Incidence and Risk Factors for Lumbar Degenerative Disc Disease in the United States Military

Transcription

1 MILITARY MEDICINE, 176, 11:1320, 2011 Incidence nd Risk Fctors for Lumbr Degenertive Disc Disese in the United Sttes Militry MAJ Andrew J. Schoenfeld, MC USA * ; CPT Jmes H. Nelson, MC USA * ; COL Robert Burks, MC USA ; LTC Philip J. Belmont Jr., MC USA * ABSTRACT The epidemiology of lumbr degenertive disc disese (DDD) is poorly understood, nd the incidence of this disorder hs not previously been chrcterized for young, physiclly ctive popultion. This study sought to evlute the incidence of lumbr DDD, nd identify risk fctors for its development, mong individuls serving in the U.S. militry over 10-yer period. The Defense Medicl Epidemiology Dtbse ws queried for the yers using the Interntionl Clssifiction of Diseses, Ninth Revision, Clinicl Modifiction code for lumbr disc degenertion (722.52). Overll incidence ws determined nd multivrite Poisson regression nlysis ws performed to identify risk fctors mong demogrphic chrcteristics such s ge, sex, rce, militry rnk, nd brnch of service. White rce, femle sex, Army, Air Force, or Mrine service, enlisted positions within the rnks, nd ge were found to be significnt risk fctors for the development of lumbr disc degenertion. Incresed ge ppered to be one of the most importnt risk fctors, with djusted incidence rtes successively incresing for ech ge group under study. The incidence of lumbr DDD in this young, rcilly diverse, nd physiclly ctive popultion is higher thn most other degenertive conditions. INTRODUCTION Lumbr degenertive disc disese (DDD) is progressive condition tht exists long continuum of pthologic processes. From desicction of the nucleus pulposus, to nnulr tering, diffuse disc bulging, nd disc spce collpse, the degenertive process cn occur over the course of decdes, culminting in substntil debilittion. 1,2 Symptoms of DDD, including bck pin nd/or rdiculopthy, cn limit work nd productivity. Additionlly, the cost of treting this condition is especilly high, with n estimted 30 to 50 billion helth cre dollrs spent on mnging degenertive spinl processes nnully. 1 Over the course of the 20th century, medicine s understnding of DDD hs evolved considerbly. 3 Nonetheless, the etiology nd nturl history of this condition remin poorly understood. 1 3 Chllenges to the effective investigtion of DDD include the lck of stndrdized definition for the condition, s well s disprities in study popultions tht inhibit comprisons between published works. 3,4 Moreover, reserchers recognize tht DDD cn occur s nturl prt of ging, nd it my be difficult to drw morphologic distinctions between expected senile chnges within the disc nd pthologic processes. 4 6 Indeed, severl investigtions hve documented morphologiclly degenertive discs in s mny s 72% of symptomtic subjects Genetic fctors1 4,11, heredity 3,4,11, ge3 6,11 14, sex3,11,15, rce3,11, level of physicl ctivity 3,5,6,11 20, smoking 6,21, nd body * Deprtment of Orthopedic Surgery, Willim Beumont Army Medicl Center, 5005 North Piedrs Street, El Pso, TX Nvl Postgrdute School, 1 University Circle, Monterey, CA All uthors re employees of the U.S. Federl Government nd the U.S. Army. The opinions or ssertions contined herein re the privte views of the uthors nd re not to be construed s officil or reflecting the views of Willim Beumont Army Medicl Center, the Deprtment of Defense, or U.S. Government. hbitus 1,3,11,22 hve ll been proposed s potentil fctors in the development of lumbr DDD. Although some investigtions hve focused on the prevlence of this condition, s well s risks implicted in its development, the incidence of lumbr DDD hs not previously been estimted for young, highdemnd popultion. The popultion of the U.S. Armed Forces is n idel group in which to study lumbr DDD. Compred to the generl popultion, militry service members represent younger cohort with higher physicl demnds, who must mintin weight requirements, nd pss seminnul physicl fitness tests. Additionlly, ll members of the Armed Forces must pss n entry physicl, where conditions such s DDD or spinl bnormlities re screened. Individuls with pre-existing DDD would, for the most prt, be excluded from initil entry into the U.S. militry. Perhps, most importntly, in terms of epidemiologic reserch, the militry opertes on closed medicl system where ll conditions for which service members re treted re documented by Interntionl Clssifiction of Diseses, Ninth Revision, Clinicl Modifiction (ICD-9-CM) code in the medicl record. Dignoses mde t militry fcilities or in nonmilitry consulttions re cptured by the system. 