed knee diso de s in young adul men Ha i K. Pihlajamäki 1,2* , Mickael C. Pa iainen 3 , Hannu Kau iainen 4,5,6 and Ilkka Ki i an a 7 Abs ac Backg ound: Musculoskele al diso de s and inju ies a e common causes o mo bidi y and loss o ac i e, physically demanding aining days in mili a y popula ions. We e alua ed he incidence, diagnosis, and isk ac o s o knee diso de s and inju ies in male Finnish mili a y consc ip s. Me hods: The s udy popula ion comp ised 5 coho s o 1000 men pe o ming hei mili a y se ice, classi ied acco ding o bi h yea (1969, 1974, 1979, 1984, and 1989). Follow-up ime o each consc ip was he indi idual consc ip ’s ull, comple ed mili a y se ice pe iod. Da a o each man we e collec ed om a s anda d p e- in o ma ion ques ionnai e used by de ense o ce heal hca e o icials and om all o iginal medical epo s o he ga ison heal hca e cen e s. Backg ound a iables o isk ac o analysis included he consc ip s’se ice da a, i.e., se ice class (A, B), leng h o mili a y se ice, age, heigh , weigh , body mass index (BMI), unde weigh , o e weigh , obesi y, smoking habi , educa ion, diseases, inju ies, and subjec i e symp oms. Resul s: O he 4029 consc ip s, 853 isi ed heal hca e p o essionals o knee symp oms du ing hei mili a y se ice, and 103 o hese had su e ed a knee inju y. Independen isk ac o s o he incidence o knee symp oms we e: olde age; se ice class A; o e weigh (BMI 25.0–29.9 kg/m 2 ); smoking habi ; comp ehensi e school educa ion only; and sel - epo ed p e ious symp oms o he musculoskele al, espi a o y, and gas oin es inal sys em. The majo i y o isi s o ga ison heal hca e se ices due o knee symp oms occu ed du ing he i s ew mon hs o mili a y se ice. Knee symp oms we e nega i ely co ela ed wi h sel - epo ed men al and beha io al diso de s. Conclusions: The p esen s udy highligh s he equency o knee diso de s and inju ies in young men du ing physically demanding mili a y aining. One- i h o he male consc ip s isi ed de ense o ce heal hca e p o essionals due o knee symp oms du ing hei se ice pe iod. Independen isk ac o s o he incidence o knee symp oms du ing mili a y se ice we e age a mili a y se ice; mili a y se ice class A; o e weigh ; smoking habi ; comp ehensi e school educa ion only; and sel - epo ed p e ious symp oms o he musculoskele al sys em, espi a o y sys em, o gas oin es inal sys em. These isk ac o s should be conside ed when planning and implemen ing p ocedu es o educe knee diso de s and inju ies du ing compulso y mili a y se ice. Keywo ds: Knee, Epidemiology, Incidence, Risk ac o s, Young adul , Mili a y aining, Physical ac i i y, Diso de s and inju ies Backg ound Knee pain and knee inju ies a e amilia complain s o bo h gene al p ac i ione s and o hopedic su geons. Knee inju ies, occu ing mos o en in young men (<30 yea s o age), a e a majo cause o pain and disabili y, and a widesp ead public heal h conce n wi h ega d o heal hca e cos s and wo k disabili y [1]. Few popula ion-based s udies o he incidence and isk ac- o s o knee inju ies in young adul s a e a ailable in he li e a u e. Physical i ness du ing young adul hood may a ec physical i ness in olde age and he e o e in e - en ion p og ams should a ge young adul hood o es- ablish heal hy habi s [2]. Eme gency depa men s in he Uni ed S a es ea ed an es ima ed 6.7 million knee inju ies om 1999 o 2008, * Co espondence: [email p o ec ed] 1 Depa men o O hopaedics and T auma ology, Seinäjoki Cen al Hospi al, Seinäjoki, Finland 2 Facul y o Medicine and Li e Sciences, Uni e si y o Tampe e, Tampe e, Finland Full lis o au ho in o ma ion is a ailable a he end o he a icle © The Au ho (s). 