THE COURSE OF LOW BACK PAIN FROM ADOLESCENCE TO ADULTHOOD: EIGHT-YEAR FOLLOW-UP OF 9600 TWINS
 
   

The Course of Low Back Pain from Adolescence to Adulthood:
Eight-year Follow-up of 9600 Twins

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:
   Frankp@chiro.org
 
   

FROM:   Spine (Phila Pa 1976) 2006 (Feb 15);   31 (4):   468–472 ~ FULL TEXT

Hestbaek L, Leboeuf-Yde C, Kyvik KO, Manniche C

Back Research Center, Backcenter Fynen,
Clinical Locomotion Science,
University of Southern Denmark,
Ringe, Denmark.
kristianoglise@hotmail.com


STUDY DESIGN:   Prospective study with 8–year follow-up.

OBJECTIVE:   To describe the evolution of low back pain from adolescence into adulthood.

SUMMARY OF BACKGROUND DATA:   High prevalence rates of low back pain among children and adolescents have been demonstrated in several studies, and it has been theorized that low back pain in childhood may have important consequences for future low back pain. It is important to understand the nature of such a link if effective preventive programs are to be established.

METHODS:   Almost 10,000 Danish twins born between 1972 and 1982 were surveyed by means of postal questionnaires in 1994 and again in 2002. The questionnaires dealt with various aspects of general health, including the prevalence of low back pain, classified according to number of days affected (0, 1–7, 8–30, >30).

RESULTS:   Low back pain in adolescence was found to be a significant risk factor for low back pain in adulthood with odds ratios as high as four. We also demonstrated a dose-response association: the more days with low back pain at baseline, the higher the risk of future low back pain. Twenty-six percent of those with low back pain for more than 30 days during the baseline year also had more than 30 days with low back pain during the follow-up year. This was true for only 9% of the rest of the sample.

CONCLUSIONS:   Our study clearly demonstrates correlations between low back pain in childhood/adolescence and low back pain in adulthood. This should lead to a change in focus from the adult to the young population in relation to research, prevention, and treatment.



From the FULL TEXT Article:

Background

Present evidence suggests that low back pain (LBP) is rarely a self-limiting disorder but characterized by unpredictable variations in pain status, with temporary, rather than permanent, remissions. The few studies in which the nature of such variations have been investigated [1–3] all confirm the fluctuating pattern of LBP. These studies were based on adult populations; thus, the knowledge of the natural course of LBP appearing already in adolescence is limited. During the past decades, there has been an increasing awareness of LBP in children and adolescents, [4] an area that previously was largely ignored. Several studies have shown that LBP occurs to a large extent in the early years of life. Combs and Caskey even showed “back pain with no organic cause” to be the most frequent primary diagnosis in a study of pediatric patients. [5] In the cohort used for the present study, the cumulative incidence of LBP was previously reported to increase considerably from 12 to 22 years with more than 50% of 20–year-olds having experienced LBP. For subjects 23 to 41 years of age, there was only a minor increase in prevalence. [6] Lifetime prevalence rates above 50% have been reported for even earlier ages in other populations. [7, 8]

Several cross-sectional studies of LBP in young people have been performed. However, there exist only a few longitudinal studies, and two of these have focused on risk factors for LBP rather than on the course of the disorder. [9, 10] To our knowledge, children and teenagers have been followed into adulthood to study the association between LBP in adolescence and LBP in adulthood in three longitudinal studies. [11–13] Both Hellsing and Bryngelsson11 and Darre et al [12] found that LBP at age 18, the time of military enlistment, significantly increased the risk of LBP at age 40 and 30, respectively, while Harreby et al found that 90% of schoolchildren with LBP suffered from LBP 25 years later. [13]

Thus, there is a need to establish the extent and the nature of the association between LBP in adolescence and LBP in adulthood. It has been theorized that LBP in childhood may have important consequences for chronic LBP in adulthood. [14] This study aims to describe the evolution of LBP as youngsters grow into adulthood. The objective is to describe the change of LBP over an 8–year period as subjects change from youngsters to adults. Besides the general description of change over time, the specific question of whether persistent LBP in adolescence predicts persistent LBP in adulthood will be addressed.



Materials and Methods

      Data Sources.