23,24 Dignoses re collected from the medicl records of service members nd stored in the Defense Medicl Epidemiology Dtbse (DMED). 24 The DMED contins dt for individuls ccording to ICD-9-CM dignosis nd cn strtify ptients by sex, rce, militry rnk, brnch of service, nd ge. The dtbse cn lso be utilized to ccurtely determine the number of service members within the U.S. militry during ny given yer. The DMED hs been successfully used in the pst to investigte the incidence nd epidemiology of severl orthopedic conditions within the Americn militry popultion MILITARY MEDICINE, Vol. 176, November 2011

2 The gol of this investigtion ws to chrcterize the incidence of lumbr DDD mong ll individuls serving in the U.S. Armed Forces from using the DMED dtbse. Additionlly, this study sought to identify risk fctors for the development of DDD, including sex, rce, level of physicl ctivity, nd ge. We hypothesized tht incresed ge, mle sex, white rce, nd high-demnd occuptions (i.e., enlisted positions within the rnk structure nd Army or Mrine Corps service) would increse the risk of lumbr DDD. MATERIALS AND METHODS Following the pprovl of our institutionl Investigtionl Review Bord, the DMED ws queried for the yers using the ICD-9-CM code (Degenertion, intervertebrl disc; lumbr or lumboscrl). Dignoses of lumbr DDD were limited to those mde in the mbultory setting, first dignosis only, nd instnces where lumbr DDD ws listed s the ptient s primry issue. Counting only the first visit in which ptient ws dignosed with lumbr DDD limits dupliction for subsequent services nd visits, nd enbles clcultion of incidence. Additionlly, selecting visits where lumbr DDD ws listed s the ptient s primry issue limits the potentil for confounding, s office visits where the dignosis my hve been mde s n incidentl finding re eliminted. Sex, rce, militry rnk, brnch of service, nd ge were obtined for ll ptients identified with lumbr DDD through the DMED. Like dt for the totl number of service members within the U.S. Armed Forces serving on ctive duty in the period of interest were lso obtined from the dtbse. In this study, sex ws determined to be mle or femle. Rce clssifiction within the DMED is determined by ptient self-report. The DMED strtifies service members s white, blck, or other, where other my denote Hispnic, Asin, Pcific Islnder, or Ntive Americn/Alskn. The rce ctegories of White, Blck, nd Other were utilized in this investigtion. Militry rnk ws strtified s: Junior Enlisted (Enlisted personnel excluding noncommissioned officers), Senior Enlisted (ll noncommissioned officers), Junior Officers (2nd Lieutennt/ Ensign-Cptin/Lieutennt nd Junior Wrrnt Officers), nd Senior Officers (Mjor/Lieutennt Commnder-Lieutennt Generl/Admirl nd Senior Wrrnt Officers). Brnch of service ws clssified s Army, Nvy, Air Force, or Mrine Corps. Age ws ctegorized ccording to the system intrinsic to the DMED: Age less thn 20, 20 to 24, 25 to 29, 30 to 34, 35 to 39, nd 40 or older. Sttisticl Anlysis The incidence of lumbr DDD ws clculted s the number of cses per 1,000 person-yers, where one person-yer represents clendr yer of exposure to militry service. Incidence ws ssessed for the group s whole, s well s for the demogrphic sub-ctegories of interest. Undjusted incidence rte rtios (IRRs) were clculted using the totl number of U.S. service members within ech subctegory s the denomintor. Adjusted rte rtios nd 95% confidence intervls (CI) were clculted using Poisson regression nlysis. Adjusted rtes for ech ctegory were computed controlling for ll other fctors in the model. Risk fctors for lumbr DDD within the model were felt to be represented by sex, rce, ctivity level (militry rnk nd brnch of service), nd ge. Adjusted rte rtios for risk fctors were clculted for ll subgroups ginst referent subctegory. All sttisticl clcultions were performed using SAS softwre version 9.1 (SAS Institute, Cry, NC). RESULTS During the 10-yer period under investigtion there were 58,842 cses of lumbr DDD dignosed mong 14,071,570 militry service members. The overll, undjusted incidence rte (IR) for lumbr DDD ws 4.18 per 1,000 person-yers. The IR for women in this series ws 4.31 per 1,000 personyers, wheres it ws 4.16 per 1,000 person-yers for men (Tble I ). Femles demonstrted significntly incresed risk of lumbr DDD when compred to men 1.21 (95% CI ) ( Tble I ). The incidence of lumbr DDD mong white service members ws 4.34 per 1,000 person-yers, wheres it ws 3.84 