2017 Open Access This a icle is dis ibu ed unde he e ms o he C ea i e Commons A ibu ion 4.0 In e na ional License (h p://c ea i ecommons.o g/licenses/by/4.0/), which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided you gi e app op ia e c edi o he o iginal au ho (s) and he sou ce, p o ide a link o he C ea i e Commons license, and indica e i changes we e made. The C ea i e Commons Public Domain Dedica ion wai e (h p://c ea i ecommons.o g/publicdomain/ze o/1.0/) applies o he da a made a ailable in his a icle, unless o he wise s a ed. Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 DOI 10.1186/s12891-017-1701-3 wi h an inju y a e o 2.29 knee inju ies pe 1000 popula- ion [3]. The highes inju y a e was in hose 15 o 24 yea s o age, wi h males ha ing a sligh ly highe inju y a e han emales [3]. A 2004 s udy conduc ed in a Uni ed Kingdom popula ion epo ed knee pain in 15% o males 16 o 44 yea s o age, which esul ed in disabili y in 16% [1]. Os eoa h i is is a p ima y cause o knee pain ha , along wi h he p e alence o knee pain, inc eases wi h age in bo h sexes [4]. Almos 40% o all spo and leisu e- ime inju ies a e o he knee [5]. Taanila e al. [6] e alua ed musculoskele al diso de s in Finnish mili a y consc ip s, and epo ed ha inju ies o he knee join (18%) we e al- mos as common as hose o he back (20%). The as ma- jo i y o he knee inju ies (91%) occu ed du ing mili a y exe cises [6]. A la ge popula ion-based s udy o he inci- dence and isk ac o s o knee inju ies in Finnish mili a y consc ip s epo ed in 2013 e ealed ha mo e han 1 in 100 young adul men will be hospi alized annually due o a knee inju y du ing hei mili a y se ice, and one- hi d o all young adul male consc ip s hospi alized wi h knee inju ies a e likely o ha e long- e m no able disabili y [7]. Olde age and obesi y a e he mos salien isk ac o s o knee inju ies in mili a y ec ui s [7]. De e mining he isk ac o s o knee inju ies and knee pain will acili a e he de elopmen o p e en i e s a - egies. The pu pose o he p esen coho s udy o male consc ip s du ing hei compulso y mili a y se ice pe iod was o e alua e he incidence and isk ac o s o knee diso de s and inju ies among young adul men. Me hods The s udy popula ion comp ised i e coho s o Finnish men pe o ming hei mili a y se ice, classi ied acco d- ing o bi h yea (1969, 1974, 1979, 1984, and 1989). We a emp ed o c ea e a longi udinally ep esen a i e g oup o young male consc ip s o e a ime-pe iod o 20 yea s by aking andomly selec ed coho s o 1000 men om he Finnish popula ion egis y e e y i h yea s a ing om he yea 1969. All Finnish males o e 18 yea s o age a e obliga ed o pe o m mili a y se ice, and app oxi- ma ely 80% ca y ou hei ull se ice pe iod. Ch onic dis- ease is he main eason o exemp ion om mili a y se ice. All consc ip s mus pass a medical examina ion pe o med by a physician be o e en e ing he se ice. A new g oup o consc ip s en e s mili a y se ice wice a yea , in Janua y and in July. The manda o y mili a y se ice pe iod is a minimum o 180 days o consc ip s wi h ank and ile du ies, 270 days o consc ip s wi h special aining, and a maximum o 362 days o o ice s and consc ip s ained o pa icula ly demanding du ies. The majo i y o consc ip s a e 19 o 20 yea s old a he ime hey pe o m hei mili a y se ice. In special cases, i is possible o en e he se ice ea lie (18 yea s) as a olun ee , o la e , by he age o 29, when mili a y se ice was o mally pos poned. As desc ibed in de ail p e iously [8–10], basic aining is pe o med by all Finnish consc ip s o 8 weeks and includes a ious physical ac i i ies o which he in