Eur Spine J DOI 10.1007/s00586-015-4118-4
ORIGINAL ARTICLE
Risks of permanent disability in low back pain patients associated with different job positions: a 5-year follow-up study Thomas Maribo1,2,5 • Berit Schiøttz-Christensen3 • Chris Jensen4 • Lone Donbæk Jensen2
Received: 4 May 2015 / Revised: 8 July 2015 / Accepted: 8 July 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Purpose To present a systematic review on ICF used in the Nordic countries from 2001 to 2013, describing and quantifying the development in utilization of ICF, and describe the extent to which the different components of the ICF have been used. Method A search was conducted in EMBASE, MEDLINE and PsycInfo. Papers from Nordic countries were included if ICF was mentioned in title or abstract. Papers were assigned to one of eight categories covering the wide rehabilitation area; furthermore, area of focus was assigned. Use of ICF components and intervention were coded in papers categorized as ‘Clinical and/or rehabilitation contexts’ or ‘Non clinical contexts’. Results 170 papers were included, of these 99 papers were from the categories ‘Clinical and/or rehabilitation contexts’ or ‘Non clinical contexts’. 42 % of the 170 included papers were published in the period 2011–2013.
& Thomas Maribo [email protected] 1
Rehabilitation Center Marselisborg, Department of Public Health, Section of Social Medicine and Rehabilitation, Aarhus University, Bygning 1B, P. P. Ørumsgade 11, 8000 Aarhus C, Denmark
2
Public Health and Quality Improvement, Central Denmark Region, Aarhus, Denmark
3
Spine Centre of Southern Denmark, Hospital Lillebaelt, Middelfart, Denmark
4
National Centre for Occupational Rehabilitation, Rauland, Norway
5
Department of Occupational Medicine, Danish Ramazzini Center, Aarhus University Hospital, Aarhus, Denmark
Conclusions There was an increase in ICF-relevant papers from 2001 to 2013, especially in the categories ‘clinical and/or rehabilitation contexts’ and ‘non clinical contexts’. The most represented focus areas were neurology, musculoskeletal and work-related areas. All five or at least four ICF components were mentioned in the results or discussions in most papers; activity was most frequently mentioned. Keywords Disability Low back pain Job Risk Register-based evaluation
Introduction Low back pain (LBP) is a highly prevalent and costly health problem [1, 25]. Most incidences of LBP are selflimiting, but about 10 % develop chronic pain [6, 7]. Despite its benign course, LBP is often associated with poor vocational prognosis [4, 13, 18], and LBP is the most common reason for work absence among younger people [9]. The probability of resuming work diminishes with time spent on sick leave [16, 24], and evidence suggest that interventions should focus on preventing LBP becoming chronic and on LBP disability rather than on preventing the onset of LBP [5]. Permanent work loss with subsequent disability pension among people with LBP is a serious event for the individual and expensive for society, where interventions focusing on recovery are needed [4]. Each year between 2001 and 2010, around 0.6 % of the Danish population aged 15–66 years were granted a disability pension (www. ast.dk/dataportal), or a flex job [2] which like disability pension is a health-dependent benefit offered in cases of permanently limited work capacity.
123
Eur Spine J
In Denmark, LBP patients are treated according to the guidelines, living only a minor group to be referred to specialized evaluation [20]. Consequently, patients evaluated at hospitals tend to have an extended current pain episode with persistent pain or symptoms of nerve root damage with need of immediate surgery. About 10 % of patients with LBP are referred to specialist evaluation and treatment in the secondary health care sector [15]. The aim of this study was to provide prognostic information on vocational outcome in a large cohort of LBP patients treated at a Danish University Hospital with a specific focus on predictors of permanent disability benefits. This information could help identify high-risk patients who may benefit from vocational counselling during treatment in the secondary healthcare sector.
Methods This is a cohort study with a register-based evaluation on public transfer payments (unemployment benefit, sickness benefit, permanent disability benefits and voluntary early retirement) to LBP patients referred to specialized evaluation in the secondary healthcare sector. The follow-up period was 5 years. Study population The study included all patients from the University Hospital in Denmark’s second-largest city with a primary diagnosis of back pain, in the period 1 January 2001 to 31 December 2005. Patients outside the hospital’s catchments
area were excluded as such patients are usually referred for highly specialized treatment. Patients with prior contact to the hospital due to LBP during the preceding 4 years were excluded. Thus, a patient became a case upon first contact and was counted only once. Patients with spondyloarthropathies and cervical diagnoses, patients younger than 18, older than 65, and patients not living in Denmark were excluded (Fig. 1). Data sources The cohort was identified by linking data from the Danish National Hospital Register [3] with person-specific data from the Danish Register for Evaluation of Marginalisation (DREAM) [11] from 1998 to 2010 (both years inclusive) using Danish civil registration numbers. In Denmark all inand outpatient contacts with public hospitals are registered in the Danish National Hospital Register, we obtained information on discharge diagnosis and date of contact; in patients with more than one diagnosis the primary discharge diagnosis was used. In this study, information on public transfer payments was obtained from DREAM, which contains weekly information on public transfer payments at an individual level [10, 13]. As regarding sick leave benefits, the threshold to enter DREAM between 2000 and 2007 was sick leave for more than two consecutive weeks, because the employer paid the first two consecutive weeks of sick leave. From the third consecutive week of sick leave, the employee was supported by tax-paid sick leave benefits registered in DREAM. DREAM includes data on all Danish citizens
Patients with a primary discharge diagnosis of back pain, i.e. ICD-10 codes: M43.0 – M54.9 and M96 between January 2001 and December 2005 (inclusive) (n= 12,583)
• • • • • • •
Spondyloarthropathies and cervical diagnosis (ICD-10 codes M43.3, M 43.4, M 43.6, M45.9 – M46.9, M47.8C, M 48.1 – M50.9, M53.0 – M53.2, M54.0 and M54.2) (n= 2,474) Not resident in the local area (n= 624) Prior contact to the Hospital due to LBP during the preceding 4 years (n= 164) Younger than 18 years (n= 221) Older than 64 years (n= 1,824) Not Danish residents (n= 39) Receiving permanent transfer payment* in the week of hospital contact (n= 1,292)
Included in the study (n= 5,945)
Fig. 1 Selection of the study population from a total of 12,583 patients diagnosed with back pain in the period 2001–2005 at a Danish University Hospital. *Permanent transfer payment including
123
disability pension, voluntary early retirement, and flex job which are economically supported jobs offered to persons with limited work capacity
Eur Spine J
