Eur Spine J (2014) 23:2090–2096 DOI 10.1007/s00586-014-3503-8
ORIGINAL ARTICLE
The dischargeable cut-off score of Oswestry disability index (ODI) in the inpatient care for low back pain with disability Sang-won Park • Ye-sle Shin • Hye-jin Kim Jin-ho Lee • Joon-Shik Shin • In-Hyuk Ha
•
Received: 14 February 2014 / Revised: 29 July 2014 / Accepted: 30 July 2014 / Published online: 7 August 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose The admission due to low back pain (LBP) became prevalent cause of international economic losses. Since LBP patients with disability are often subject to inpatient care, it is important to determine the appropriate time of discharge. The purpose of this study is to set the cut-off value of appropriate Oswestry Disability Index (ODI) at the time of discharge. Methods Of 1,394 LBP patients admitted in hospital specialized in spinal disease, 774 eligible patients with disability were included in this study. And several clinical variables including numerical rating score, ODI, satisfaction level were observed during the hospital stay. We considered satisfaction level as an important factor for discharge, categorized patients into satisfied group and dissatisfied group. Through the statistical analysis, appropriate factor for determining dischargeable patients satisfied with their current condition and its cut-off value of ODI were found. And proper predictors for the cut-off value were extracted statistically and logically from a pool of several clinical indexes. Results The ODI at the time of discharge was most accurate in determining dischargeable patients. The cut-off value of ODI was 30. Predictors were ODI questions 4 and 6. Conclusion We set the cut-off value of dischargeable ODI for LBP inpatient with disability and found its predictor.
S. Park Y. Shin H. Kim J. Lee J.-S. Shin I.-H. Ha (&) Jaseng Spine and Joint Research Institute, Jaseng Medical Foundation, Jaseng Hospital of Korean Medicine, 858 Eonju-ro, Gangnam-Gu, Seoul, Republic of Korea e-mail: [email protected]
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Keywords Oswestry Disability Index (ODI) Cut-off value Discharge Low back pain (LBP)
Introduction Low back pain (LBP) is an impending problem in the field of public health due to its high prevalence rate. The total prevalence rate of LBP was 31.0 % in a 2012 study and LBP is known to affect time off work more than any other medical condition [1, 2]. Despite the fact that LBP accompanied by functional disability is relatively less prevalent than LBP alone, patients with disability are responsible for the majority of the total medical expenses that go into LBP treatment [3]. As patients with functional disability cannot fully participate in everyday activities, they are often subject to inpatient care. In the USA, disorders associated with LBP were the 2nd and 4th most frequent causes of hospitalization in the 18–44 and 45–64-year-old population, respectively [4]. As for Korea, where a dual healthcare system (a system where both conventional medicine and Korean Medicine are legally recognized by the government) has been settled, LBP was the 7th most prevalent cause of inpatient care in conventional hospitals and 1st in Korean Medicine hospitals [5]. According to a 2012 study by a national institution in Korea that specializes in complementary alternative medicine (CAM), inpatients hospitalized for lumbar spinal disorders spent six times more total medical costs than outpatients [6]. This implies that inpatient care causes considerable socioeconomic losses. However, there are no guidelines for admission/discharge of patients with LBP. In clinical settings, decisions to admit/discharge patients tend to be based solely on subjective opinion of the doctor [7]. Not only is quick
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recovery and return to social life important for the patient’s quality of life, it is important for socioeconomic reasons as well. Therefore, for best effective inpatient care, an appropriate cut-off point is needed. The Oswestry Disability Index (ODI, version 2.0) has been validated in Korean and thus has proprietary [8, 9]. Because ODI is sensitive to continuous pain with severe disability [10], it is better than the Roland-Morris Disability Questionnaire for evaluating patients who have been considered for hospitalization. The ODI includes 1 question about pain and 9 questions about daily life. It is an easy-to-use, psychometric, practical tool [10]. The purpose of this study is to set a cut-off ODI score that represents a ‘‘satisfactory’’ condition; a condition appropriate for discharge. A cut-off value can provide objective guidelines to decisions that were once made by subjective judgment. Another purpose of this study is to identify any factors that can be examined to predict whether the patient’s ODI will exceed the cut-off.