ensi y le el is g ad- ually inc eased. This 8-week basic aining pe iod com- p ises 135 h o physical aining (17 h/week), including ma ching, cycling, d ill aining, comba aining, and o he aining in ol ing hea y physical loading. Comba aining and ma ching equi e consc ip s o ca y om ~26 kg (in summe ) o ~35 kg (in win e ) o pe sonal comba gea and occasionally an ex a 5–20 kg o special equipmen . The consc ip s also pe o m 56 h (7 h/week) o p og ammed physical exe cises, such as jogging, eam spo s, o ci cui aining. A he end o he 8-week ain- ing pe iod, consc ip s a e expec ed o ha e a ained a physical le el enabling hem o ma ch o ski a dis ance o 15 km in one day and he same dis ance once again he nex day ca ying a ull mili a y pack weighing 25 kg and a i le, while main aining hei i ness o ba le [8–10]. A e he basic aining pe iod, he amoun o mode a e and high-in ensi y p og ammed physical exe cises is e- duced o 15 h/week depending on he mili a y b anch. The in ensi y and olume o mili a y aining wi h comba gea , howe e , inc eases o e he ollowing 4 mon hs o se ice (special and eam aining pe iod), while he amoun o mode a e and high-in ensi y physical aining is main ained a he same le el in di e en companies. Each consc ip comple es app oxima ely 450 h (19 h/week) o ins uc ed physical aining du ing he i s 6 mon hs o mili a y se ice. One yea be o e en e ing he mili a y se ice, e e y man o woman is e alua ed and examined in a sys em- a ic heal h examina ion, usually pe o med by a gene al p ac i ione . Special a en ion is paid o sel - epo ed symp oms and diseases de ec ed in he heal h examin- a ion o assess he eligibili y o each man o woman o pe o m mili a y se ice. The se ice class o he con- sc ip s, Class A ( ull comba o ield oop aining) o Class B (ligh ened o se ice aining), is de e mined based on hei ul illmen o he heal h equi emen s [9]. Acco ding o he policy o he Finnish de ense o ces, all consc ip s a e adminis e ed a s anda d p e-in o ma ion ques ionnai e ega ding hei p e ious illnesses and symp- oms du ing he i s week o mili a y se ice. The ques- ionnai e cha s he consc ip s’socio-economic ac o s, sel -assessed heal h, and heal h beha io (e.g., physical ac- i i y) a baseline. The ques ionnai e also includes ques- ions abou school success, educa ion le el, a he ’s occupa ional g oup, and u baniza ion le el o hei place o esidence; amoun o physical exe cise, p io spo ing ac i i ies, membe ship in a spo s club, and possible pa - icipa ion in compe i i e spo s; signi ican heal h ac o s, p e ious spo s inju ies, o hopedic ope a ions, egula medica ion, and any ch onic disease, impai men o Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 Page 2 o 7 disabili y; and whe he he consc ip has expe ienced pain in se en di e en ana omic egions du ing he pas mon h. Gene al ques ions ega ding heal h beha io in- clude use o obacco and alcohol, and equency o d unk- enness. A en ion is paid o he indi idual opinion o each consc ip , how he conside s his heal h compa ed o age ma es, and his opinion abou he physical demands placed on a soldie . The ques ionnai e was desc ibed p e iously [11–14]. In addi ion o he heal h examina ion pe o med by a physician app oxima ely 1 yea be o e en e ing he mili- a y se ice and comple ing he a o emen ioned p e- in o ma ion ques ionnai e, a physician e-examines he heal h s a us o e e y consc ip du ing he i s 2 weeks o mili a y se ice o e i y ha all consc ip s mee he heal h equi emen s o pe o ming mili a y se ice. Du ing his isi o he ga ison heal hca e cen e , he heigh and weigh o a consc ip is measu ed and e- co