who have received welfare benefits since 1991. Each person is registered once a week with a code indicating the type of welfare benefit received. DREAM has 100 % coverage of those granted public transfer payments in Denmark from 2000 [10]. Outcome measure and independent variables The main outcome measure—permanent disability benefits including disability pension and flex job was as the others measures of vocational status—obtained from DREAM register and recoded into groups: (1) employment, (2) unemployment benefit, (3) sickness benefit including other non-permanent transfer payments for vocational rehabilitation or social assistance, (4) permanent disability benefits including disability pension and flex job, (5) old-age pension including voluntary early retirement and (6) emigration and death. You can only receive one transfer income at a time. During the study period sickness benefit was restricted to 1 year, whereas it was possible to receive unemployment benefit for up to 4 years which have the consequence that person who have used their 1 year of sick leave payment in some situations change to unemployment benefit. Thus, estimating the number of sick leave weeks while neglecting other types of transfer payments would underestimate weak vocational orientation. The independent variable was job position at time of diagnosis; co-variables were gender, age, diagnosis, surgery, weak vocational orientation in the years before hospital contact and ethnicity. Job position was assessed on the basis of information from the time of diagnosis on the patient’s most recent membership of an unemployment insurance fund. Based on the International Standard Classification of Occupations patients were recoded into six groups: (1) blue-collar, (2) office (clerks and other skilled office workers), (3) teaching and nursing, (4) managers and academics, (5) self-employed and (6) workers with unknown job position. The group ‘‘workers with unknown job position’’ included persons with membership of an unemployment fund which does not cover a specific job position group (n = 571), persons who were not members of an unemployment insurance fund (n = 287), and persons who were not in the DREAM register because they had not received any transfer payments in the years of activity of the register (n = 404). Low back diagnoses (ICD-10 codes) were recoded into four diagnostic groups (1) non-specific LBP (M43.0; M43.2; M43.5; M43.8; M43.9; M47.0–M47.2; M47.8; M47.9; M53.3; M53.8; M53.9; M54.1; M54.3; M54.5; M54.6; M54.8; M54.9; M99.1), (2) LBP with radiculopathies (M51.0; M51.1; M51.2; M51.3; M51.9; M54.4;
M96.1), (3) spinal stenosis (M48.0, M99.3–M99.6) and (4) spondylolisthesis (M43.1). Treatment was described as non-surgery vs. surgery the first year after diagnosis. The severity of surgery was described as simple discectomy vs. lumbar fusion, the latter including patients with both discectomy and lumbar fusion. Weak vocational orientation was defined as less than 40 weeks of employment within year two or three before hospital contact, established by the weekly status from the DREAM database of any type of unemployment benefit or sickness benefit [13]. Data on ethnicity were obtained from the DREAM database. Ethics The study was authorized by the Danish Data Protection Agency. According to Danish law, register-based studies do not require approval by ethical and scientific committees, nor informed consent. Statistical analysis After linking data from the two registers, the hospital and vocational record for each person was established. The hazard ratio (HR) of permanent disability benefits following hospital contact for LBP was estimated by Cox proportional hazard models. Follow-up began in the week after diagnosis and ended in the week of permanent disability benefits, old-age pension, or death, or in the week 5 years after hospital contact, whichever came first. Death and old-age pension were considered as competing risks. HR’s were calculated for the following variables: job position, using managers and academics as reference; gender; age groups; surgery; weak vocational orientation; ethnicity other than Danish; and year of inclusion. Crude and mutually adjusted HR were calculated, and 95 % CIs presented. The proportional HR assumption was evaluated by assessing log-minus-log survival curves in the unadjusted model as well as in the fully adjusted model. Cumulated incidence curves for the full follow-up period were stratified according to job position. Statistical analysis was performed using STATA statistical software, version 13.1.
Results From 1 January 2001 to 31 December 2005, 12,583 LBP patients were discharged from Aarhus University Hospital. A flow chart addressing the study population is shown in Fig. 1, presenting the 5945 patients who fulfilled the
123
Eur Spine J
inclusion criteria, 10.4 % inpatients and 89.6 % outpatients. Men were overrepresented in the study population. A marked difference was observed in gender segregation between the job position groups with an excess of men among managers, academics and self-employed and a higher representation of women among skilled office workers and the teaching and nursing group (Table 1). The extent of weak vocational orientation was substantially different between the job position groups during all 3 years before hospital contact (Table 1). The proportion was
approximately two to three times higher among blue-collar workers and workers with unknown job positions than among managers and academics. Risk of permanent disability benefits 5 years after the week of diagnosis is presented in Table 2 with incidence, crude and mutually adjusted HR. The risk was associated with job position, weak vocational orientation status before diagnosis, age, surgery, female gender, and ethnicity other than Danish. Year of inclusion was not associated with the outcome measure.
Table 1 Characteristics of the study population at diagnosis in total and according to latest job position
N (% of the study population)
Total population
Managers and academics
Skilled office workers
Teaching and nursing
Selfemployed
Blue-collar
Unknown job position
5945 (100 %)
642 (10.80 %)
779 (13.10 %)
893 (15.02 %)
455 (7.65 %)
1914 (32.09 %)
1262 (21.21 %)
Gender (%) Male
53.3
69.8
40.8
29.5
73.4
60.9
50.8
Female
46.7
30.2
59.2
70.6
26.6
39.1
49.2
18–30
13.7
14.6
14.9
11.0
5.5
10.2
19.7
31–40
26.3
26.8
26.6
24.6
24.0
24.4
30.7
41–50
30.0
27.1
27.7
34.5
31.2
32.0
26.2
51–64
30.7
31.5
30.8
29.9
39.3
33.5
23.4
1st year before hospital contact 2nd year before hospital contact
37.5
14.5
33.1
24.6
34.3
44.9
50.8
27.5
11.5
26.6
16.1
23.3
29.3
42.8
3rd year before hospital contact
24.9
9.0
21.6
15.6
18.7
27.6
40.7
Yes
87.6
95.5
93.8
95.7
88.6
89.0
70.8
No
12.4
4.5
6.2
4.3
11.4
11.
29.2
39.1 52.6
31.6 59.8
40.3 50.7
35.3 57.1
33.0 55.6
41.6 50.5
42.9 48.7
Age group (%)
Weak vocational orientation* (%)
Danish ethnicity (%)
Low back diagnosis (%) Non-specific LBP LBP with radiculopathies Spinal stenosis
4.6
4.5
4.8
3.2
6.2
5.1
4.4
Spondylolisthesis
3.9
4.0
4.2
4.6
5.3
2.8
4.0
Off. work sick for more than 6 weeks (%) Yes
44.7
29.6
53.8
51.9
44.2
59.1
72.7
No
55.3
70.4
46.2
48.2
55.8
40.9
27.3
Surgery (%) No surgery
77.6
75.2
76.1
77.0
76.7
77.4
80.9
Discectomy
17.5
20.4
18.1
18.1
18.5
17.5
14.4
4.9
4.4
5.3
4.8
4.8
5.2
4.7
Lumbar fusion n = 5945
* Less than 40 weeks of employment
123
Eur Spine J Table 2 Cumulated incidence and hazard ratio (HR) of permanent disability benefits among low back pain patients 5 years after hospital contact Variables
No.