Materials and methods 1,394 inpatients admitted to an integrative hospital specializing in spinal disorders between June 2012 and September 2013 were considered. Patients admitted multiple times were recognized once, only for their first admission. 849 patients responded to both ODI questionnaires (at admission and discharge) and a satisfaction level survey (at discharge). An ODI score greater than 12 is considered to be indicative of functional disability [16]. Therefore, 35 patients who reported an ODI score of less than 12 were excluded. 40 patients who reported increased ODI scores despite being ‘‘satisfied’’ were excluded because such responses were considered irrational. A total of 774 patients were included (Fig. 1) in the final study. Baseline characteristics, including the chief disease as diagnosed by a doctor, were tested for any significant differences between the satisfied and unsatisfied groups. This study was recognized by the IRB at Jaseng Hospital of Korean Medicine. Physicians interviewed the patient for baseline characteristics, current symptoms, and outcome measures numeric rating scale (NRS), ODI at the time of admission (ODI1), ODI at the time of discharge (ODI2), satisfaction level. They performed any necessary physical examinations and entered the information to an electronic medical data system devised for prospective research. The Korean version of the ODI, verified as reliable and valid by Kim et al. [9] was used. A 4-point Likert scale (excellent, satisfactory, poor, and extremely poor) was used to evaluate satisfaction levels at the time of discharge. While Likert scales usually include 5
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Fig. 1 Flow diagram of the study. ODI Oswestry Disability Index, ODI1 ODI at the time of admission, ODI2 ODI at the time of discharge. *In case of the patient who admitted several times, his/her first admission was only considered
or 7 points, a 4-point scale was used to avoid central tendency bias [11]. Patients who responded ‘‘excellent’’ and ‘‘satisfactory’’ were considered to be satisfied and ‘‘poor’’ and ‘‘extremely poor’’ to be unsatisfied. The difference in the ODI scores between the two groups was important for setting the cut-off value. Statistical analyses A Chi squared test was used to identify the differences in the baseline characteristics between the satisfied and unsatisfied groups that may affect satisfaction levels. For the individual items of each subgroup, the differences were validated by a t test. As for the distribution of different types of disorders, fisher’s exact test was used. To evaluate the accuracy of the tests intended to predict outcomes of either/or questions, sensitivity and specificity are commonly used. To determine the effectiveness of the analysis and to set a cut-off ODI value, a receiver operation characteristic (ROC) curve was used. The area under ROC curve (AUC) was observed to compare the three ODIs [ODI2, ODI1–ODI2, and derived ODI by a regression model (ODId)]. The accuracy of an ROC curve can be determined as uninformative (AUC B0.5), less accurate (0.5 \ AUC B 0.7), somewhat accurate (0.7 \ AUC B 0.9), very accurate (0.9 \ AUC \ 1) and perfectly accurate (AUC = 1) [12]. A cut-off value was set using an ROC curve where positive values represented the ‘‘satisfied’’ group. Based on clinical experience, five factors that were most likely to affect ODI2 (sex, age, ODI1, duration of pain, presence of radiculopathy) were selected. The statistical significance of the five factors was verified with a multivariate regression analysis (R-square 0.27) and ODId was
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derived using this model. Although the adjusted R-square value was a low 0.27, the purpose of this modeling was not to pinpoint a specific ODI score but to derive ODI scores reflecting the individual characteristics of the patient. Thus, this modeling seems to be appropriate. Of the three ODIs, the one with an AUC value closest to 1 was considered to be the most acceptable. The best fit classifier was used to set a cut-off value. To identify any pre-indicators for differentiating patients below the cut-off value from the patients above it, t tests were conducted for 30 factors. The five that showed the most significant differences were considered to be possible pre-indicators. SPSS software (Version 18.0, SPSS Corp., Chicago, IL, USA) was used.