ded in his ile. I he medical examina ion e eals se- quelae o knee inju ies, o he p e ious se e e knee diso de s, o sequelae o knee ope a ions leading o se- e e disabili y, he consc ip is discha ged om mili a y se ice, and hus no consc ip s wi h his his o y we e in- cluded in he p esen s udy. Bo h Class A ( ull comba o ield oop aining) and Class B (ligh ened o se ice aining) consc ip s [9] pa icipa ed in he p esen s udy. Fo he p esen s udy, all o iginal medical epo s o he consc ip s we e sc u inized and e iewed. No da a we e collec ed om men excluded om he a my be o e o du ing he se ice due o heal h easons, and hese men we e no included in he s udy popula ion. Mili a y consc ip s seeking medical ca e mus use he p ima y mili a y heal h-ca e uni s and mili a y hospi al. Ei he ICD-9 o ICD-10 coding, acco ding o he ime pe iod o he mili a y se ice, was used by he mili a y physicians o eco d he diagnoses. All heal hca e isi s o he consc ip s in he p esen s udy popula ion o any knee symp om we e ca e ully sc u inized and e iewed o eco d all complain s due o disease and o he dis- o de o he knee o knee inju y. The incidence o knee diso de s and diseases o knee inju ies was eco ded acco ding o he leng h o se ice and compa ed o possible isk ac o s eco ded om he p e-in o ma ion ques ionnai e. S ess ac u es o he knee egion we e included in he knee diso de s. The ollowing in o ma ion was collec ed om he o iginal medical epo s o each isi o he ga ison heal hca e cen e : da e o he isi , symp oms, diagnosis, possible e iologic mechanism (i.e., o e use, acu e auma, o he , unknown), and exemp ions om du y. Body mass index (BMI) was compu ed as he weigh in kilog ams di ided by he squa e o he heigh in me e s (kg/m 2 ). The In e - na ional Classi ica ion o adul unde weigh , o e weigh , and obesi y acco ding o BMI by he Wo ld Heal h O ganiza ion was used o assign he consc ip s o he ollowing ca ego ies: BMI <18.50, unde weigh ; BMI 18.50–24.99, no mal; BMI 25.00–29.99, o e weigh ; and BMI >30, obese. The Ins i u ional Re iew Boa d o he Finnish De ence Fo ces app o ed he s udy plan. The E hics Commi ee o he Hospi al Dis ic o Helsinki and Uusimaa ap- p o ed he s udy (267/13/03/09). The da a a e p esen ed as means wi h s anda d de ia- ions o as coun s wi h pe cen ages. The s a is ical sig- ni icance o di e ences be ween g oups was es ed using a - es o chi-squa e es . Time- o-e en analysis was based on he p oduc limi es ima e o he cumula i e incidence unc ion. A mul i a ia e Poisson eg ession model wi h a obus es ima e o a iance was used o in- es iga e ac o s ela ed o he incidence o knee symp- oms. The assump ion o o e dispe sion in he Poisson model was es ed using he Lag ange mul iplie es . The S a a 14.1, S a aCo p LP (College S a ion, TX, USA) s a - is ical package was used o he analyses. Resul s O he 5000 pa icipan s andomly selec ed o he p esen s udy using he Finnish popula ion egis y, doc- umen s conce ning hei mili a y se ice we e con i med o 4327 men. The lack o mili a y documen s indica es ha hese men had no pe o med hei mili a y se ice a he ime he pa icipan s we e selec ed o he p esen s udy. Some o hese men may ha e pos poned hei mili a y se ice due o ongoing s udies in he uni e si y o o he lea ning ins i u ion. O he s may ha e selec ed ci il se ice ins ead o mili a y se ice be o e en e ing he a my. Some o he missing pe sons had been elie ed o hei du y o pe o m mili a y se ice on he basis o physician examina ions p io o en e ing he a my. The a o emen ioned g oups o men lack mili a y se ice doc- umen s because hey had no en e ed he mili a y se - ice