Permanent disability benefits* (%)
HR (95 % CI)
Adjusted HR (95 % CI)
P
Male
3169
22.72
1
1
\0.001
Female
2776
27.70
1.22 (1.10; 1.34)
1.24 (1.12; 1.37)
Gender
Age group \0.001
18–30
777
12.10
1
1
31–40
1562
23.11
1.97 (1.58; 2.44)
1.89 (1.52; 2.35)
41–50 51–64
1782 1824
31.31 26.10
2.77 (2.25; 3.42) 3.00 (2.43; 3.71)
2.81 (2.28; 3.47) 3.47 (2.81; 4.30)
Job position at time of diagnosis 6.07
\0.001
Managers and academics
642
1
1
Clerks and skilled office workers
779
22.8
3.66 (2.65; 5.06)
3.05 (2.20; 4.22)
Teaching and nursing
893
19.6
3.22 (2.34; 4.45)
2.85 (2.06; 3.94)
Self-employed
455
17.80
2.97 (2.08; 4.24)
2.50 (1.75; 3.57)
Blue-collar workers
1914
35.03
6.48 (4.81; 8.73)
5.35 (3.97; 7.22)
Unknown job position
1262
27.42
4.59 (3.38; 6.24)
3.45 (2.53; 4.71)
Weak vocational orientation 2nd year before hospital contact \0.001
No
4313
19.01
1
1
Yes
1632
40.99
2.52 (2.29; 2.78)
2.44 (2.19; 2.71)
Surgery \0.001
No surgery
4615
23.77
1
1
Discectomy etc
1038
25.72
1.05 (0.93; 1.20)
1.23 (1.08; 1.40)
Lumbar fusion Danish ethnicity
292
42.81
2.01 (1.68; 2.40)
1.89 (1.58; 2.27)
Yes
5216
23.29
1
1
No
729
37.59
1.60 (1.41; 1.82)
1.21 (1.05; 1.39)
0.009
n = 5945 Adjusted hazard ratio adjustment for all variables in table and year of diagnosis, 95 % CI 95 % confidence of interval * 5 years after hospital contact
Table 3 Distribution in employment, unemployment benefit, permanent disability benefits, sickness benefit, old-age pension, emigration and dead, in the week of hospital contact and 1, 2, 3, 4 and 5 years after hospital contact due to low back pain In the week of hospital contact
1 Year after hospital contact
2 Years after hospital contact
3 Years after hospital contact
4 Years after hospital contact
5 Years after hospital contact
No. public transfer payments
2807 (47.2 %)
3639 (61.2 %)
3656 (61.5 %)
3520 (59.2 %)
3386 (57.0 %)
3187 (53.6 %)
Unemployment benefit
749 (12.6 %)
768 (12.9 %)
701 (11.8 %)
576 (9.7 %)
424 (7.1 %)
375 (6.3 %)
Permanent disability benefits
0
348 (5.9 %)
834 (14.0 %)
1134 (19.1 %)
1350 (22.7 %)
1489 (25.1 %)
Sickness benefit
2389 (40.2 %)
1078 (18.1 %)
510 (8.6 %)
360 (6.1 %)
312 (5.3 %)
282 (4.7 %)
Old-age pension and voluntary early retirement Emigrated
0
69 (1.6 %)
173 (2.9 %)
259 (4.4 %)
356 (6.0 %)
471 (7.9 %)
0
20 (0.3 %)
31 (0.5 %)
35 (0.6 %)
40 (0.7 %)
46 (0.8 %)
Dead
0
23 (0.4 %)
40 (0.7 %)
61 (1.0 %)
77 (1.3 %)
95 (1.6 %)
Total
5945
5945
5945
5945
5945
5945
123
Eur Spine J
Fig. 2 Distribution of permanent disability benefits, unemployment benefit, sickness benefit, employment, and other every week in the 3 years before and 5 years after hospital contact due to LBP. The group other includes old-age pension, voluntary early retirement, emigration and dead. The vertical line indicates time of hospital diagnosis with LBP
Table 3 presents the distribution of the main vocational status groups—employment, unemployment benefit, permanent disability benefits, sickness benefit, old-age pension, emigration and dead—within the week of hospital contact and the following 5 years. Figure 2 shows the development week-by-week 3 years before until 5 years after hospital contact due to LBP. There was a positive development in employment between the first and second year after diagnosis, and the position was kept through the second year. During the years 3–5, there was a negative development in employment, and after 5 years only 53 % were employed and 26 % received permanent disability benefits. Cumulative incidence curves of permanent disability benefits with old-age pension and death as competing risk by job position are shown in Fig. 3. The risk of permanent disability benefits was considerably higher in blue-collar workers [adjusted HR, 5.35 (95 % CI 3.97–7.22)].
Discussion Data from two national registers offered possibilities of identifying subpopulations of LBP patients at high risk of requiring permanent disability benefit and poor vocational prognosis. The present study reports findings from data representing virtually complete registers on 5945 LBP patients from the secondary healthcare sector, merging the population with data on vocational status before and after the LBP diagnosis. A pronounced difference in the risk of requiring permanent disability benefits is evident between
123
Fig. 3 Cumulative incidence of permanent disability benefits in LBP patients. Old-age pension and death were considered as competing risk. Data were stratified according to job position (n = 5945)
various job positions, with an adjusted HR of 5.35 for bluecollar workers compared to managers and academics. The percentage of employed LBP patients seems quite stable just 1 year after hospital contact, the migration to the group of patients on permanent disability benefit reaches a plateau at about, whereas 14 % of the patients were granted permanent disability benefit during the first 2 years after hospital contact; the exception is blue-collar workers and patients with unknown job position, where this migration continues. The strengths of this study were the longitudinal study design with a follow-up time of 5 years, the large size of the study population, and well-defined outcome measures. The registers are thought to be virtually complete because of the financial incentive for both public and private employers to report sick leave and the compulsory reporting from public hospitals to the Danish National Patient Register. The DREAM register has been shown to be feasible for register-based follow-up on social and economic consequences of disease [19]. The unique characteristics of the DREAM database offers valid week-byweek data on disability benefits and sick leave spells of at least 2 weeks, unemployment and social security, in addition to information on membership of an unemployment insurance fund [11, 19]. The risk factors found in this study are consistent with other authors reporting associations between work absence due to LBP and older age, ethnicity, lower level of education and poor vocational orientation [8, 9, 12, 22]. The main limitation of the present study was the lack of information on severity of symptoms and other clinical data apart from diagnosis and back operation. Due to lack of clinical data, the present study did not allow us to
Eur Spine J
distinguish between semi-acute episodes of LBP and cases where the symptoms had a prolonged course prior to hospital visit; all factors that could have influenced the vocational outcome. Most of the patients (89.6 %) were outpatients seen 2–10 weeks after referral. In the presented cohort, inpatient status was not a statistically significant risk factor, and including this variable in the multivariable model only changed the HR marginally. Although diagnostic misclassification cannot be ruled out, we used the primary discharge diagnosis which should represent the most important diagnosis characterizing the episode. The precision of the different ICD-10 codes in LBP is, however, a matter of debate. A review describes precise diagnosis in LBP patients as elusive and often problematic [17]. To the best of our knowledge, the patients in this study suffer from LBP—the question is just the validity of the diagnostic groups. In order not to bias results we chose to replace ‘‘diagnostic group’’ with ‘‘operation’’ in the model. The operation code is verified several times, and thereby more valid [17]. A large majority of patients (77.6 %) received non-operative interventions. In Denmark, such interventions are delivered in the primary sector and thus multi faceted and not traceable in the national registers. Another limitation was that information on job position was unavailable for 21.2 % of the population. This group is a mixed group of people with no membership of an unemployment insurance fund due to either (1) very weak connection to the labour market, preventing membership, or (2) great confidence in their own employment and employability. Thus, the group with unknown job position was a priori expected to be rather inhomogeneous. Excluding the group with unknown job position from the analysis only marginally changed the risk estimates. Using data from registers leave us no possibility to check for confounding factors between job and disability due to things at patient’s individual level i.e. psychosocial factors, vocational environments or other things related to the specific job. LBP may not be the distinct reason for permanent disability benefit in all patients in the cohort, but data on the cause of disability benefit are not available. After 1 year, we found 6.3 % on permanent disability benefit. Some of these patients may have been en route to disability benefit before the diagnosis. It is not possible to determine the number of such patients, but the result might be overestimated. Subsequent analysis, where patients on sickness benefit for more than half a year at the time of diagnosis were excluded and did not change the results markedly. There is no information available on the optimal length of such a wash-out period but as our data suggest it will possibly be dependent of socio-economic factors, and as it
might introduce more severe bias no further attempts were made. Of the population 1489 (25.1 %) ended up on permanent disability benefits after 5 years. The group on permanent disability benefits comprises persons on disability pension (n = 884), and flex job (n = 605). In an age-matched Danish population, there is a 2.33 % risk of disability pension in 5 years [21]. If the LBP population had the same 5-year risk of disability pension, it would result in 139 persons on disability pension, leaving a surplus of 745 LBP patients on disability pension in the present study. It is not possible to compare flex jobs in the time period, but the same pattern is to be expected [2]. The investigation included all specialized departments seeing LBP patients at the hospital, which excluded selection bias caused by general practitioners’ preference for referring to certain departments. Denmark has a public and free healthcare system, which minimizes socio-economic differences in access to care. Some patients were seen at private clinics without contact to a public hospital. Both public hospitals and private clinics are free for LBP patients referred from GP’s, but no information exists on differences between LBP patients treated at public hospitals and private clinics. In a previous study including LBP patients, we found no difference in severity of LBP between public hospitals and private clinics [14]. A recent review examined prognostic factors for return to work in chronic non-specific LBP patients [23], they stated that most return-to-work studies had reduced validity due to small sample size and self-reported sick leave absence. The review found little evidence as to which prognostic factors are of value in chronic non-specific LBP patients [23]. In conclusion, we found that LBP patients have a poor vocational prognosis; one in four (25.1 %) ended up on permanent disability benefit after 5 years. Different job positions marked a difference in risk; with blue-collar workers at high risk compared to managers and academics. In secondary, health care clinicians should be aware of the poor vocational prognosis and consider interventions to prevent work disability in addition to specific health care treatment. Emphasis should be placed on blue-collar workers and patients with poor vocational orientation before LBP diagnosis. Compliance with ethical standards Conflict of interest of interest.
