Contrary to what one may expect, self-reported BP in the general population does not get worse with old age. In fact, if anything, it seems like the prevalence of BP might decline with age. Furthermore, 60 years of age does not seem to be a critical age for BP, as there was no sign of an increased occurrence at that time of life.
Possible explanations
These findings could be explained by a cohort effect, with people born during certain periods of time having a more or less robust physique. Only long-term (more or less life-long) longitudinal studies would be able to provide truly valid answers in relation to the course of BP, but no such studies exist. Other relevant explanations would be an increased tolerance to pain with age [21] and survival of the fittest; both resulting in lower reporting rates. A fourth explanation could be a decreased need to be physically active in old age, i.e. a reduction of pain provoking circumstances. This appears a likely explanation, as BP seems actually to diminish in the oldest old, who would be least likely to perform heavy physical activities. In three studies [10, 11, 18], was it obvious that the researchers had taken steps not to exclude the frail elderly (i.e. including also those with terminal illness, severe psychiatric disorders or severe dementia). It is not known if frail old people are more or less likely to have BP, so it is not known, in what direction – if any – this imbalance may push the results.
Comparisons with other reviews
Only two previous reviews on the prevalence of BP in the elderly population have been identified [6, 22]. Bressler et al. included articles between 1966 and 1999 [22]. As this current review includes articles from 2000 and onwards it would thus be interesting to compare their findings with those from the current review to see if any age related trends have changed over time. Unfortunately their objective was not to examine any trends in prevalence of low back pain with increasing age, but merely to try to establish overall prevalence estimates in the elderly population. Therefore no relevant comparisons were possible.
Age trends were, however, the main objective in Dionne et al.’s review [6]. They grouped studies by definition of BP and country of origin and dealt with any age including 65 but did not look specifically at the cut-point between middle age and old age. They reported a number of different types of curves (an increased prevalence with age, a decreased prevalence with age, a curvilinear relationship, and a flat curve) taking into account all age groups, including the younger people. In relation to middle age to old age, they found a curvilinear relationship (highest at 55) particularly for one-year period prevalence measures and for some measures of chronic pain. They also reported on the results of a weighted analysis for those aged 60 and more (with all types of BP problems); showing a relatively flat trend. A graph of a weighted calculation of severe BP predicted an increase of a few percent between the ages of 54 and 60 and about 5% between 60 and 90 years. Their study was published in 2004, and since then some additional large scale studies have been published and included in the current review. Nevertheless, our results were no different from theirs, i.e. no positive association between age and BP after middle age and into old age was found.
Methodological considerations of the review
This review had some potential and real limitations but also some strengths. Only one electronic database (Pubmed) was included in the search and thus some relevant articles may have been missed. Based on other reviews on similar musculoskeletal conditions, who have included other electronic databases (i.e. EMBASE, CINAHL, etc.), It is therefore possible that some potentially relevant articles may have been missed [6, 22]. However, unless such articles had completely different results, the occasional missing report would not affect the results, as the results were largely homogeneous.
The search strategy was also limited to the elderly population through MeSH terms. This may have lead to exclusion of some studies if for some reason they were not properly indexed in Pubmed. Finally, as only English language articles were included, any articles published in national non-English medical journals are missing in this literature review.
The review was uncritical, in the sense that although some methodological issues relating to bias were included, no attempt was made at grading the articles in relation to risk of bias. Also there were no predefined minimal criteria for acceptance in relation to quality. Had the results varied between studies, it would have been necessary to analyze study methodology and definitions, in order to understand such differences. However, this simplistic approach was apparently acceptable, as there were no difference in results across the review material, indicating that the results are fairly robust, at least in epidemiologic studies that made the effort of obtaining a relatively representative study sample.
The review was performed by two independent persons. It was always possible to reach consensus, meaning that the results probably are reproducible. Another advantage was the simplistic approach; that of dealing only with obvious difference of prevalence estimates, without confusing the picture with numerous different definitions of BP.
The heterogeneity of pain definitions is already a well known problem as it makes it difficult to compare results from different studies. It is not realistic to expect complete conformity in this area, as researchers may have had specific reasons for why they use a unique pain definition. Standardized and well defined questions are obviously important for study subjects so they know what they answer to. However, it is not important in the present review that BP definitions are all similar. Specific BP definitions would only have been necessary if there had been a need to relate prevalence estimates to the different age groups. However, as this study only attempted to find an increased prevalence over age, no attempts were made to pool results in relation to specific definitions of BP. The reason for this was that an increased prevalence of BP would be apparent regardless its definition. The decision not to concentrate on the various definitions of BP was shown to be an acceptable approach, as the findings in the present review were unequivocal across all definitions and regardless the different age-group definitions.
However, this review did not deal with the consequences of BP, nor of the duration and accompanying symptoms. Only very little information was also found on severity and chronicity. It would not be unreasonable to assume that recovery of BP is slower in old age or that some specific symptoms develop as the spine continues to degenerate. Therefore, although the prevalence of BP does not increase in old age, it is possible that specific symptoms and consequences may develop, giving a different profile of BP as the years roll on. To investigate further this concept, epidemiologic studies would have to relate age to more detailed descriptions of symptoms and consequences of BP.