per 1,000 person-yers for blcks, nd 3.80 per 1,000 person yers for other rce service members. White individuls were found to hve significntly incresed risk of lumbr DDD when compred to blcks, with n djusted IRR of 1.48 (95% CI ). The incidence of lumbr DDD by militry rnk ws 1.99 per 1,000 person yers for junior enlisted, 6.36 per 1,000 person-yers for senior enlisted, 3.52 per 1,000 person yers for junior officers, nd 7.49 per 1,000 person yers for senior officers. When controlling for other fctors, however, enlisted personnel were t the gretest risk of developing the condition when compred to senior level officers ( Tble I ). Compred to senior officers, junior enlisted nd senior enlisted personnel hd djusted IRRs of 1.80 (95% CI ) nd 1.68 (95% CI ), respectively. Among the four rmed services, the incidence of lumbr DDD ws 5.67 per 1,000 person yers for the Army, 3.02 per 1,000 person-yers for the Nvy, nd 4.09 nd 2.62 per 1,000 person yers for the Air Force nd Mrine, respectively. When controlling for other fctors, members of the Army, Air Force, nd Mrines were found to be t significntly greter risk for developing lumbr DDD thn those in the Nvy. The djusted IRRs for the vrious brnches of service compred to the Nvy were: 2.03 (95% CI ) for Army, 1.28 (95% CI ) for Air Force, nd 1.31 (95% CI ) for Mrine Corps. Age ws lso found to ply n importnt role in the incidence of lumbr DDD ( Tble II ). In this investigtion, the undjusted IR successively incresed for ech ge group, with individuls 40 nd over demonstrting n incidence of MILITARY MEDICINE, Vol. 176, November

3 TABLE I. Undjusted IRs nd Adjusted IRRs of Lumbr DDD Among U.S. Militry Service Members, Ctegory Number of cses Person-yers Undjusted IR Adjusted IRR (95% CI) Mle N/A Femle ( ) b Blck N/A Other ( ) c White ( ) c Junior Enlisted ( ) d Junior Officers ( ) d Senior Enlisted ( ) d Senior Officers N/A Army ( ) e Nvy N/A Air Force ( ) e Mrines ( ) e Incidence rte is per 1,000 person-yers. b Adjusted for ge, rce, rnk group, nd service. Mle ws the referent ctegory. c Adjusted for ge, sex, rnk group, nd service. Blck ws the referent ctegory. d Adjusted for ge, sex, rce, nd service. O4 O9 ws the referent ctegory. e Adjusted for ge, sex, rce, nd rnk group. Nvy ws the referent ctegory. N/A = not pplicble becuse this vrible ws used s the referent ctegory for clcultions. TABLE II. IRR of Lumbr DDD Among Service Members in the U.S. Militry, , by Age Group Age Group No. of cses Person-yers IR Adjusted IRR (CI) b < N/A ( ) ( ) ( ) ( ) ( ) Incidence rte is per 1,000 person-yers. b Adjusted for sex, service, rnk group, nd rce. The 20- to 24-yer-old group ws used s the referent ctegory. N/A = not pplicble becuse this ctegory ws used s the referent per 1,000 person-yers. Adjusted IRRs indicted n even more significnt ssocition for ge when other fctors were controlled for during the nlysis ( Tble II ). Compred to those service members ged <20, ll other ge groups were found to be t significntly incresed risk for lumbr degenertion. Those ged >40 were found to be t gretest risk, with n djusted IRR of (95% CI ). DISCUSSION Despite numerous studies tht hve investigted spects of lumbr DDD over the lst 2 decdes, little is known regrding the risk fctors, etiology, nd nturl history of this condition. Few investigtions hve been ble to determine true incidence for lumbr DDD, nd mny hve drwn contrdictory conclusions regrding risk fctors resulting from disprities in the popultions under study. For exmple, in two seprte investigtions conducted by the sme reserch tem on risks for lumbr DDD in identicl twins, smoking ws found to increse the risk of DDD in one study 21 but ws not identified s risk fctor in nother. 6 Similr discordnce hs risen in studies exmining the effect of physicl ctivity on the development of DDD s well. 15,17 20 TABLE III. Undjusted IRs for Common Musculoskeletl Conditions in U.S. Militry Service Members. Condition Undjusted IR Plntr Fsciitis Lumbr DDD 4.18 ACL Disruption Men ACL Disruption Women Shoulder Disloction Hip Arthritis Incidence rte is per 1,000 person-yers. In this investigtion, we found the incidence of lumbr DDD to be 4.18 per 1,000 person-yers. Additionlly, femle sex; white rce; enlisted rnk; Army, Air Force, nd Mrine service; nd incresing ge were found to be significnt fctors in the development of the condition. It is interesting to note tht, when compred to other common musculoskeletl disorders previously exmined mong the militry popultion, the incidence of lumbr DDD is higher thn the rtes of most