The authors declare that they have no conflict
References 1. Airaksinen O, Brox JI, Cedraschi C, Hildebrandt J, KlaberMoffett J, Kovacs F, Mannion AF, Reis S, Staal JB, Ursin H, Zanoli G (2006) European guidelines for the management of
123
Eur Spine J
2.
3.
4. 5.
6.
7.
8.
9.
10. 11.
12.
chronic nonspecific low back pain. Eur Spine J 15(Suppl 2):S192–S300 Andersen IH (2008) Fewer receive disability pension and flexjob, in Danish. Ugebrevet A4 2008 43:21–23. http://www.ugeb reveta4.dk/faerre-faar-foertidspension-og-fleksjob_18679.aspx Andersen TF, Madsen M, Jorgensen J, Mellemkjoer L, Olsen JH (1999) The Danish National Hospital Register. A valuable source of data for modern health sciences. Dan Med Bull 46:263–268 Balague F, Mannion AF, Pellise F, Cedraschi C (2012) Nonspecific low back pain. Lancet 379:482–491 Burton AK, Balague F, Cardon G, Eriksen HR, Henrotin Y, Lahad A, Leclerc A, Muller G, van der Beek AJ (2005) How to prevent low back pain. Best Pract Res Clin Rheumatol 19:541–555 Burton AK, Balague F, Cardon G, Eriksen HR, Henrotin Y, Lahad A, Leclerc A, Muller G, van der Beek AJ (2006) European guidelines for prevention in low back pain: november 2004. Eur Spine J 15(Suppl 2):S136–S168 Carey TS, Evans AT, Hadler NM, Lieberman G, Kalsbeek WD, Jackman AM, Fryer JG, McNutt RA (1996) Acute severe low back pain. A population-based study of prevalence and careseeking. Spine (Phila Pa 1976) 21:339–344 Coggon D, Ntani G, Palmer KT, Felli VE, Harari R, Barrero LH, Felknor SA, Gimeno D, Cattrell A, Serra C, Bonzini M, Solidaki E, Merisalu E, Habib RR, Sadeghian F, Masood KM, Warnakulasuriya SS, Matsudaira K, Nyantumbu B, Sim MR, Harcombe H, Cox K, Marziale MH, Sarquis LM, Harari F, Freire R, Harari N, Monroy MV, Quintana LA, Rojas M, Salazar Vega EJ, Harris EC, Vargas-Prada S, Martinez JM, Delclos G, Benavides FG, Carugno M, Ferrario MM, Pesatori AC, Chatzi L, Bitsios P, Kogevinas M, Oha K, Sirk T, Sadeghian A, Peiris-John RJ, Sathiakumar N, Wickremasinghe AR, Yoshimura N, Kelsall HL, Hoe VC, Urquhart DM, Derrett S, McBride D, Herbison P, Gray A (2013) Disabling musculoskeletal pain in working populations: is it the job, the person, or the culture? Pain 154:856–863 Fourney DR, Andersson G, Arnold PM, Dettori J, Cahana A, Fehlings MG, Norvell D, Samartzis D, Chapman JR (2011) Chronic low back pain: a heterogeneous condition with challenges for an evidence-based approach. Spine (Phila Pa 1976) 36:S1–S9 Hedegaard Rasmussen J (2012) DREAM Database. The National Labor Market Authority, Ministry of Employment. Version 28 Hjollund NH, Larsen FB, Andersen JH (2007) Register-based follow-up of social benefits and other transfer payments: accuracy and degree of completeness in a Danish interdepartmental administrative database compared with a population-based survey. Scand J Public Health 35:497–502 Ijzelenberg W, Burdorf A (2005) Risk factors for musculoskeletal symptoms and ensuing health care use and sick leave. Spine (Phila Pa 1976) 30:1550–1556
123
13. Jensen LD, Frost P, Schiotz-Christensen B, Maribo T, Christensen MV, Svendsen W (2011) Predictors of vocational prognosis after herniated lumbar disc—a two year follow up study of 2039 patients diagnosed at hospital. Spine (Phila Pa 1976) 36:E791–E797 14. Jensen LD, Maribo T, Schiottz-Christensen B, Madsen FH, Gonge B, Christensen M, Frost P (2012) Counselling low-backpain patients in secondary healthcare: a randomised trial addressing experienced workplace barriers and physical activity. Occup Environ Med 69:21–28 15. Løvschall C, Bech M, Rasmussen C, Petersen T, Hartvigsen J, Jensen C, Douw K (2010) Transdiciplinary and cross-sectorial intervention in low back pain patients—a health technology assessment in Danish. Danish Health and Medicines Authority, Copenhagen 16. Lund T, Kivimaki M, Labriola M, Villadsen E, Christensen KB (2008) Using administrative sickness absence data as a marker of future disability pension: the prospective DREAM study of Danish private sector employees. Occup Environ Med 65:28–31 17. Manchikanti L, Derby R, Wolfer L, Singh V, Datta S, Hirsch JA (2009) Evidence-based medicine, systematic reviews, and guidelines in interventional pain management part 7: systematic reviews and meta-analyses of diagnostic accuracy studies. Pain Physician 12:929–963 18. McIntosh G, Frank J, Hogg-Johnson S, Bombardier C, Hall H (2000) Prognostic factors for time receiving workers’ compensation benefits in a cohort of patients with low back pain. Spine (Phila Pa 1976) 25:147–157 19. Stapelfeldt CM, Jensen C, Andersen NT, Fleten N, Nielsen CV (2012) Validation of sick leave measures: self-reported sick leave and sickness benefit data from a Danish national register compared to multiple workplace-registered sick leave spells in a Danish municipality. BMC Public Health 12:661 20. Statens Institute for MT (1999) Low-back pain: frequency, management and prevention from an HTA perspective, in Danish. Danish Health and Medicines Authority, Copenhagen 21. Statistics Denmark (2013) StatBank Denmark 22. Svendsen SW, Frost P, Jensen LD (2012) Time trends in surgery for non-traumatic shoulder disorders and postoperative risk of permanent work disability: a nationwide cohort study. Scand J Rheumatol 41:59–65 23. Verkerk K, Luijsterburg PA, Miedema HS, Pool-Goudzwaard A, Koes BW (2012) Prognostic factors for recovery in chronic nonspecific low back pain: a systematic review. Phys Ther 92:1093–1108 24. Waddell G, Burton AK, Kendall NAS (2008) Vocational rehabilitation: what works, for whom, and when?, London 25. Walker BF (2000) The prevalence of low back pain: a systematic review of the literature from 1966 to 1998. J Spinal Disord 13:205–217
ORIGINAL ARTICLE
Risks of permanent disability in low back pain patients associated with different job positions: a 5-year follow-up study Thomas Maribo1,2,5 • Berit Schiøttz-Christensen3 • Chris Jensen4 • Lone Donbæk Jensen2
Received: 4 May 2015 / Revised: 8 July 2015 / Accepted: 8 July 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Purpose To present a systematic review on ICF used in the Nordic countries from 2001 to 2013, describing and quantifying the development in utilization of ICF, and describe the extent to which the different components of the ICF have been used. Method A search was conducted in EMBASE, MEDLINE and PsycInfo. Papers from Nordic countries were included if ICF was mentioned in title or abstract. Papers were assigned to one of eight categories covering the wide rehabilitation area; furthermore, area of focus was assigned. Use of ICF components and intervention were coded in papers categorized as ‘Clinical and/or rehabilitation contexts’ or ‘Non clinical contexts’. Results 170 papers were included, of these 99 papers were from the categories ‘Clinical and/or rehabilitation contexts’ or ‘Non clinical contexts’. 42 % of the 170 included papers were published in the period 2011–2013.
