Incidence of nonspecific and radiating low back pain: followup of 24–39-year-old adults of the Young Finns Study

Authors


Abstract

Objective

The full panorama of the types and severity of low back pain during the life course is poorly known. We studied the incidence and severity of nonspecific and radiating low back pain based on a recent followup on a representative sample of the Finnish general population.

Methods

As part of the ongoing Young Finns Study, participants ages 24–39 years who were free from low back pain at baseline in 2001 were included (n = 1,224). We estimated the incidence of nonspecific and radiating low back pain in 2007.

Results

The incidence of moderate (8–30 days duration in the past 12 months) nonspecific low back pain was 13.2%, and that of radiating low back pain was 8.6%. The rates did not differ between men and women. The incidence of major (>30 days in the past 12 months) nonspecific low back pain was 7.8%, and that of radiating low back pain was 3.4%. The incidence of major nonspecific low back pain was higher in women than in men (P = 0.02). Moderate as well as major nonspecific low back pain declined with age, whereas major radiating low back pain increased with age.

Conclusion

Our findings indicate that low back pain is a common condition in adults already in their 30s. It becomes more severe around the age of 40 years, showing different development of nonspecific and radiating low back pain. We recommend monitoring low back health in health surveillance, starting early and differentiating between nonspecific and radiating pain.

INTRODUCTION

Low back pain is a common health problem (1). The annual prevalence of low back pain has ranged between 25% and 60% (2–4), and that of sciatic pain or sciatica has ranged between 2% and 34% (5), depending on definition characteristics. Curiously, the full panorama of the types and severity of low back pain during the life course is poorly known. Most patients with acute low back pain improve within 1–3 months (6). However, minor pain will often persist and the majority of patients will have at least one recurrence within a year (6). Some percentage of patients develop chronic low back pain that causes work-related disability, loss of productivity, and sickness absence (3).

The 1-year incidence of low back pain for ≥1 day has ranged between 13% and 38% (7–10), and that of chronic back pain has ranged between 4% and 14% (11, 12). Moreover, 21% of a working population reported incident low back pain for >7 days (13), and 25% were bothered by low back pain at least to some extent (14).

Previous studies have reported inconsistent results regarding the role of age (7, 8, 10, 13, 15) and sex (8, 9, 13) in low back pain. There is some evidence suggesting that nonspecific and radiating low back pain have different risk factors (16, 17). However, few epidemiologic studies have looked at nonspecific and radiating low back pain separately. A study on a selected population suggests that the prevalence of local low back pain decreases and that of radiating low back pain increases with age (18), and the occurrence of radiating low back pain is higher in men compared with women (19).

The aim of the current study was to estimate the incidence of low back pain using a representative sample of the Finnish general population. We studied the severity of nonspecific and radiating low back pain in a recent followup of a population cohort in their 20s and 30s.

SUBJECTS AND METHODS

Population.

This study is part of an ongoing long followup study, the Young Finns Study. In 1980, children and adolescents age 3, 6, 9, 12, 15, or 18 years (n = 4,320) were invited to participate in the first cross-sectional assessment. Of those invited, 3,596 (83%) participated (Table 1) (20). The study was carried out in 5 Finnish university cities (Helsinki, Kuopio, Oulu, Tampere, and Turku) and their surrounding rural municipalities. Equal numbers of girls and boys were randomly chosen from each center. Those subjects who participated in 1980 (n = 3,596) were invited to participate in later examinations. The followup studies were carried out in 1983, 1986, 2001, and 2007 in all 5 centers, with the 2 latest followups including questions on low back pain. A total of 2,620 (73% of those who participated at baseline) participated in 2001, and 2,231 (62%) participated in 2007 (Table 1) (21, 22). The study protocol was approved by the local ethics committees, and all subjects gave a written informed consent.