The Danish Twin Register is the most comprehensive population-based twin register in the world, spanning a period of more than 100 years. The twins of interest for this study were born between 1972 and 1982. They were identified through the Danish civil registration system and represent 95% of the twins born during that period. The twins can be regarded as representative of the general population since they have previously been shown to have the same mortality rate [15] and the same prevalence of various diseases as the population at large, e.g., insulin-dependent diabetes, [16] hand eczema, [17] asthma and allergic rhinitis, [18] and LBP. [19] The database is described in detail elsewhere. [20] Since the population can be regarded as representative for the general population, the register provides a valuable population-based study population for various purposes. The fact that they are twins is of no interest for the purpose of this study. In 1994, when the sample was 12 to 22 years old, comprehensive questionnaires were sent to twins who previously had agreed to participate in future studies (96%). The questionnaires contained items relating to disease, health, and health-related behavior. Similar questionnaires were sent to the same population in 2002, when they were 20 to 30 years of age. The variable of interest for this paper was the number of days with LBP during the past year (LBP-days). The exact wording of the question was: “How many days have you altogether had trouble with the lower part of your back during the past year?” The possibilities for answering were: “0 days,” “1–7 days,” “8–30 days,” “more than 30 days, but not daily,” or “daily.” The group with daily pain was too small for reasonable analyses; therefore, the two groups “more than 30 days, but not daily” and “daily” were combined into one group: “more than 30 days.” Furthermore, the question, “Have you ever had trouble with the lower part of your back?” (LBP-ever), was used for validation-purposes.

      Validation.

The questions regarding LBP were modeled on the Nordic Back Pain questionnaire, [21] which has been validated previously. [22] The reliability of LBP questions from the 1994 omnibus has previously been considered satisfactory through identification of logical errors. [23] Similarly, analyses of validity were performed on the data from the 2002 omnibus by crosstabulating LBP-days with LBP-ever. Finally, to get an indication of the validity of lifetime recall in a young population, the response to LBP-ever in 1994 was compared with the response to the same question in 2002.

      Representativeness.

Responders and nonresponders at follow-up were compared with regard to age, gender, and LBP status at baseline.

      Analyses.
Table 1

Table 2

Persistent LBP (LBP-long) was defined as LBP for more than 30 days during the previous year and LBP during the past year (LBP-year) as LBP for more than zero days during the previous year. The distributions between LBP categories in 1994 and in 2002 are presented in Tables 1 and 2 as proportions. Odds ratios for having LBP-year and, specifically, for having persistent LBP at follow-up were calculated for subgroups, based on LBP status in 1994, by means of logistic regression and adjusted for age and gender.

All analyses were done using STATA 8.0 statistical software package. We were not testing any hypotheses but merely describing the pattern of LBP in our population; thus, no significance testing was performed. Instead, all results are presented with 95% confidence intervals as they provide the key for referring from our sample back to the general Danish population of that age. [24]



Results

      Description of Cohort

In 1994, the overall response rate was 84%, of which 98% answered the LBP questions, resulting in 9,569 participants. Of those 9,569 individuals, 71% responded in 2002. Ninety-six percent of these answered the question regarding number of days with LBP, leaving 6,540 individuals for longitudinal analyses, i.e., 68% of the optimal study sample.

The mean age of this part of the cohort was 17.37 years (SD = 3.14 years; range, 12–22 years) in 1994 and the male/female ratio was 43:57. The prevalence of LBP in relation to age group and gender is shown in Table 1 for both 1994 and 2002. Table 1 shows that the 1–year prevalence of LBP increases for the youngest group and decreases for the older groups, whereas the prevalence of persistent LBP increases for all age groups, although this increase is not significant for the oldest group.

      Validation

Cross-tabulation of LBP-ever with LBP-days showed an unacceptable response (“No” to “Have you ever had trouble with the lower part of your back?” and more than zero to “How many days have you altogether had trouble with the lower part of your back during the past year?”) in 1.4% of cases in 1994, and 0.3% of cases in 2002. We considered this to be an acceptable level of invalid answers (logical errors). As for long-term recall, 35% of those reporting having had LBP in 1994 claimed never to have experienced LBP in 2002. However, this variable was only used for validation purposes in this study.

      Representativeness

Comparisons between responders (n = 6,540) and nonresponders (n = 3,029) at follow-up in 2002 demonstrate similar age (responders: mean age = 17.00; SD  3.13; range, 12–22; nonresponders: mean age = 17.37 years; SD = 3.14 years; range, 12–22 years) and a similar distribution of persistent LBP in 1994 (6%; range, 6%–7%; and 6%; range, 5%–7%, for responders and nonresponders, respectively, P = 0.262). However, there is a significant overrepresentation of females (57%; range, 55%–58%; vs. 39%; range, 37%–41%; P < 0.001) at follow-up and likewise, subjects with LBP-year in 1994 are overrepresented among responders in 2002 (35%; range, 34%–37%; vs. 29%; range, 28%–31%; P < 0.001).

      Transition in LBP Status

The most stable group, as seen in Table 2, is the pain-free group with 69% remaining pain-free from baseline to follow- up. Among the subjects with persistent LBP at baseline, there is a disproportionately large proportion of subjects with persistent LBP in 2002 (26% vs. 9% for those with none or nonpersistent LBP at baseline) and likewise a relatively small proportion being pain free in 2002 (33% vs. 63% for those with none or nonpersistent LBP at baseline).