a he ime we selec ed he coho s. O he 4327 men wi h documen a ion, 298 we e excluded because hey selec ed ci il se ice ins ead o he a my a e en e - ing mili a y se ice o hey we e discha ged o heal h easons. Al oge he , da a we e collec ed o analysis om 4029 consc ip s. O hese 4029 consc ip s, 853 (21.2%) isi ed heal hca e p o essionals (physicians o nu ses) o knee symp oms a leas once du ing hei mili a y se - ice pe iod. These 853 consc ip s isi ed he mili a y medical se ice acili ies o knee symp oms a o al o 2118 imes du ing hei se ice pe iod. O hese 2118 isi s o seek medical ad ice, 232 (11%) we e o a ecen knee inju y (95% CI: 9.6–12.3). Fo he whole s udy popula ion o 4029 men, he o al numbe o isi s o he ga ison heal hca e cen e was 32,510. The demog aphic and clinical cha ac e is ics o con- sc ip s be o e en y in o he mili a y se ice a e shown Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 Page 3 o 7 in Table 1. Finnish consc ip s assigned o Class A mili- a y se ice we e a g ea e isk o knee diso de s and inju ies du ing hei compulso y mili a y se ice pe iod. Consc ip s wi h a his o y o men al and beha io al diso - de s be o e en e ing he mili a y se ice had a lowe isk o knee diso de s and inju ies du ing hei mili a y se - ice (Table 1). O consc ip s wi h men al symp oms, 188 (5.0%) se ed as Class A soldie s and 90 (29.7%) as Class B soldie s (p< 0.001). The cumula i e incidence [24.6% (95% CI: 22.9 o 26.4)] o knee symp oms is shown in Fig. 1. Peak inci- dence occu ed du ing he i s ew mon hs o mili a y se ice, and he numbe o isi s dec eased o e ime in he se ice. In he uni a ia e analysis, he g oups wi h o wi hou knee symp oms di e ed in age, mili a y se ice class, smoking habi , men al diso de s, and p e ious in- ju ies, as well as as hma condi ion and o he espi a o y and men al symp oms (Table 1). In he mul i a ia e ana- lysis, age a mili a y se ice, mili a y se ice class A, o e weigh (BMI 25.0–29.9 kg/m 2 ), smoking habi , comp ehensi e school only, sel - epo ed p e ious symp- oms o he musculoskele al sys em, sel - epo ed p e i- ous symp oms o he espi a o y sys em, and sel - epo ed p e ious symp oms o he gas oin es inal sys- em we e independen isk ac o s o he incidence o knee symp oms du ing mili a y se ice (Table 2). Discussion The main inding o he p esen s udy was ha 20% o he male consc ip s isi ed de ense o ce heal hca e p o- essionals a leas once du ing hei compulso y mili a y se ice pe iod o symp oms ela ed o a knee diso de o inju y. Thus, a o al o 853 o 4029 young adul males sough medical ad ice ega ding knee symp oms a leas once du ing hei mili a y se ice. In a p e ious s udy o knee inju ies equi ing hospi aliza ion o consc ip s, he incidence a e was 11 cases pe 1000 pe son-yea s, indi- ca ing ha a leas 1 o 100 young adul males is hospi- alized each yea due o knee inju y du ing hei consc ip ion [7]. In he p esen in es iga ion, we also Table 1 Demog aphic and clinical cha ac e is ics o consc ip s be o e en y in o he mili a y se ice s a i ied by knee symp oms du ing mili a y se ice Cha ac e is ic Knee symp oms du ing mili a y se ice Yes N= 853 No N= 3176 P- alue Age a mili a y se ice, yea , mean (SD) 19.2 (1.0) 19.3 (1.2) 0.094 Mili a y Se ice Class A, n (%) 811(95.1) 2915 (91.8) <0.001 BMI, mean (SD) 23.1 (3.7) 23.3 (3.8) 0.26 Smoking (ciga e es/day), n (%) 0.004 0 458 (62.6) 1834 (37.4) 1–9 62 (8.5) 263 (9.7) 10–19 150 (20.5) 474 (17.4) ≥20 61 (8.3) 151 (5.5) Comp ehensi e school only, n (%) 499 (58.6) 1846 (58.5) 0.96 High physical ac i i y, n (%) 283 (38.8) 1025 (37.6) 0.56 Diseases and inju ies de ec ed by