Abstract
Purpose
The Oswestry Disability Index (ODI) is one of the most common scoring systems used for patients with low back pain (LBP). Although the normative score of the ODI was reported to be 10.19 in a review article, no study has calculated the normative score after adjusting the value based on the age distribution. In addition, none of the previous studies has estimated the cut-off value which separates LBP with disability from LBP without disability. The purpose of this study was to estimate the normative score by adjusting the data for age distribution in Japan, and to determine the cut-off value which separates LBP with disability from LBP without disability.
Methods
We conducted an internet survey on LBP using the Japanese version of the ODQ. A total of 1,200 respondents, composed of 100 males and 100 females in each age group (from the 20s to 70s), participated in this study. We also asked them to provide information about their backgrounds. We estimated the normative score after correcting for the age distribution of Japan. We also estimated the ODI of those with or without disability, the factors associated with the ODI, and the cut-off value which separates LBP with disability from LBP without disability.
Results
The participants’ backgrounds were similar to the national survey. The normative score of the ODI was estimated at 8.73. The ODI of the LBP with disability group was 22.07. Those with sciatica and obese subjects showed higher ODI than those without. The optimal cut-off value was estimated to be 12.
Conclusions
We defined the normative score and the cut-off value of the ODI.
Electronic supplementary material
The online version of this article (doi:10.1007/s00586-012-2173-7) contains supplementary material, which is available to authorized users.
Keywords: The Oswestry Disability Index (ODI), Normative score, Cut-off value, Internet survey
Introduction
Most adults experience some degree of low back pain (LBP) at some point in their lives, and approximately 85–90% has been classified as “non-specific LBP” [1]. As in many industrialized countries, LBP is one of the most common health disabilities in Japan. The one-month prevalence was 30.6% in a population-based survey [2]. Therefore, the low back is the most common area with pain reported in the research studies on chronic pain [3, 4].
The Oswestry Disability Questionnaire (ODQ) has been one of the most commonly used disease-specific measures for patients with LBP [5]. The Oswestry Disability Index (ODI) is calculated based on each score of the ODQ, which consists of ten items. Each of the ten items is scored from 0 to 5, and the total is added and multiplied by 2. Therefore, the ODI ranges from 0 to 100. A higher score on the ODI indicates a more severe disability caused by LBP. The ODQ has been translated into many languages [6], including Japanese in 2003 [7].
The normative score of the ODI was reported to be 10.19 in a review article by Fairbank et al. [6]. However, no study has calculated the normative score after adjusting the value by the age distribution. In addition, the cut-off values were only reported as the change between before and after the therapy [8–10].
To estimate the normal score of the ODI, calculating the score from a “normal” pain-free population seems logical, but its clinical significance is doubtful, because LBP itself is common at some point in most of the population, regardless of sex or age. The severity of pain correlates with disability, as shown by von Korff et al. [11], and the present goal of LBP treatment is to help patients to become or remain free from disability. Therefore, we think that estimating a cut-off value which discriminates between people with no or mild LBP without disability and people with disability would be clinically meaningful.
The purpose of this study was to estimate the normative score of the ODI by adjusting the data based on the age distribution in Japan, and to estimate the cut-off value of the ODI which separates patients with LBP with disability from LBP without disability.
Materials and methods
We conducted an internet survey on LBP using a Japanese version of the ODQ [7]. Two validated versions of the Japanese ODI are available [7, 12]. We chose Fujiwara’s version, which was translated from the ODI version 2.0, except that distances were not expressed in miles, but in kilometers, for the questions in Sect. 4. The reliability and validity of this version was evaluated in their previous study, and was sufficient to use for outcome studies in Japan. We asked 13,180 people to participate in this study by e-mail with the assistance of a single internet research company. The company has 1,888,778 registered members, and we chose members sequentially with a legitimate method for random sampling of the company. Finally, a total of 1,200 participants, composed of 100 males and 100 females in each age group (20s, 30s, 40s, 50s, 60s and 70s), were selected from different regions for the study in October 2010, and all of them voluntarily participated in the research study on a first-come, first-served basis. There was no missing data, because the participants could not finish the questionnaire in the web browser until all questions had been answered. The participants received points for online shopping as financial incentive. Improper users were periodically deleted by managing e-mail addresses to prevent double registration.