Table 1. Age cohorts (age at study year) of the Young Finns Study
Study yearSample, no.Age, years
19803,596369121518        
20012,620      242730333639  
20072,231        303336394245

This study on the incidence of low back pain is based on the 2001–2007 followup with information on low back pain. A total of 1,991 subjects responded to both the 2001 and 2007 surveys. Subjects with missing information on the severity of low back pain in 2001 or 2007 (n = 58) were excluded, leaving 1,933 qualified individuals. Of these, subjects with low back pain for >7 days in 2001 (n = 709) were excluded and those free from low back pain (≤7 days in the past 12 months; n = 1,224) were included in the study.

The nonrespondents to the 2007 followup (n = 641) did not differ markedly from the respondents (n = 1,979) regarding the prevalence of low back pain for >7 days in the past 12 months at baseline in 2001 (33.1% versus 36.6%). However, they were on average 1 year younger and were more frequently men (48.7% versus 43.6%) than the respondents.

Outcome.

The incidence in 2007 of a new episode of nonspecific or radiating low back pain was estimated based on 3 questions. The first question on the presence or absence of low back pain was: “Have you had low back trouble (pain, ache, unpleasant sensations) in the past 12 months?” A manikin was used to denote the anatomic area, and the alternative responses were no and yes. If the answer was yes, the following second and third questions addressed radiating and nonspecific low back pain using a modified version of the Nordic questionnaire (23): “What is the total length of time you have had low back trouble radiating below the knee in the past 12 months?” and “What is the total length of time you have had low back trouble other than radiating in the past 12 months?” The alternative responses for each question were 1) no; 2) 1–7 days; 3) 8–30 days; 4) over 30 days, but not daily; and 5) daily.

In the current study we estimated the incidence of low back pain among subjects who were nonsymptomatic in 2001 but symptomatic in 2007. Low back pain is an episodic symptom, and therefore “incidence” in this paper does not mean the probability of the first occurrence.

We defined radiating low back pain as low back pain radiating below the knee level, and nonspecific low back pain as having low back pain without such radiation. We defined the severity of low back pain based on the number of days with pain in the past 12 months. Those with no pain and pain on 1–7 days were classified as having no or minor low back pain, those with pain on 8–30 days as having moderate low back pain, and those with pain on >30 days as having major low back pain.

Statistical analysis.

All statistical tests were 2-tailed and P values less than 0.05 were considered significant. The association between sex and low back pain and tests for trend (linearity) by age were assessed with multinomial logistic regression. We included age as a continuous independent variable in the models. We assessed 2 3-level outcomes: nonspecific low back pain (no, moderate, major) and radiating low back pain (no, moderate, major). For incidence rates, 95% confidence intervals (95% CIs) were calculated. We used Stata software, version 10 (Stata Corporation, College Station, TX) to analyze the data.

RESULTS

Overall, the incidence of moderate (8–30 days of) nonspecific low back pain in the past 12 months was 13.2% (95% CI 11.2, 15.1), and that of major (>30 days) nonspecific low back pain was 7.8% (95% CI 6.3, 9.4). The incidence of moderate radiating low back pain in the past 12 months was 8.6% (95% CI 7.0, 10.2), and that of major radiating low back pain was 3.4% (95% CI 2.3, 4.4). The incidence of moderate and major nonspecific low back pain declined with age (P = 0.005 and P = 0.007, respectively), whereas that of major radiating low back pain increased with age (P = 0.041) (Figure 1).

Figure 1.

Age-specific (in years) incidence rate (percentage and 95% confidence interval) of nonspecific or radiating low back pain in the Young Finns Study, Finland, 2001–2007. A, incidence of moderate (8–30 days of pain in the preceding 12 months) low back pain; B, incidence of major (>30 days during the preceding 12 months) low back pain.

In the sex-specific analysis, the incidence of moderate nonspecific low back pain did not differ between men and women (Table 2). It declined with age in both sexes; however, the trend was statistically significant in men (P = 0.034), but not in women (P = 0.076) (Table 2). The incidence of moderate radiating low back pain did not change with age in either sex.

Table 2. Sex-specific incidence of nonspecific or radiating low back pain in the Young Finns Study, Finland, 2001–2007*
Age at followup, yearsSample, no.NonspecificRadiating
ModerateMajorModerateMajor
  • *

    Values are the percentage (95% confidence interval) unless otherwise indicated.