mili a y physicians, n (%) Men al o beha io al diso de s 9 (1.1) 169 (5.3) <0.001 Diseases o he eye and adnexa 219 (25.7) 883 (27.8) 0.22 Diseases o he espi a o y sys em 142 (16.6) 450 (14.2) 0.069 Diseases o he skin and subcu aneous issue 46 (5.4) 184 (5.8) 0.65 Diseases o he musculoskele al sys em 84 (9.8) 264 (8.3) 0.16 Inju ies 103 (12.1) 315 (9.9) 0.067 Fla oo de o mi y, n (%) 14 (1.6) 78 (2.5) 0.16 Subjec i e symp oms epo ed in o icial ques ionnai e be o e en e ing mili a y se ice, n (%) Symp oms o he musculoskele al sys em 93 (10.9) 261 (8.2) 0.014 Symp oms o he espi a o y sys em 195 (22.9) 646 (20.3) 0.11 Symp oms o he gas oin es inal sys em 25 (2.9) 63 (2.0) 0.093 Men al symp oms 24 (2.8) 117 (3.7) 0.22 Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 Page 4 o 7 calcula ed all consc ip isi s o heal hca e p o essionals due o any knee symp oms, no only knee inju ies lead- ing o hospi aliza ion o he pa ien . The esul s o he p esen s udy highligh he equency o knee diso de s and inju ies in young male adul s du ing physically de- manding mili a y aining, and indica e he need o p e- en i e measu es o diminish knee diso de s and inju ies du ing mili a y se ice. The peak incidence o consc ip isi s o seek medical ad ice due o knee symp oms in mili a y heal hca e acil- i ies occu ed du ing he i s ew mon hs o mili a y se - ice, which migh be due o he ac ha all Finnish consc ip s s a hei basic aining wi h 8 weeks o phys- ical ac i i y ha g adually inc eases in in ensi y o e ime. Acco ding o he indings o he p esen s udy, o e - weigh (BMI 25.0–29.9 kg/m 2 ) was a isk ac o o he incidence o knee symp oms du ing mili a y se ice. P e- ious s udies o mili a y popula ions epo ed ha o e - weigh is a signi ican isk ac o o musculoskele al inju ies in gene al [1, 9, 15]. Mo eo e , a s udy o Is aeli consc ip s epo ed an associa ion be ween o e weigh and lowe ex emi y join condi ions [16]. In ano he s udy o 17 yea -old adolescen s, obesi y was associa ed wi h knee pain [17]. Weigh gain is epo edly associa ed wi h mo e se e e knee pain, and weigh loss is epo ed o elie e knee symp oms [18]. F ilande e al. [19] e- po ed in a s udy o Finnish consc ip s ha becoming se e ely o e weigh du ing he ollow-up a e mili a y se ice is associa ed wi h knee pain, and becoming se- e ely obese p edic s he de elopmen o unc ional limi- a ions. Acco ding o ha s udy, auma ic knee p oblems du ing mili a y se ice pa ly media e he e - ec o obesi y on unc ional limi a ions [19]. The p esen s udy also e ealed ciga e e smoking o be an independen isk ac o o he incidence o knee symp oms du ing mili a y se ice. A p e ious s udy e- po ed he p e alence o ciga e e smoking among Finnish consc ip s and demons a ed ha he p e alence o a smoking habi dec eased om 42% o 34% du ing he pe iod om 1999 o 2010 [20]. Acco ding o a popula ion-based s udy on 58-yea -old pe sons, howe e , smoking is no associa ed wi h knee pain [21]. In addi ion, a ecen me a-analysis o isk ac o s o knee os eoa h i is in olde adul s e ealed no associa ion be- ween smoking and he onse o knee os eoa h i is [22]. No popula ion-based s udies ha e examined he associ- a ion o smoking and knee pain among younge adul s wi hou knee os eoa h i is. Age a mili a y se ice and p e ious educa ion comp is- ing only comp ehensi e school we e also independen isk Fig. 1 Cumula i e incidence and haza d a e o knee symp oms du ing mili a y se ice Table 2 Poisson eg ession model o numbe o knee diso de s o inju ies IRR (95% CI) P- alue Age 0.92 (0.87–0.96) <0.001 Mili a y Se ice Class A 1.29 (1.05–1.57) 0.014 BMI (Body Mass Index) < 