We also asked the participants to provide information about their height, weight, previous and present smoking habits, and exercise habits. A body mass index (BMI) of over 25 kg/m2 was defined as obesity. A previous smoking habit was defined as the experience of smoking 100 cigarettes or more during a 6-month period. A present smoking habit was defined as smoking everyday during the past 1 month. An exercise habit was defined as exercise more than twice a week and of more than 30 min each time for more than the past year. These definitions matched with those of the national annual survey on health and nutrition in 2008 published by Japanese Ministry of Health, Labour and Welfare [13]. Although a BMI of over 30 kg/m2 is usually considered obese in Western countries, a BMI over 25 kg/m2 has been defined as obese in the Japanese national annual survey, because Japanese people are less obese than people in Western countries. Therefore, we set 25 kg/m2 was set as the cut-off for obesity in this study.
In addition to the ODQ, we asked the participants whether they suffered from LBP, which was defined as pain localized between the costal margin and the inferior gluteal folds with or without lower extremity pain in the past 4 weeks, in reference to the past literature [1]. The area was shown diagrammatically on the online questionnaire (Fig. 1); [14]. We asked them to exclude pain associated with menstruation, fever, or cancer in the question. We did not ask about the pain intensity, pain duration, or pain pattern. However, we asked participants who had LBP whether the LBP caused disability, with disability being defined as the inability to engage in routine work for more than 1 day caused by the LBP, in reference to a past study by Von Korff [11]. In the main analysis, we classified the participants with LBP into three groups: “LBP with disability”, “LBP without disability”, and “no LBP”. We also asked them whether they suffered from sciatica. We defined sciatica as pain radiating down the leg below the knee. Although this definition may exclude patients with upper lumbar radiculopathy, such as L3, pain radiating down the leg above the knee may include pain derived from diseases of the hip or the pelvis. A recent consensus study on LBP definitions for survey research has suggested that “pain below the knee” is a reasonable proxy for sciatica [14].
Fig. 1.
The optimal definition of lower back pain (LBP) quoted from the past literature [9]. LBP was defined as pain localized between the costal margin and the inferior gluteal folds, which was shown on the diagram
First, we estimated the normative score of the ODI after correcting for the age distribution of Japan based on the 2005 population census taken by the Japanese Ministry of Internal Affairs and Communications [15]. In addition, we estimated the ODI of those with or without disability, and evaluated the possible relationship between the ODI score and such factors as sciatica, obesity, and exercise habits. Finally, we estimated the cut-off value of the ODI using the receiver-operating characteristic (ROC) curve by setting the LBP with disability as positive. The area under the curve (AUC), as well as the sensitivity and the specificity, were calculated from the ROC curve.
The statistical analysis was performed using the JMP7.0 software program on a personal computer. p < 0.05 was considered to be significant.
This study had the prior approval of the University of Tokyo ethics committee.
Results
The participant’s demographic data were similar to those reported by the national survey (Table 1). The prevalence of LBP was 47.5%. One-fourth of the subjects had visited clinics for their LBP. LBP with disability accounted for 12.8% of all participants (Fig. 2).
Table 1.