& Thomas Maribo [email protected] 1
Rehabilitation Center Marselisborg, Department of Public Health, Section of Social Medicine and Rehabilitation, Aarhus University, Bygning 1B, P. P. Ørumsgade 11, 8000 Aarhus C, Denmark
2
Public Health and Quality Improvement, Central Denmark Region, Aarhus, Denmark
3
Spine Centre of Southern Denmark, Hospital Lillebaelt, Middelfart, Denmark
4
National Centre for Occupational Rehabilitation, Rauland, Norway
5
Department of Occupational Medicine, Danish Ramazzini Center, Aarhus University Hospital, Aarhus, Denmark
Conclusions There was an increase in ICF-relevant papers from 2001 to 2013, especially in the categories ‘clinical and/or rehabilitation contexts’ and ‘non clinical contexts’. The most represented focus areas were neurology, musculoskeletal and work-related areas. All five or at least four ICF components were mentioned in the results or discussions in most papers; activity was most frequently mentioned. Keywords Disability Low back pain Job Risk Register-based evaluation
Introduction Low back pain (LBP) is a highly prevalent and costly health problem [1, 25]. Most incidences of LBP are selflimiting, but about 10 % develop chronic pain [6, 7]. Despite its benign course, LBP is often associated with poor vocational prognosis [4, 13, 18], and LBP is the most common reason for work absence among younger people [9]. The probability of resuming work diminishes with time spent on sick leave [16, 24], and evidence suggest that interventions should focus on preventing LBP becoming chronic and on LBP disability rather than on preventing the onset of LBP [5]. Permanent work loss with subsequent disability pension among people with LBP is a serious event for the individual and expensive for society, where interventions focusing on recovery are needed [4]. Each year between 2001 and 2010, around 0.6 % of the Danish population aged 15–66 years were granted a disability pension (www. ast.dk/dataportal), or a flex job [2] which like disability pension is a health-dependent benefit offered in cases of permanently limited work capacity.
123
Eur Spine J
In Denmark, LBP patients are treated according to the guidelines, living only a minor group to be referred to specialized evaluation [20]. Consequently, patients evaluated at hospitals tend to have an extended current pain episode with persistent pain or symptoms of nerve root damage with need of immediate surgery. About 10 % of patients with LBP are referred to specialist evaluation and treatment in the secondary health care sector [15]. The aim of this study was to provide prognostic information on vocational outcome in a large cohort of LBP patients treated at a Danish University Hospital with a specific focus on predictors of permanent disability benefits. This information could help identify high-risk patients who may benefit from vocational counselling during treatment in the secondary healthcare sector.
Methods This is a cohort study with a register-based evaluation on public transfer payments (unemployment benefit, sickness benefit, permanent disability benefits and voluntary early retirement) to LBP patients referred to specialized evaluation in the secondary healthcare sector. The follow-up period was 5 years. Study population The study included all patients from the University Hospital in Denmark’s second-largest city with a primary diagnosis of back pain, in the period 1 January 2001 to 31 December 2005. Patients outside the hospital’s catchments
area were excluded as such patients are usually referred for highly specialized treatment. Patients with prior contact to the hospital due to LBP during the preceding 4 years were excluded. Thus, a patient became a case upon first contact and was counted only once. Patients with spondyloarthropathies and cervical diagnoses, patients younger than 18, older than 65, and patients not living in Denmark were excluded (Fig. 1). Data sources The cohort was identified by linking data from the Danish National Hospital Register [3] with person-specific data from the Danish Register for Evaluation of Marginalisation (DREAM) [11] from 1998 to 2010 (both years inclusive) using Danish civil registration numbers. In Denmark all inand outpatient contacts with public hospitals are registered in the Danish National Hospital Register, we obtained information on discharge diagnosis and date of contact; in patients with more than one diagnosis the primary discharge diagnosis was used. In this study, information on public transfer payments was obtained from DREAM, which contains weekly information on public transfer payments at an individual level [10, 13]. As regarding sick leave benefits, the threshold to enter DREAM between 2000 and 2007 was sick leave for more than two consecutive weeks, because the employer paid the first two consecutive weeks of sick leave. From the third consecutive week of sick leave, the employee was supported by tax-paid sick leave benefits registered in DREAM. DREAM includes data on all Danish citizens
Patients with a primary discharge diagnosis of back pain, i.e. ICD-10 codes: M43.0 – M54.9 and M96 between January 2001 and December 2005 (inclusive) (n= 12,583)
• • • • • • •
Spondyloarthropathies and cervical diagnosis (ICD-10 codes M43.3, M 43.4, M 43.6, M45.9 – M46.9, M47.8C, M 48.1 – M50.9, M53.0 – M53.2, M54.0 and M54.2) (n= 2,474) Not resident in the local area (n= 624) Prior contact to the Hospital due to LBP during the preceding 4 years (n= 164) Younger than 18 years (n= 221) Older than 64 years (n= 1,824) Not Danish residents (n= 39) Receiving permanent transfer payment* in the week of hospital contact (n= 1,292)
Included in the study (n= 5,945)
Fig. 1 Selection of the study population from a total of 12,583 patients diagnosed with back pain in the period 2001–2005 at a Danish University Hospital. *Permanent transfer payment including
123
disability pension, voluntary early retirement, and flex job which are economically supported jobs offered to persons with limited work capacity
Eur Spine J