25.0 kg/m 2 1.00 (Re e ence) 25.0–29.9 kg/m 2 1.15 (1.03–1.30) 0.016 ≥30 kg/m 2 0.98 (0.80–1.20) 0.87 High physical ac i i y 0.99 (0.90–1.10) 0.91 Smoking (ciga e es/day) 0 1.00 (Re e ence) 1–9 1.24 (1.06 o 1.45) 0.009 10–19 1.37 (1.21 o 1.55) <0.001 ≥20 1.35 (1.11 o 1.64) <0.001 Comp ehensi e school only 1.10 (1.00–1.22) 0.046 Inju ies 1.07 (0.93–1.23) 0.34 Symp oms o he musculoskele al sys em 1.59 (1.39–1.82) <0.001 Symp oms o he espi a o y sys em 1.17 (1.05–1.30) 0.005 Symp oms o he gas oin es inal sys em 1.67 (1.31–2.12) <0.001 Men al symp oms 0.82 (0.64–1.06) 0.13 Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 Page 5 o 7 ac o s o he incidence o knee symp oms du ing mili- a y se ice. Mo eo e , consc ip s assigned o Class A mili a y se ice had a s a is ically highe isk o knee symp oms. One po en ial explana ion o his is ha he mili a y aining o Class A consc ip s is physically mo e demanding han ha o consc ip s se ing as Class B consc ip s. Men al symp oms and psychia ic diagnoses in ei he o bo h o he p e-in o ma ion ques ionnai es and du ing mili a y se ice co ela ed nega i ely wi h knee symp oms. Consc ip s wi h men al o beha io al diso de s a e o en en e ed in o Class B se ice and hus ha e ligh e physical se ice and aining han Class A consc ip s. Ac- co ding o he indings o he p esen s udy, only 5.0% o consc ip s wi h men al symp oms se ed as Class A con- sc ip s and 30% as Class B consc ip s. Sel - epo ed p e i- ous symp oms o he musculoskele al sys em, sel - epo ed p e ious symp oms o he espi a o y sys em, and sel - epo ed p e ious symp oms o he gas oin es inal sys em we e also independen isk ac o s o he incidence o knee symp oms du ing mili a y se ice. This s udy has se e al s eng hs. Fi s , his s udy in- cludes a la ge s udy popula ion o 4029 male consc ip s om i e di e en age coho s in a na ion whe e mili a y se ice is compulso y o male ci izens. Second, because mili a y se ice is compulso y in Finland, he male con- sc ip s ep esen young Finnish adul s ha we e consid- e ed heal hy enough o en e mili a y se ice based on a comple e examina ion pe o med by a physician. The indings o he p esen s udy ega ding knee inju ies in consc ip s a e hus gene alizable o he young adul male popula ion. Compulso y mili a y se ice is a use ul indi- ca o o he esponse o a p og essi e physical exe cise egimen by young adul s in he gene al popula ion. Thi d, impo an ly, consc ip s a e equi ed o use he p ima y mili a y heal h-ca e uni s and Cen al Mili a y Hospi al o all medical ea men . Fou h, he da a ana- lyzed in he p esen s udy we e collec ed om o iginal p e-mili a y se ice medical eco ds as well as he mili- a y se ice medical eco ds and an o icial s anda d p e- in o ma ion ques ionnai e ega ding p e ious illnesses and symp oms comple ed by e e y consc ip . Only males we e included in his s udy, which may limi in e p e a ion o he indings. Fu he , in he olde age coho s, some medical epo s we e manually docu- men ed, and he no es we e no s anda dized. F om he o iginal s udy popula ion o 5000 subjec s, medical e- po s we e ob ained o 4327. Mos o he missing e- po s we e o hose bo n in 1989, because some o hese men we e cu en ly se ing o we e abou o se e in he nea u u e, and hus se ice da a we e no ye a ailable o inclusion in he p esen s udy. Due o he apid eco e y and mild na u e o he majo i y he knee symp oms o he consc ip s, he exac diagnosis o he knee diso de was seldom a ailable in he medical eco ds. Thus, classi ica ion o he pa ien s based on he exac diagnosis was no possible; ins ead, we classi ied he knee diso de s as auma ic