  • Low back pain for 8–30 days during the preceding 12 months.

  • Low back pain for >30 days during the preceding 12 months.

Men     
 3010116.7 (9.3, 24.0)6.9 (1.8, 11.9)8.8 (3.2, 14.4)2.0 (−0.8, 4.7)
 338819.3 (10.9, 27.7)8.0 (2.1, 13.7)6.8 (1.4, 12.2)3.4 (−0.4, 7.3)
 3611214.3 (7.7, 20.9)7.1 (2.3, 12.0)7.1 (2.3, 12.0)3.6 (0.1, 7.1)
 399616.7 (9.0, 24.3)5.2 (0.7, 9.7)8.3 (2.7, 14.0)3.1 (−0.4, 6.7)
 4210112.9 (6.2, 19.5)5.0 (0.6, 9.3)5.0 (0.6, 9.3)5.0 (0.6, 9.3)
 45827.3 (1.5, 13.1)2.4 (−0.9, 5.9)9.8 (3.2, 16.3)6.1 (0.8, 11.4)
 Overall58114.6 (11.7, 17.5)5.9 (3.9, 7.8)7.6 (5.4, 9.8)3.8 (2.2, 5.4)
Women     
 309214.1 (6.8, 21.4)15.2 (7.7, 22.7)8.7 (2.8, 14.6)3.3 (−0.4, 7.0)
 3312115.7 (9.1, 22.3)9.9 (4.5, 15.3)7.4 (2.7, 12.2)1.7 (−0.6, 4.0)
 3610010.0 (4.0, 16.0)12.0 (5.5, 18.5)11.0 (4.7, 17.2)1.0 (−1.0, 3.0)
 3912210.7 (5.1, 16.2)6.6 (2.1, 11.0)11.5 (5.7, 17.2)2.5 (−0.3, 5.3)
 4211311.5 (5.5, 17.5)7.1 (2.3, 11.9)12.4 (6.2, 18.6)4.4 (0.6, 8.3)
 45958.4 (2.7, 14.1)8.4 (2.7, 14.1)5.3 (0.7, 9.8)5.3 (0.7, 9.8)
 Overall64311.8 (9.3, 14.3)9.6 (7.3, 11.9)9.5 (7.2, 11.8)3.0 (1.6, 4.3)

The incidence of major nonspecific low back pain was higher in women compared with men (P = 0.02) and tended to decline with age in both sexes (Table 2). However, the trend was statistically significant in women (P = 0.036), but not in men (P = 0.079). The incidence of major radiating low back pain did not differ between men and women and tended to increase with age in both sexes (for both, P = 0.14) (Table 2).

DISCUSSION

Our findings indicate that low back pain is a common condition in adults already in their 30s. The incidence of major nonspecific low back pain decreased, whereas that of major radiating low back pain increased, with age. The incidence of major nonspecific low back pain was higher in women than in men.

Here, we report incidence figures for low back pain, classifying them into nonspecific and radiating low back pain. Commonly agreed diagnostic criteria for low back disorders do not exist. Low back disorders present typically with episodic symptoms. During a longer followup, such as 6 years in this study, a person can have several symptom episodes with recovery between the episodes. In our study, “incidence” denotes the 6-year net incidence rate, not the probability of the first occurrence of low back pain.

Most epidemiologic studies rely on self-reported symptoms as the outcome. We used a 12-month recall period for low back pain. In low back pain reporting, longer recall periods are affected by strong recall bias and are therefore not recommended (24, 25), even when the followup period is longer. Our definitions of the outcomes based on the number of days with low back pain in a given time period correspond well to the definitions of low back pain recommended recently, with low back pain >30 days in the past 12 months classified as chronic low back pain (24). The cutoff value between no or minor and moderate pain was set at 7 days, because previous studies have shown that those with pain of a shorter duration recover quickly (26). Moreover, distinguishing nonspecific and radiating low back pain will enable us to capture entities with different risk factors (16, 17) and clinical course (27).