Demographic data of the participants
| This study | Japanese national annual survey | |||
|---|---|---|---|---|
| Mean (SD) | N | Mean (SD) | N | |
| Weight (kg) | ||||
| Male | 67.3 (11.7) | 600 | 65.8 (11.1) | 2,930 |
| Female | 52.9 (7.7) | 600 | 52.7 (8.8) | 3,567 |
| Height (cm) | ||||
| Male | 169.5 (6.4) | 600 | 166.9 (7.2) | 2,940 |
| Female | 157.3 (5.6) | 600 | 153.8 (6.9) | 3,592 |
| BMI (kg/m2) | ||||
| Male | 23.4 (3.5) | 600 | 23.6 (3.5) | 2,930 |
| Female | 21.4 (2.9) | 600 | 22.3 (3.6) | 3,558 |
| Previous smoking habit (%) | 42 | 1,200 | 37 | 7,668 |
| Present smoking habit (%) | 19 | 1,200 | 24 | 7,668 |
| Exercise habit (%) | 30 | 1,200 | 27 | 4,817 |
Fig. 2.
The proportion of LBP subjects with and without disability
The average ODI was 8.75 for the 1,200 participants. The ODI by sex and age groups are shown in Table 2. After correcting for the age distribution in Japan, the normative score of the ODI was estimated to be 8.73; 8.80 in males and 8.66 in females. There was a tendency for the ODI to increase gradually with advancing age. Participants in their 70s had the highest score.
Table 2.
Oswestry Disability Index (ODI) by sex and age groups
| N | Mean | 95% Confidence interval | Lower quartile | Median | Upper quartile | |
|---|---|---|---|---|---|---|
| Male | ||||||
| 20s | 100 | 6.38 | 4.71–8.05 | 0 | 2 | 8 |
| 30s | 100 | 7.42 | 5.39–9.45 | 0.5 | 4 | 12 |
| 40s | 100 | 8.32 | 6.44–10.20 | 2 | 4 | 12 |
| 50s | 100 | 9.52 | 7.38–11.66 | 2 | 5 | 16 |
| 60s | 100 | 10.78 | 8.45–13.11 | 2 | 6 | 18 |
| 70s | 100 | 10.54 | 8.37–12.71 | 2 | 7 | 18 |
| Total | 600 | 8.83 | 7.99–9.66 | 2 | 4 | 14 |
| Female | ||||||
| 20s | 100 | 5.04 | 3.87–6.21 | 0 | 2 | 8 |
| 30s | 100 | 6.94 | 5.42–8.46 | 2 | 4 | 12 |
| 40s | 100 | 8.06 | 6.32–9.80 | 2 | 4 | 12 |
| 50s | 100 | 8.58 | 6.67–10.49 | 2 | 5 | 14 |
| 60s | 100 | 9.12 | 6.88–11.36 | 2 | 4 | 14 |
| 70s | 100 | 14.32 | 11.45–17.19 | 2 | 9 | 23.5 |
| Total | 600 | 8.68 | 7.85–9.51 | 2 | 4 | 14 |
| Total | ||||||
| 20s | 200 | 5.71 | 4.69–6.73 | 0 | 2 | 8 |
| 30s | 200 | 7.18 | 5.92–8.44 | 2 | 4 | 12 |
| 40s | 200 | 8.19 | 6.92–9.46 | 2 | 4 | 12 |
| 50s | 200 | 9.05 | 7.63–10.47 | 2 | 5 | 16 |
| 60s | 200 | 9.95 | 8.34–11.56 | 2 | 6 | 16 |
| 70s | 200 | 12.43 | 10.63–14.23 | 2 | 8 | 20 |
| Total | 1,200 | 8.75 | 8.16–9.34 | 2 | 4 | 14 |
The ODI of the LBP without disability group was 11.88. The ODI of the LBP with disability group was 22.07. The ODI of those with disability was the highest in the subjects in their 70s followed by those in their 50s, and it was the lowest in the subjects in their 20s (Fig. 3; Table 3).
Fig. 3.
A histogram of the ODI by LBP with disability. The histogram of the ODI of the group that had LBP with disability is shown by a black bar, while that of the group that had LBP without disability or no LBP is shown by the diagonal bar. The mean ODI of the LBP with disability group was 22.07
Table 3.
