The results of this study demonstrate that although LBP is the most prevalent complaint in the general population, the relative proportions of people with back pain, including radiating pain, and the relative proportions of people reporting consequences thereof, are similar in all three spinal regions. It is particularly interesting that the relative percentage of people with pain in a spinal region, who also report to have had radiating pain from that particular region, is almost identical despite anatomical, functional and symptomatic differences in the three regions.
Our findings suggest that there are no obvious or unique pain patterns for individual spine regions, at least not on the variables that we studied. Rather, these similar pain patterns may reflect a general expression of pain and if this is correct then this distribution may also be found in other musculoskeletal pain syndromes. A literature search revealed two Nordic studies of the general population, in which pain data could be extrapolated in a similar manner. In the first study, based on 850 adults from Iceland , pain in the past year and in the past week were reported for the neck, upper back, and low back, and all major joints in the body. The proportions of people who had experienced pain in the past week out of those who reported to have had pain in the past year were remarkably similar (about 50%) for six of their nine musculoskeletal sites. In the second study, based on 46,901 Norwegian adults , the duration of pain in the past month was reported as < 15 days for about 1/3 of the study sample, regardless if pain was noted for the neck, upper back or low back. The same proportion was found also for the hips, knees, ankles/feet, elbows, and wrist/hands.
We also found similarities in relation to the consequences of back pain. For all three regions of the spine, slightly more than half of those who had experienced pain during the past year also reported some type of consequence of the pain. The majority reported one or two consequences, which were typically care-seeking or reduced physical activities. Regardless of the region and duration of the pain, the hierarchy of consequences was remarkably similar. Although, the hierarchy of the five consequences demonstrates a logical preference of choices for any musculoskeletal pain, it is nevertheless striking how the relative proportions are almost identical for the three spinal regions even with longer pain durations. This, too, indicates that the pattern of reactions may have some common mechanisms or expressions based on similarity in the condition or a similarity in how people react to spine-related pain regardless of where it hurts.
Despite the obvious similarities for all three spinal regions, some variations were noted. In particular, LBP resulted in relatively more consequences compared to MBP and NP. This is in accordance with other studies, in which especially sick-leave and care seeking are more commonly reported in people with LBP . These findings indicate either that problems in the lumbar spine affect people's life more than problems in the neck/mid back or that there is a subgroup of people with LBP, who have a different type of condition, and that this type of LBP creates more problems than non-specific pain in the neck or the mid back.
Strengths and limitations
This study was conducted on a large Danish cohort of twins that has been shown to be representative of its background population [13, 21]. Although the twins received a 20-page long questionnaire, the response rate was rather high (74%), which gives this study a strong external validity. As the questionnaire entailed a large number of other health related issues, we have no reasons to suspect any 'distortions' of our data, as it would not have attracted specifically people with back problems. Finally, a previously validated questionnaire was used . So all in all, our results are not likely to be biased in any major way.
It is relevant to note that there are no financial barriers to access the Danish health-care system and that sick-leave is available regardless of the cause of the disease. Hence, people's choice of consequences in this study was not based on financial issues to any significant extent. However, individuals in countries with other health care systems may of course be subjected to other constraints, which may affect the hierarchy of consequences.
Still, this was a cross-sectional study and it is therefore impossible to study causality and the order of events (e.g. in relation to the consequences). Additionally, any specific diagnoses cannot be determined in this cohort. However, people with LBP in the general population would be classified as having non-specific back pain. Therefore, the issue of diagnosis becomes irrelevant. Additional strengths and limitations of the study have been discussed in a previous publication based on the same study sample [16, 17].
While our study showed many similarities between the spinal regions, one needs to keep in mind that there would be a fair degree of concurrent pain sites [1, 3–7]. Thus, it is possible that memories of pain and its consequences may be confused between the different spinal regions. The next question is therefore if those with multi-site back pain differ from those with localized back pain in terms of the reported pain patterns and consequences. Hence, a follow-up on this study will be a comparison between widespread back pain and localized back pain. This way, it will be possible to determine if our main results can be reproduced.