other conditions, including nterior crucite ligment disruption nd cute shoulder disloction (Tble III ). Few studies hve focused on the role of sex in the development of lumbr DDD. Mny epidemiologicl investigtions, including twin studies, hve been conducted exclusively in men. Tktlo et l 12 reported tht men were t greter risk for developing lumbr degenertion thn women, while Evns et l 15 found women to be t greter risk for DDD thn men. The study published by Knym et l 16 found tht sex ws not significntly ssocited with the risk of lumbr DDD, nd some hve postulted tht the life-time risk of developing the condition is the sme between sexes, only women hve onset of the disorder 10 yers lter thn men. 3 Results presented here would seem to indicte tht, t lest in physiclly ctive popultion, women re t n elevted risk of lumbr DDD reltive to men. White service members in this study were t n incresed risk of developing lumbr DDD when compred to individuls 1322 MILITARY MEDICINE, Vol. 176, November 2011

4 listed s blck ( Tble I ). To the best of our knowledge, this investigtion is the first to exmine the incidence of lumbr DDD mong disprte rcil groups. Most prior epidemiologic studies, prticulrly twin-bsed investigtions, hve not reported results by rce or were conducted within predominntly white, or ll-white popultions. 4,6,12,19,20,21 It is interesting to note tht studies regrding plntr fsciitis 28 nd hip osteorthritis29 in militry popultions found the incidence of those degenertive conditions to be higher mong blck service members. Unfortuntely, becuse of the lck of dditionl investigtions on this topic, it is difficult to drw ny conclusions from the rcil dt presented here. Results lso indicte higher risk for lumbr DDD mong enlisted personnel nd greter incidence of the condition mong those serving in the Army, Air Force, nd Mrines. Our intention ws to hve brnch of service nd militry rnk ct s proxy for ctivity level, with enlisted individuls, nd those serving in combt rms brnches like the Army nd Mrine Corps, generlly experiencing greter levels of physicl ctivity nd higher occuptionl demnds. Numerous studies hve documented n ssocition between hevy physicl ctivity nd lumbr DDD. 3,5,6,11 20 In their study on the effects of physicl loding nd exercise on spinl pthology, Videmn et l 20 concluded tht incresed xil loding, s well s sudden torsionl nd flexion moments, were ssocited with ccelerted disc degenertion. Militry service members generlly mintin higher levels of physicl ctivity nd occuptionl demnds thn civilin counterprts. Becuse of the bsence of other studies documenting the incidence of DDD mong civilins, it is difficult to ssess the contribution of militry ctivities to the development of DDD s whole. We would expect tht enlisted individuls, who often hve more physiclly demnding jobs thn officers, would hve higher incidence of lumbr DDD. Moreover, it is interesting to note tht, despite being younger on verge, the djusted incidence of disc degenertion ws higher mong junior enlisted personnel thn senior enlisted ( Tble I ). Service in combt rms brnches, such s the Army nd Mrine Corps, ws found to predictbly increse the risk of lumbr DDD. This my be explined by the incresed physicl stress experienced in these services, such s xil loding of the spine to 70 lbs or more when crrying full bttle ger, when compred to brnches such s the Nvy nd Air Force. We cnnot explin the lower djusted incidence of documented lumbr DDD mong members of the Mrine Corps s compred to those in the Army, however. It my be tht the Mrine brnch s culture prevents individuls from seeking medicl cre. It is lso possible tht, s primrily combt rms brnch, Mrine Corps service members with bck-relted issues re unble to meet retention stndrds for their service nd re dischrged before being evluted or dignosed with DDD. Not surprisingly, ge ppered to be the most significnt risk fctor in the development of lumbr DDD in this investigtion. Adjusted IRRs, controlling for other fctors in the model, confirmed this ssocition with ll ge groups found to be t significnt risk of the condition when compred to service members ged <20. Individuls ged 40 nd over were found to hve the gretest risk, with n djusted incidence of A number of prior studies hve identified ptient ge s n importnt fctor in the development of DDD. 2,6,11 14 Videmn et l 5 reported tht mgnetic resonnce imging findings of lumbr DDD, including decresed signl intensity, loss of disc height, nd osteophyte formtion, were ssocited with incresing ptient