Mean (lower quartile, median, upper quartile) of ODI by disability in the participants who had low back pain (LBP)
| Male | Female | Total | ||||
|---|---|---|---|---|---|---|
| Disability | + | – | + | – | + | – |
| 20s | 21.00 (11, 17, 34) | 9.94 (4, 8, 16) | 12.00 (1.5, 12, 19.5) | 8.58 (4, 8, 14) | 15.86 (7.5, 15, 22) | 9.28 (4, 8, 14) |
| 30s | 16.84 (4, 10, 28) | 10.14 (4.5, 11, 16) | 20.25 (12, 21, 31.5) | 10.50 (4, 11, 16) | 17.85 (4, 12, 30) | 10.34 (4, 11, 16) |
| 40s | 16.67 (8.5, 13, 25.5) | 12.97 (6, 12, 20) | 17.86 (7.5, 17, 25) | 11.00 (4, 10, 16) | 17.31 (8, 15, 24.5) | 12.00 (5, 12, 16) |
| 50s | 25.23 (16, 22, 31) | 14.06 (8, 14, 18.5) | 27.25 (19.5, 28, 29.5) | 11.30 (6, 12, 17.5) | 26.00 (18, 26, 30) | 12.57 (6, 12, 18) |
| 60s | 22.21 (10, 20, 36) | 13.44 (6, 10, 20) | 22.92 (13, 18, 32) | 10.17 (4, 8, 15.5) | 22.50 (12.5, 20, 34.5) | 11.81 (6, 9, 17.5) |
| 70s | 21.83 (12.5, 21, 31.5) | 15.17 (8, 14, 24) | 33.05 (20, 34, 47) | 14.64 (6.5, 10, 22) | 28.97 (20, 26, 36) | 14.96 (8, 14, 22) |
| Total | 20.47 (9, 20, 29) | 12.80 (6, 12, 18) | 23.86 (14, 23, 33.5) | 10.96 (4, 10, 16) | 22.07 (12, 20, 31) | 11.88 (6, 10, 16) |
Sciatica was reported in 23.6% of the participants who had LBP. In particular, about half of females in their 70s suffered from sciatica. Half of those with sciatica had disability, whereas two-fifths of the LBP with disability group had sciatica. The ODI of those with sciatica was significantly higher than that of those without sciatica (23.07 vs. 12.02; t test, p < 0.0001) (Online Resource 1). Females in their 70s had the highest score, and the ODI increased with advancing age.
The ODI of obese subjects was significantly higher than that of non-obese subjects (11.43 vs. 8.14; t test, p < 0.0001) (Online Resource 2).
There was no significant difference between the ODI of those who had an exercise habit and those who did not (8.08 vs. 9.04; t test, p = 0.1399) (Online Resource 3). However in the subjects in their 60s and 70s, the ODI of those with an exercise habit was significantly lower than that of those without (t test, p = 0.0131 and p = 0.0034).
The cut-off value of the ODI which separated LBP with disability from LBP without disability was 12. The AUC of the ROC curve was 0.83, and the sensitivity and the specificity were 76.4 and 75.6%, respectively (Fig. 4).
Fig. 4.
A receiver-operating characteristic (ROC) curve of the ODI in the group that had LBP with disability. The cut-off value was estimated to be 12
Discussion
The normative score of the ODI in our study was estimated to be 8.73. The similar normative score reported in the review article by Fairbank et al. (10.19) [6] supports the present results. The score of 10.19 in their review was derived from data reported in six publications [16–21], which were performed on subjects from Canada and Finland. Each study showed the normative score of the ODI as a control for its research; however, the population composition of a control varied among these studies. With regard to the adequacy of sampling, we covered the age groups of the participants from their 20s to their 70s, with the expectation of answering properly, because LBP was experienced in all age groups of adults. The ratio of males to females was 1 to 1. The BMI and the rate of exercise in each age group were similar to the results of the national survey, and the rate of previous and present smoking habits was also comparable. Therefore, we think that the backgrounds of the participants were similar to those in the national survey, and that this group was representative of the general Japanese population.