who have received welfare benefits since 1991. Each person is registered once a week with a code indicating the type of welfare benefit received. DREAM has 100 % coverage of those granted public transfer payments in Denmark from 2000 [10]. Outcome measure and independent variables The main outcome measure—permanent disability benefits including disability pension and flex job was as the others measures of vocational status—obtained from DREAM register and recoded into groups: (1) employment, (2) unemployment benefit, (3) sickness benefit including other non-permanent transfer payments for vocational rehabilitation or social assistance, (4) permanent disability benefits including disability pension and flex job, (5) old-age pension including voluntary early retirement and (6) emigration and death. You can only receive one transfer income at a time. During the study period sickness benefit was restricted to 1 year, whereas it was possible to receive unemployment benefit for up to 4 years which have the consequence that person who have used their 1 year of sick leave payment in some situations change to unemployment benefit. Thus, estimating the number of sick leave weeks while neglecting other types of transfer payments would underestimate weak vocational orientation. The independent variable was job position at time of diagnosis; co-variables were gender, age, diagnosis, surgery, weak vocational orientation in the years before hospital contact and ethnicity. Job position was assessed on the basis of information from the time of diagnosis on the patient’s most recent membership of an unemployment insurance fund. Based on the International Standard Classification of Occupations patients were recoded into six groups: (1) blue-collar, (2) office (clerks and other skilled office workers), (3) teaching and nursing, (4) managers and academics, (5) self-employed and (6) workers with unknown job position. The group ‘‘workers with unknown job position’’ included persons with membership of an unemployment fund which does not cover a specific job position group (n = 571), persons who were not members of an unemployment insurance fund (n = 287), and persons who were not in the DREAM register because they had not received any transfer payments in the years of activity of the register (n = 404). Low back diagnoses (ICD-10 codes) were recoded into four diagnostic groups (1) non-specific LBP (M43.0; M43.2; M43.5; M43.8; M43.9; M47.0–M47.2; M47.8; M47.9; M53.3; M53.8; M53.9; M54.1; M54.3; M54.5; M54.6; M54.8; M54.9; M99.1), (2) LBP with radiculopathies (M51.0; M51.1; M51.2; M51.3; M51.9; M54.4;
M96.1), (3) spinal stenosis (M48.0, M99.3–M99.6) and (4) spondylolisthesis (M43.1). Treatment was described as non-surgery vs. surgery the first year after diagnosis. The severity of surgery was described as simple discectomy vs. lumbar fusion, the latter including patients with both discectomy and lumbar fusion. Weak vocational orientation was defined as less than 40 weeks of employment within year two or three before hospital contact, established by the weekly status from the DREAM database of any type of unemployment benefit or sickness benefit [13]. Data on ethnicity were obtained from the DREAM database. Ethics The study was authorized by the Danish Data Protection Agency. According to Danish law, register-based studies do not require approval by ethical and scientific committees, nor informed consent. Statistical analysis After linking data from the two registers, the hospital and vocational record for each person was established. The hazard ratio (HR) of permanent disability benefits following hospital contact for LBP was estimated by Cox proportional hazard models. Follow-up began in the week after diagnosis and ended in the week of permanent disability benefits, old-age pension, or death, or in the week 5 years after hospital contact, whichever came first. Death and old-age pension were considered as competing risks. HR’s were calculated for the following variables: job position, using managers and academics as reference; gender; age groups; surgery; weak vocational orientation; ethnicity other than Danish; and year of inclusion. Crude and mutually adjusted HR were calculated, and 95 % CIs presented. The proportional HR assumption was evaluated by assessing log-minus-log survival curves in the unadjusted model as well as in the fully adjusted model. Cumulated incidence curves for the full follow-up period were stratified according to job position. Statistical analysis was performed using STATA statistical software, version 13.1.
Results From 1 January 2001 to 31 December 2005, 12,583 LBP patients were discharged from Aarhus University Hospital. A flow chart addressing the study population is shown in Fig. 1, presenting the 5945 patients who fulfilled the
123
Eur Spine J
inclusion criteria, 10.4 % inpatients and 89.6 % outpatients. Men were overrepresented in the study population. A marked difference was observed in gender segregation between the job position groups with an excess of men among managers, academics and self-employed and a higher representation of women among skilled office workers and the teaching and nursing group (Table 1). The extent of weak vocational orientation was substantially different between the job position groups during all 3 years before hospital contact (Table 1). The proportion was
approximately two to three times higher among blue-collar workers and workers with unknown job positions than among managers and academics. Risk of permanent disability benefits 5 years after the week of diagnosis is presented in Table 2 with incidence, crude and mutually adjusted HR. The risk was associated with job position, weak vocational orientation status before diagnosis, age, surgery, female gender, and ethnicity other than Danish. Year of inclusion was not associated with the outcome measure.
Table 1 Characteristics of the study population at diagnosis in total and according to latest job position
N (% of the study population)
Total population
Managers and academics
Skilled office workers
Teaching and nursing
Selfemployed
Blue-collar
Unknown job position
5945 (100 %)
642 (10.80 %)
779 (13.10 %)
893 (15.02 %)
455 (7.65 %)
1914 (32.09 %)
1262 (21.21 %)
Gender (%) Male
53.3
69.8
40.8
29.5
73.4
60.9
50.8
Female
46.7
30.2
59.2
70.6
26.6
39.1
49.2
18–30
13.7
14.6
14.9
11.0
5.5
10.2
19.7
31–40
26.3
26.8
26.6
24.6
24.0
24.4
30.7
41–50
30.0
27.1
27.7
34.5
31.2
32.0
26.2
51–64
30.7
31.5
30.8
29.9
39.3
33.5
23.4
1st year before hospital contact 2nd year before hospital contact
37.5
14.5
33.1
24.6
34.3
44.9
50.8
27.5
11.5
26.6
16.1
23.3
29.3
42.8
3rd year before hospital contact
24.9
9.0
21.6
15.6
18.7
27.6
40.7
Yes
87.6
95.5
93.8
95.7
88.6
89.0
70.8
No
12.4
4.5
6.2
4.3
11.4
11.
29.2
39.1 52.6
31.6 59.8
40.3 50.7
35.3 57.1
33.0 55.6
41.6 50.5
42.9 48.7
Age group (%)
Weak vocational orientation* (%)
Danish ethnicity (%)
Low back diagnosis (%) Non-specific LBP LBP with radiculopathies Spinal stenosis
4.6
4.5
4.8
3.2
6.2
5.1
4.4
Spondylolisthesis
3.9
4.0
4.2
4.6
5.3
2.8
4.0
Off. work sick for more than 6 weeks (%) Yes
44.7
29.6
53.8
51.9
44.2
59.1
72.7
No
55.3
70.4
46.2
48.2
55.8
40.9
27.3
Surgery (%) No surgery
77.6
75.2
76.1
77.0
76.7
77.4
80.9
Discectomy
17.5
20.4
18.1
18.1
18.5
17.5
14.4
4.9
4.4
5.3
4.8
4.8
5.2
4.7
Lumbar fusion n = 5945
* Less than 40 weeks of employment
123
Eur Spine J Table 2 Cumulated incidence and hazard ratio (HR) of permanent disability benefits among low back pain patients 5 years after hospital contact Variables
No.