      LBP in Adolescence as a Predictor for Persistent LBP in Adulthood

Table 3

Odds ratios stratified for age indicate no difference between ages. Thus, results are not presented stratified. Likewise, there is no gender difference. To illustrate this, odds ratios are presented both raw and adjusted for age and gender in Table 3.

Table 3 shows a significant increase in the probability of getting LBP-year as well as persistent LBP at follow-up in case of LBP in adolescence. Thus, LBP in adolescence is a significant risk factor for LBP in adulthood. Furthermore, the risk increases with increasing duration of LBP in adolescence.



Discussion

The pattern demonstrated in this study is similar to that demonstrated in adults, [1–3] with one exception. There are, despite a large number remaining in the group with more than 30 days of LBP, 33% with persistent LBP at baseline who are symptom-free at follow-up, compared with only 9% found in an adult population. [2] This might reflect a specific subgroup of LBP that is active in early years but nonsymptomatic in adults. Previous populationbased MRI studies of 13– and 40–year-olds showed that endplate defects are associated with pain in children but not in adults. [25, 26] We therefore speculate that this could represent one etiologic explanation of the relatively large group of children, who recover from persistent LBP.

In accordance with previous studies, [11–13] we also found LBP at baseline to be a significant predictor for LBP at follow-up. We further demonstrated a doseresponse association between number of days with LBP at baseline and the occurrence of LBP at follow-up, i.e., the more days with LBP at baseline, the higher the risk of future LBP. To our knowledge, this has not been shown before.

Our cohort has two major strengths: its large sample size and the fact that it covers the transition from childhood into adulthood. It could be argued that the spread in age of the cohort represents a problem, i.e., the development from 12 to 20 years of age is significantly different from that of 22 to 30. However, when results are stratified for age, there is no difference between groups; therefore, we do not consider this to devaluate our results. The response rate of our study is not completely satisfying, but the fact that 96% of responders answered the LBP-questions diminishes the risk of disease-specific bias. With regard to representativeness, the overrepresentation of people with LBP-year at baseline must be considered, when comparing the 1–year prevalence in 1994 with that from 2002. This could lead to an inflated estimate for 2002 compared with the target population. Fortunately, the equal distribution of persistent LBP among responders and nonresponders lend credibility to our results relating to this variable. Likewise, the transition in LBP status is equal for males and females; thus, the female overrepresentation is unlikely to influence our results.

Finally, we found long-term recall to be of limited value. Researchers should take the large number of forgotten episodes of LBP (at least 35%) into account in future studies. These findings are in line with other studies, where lifetime history of LBP has proven unreliable. Burton et al reported that 60% of adolescents forgot previous episodes of pain [27]; and in a study by Szpalski et al, [10] 50 of 51 children reporting LBP within the past 2 years also reported having had LBP the day before examination. As it is highly unlikely that 98% of all LBP cases during the previous 2 years involved the same day, such a pattern of reporting must indicate severe recall bias. Therefore, we feel confident that the problem is related to long-term recall, rather than to the quality of the used questionnaire. Therefore, the poor validity of the variable does not affect the validity of our study, since the lifetime prevalence variable was used only for validation purposes in our analyses.

Our results leave no doubt that LBP, and especially persistent LBP, at an early age is a strong predictor of persistent LBP later in life with odds ratios as high as 4, and that the importance of early LBP as a risk factor is independent of both age and gender. This indicates that our findings are not specifically linked to adolescence but can be applied to all incidence cases of LBP regardless of age, bearing in mind that the majority of incidence cases occur before the age of 20 years. In clinical practice, this line of thought could lead to more attention to first-time cases of LBP, regardless of severity, to prevent later chronicity. It might be counterproductive to postpone treatment/ prevention until the problems become more severe and chronic.



Conclusion

We have aimed for a better understanding of the importance of LBP in adolescence. The age of our cohort and the length of follow-up allow us to investigate the change from adolescence into adulthood. Our study showed strong correlations between LBP in adolescence and LBP in adulthood, especially for persistent LBP, which demonstrated a four times increase in risk.


Key Points

  • A total of 35% of those reporting low back pain in 1994 claimed in 2002 never to have experienced low back pain.

  • Odds ratio for having low back pain in 2002 in case of persistent low back pain in 1994 was 4.29 (95% confidence interval, 3.45–5.34).

  • A total of 26% of those with persistent low back at baseline also had persistent low back pain at follow-up; this was true for 9% of the rest.

  • A total of 69% of those pain free at baseline were also pain free at follow-up; this was true for 46% of the rest.



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