The ODI of the LBP with disability group in our study was 22.07, whereas that of the LBP without disability group was 11.88. Although the mean scores varied based on the definition of disability, we defined disability as the inability to engage in routine work for more than 1 day caused by the LBP, with reference to the past literature [11].
We have found that several factors affected the ODI score. The ODI of those with sciatica was significantly higher than that in those without sciatica. As a recent report showed that the clinical course of those with LBP with referred leg pain was worse than that of patients with LBP alone [22], it may be preferable that those with sciatica and those without sciatica are separately analyzed in outcome studies of LBP. The prevalence of sciatica was 23.6% in this study, while it was previously reported to range from 1.6 to 43% [23]. These differences may indicate that the prevalence may be affected by the definition of sciatica. The diagnosis of sciatica, which was assessed via self-reported questionnaire by participants, may not be accurate, because they are not physicians. Pain radiating below the knee may also include pain derived from osteoarthritis of the knee, especially in aged participants, while this definition may exclude upper lumbar radiculopathy, such as L3. In addition, the ODI of the obese participants whose BMI was over 25 kg/m2 in this study was significantly higher than that of the normal weight subjects. A systematic review showed that overweight and obese people have a higher prevalence of LBP, where overweight was defined as a BMI of over 25 kg/m2 and obesity was defined as a BMI of over 30 kg/m2 [24]. Another difference in the definition between the review and this study was the time when the participants suffered from LBP. It was defined as occurrence in the past year in the review, while we defined it as in the past 4 weeks in this study. However, our results were similar to the past study. Although the relationship between LBP and exercise habits is controversial [25, 26], our results show that those with exercise habits have a lower prevalence of LBP, especially in aged people. With regard to the factors associated with the ODI in this study, another study is needed to verify their clinical significance.
We estimated the cut-off value of the ODI on LBP with disability as 12. There has been no previous report of the cut-off value of the ODI, by which we can separate LBP populations into those who have LBP with and without disability. At present, LBP is prevalent in all adult populations, and only a few subjects become disabled. However, these patients are responsible for most of the treatment cost [27]. Efforts at preventing LBP with disability instead of LBP itself are likely to be more effective and efficient. Therefore, we think that estimating a cut-off value which can discriminate people with no or mild LBP without disability from people with disability would be clinically meaningful. Although the cut-off value depends on the definition of disability, this cut-off value can be of great help not only to identify the LBP population who need treatment, but also as a criterion to assess the effects of treatment.
There are some limitations to this study. First, an internet survey may have some bias. One bias is that all the participants in this study had the ability to access and use the internet. They might therefore have been more educated and intelligent than those who did not use the internet, especially in the older age groups. In addition, the participants may therefore not have been members from a lower socioeconomic strata. However, the similarity between the characteristics of the participants and those of the population census in Japan demonstrated that there was adequate sampling. Additionally, some researchers have reported that there is no difference between an internet survey and a paper and pencil survey method, even in older participants [28, 29]. Another potential bias is the sampling-bias that is caused by the number (1,200) used for the sampling. The best design to estimate the normative score may be stratified sampling from the entire Japanese population. However, such a study would be prohibitively time-, labor- and cost-intensive. In the present study, candidates from a representative population of over one million people were chosen by random sampling, and the participants had similar backgrounds as the subjects in the Japanese national survey. Therefore, we think that we were able to obtain equivalent results to the entire population, with a modest cost. Additionally, the estimated normative score of the ODI after correcting for the age distribution in Japan was not substantially different from the average ODI of the 1,200 participants. Therefore, the ODI of the LBP with or without disability, as is shown in Table 3 without correcting for the age distribution, can be considered to be the score for the entire population. Second, the present data was collected from people in Japan who can understand Japanese. Therefore, generalization of the normative score and the cut-off value in this study needs careful consideration, and a further investigation is warranted.
Electronic supplementary material
Conflict of interest
None.
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