Permanent disability benefits* (%)
HR (95 % CI)
Adjusted HR (95 % CI)
P
Male
3169
22.72
1
1
\0.001
Female
2776
27.70
1.22 (1.10; 1.34)
1.24 (1.12; 1.37)
Gender
Age group \0.001
18–30
777
12.10
1
1
31–40
1562
23.11
1.97 (1.58; 2.44)
1.89 (1.52; 2.35)
41–50 51–64
1782 1824
31.31 26.10
2.77 (2.25; 3.42) 3.00 (2.43; 3.71)
2.81 (2.28; 3.47) 3.47 (2.81; 4.30)
Job position at time of diagnosis 6.07
\0.001
Managers and academics
642
1
1
Clerks and skilled office workers
779
22.8
3.66 (2.65; 5.06)
3.05 (2.20; 4.22)
Teaching and nursing
893
19.6
3.22 (2.34; 4.45)
2.85 (2.06; 3.94)
Self-employed
455
17.80
2.97 (2.08; 4.24)
2.50 (1.75; 3.57)
Blue-collar workers
1914
35.03
6.48 (4.81; 8.73)
5.35 (3.97; 7.22)
Unknown job position
1262
27.42
4.59 (3.38; 6.24)
3.45 (2.53; 4.71)
Weak vocational orientation 2nd year before hospital contact \0.001
No
4313
19.01
1
1
Yes
1632
40.99
2.52 (2.29; 2.78)
2.44 (2.19; 2.71)
Surgery \0.001
No surgery
4615
23.77
1
1
Discectomy etc
1038
25.72
1.05 (0.93; 1.20)
1.23 (1.08; 1.40)
Lumbar fusion Danish ethnicity
292
42.81
2.01 (1.68; 2.40)
1.89 (1.58; 2.27)
Yes
5216
23.29
1
1
No
729
37.59
1.60 (1.41; 1.82)
1.21 (1.05; 1.39)
0.009
n = 5945 Adjusted hazard ratio adjustment for all variables in table and year of diagnosis, 95 % CI 95 % confidence of interval * 5 years after hospital contact
Table 3 Distribution in employment, unemployment benefit, permanent disability benefits, sickness benefit, old-age pension, emigration and dead, in the week of hospital contact and 1, 2, 3, 4 and 5 years after hospital contact due to low back pain In the week of hospital contact
1 Year after hospital contact
2 Years after hospital contact
3 Years after hospital contact
4 Years after hospital contact
5 Years after hospital contact
No. public transfer payments
2807 (47.2 %)
3639 (61.2 %)
3656 (61.5 %)
3520 (59.2 %)
3386 (57.0 %)
3187 (53.6 %)
Unemployment benefit
749 (12.6 %)
768 (12.9 %)
701 (11.8 %)
576 (9.7 %)
424 (7.1 %)
375 (6.3 %)
Permanent disability benefits
0
348 (5.9 %)
834 (14.0 %)
1134 (19.1 %)
1350 (22.7 %)
1489 (25.1 %)
Sickness benefit
2389 (40.2 %)
1078 (18.1 %)
510 (8.6 %)
360 (6.1 %)
312 (5.3 %)
282 (4.7 %)
Old-age pension and voluntary early retirement Emigrated
0
69 (1.6 %)
173 (2.9 %)
259 (4.4 %)
356 (6.0 %)
471 (7.9 %)
0
20 (0.3 %)
31 (0.5 %)
35 (0.6 %)
40 (0.7 %)
46 (0.8 %)
Dead
0
23 (0.4 %)
40 (0.7 %)
61 (1.0 %)
77 (1.3 %)
95 (1.6 %)
Total
5945
5945
5945
5945
5945
5945
123
Eur Spine J
Fig. 2 Distribution of permanent disability benefits, unemployment benefit, sickness benefit, employment, and other every week in the 3 years before and 5 years after hospital contact due to LBP. The group other includes old-age pension, voluntary early retirement, emigration and dead. The vertical line indicates time of hospital diagnosis with LBP
Table 3 presents the distribution of the main vocational status groups—employment, unemployment benefit, permanent disability benefits, sickness benefit, old-age pension, emigration and dead—within the week of hospital contact and the following 5 years. Figure 2 shows the development week-by-week 3 years before until 5 years after hospital contact due to LBP. There was a positive development in employment between the first and second year after diagnosis, and the position was kept through the second year. During the years 3–5, there was a negative development in employment, and after 5 years only 53 % were employed and 26 % received permanent disability benefits. Cumulative incidence curves of permanent disability benefits with old-age pension and death as competing risk by job position are shown in Fig. 3. The risk of permanent disability benefits was considerably higher in blue-collar workers [adjusted HR, 5.35 (95 % CI 3.97–7.22)].
Discussion Data from two national registers offered possibilities of identifying subpopulations of LBP patients at high risk of requiring permanent disability benefit and poor vocational prognosis. The present study reports findings from data representing virtually complete registers on 5945 LBP patients from the secondary healthcare sector, merging the population with data on vocational status before and after the LBP diagnosis. A pronounced difference in the risk of requiring permanent disability benefits is evident between
123
Fig. 3 Cumulative incidence of permanent disability benefits in LBP patients. Old-age pension and death were considered as competing risk. Data were stratified according to job position (n = 5945)
various job positions, with an adjusted HR of 5.35 for bluecollar workers compared to managers and academics. The percentage of employed LBP patients seems quite stable just 1 year after hospital contact, the migration to the group of patients on permanent disability benefit reaches a plateau at about, whereas 14 % of the patients were granted permanent disability benefit during the first 2 years after hospital contact; the exception is blue-collar workers and patients with unknown job position, where this migration continues. The strengths of this study were the longitudinal study design with a follow-up time of 5 years, the large size of the study population, and well-defined outcome measures. The registers are thought to be virtually complete because of the financial incentive for both public and private employers to report sick leave and the compulsory reporting from public hospitals to the Danish National Patient Register. The DREAM register has been shown to be feasible for register-based follow-up on social and economic consequences of disease [19]. The unique characteristics of the DREAM database offers valid week-byweek data on disability benefits and sick leave spells of at least 2 weeks, unemployment and social security, in addition to information on membership of an unemployment insurance fund [11, 19]. The risk factors found in this study are consistent with other authors reporting associations between work absence due to LBP and older age, ethnicity, lower level of education and poor vocational orientation [8, 9, 12, 22]. The main limitation of the present study was the lack of information on severity of symptoms and other clinical data apart from diagnosis and back operation. Due to lack of clinical data, the present study did not allow us to
Eur Spine J
distinguish between semi-acute episodes of LBP and cases where the symptoms had a prolonged course prior to hospital visit; all factors that could have influenced the vocational outcome. Most of the patients (89.6 %) were outpatients seen 2–10 weeks after referral. In the presented cohort, inpatient status was not a statistically significant risk factor, and including this variable in the multivariable model only changed the HR marginally. Although diagnostic misclassification cannot be ruled out, we used the primary discharge diagnosis which should represent the most important diagnosis characterizing the episode. The precision of the different ICD-10 codes in LBP is, however, a matter of debate. A review describes precise diagnosis in LBP patients as elusive and often problematic [17]. To the best of our knowledge, the patients in this study suffer from LBP—the question is just the validity of the diagnostic groups. In order not to bias results we chose to replace ‘‘diagnostic group’’ with ‘‘operation’’ in the model. The operation code is verified several times, and thereby more valid [17]. A large majority of patients (77.6 %) received non-operative interventions. In Denmark, such interventions are delivered in the primary sector and thus multi faceted and not traceable in the national registers. Another limitation was that information on job position was unavailable for 21.2 % of the population. This group is a mixed group of people with no membership of an unemployment insurance fund due to either (1) very weak connection to the labour market, preventing membership, or (2) great confidence in their own employment and employability. Thus, the group with unknown job position was a priori expected to be rather inhomogeneous. Excluding the group with unknown job position from the analysis only marginally changed the risk estimates. Using data from registers leave us no possibility to check for confounding factors between job and disability due to things at patient’s individual level i.e. psychosocial factors, vocational environments or other things related to the specific job. LBP may not be the distinct reason for permanent disability benefit in all patients in the cohort, but data on the cause of disability benefit are not available. After 1 year, we found 6.3 % on permanent disability benefit. Some of these patients may have been en route to disability benefit before the diagnosis. It is not possible to determine the number of such patients, but the result might be overestimated. Subsequent analysis, where patients on sickness benefit for more than half a year at the time of diagnosis were excluded and did not change the results markedly. There is no information available on the optimal length of such a wash-out period but as our data suggest it will possibly be dependent of socio-economic factors, and as it
might introduce more severe bias no further attempts were made. Of the population 1489 (25.1 %) ended up on permanent disability benefits after 5 years. The group on permanent disability benefits comprises persons on disability pension (n = 884), and flex job (n = 605). In an age-matched Danish population, there is a 2.33 % risk of disability pension in 5 years [21]. If the LBP population had the same 5-year risk of disability pension, it would result in 139 persons on disability pension, leaving a surplus of 745 LBP patients on disability pension in the present study. It is not possible to compare flex jobs in the time period, but the same pattern is to be expected [2]. The investigation included all specialized departments seeing LBP patients at the hospital, which excluded selection bias caused by general practitioners’ preference for referring to certain departments. Denmark has a public and free healthcare system, which minimizes socio-economic differences in access to care. Some patients were seen at private clinics without contact to a public hospital. Both public hospitals and private clinics are free for LBP patients referred from GP’s, but no information exists on differences between LBP patients treated at public hospitals and private clinics. In a previous study including LBP patients, we found no difference in severity of LBP between public hospitals and private clinics [14]. A recent review examined prognostic factors for return to work in chronic non-specific LBP patients [23], they stated that most return-to-work studies had reduced validity due to small sample size and self-reported sick leave absence. The review found little evidence as to which prognostic factors are of value in chronic non-specific LBP patients [23]. In conclusion, we found that LBP patients have a poor vocational prognosis; one in four (25.1 %) ended up on permanent disability benefit after 5 years. Different job positions marked a difference in risk; with blue-collar workers at high risk compared to managers and academics. In secondary, health care clinicians should be aware of the poor vocational prognosis and consider interventions to prevent work disability in addition to specific health care treatment. Emphasis should be placed on blue-collar workers and patients with poor vocational orientation before LBP diagnosis. Compliance with ethical standards Conflict of interest of interest.