A few population-based studies have reported sex differences in low back pain incidence. However, the studies did not differentiate between nonspecific and radiating low back pain or the duration or severity of the symptoms. Among working populations, the 1-year incidence of low back pain for ≥1 day has ranged between 13% and 35% in men (7–9) and between 17% and 38% in women (8–10). However, women reported incident chronic back pain more frequently than men (11, 12). Our findings support a higher risk of chronic nonspecific low back pain in women compared with men, as well. The perception of pain may differ between men and women. Experimental studies have shown that women have lower pain thresholds, greater ability to discriminate pain, and less tolerance of noxious stimuli than men (28, 29). Moreover, their mechanical pain thresholds increase with age (30, 31).

Previous studies have reported inconsistent findings on the role of age in low back pain. A systematic review (32) showed that the prevalence of mild back pain decreases, whereas that of severe or disabling back pain increases, with age. Some studies have found an increase in the incidence of low back pain with age (13, 15), whereas others have not (7, 8, 10). Having differentiated between nonspecific and radiating pain as well as between moderate and major pain, we found that the incidence of major nonspecific low back pain decreases, whereas that of radiating low back pain increases, with age. Nevertheless, for moderate low back pain, only nonspecific low back pain showed an association (the incidence declining) with age.

In this study, we included subjects free from low back pain for >7 days at baseline. The association between age and low back pain was not affected by excluding subjects with low back pain at baseline. We found similar results when the analysis was repeated with the total study population (n = 1,933). Moreover, nonrespondents to the followup survey did not differ from the respondents with regard to the prevalence of low back pain at baseline.

Radiating pain is a symptom of the sciatic syndrome, which may be associated with considerable loss of function. Our findings indicate that chronic radiating low back pain increases around the age of 40 years. Moreover, after an initial decline with age, the incidence of chronic nonspecific low back pain does not decline further after the age of 40 years. Our earlier results from a different population showed that nonspecific low back pain precedes radiating low back pain and can be transient, whereas radiating low back pain typically is not (Riihimäki H: unpublished results). Both of our data sets, as well as earlier findings (19), suggest that low back pain becomes more severe with age and that nonspecific and radiating low back pain tend to co-occur.

The accumulated knowledge on the risk factors of low back pain indicates that both individual and environmental risk factors play a role. Some of the evidence is contradictory, possibly reflecting inconsistencies in the methods used to assess low back pain. Efforts to accumulate data on the incidence of low back disorders and their determinants will aid in preventing major loss of working days and major economical losses. Epidemiologic studies on different types of low back disorders may also help us understand the etiologies and pathomechanistic pathways likely to be shared by several chronic diseases. Some evidence suggests that there are common risk factors for cardiovascular diseases and low back disorders, especially sciatic pain and sciatica (16, 33, 34). Studying the incidence of low back pain and differentiating between nonspecific and radiating low back pain would allow researchers to better identify groups for targeted prevention.

In summary, musculoskeletal health is a cornerstone of functional capacity and work ability. Radiating low back pain, which we showed to already be increasing in people in their early 30s, can be a sign of the sciatic syndrome or other serious types of low back disorder. Good low back health is a prerequisite for being physically active, and therefore of value in the prevention of chronic and disabling diseases. The health care systems are currently monitoring cardiovascular health indicators; however, widening the scope to also include measures of low back health should be considered.

Our findings indicate that low back pain is a common condition in young adults and becomes more severe around the age of 40 years. We recommend monitoring low back health in health surveillance, starting early and differentiating between nonspecific and radiating pain.

AUTHOR CONTRIBUTIONS

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Shiri had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Shiri, Solovieva, Husgafvel-Pursiainen, Viikari, Raitakari, Viikari-Juntura.

Acquisition of data. Shiri, Solovieva, Viikari, Raitakari, Viikari-Juntura.

Analysis and interpretation of data. Shiri, Solovieva, Husgafvel-Pursiainen, Raitakari, Viikari-Juntura.

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