o non- auma ic. Conclusions The esul s o he p esen s udy highligh he equency o knee diso de s and inju ies in young male adul s du - ing physically demanding mili a y aining. One- i h o he male consc ip s isi ed de ense o ce heal hca e p o- essionals due o knee symp oms du ing hei se ice pe iod. Based on he indings o he p esen s udy, age a mili a y se ice, mili a y se ice class A, o e weigh (BMI 25.0–29.9 kg/m 2 ), smoking habi , comp ehensi e school only, sel - epo ed p e ious symp oms o he musculoskele al sys em, sel - epo ed p e ious symp- oms o he espi a o y sys em, and sel - epo ed p e i- ous symp oms o he gas oin es inal sys em a e independen isk ac o s o he incidence o knee symp- oms du ing mili a y se ice. These isk ac o s should be aken in o accoun when planning and implemen ing p ocedu es o educe knee diso de s and inju ies du ing compulso y mili a y se ice. Abb e ia ions BMI: Body Mass Index Funding This s udy was inancially suppo ed by he Compe i i e S a e Resea ch Financing o Seinäjoki Cen al Hospi al, he Finnish Scien i ic Ad iso y Boa d o De ense (MATINE). A ailabili y o da a and ma e ials The da ase s gene a ed and/o analyzed du ing he cu en s udy a e no publicly a ailable because hey we e e ospec i ely ob ained om ins i u ional egis ies and eco ds ha a e no a ailable o an open access eposi o y. The da a a e a ailable om he co esponding au ho upon easonable eques . Au ho s’con ibu ions HKP and IK we e in cha ge o he s udy and con ibu ed o all s ages o he s udy. HKP, HK, and IK we e esponsible o he o iginal da a collec ion and pa icipa ed in he s udy design and da a in e p e a ion. HKP w o e he o iginal e sion o he manusc ip . MCP con ibu ed o he da a in e p e a ion, s a is ical analysis and e iewed he manusc ip . All au ho s e iewed and app o ed he inal manusc ip . E hics app o al and consen o pa icipa e The E hics Commi ee o he Hospi al Dis ic o Helsinki and Uusimaa app o ed he s udy (267/13/03/09). The cu en s udy was based on egis y da a and no clinical pa ien s we e en olled; he e o e, in o med consen o he pa ien s was no equi ed. App o al o use he da a was g an ed by Ins i u ional Re iew Boa d o he Finnish De ence Fo ces. Consen o publica ion No applicable. Compe ing in e es s The au ho s decla e ha hey ha e no compe ing in e es s. Publishe ’sNo e Sp inge Na u e emains neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a ilia ions. Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 Page 6 o 7 Au ho de ails 1 Depa men o O hopaedics and T auma ology, Seinäjoki Cen al Hospi al, Seinäjoki, Finland. 2 Facul y o Medicine and Li e Sciences, Uni e si y o Tampe e, Tampe e, Finland. 3 Mehiläinen Medical Cen e, Helsinki, Finland. 4 Uni o P ima y Heal h Ca e, Helsinki Uni e si y Cen al Hospi al, Helsinki, Finland. 5 Depa men o Gene al P ac ice, Uni e si y o Helsinki, Helsinki, Finland. 6 Uni o P ima y Heal h Ca e, Kuopio Uni e si y Hospi al, Kuopio, Finland. 7 Depa men o O hopaedics and T auma ology, Helsinki Uni e si y Hospi al and Uni e si y o Helsinki, Helsinki, Finland. 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Os eoa h Ca il. 2015;23:507–5. • We accep p e-submission inqui ies • Ou selec o ool helps you o ind he mos ele an jou nal • We p o ide ound he clock cus ome suppo • Con enien online submission • Tho ough pee e iew • Inclusion in PubMed and all majo indexing se ices • Maximum isibili y o you esea ch Submi you manusc ip a www.biomedcen al.com/submi Submi you nex manusc ip o BioMed Cen al and we will help you a e e y s ep: Pihlajamäki e al. BMC Musculoskele al Diso de s (2017) 18:340 Page 7 o 7