The authors declare that they have no conflict
References 1. Airaksinen O, Brox JI, Cedraschi C, Hildebrandt J, KlaberMoffett J, Kovacs F, Mannion AF, Reis S, Staal JB, Ursin H, Zanoli G (2006) European guidelines for the management of
123
Eur Spine J
2.
3.
4. 5.
6.
7.
8.
9.
10. 11.
12.
chronic nonspecific low back pain. Eur Spine J 15(Suppl 2):S192–S300 Andersen IH (2008) Fewer receive disability pension and flexjob, in Danish. Ugebrevet A4 2008 43:21–23. http://www.ugeb reveta4.dk/faerre-faar-foertidspension-og-fleksjob_18679.aspx Andersen TF, Madsen M, Jorgensen J, Mellemkjoer L, Olsen JH (1999) The Danish National Hospital Register. A valuable source of data for modern health sciences. Dan Med Bull 46:263–268 Balague F, Mannion AF, Pellise F, Cedraschi C (2012) Nonspecific low back pain. Lancet 379:482–491 Burton AK, Balague F, Cardon G, Eriksen HR, Henrotin Y, Lahad A, Leclerc A, Muller G, van der Beek AJ (2005) How to prevent low back pain. Best Pract Res Clin Rheumatol 19:541–555 Burton AK, Balague F, Cardon G, Eriksen HR, Henrotin Y, Lahad A, Leclerc A, Muller G, van der Beek AJ (2006) European guidelines for prevention in low back pain: november 2004. Eur Spine J 15(Suppl 2):S136–S168 Carey TS, Evans AT, Hadler NM, Lieberman G, Kalsbeek WD, Jackman AM, Fryer JG, McNutt RA (1996) Acute severe low back pain. A population-based study of prevalence and careseeking. Spine (Phila Pa 1976) 21:339–344 Coggon D, Ntani G, Palmer KT, Felli VE, Harari R, Barrero LH, Felknor SA, Gimeno D, Cattrell A, Serra C, Bonzini M, Solidaki E, Merisalu E, Habib RR, Sadeghian F, Masood KM, Warnakulasuriya SS, Matsudaira K, Nyantumbu B, Sim MR, Harcombe H, Cox K, Marziale MH, Sarquis LM, Harari F, Freire R, Harari N, Monroy MV, Quintana LA, Rojas M, Salazar Vega EJ, Harris EC, Vargas-Prada S, Martinez JM, Delclos G, Benavides FG, Carugno M, Ferrario MM, Pesatori AC, Chatzi L, Bitsios P, Kogevinas M, Oha K, Sirk T, Sadeghian A, Peiris-John RJ, Sathiakumar N, Wickremasinghe AR, Yoshimura N, Kelsall HL, Hoe VC, Urquhart DM, Derrett S, McBride D, Herbison P, Gray A (2013) Disabling musculoskeletal pain in working populations: is it the job, the person, or the culture? Pain 154:856–863 Fourney DR, Andersson G, Arnold PM, Dettori J, Cahana A, Fehlings MG, Norvell D, Samartzis D, Chapman JR (2011) Chronic low back pain: a heterogeneous condition with challenges for an evidence-based approach. Spine (Phila Pa 1976) 36:S1–S9 Hedegaard Rasmussen J (2012) DREAM Database. The National Labor Market Authority, Ministry of Employment. Version 28 Hjollund NH, Larsen FB, Andersen JH (2007) Register-based follow-up of social benefits and other transfer payments: accuracy and degree of completeness in a Danish interdepartmental administrative database compared with a population-based survey. Scand J Public Health 35:497–502 Ijzelenberg W, Burdorf A (2005) Risk factors for musculoskeletal symptoms and ensuing health care use and sick leave. Spine (Phila Pa 1976) 30:1550–1556
123
13. Jensen LD, Frost P, Schiotz-Christensen B, Maribo T, Christensen MV, Svendsen W (2011) Predictors of vocational prognosis after herniated lumbar disc—a two year follow up study of 2039 patients diagnosed at hospital. Spine (Phila Pa 1976) 36:E791–E797 14. Jensen LD, Maribo T, Schiottz-Christensen B, Madsen FH, Gonge B, Christensen M, Frost P (2012) Counselling low-backpain patients in secondary healthcare: a randomised trial addressing experienced workplace barriers and physical activity. Occup Environ Med 69:21–28 15. Løvschall C, Bech M, Rasmussen C, Petersen T, Hartvigsen J, Jensen C, Douw K (2010) Transdiciplinary and cross-sectorial intervention in low back pain patients—a health technology assessment in Danish. Danish Health and Medicines Authority, Copenhagen 16. Lund T, Kivimaki M, Labriola M, Villadsen E, Christensen KB (2008) Using administrative sickness absence data as a marker of future disability pension: the prospective DREAM study of Danish private sector employees. Occup Environ Med 65:28–31 17. Manchikanti L, Derby R, Wolfer L, Singh V, Datta S, Hirsch JA (2009) Evidence-based medicine, systematic reviews, and guidelines in interventional pain management part 7: systematic reviews and meta-analyses of diagnostic accuracy studies. Pain Physician 12:929–963 18. McIntosh G, Frank J, Hogg-Johnson S, Bombardier C, Hall H (2000) Prognostic factors for time receiving workers’ compensation benefits in a cohort of patients with low back pain. Spine (Phila Pa 1976) 25:147–157 19. Stapelfeldt CM, Jensen C, Andersen NT, Fleten N, Nielsen CV (2012) Validation of sick leave measures: self-reported sick leave and sickness benefit data from a Danish national register compared to multiple workplace-registered sick leave spells in a Danish municipality. BMC Public Health 12:661 20. Statens Institute for MT (1999) Low-back pain: frequency, management and prevention from an HTA perspective, in Danish. Danish Health and Medicines Authority, Copenhagen 21. Statistics Denmark (2013) StatBank Denmark 22. Svendsen SW, Frost P, Jensen LD (2012) Time trends in surgery for non-traumatic shoulder disorders and postoperative risk of permanent work disability: a nationwide cohort study. Scand J Rheumatol 41:59–65 23. Verkerk K, Luijsterburg PA, Miedema HS, Pool-Goudzwaard A, Koes BW (2012) Prognostic factors for recovery in chronic nonspecific low back pain: a systematic review. Phys Ther 92:1093–1108 24. Waddell G, Burton AK, Kendall NAS (2008) Vocational rehabilitation: what works, for whom, and when?, London 25. Walker BF (2000) The prevalence of low back pain: a systematic review of the literature from 1966 to 1998. J Spinal Disord 13:205–217