ge. Similrly, Boos et l 4 histologiclly correlted degenertive chnges within the lumbr disc with incresed ptient ge in postmortem study. Bttié et l 3,6,11 found strong correltion between dvnced ptient ge nd disc signl intensity, disc height loss, disc bulging, nd osteophyte formtion. Cheung et l 13 confirmed n increse in lumbr DDD with dvncing ptient ge nd linked these findings to n incresed risk of bck-relted symptoms. Results presented here pper to support such correltion s well. We recognize tht this study suffers from severl limittions. Foremost, this reserch ws conducted using dtbse nd suffers from limittions inherent to such design. As result, we were unble to chrcterize symptomtology, specific level of DDD within the lumbr spine, nd the number of levels involved. Additionlly, we could not strtify ge-relted dt beyond the ctegories contined within the DMED. For exmple, ll ptients over the ge of 40 were grouped together in terms of DDD. As this is the ge group most t risk of developing lumbr DDD, 3,5,6,11,13,16,19,20,21 it would hve been helpful to further strtify this group into subpopultions. However, such strtifiction ws not possible becuse of the wy informtion is presented within the DMED. Furthermore, s BMI, smoking sttus, nd genetic mkeup were not recorded in the dtbse, we were unble to scertin the contributions of these potentilly importnt risk fctors 1 3,6,11,21,22 to lumbr disc degenertion. A further limittion of this study is tht its ccurcy is solely dependent on the qulity of dt entered into the DMED. Errors in ICD-9-CM coding, missing dt, or the inbility of physicins to ccurtely dignose lumbr DDD could dversely impct the qulity of this reserch. Although we were ble to identify n incidence of lumbr DDD using our methodology, it is possible tht some individuls with the condition were missed becuse of coding or errors in dt entry. Additionlly, our methodology did not llow us to cpture service members with lumbr DDD who did not present for medicl evlution, s well s those who my hve hd DDD before service but did not report this fct during their initil militry physicl. As result, the incidence of lumbr DDD in this popultion my ctully be underestimted. While ccepting these limittions, it is importnt to point out tht the DMED conveys severl dvntges over similr civilin-bsed systems. As dt entered into the DMED system is cross-referenced with the Defense Mnpower Dt Center, n ccurte determintion of the popultion t risk cn be mde tht is essentilly not possible with civilin-bsed records.23,25 27 The ccurcy of the DMED is lso incresed when compred to civilin dtbses s stndrdized mbultory cre records within closed helth cre system llow MILITARY MEDICINE, Vol. 176, November

5 ll ICD-9-CM dignoses (whether mde in militry or civilin tretment fcility) to be cptured in the service member s medicl record. There re lso provisions within the protocol for DMED dt collection tht ttempt to ensure consistent cquisition s well s dt vlidtion. 24 At the current time, the dt presented here represents the best vilble evidence regrding the incidence of lumbr DDD in young, highdemnd popultion. To the best of our knowledge, there re no other studies vilble in the literture to which comprisons cn be drwn. In conclusion, the incidence of lumbr DDD in this young, rcilly diverse, nd physiclly ctive popultion ws 4.18 per 1,000 person-yers. Advnced ge nd, to lesser extent, white rce, femle sex, enlisted positions within the rnk structure, nd service in the Army, Air Force, nd Mrines, ppered to influence the risk of developing this condition. Undoubtedly, more work must be performed in the future, including lrge prospective ptient cohorts, before risk fctors for lumbr DDD cn be fully quntified. It is hoped tht the results presented here my serve s bseline to which future investigtions my be compred. Additionlly, our findings cn be used s mens by which high-risk groups within physiclly ctive popultion re identified to implement protective mesures or disese-specific screening. REFERENCES 1. Dickmn RD, Zigler JE : Discogenic bck pin. In: Orthopedic Knowledge Updte: Spine 3, pp Edited by Spivk JM, Connolly PJ. Rosemont, IL, North Americn Spine Society, Burden of Musculoskeletl Diseses in the United Sttes Project : Spine: low bck nd neck pin. In: The Burden of Musculoskeletl Disese in the United Sttes: Prevlence, Societl nd Economic Cost. Avilble t htm ; ccessed June 22, Bttié MC, Videmn T : Lumbr disc degenertion: epidemiology nd genetics. 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