Results The study population was 43.13 years old and 48 % male. Mean hospital day was 23.26 days, and the mean ODI1 was 49.63. The mean NRS of LBP was 5.99 whereas NRS of radiating pain was 5.36. 32 % had experienced LBP for less than 4 weeks, 21 % for 4–12 weeks, 15 % for 13–24 weeks, and 32 % for more than 24 weeks. The majority of the patients had acute LBP (onset \4 weeks ago) or chronic LBP (onset [24 weeks ago). 55 % had LBP with radiculopathy. The factors that were significantly different between the satisfied/unsatisfied groups were age, presence of any radiculopathy, and ODI scores. Distributions of chief diseases were not significantly different. Preexisting degenerative conditions such as spinal stenosis did not affect satisfaction levels. Even baseline characteristics that were significantly different between the two groups were not greatly different; all the above-mentioned factors have been put under consideration for our prediction model (Table 1). The mean ODI2 was 22.91 (n = 527) and 42.99 (n = 247) in the satisfied and unsatisfied group, respectively (p \ 0.0001). The differences in the ODI scores were notable as well; satisfied patients reported a 24.16 decrease in their ODI scores while unsatisfied patients reported a 12.12 decrease (p \ 0.0001) (Table 2). Based on such results, satisfaction levels were hypothesized to be a valid pre-indicator for discharge and thus a subsequent ROC analysis was conducted. Regression analysis showed that the five factors considered were significantly correlated with actual ODI scores at discharge (p \ 0.05). The regression model was then used to predict ODI2, taking into account the individual characteristics of the patient. A comparison of AUC values on the ROC curve showed that the difference in ODI scores (ODI1–ODI2) and the
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ODId were not any better than the ODI2. The AUC of ODId was 0.679 and the ODI1–ODI2 was 0.692, the ODI2 was 0.88 (Fig. 2). The cut-off ODI at 78 % sensitivity and 82 % specificity was 30. Then, any pre-indicators that could be used to differentiate between the ODI [30 group and the ODI B30 group were looked for. For this, 30 factors (The NRS of LBP and radiating pain, the difference of the NRS scores at baseline and discharge, the difference in total ODI, responses to individual questions of the ODI1 and ODI2, SLR, ROM) were tested for any correlation with ODI2 scores. The two groups were significantly different for all 30 factors. The 5 factors that were most different were questions 3, 4, 6, 9, and 10; lifting, walking, standing, social activities, and traveling. Of the 5 questions, those that the patients in the ODI [30 group and the ODI B30 group replied most differently to were searched for. Questions where (1) 80 % or more of the ODI B30 group chose 1 or 2 or (2) the difference between the percentage of respondents choosing 1–2 was greater than 40 % in the two groups were questions 4 (walking) and 6 (standing) (Fig. 3).
Discussion This study reported that satisfaction levels of patients hospitalized for LBP can be predicted using the ODI2. The AUC value was 0.88, making this an appropriate approach. The cut-off point of ODI2 was 30. Of the many clinical variables, those best suited for the prediction of cut-off scores were questions 4 and 6 of the ODI questionnaire. Tonosu et al. [13] reported that the mean ODI of patients experiencing more than one day of job loss was 22.07 whereas the mean ODI score of patients with no disability was 11.88. The cut point between the two was 12. On the other hand, the results of this study showed that the mean ODI of satisfied patients were 24.13 and the cut point between satisfaction and dissatisfaction was 30. Such a difference may be because Tonosu et al. study defined functional disability as a day or more of job loss but such patients may not consider inpatient care. Only 20–30 % of LBP patients seek medical care [14, 15]. Because there is not a notable difference between the normative score (8) and the cut-off score (12), this does not seem to be an appropriate way to filter out LBP patients with severe problems. The patients included in this study are patients in more severe conditions and are therefore more interesting subjects for research. The cut-off values presented in this study was close to the cut-off ODI value presented in a previous study that reported 29 to be a cut-off ODI score for somewhat satisfied patients who had undergone surgery [17].
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Table 1 Basic demographics at admission
Satisfied group
Unsatisfied group
Sex, male (%)
50 (266)
43 (105)
Age (years), mean (SD)
41.09 (13.89)
47.12 (14.97)
0.039b \0.001c 0.328b
Exercise Regular exercise
p value
43 % (206)
39 % (82)
Frequency (days/week), mean (SD)
3.65 (1.79)
3.82 (1.85)
0.419c
Time (min/day), mean (SD)
62.20 (47.30)
66.50 (53.30)
0.394c
57 % (277)
61 % (130)
Irregular exercise or no
0.063b
Job distribution Manager or professional
24 % (106)
22 % (47)
Clerks
23 % (104)
16 % (34)
Service or sales
12 % (55)
11 % (24)
Skilled agricultural, forestry and fishery
3 % (12)
5 % (11)
Craft or equipment operation and assembling
2 % (9)
2 % (4)
Elementary
3 % (14)
4 % (9)
33 % (149)
41 % (88)
Housewife or student (not specific) Smoking status Yes
0.955b 32 % (170)
32 % (78)
Average smoking year
14.94 (7.21)
16.53 (11.46)
0.297b
Average smoking cigarettes/day
13.65 (7.21)
14.96 (10.05)
0.571b
58 % (306)
58 % (144)
No
0.418b
Drinking experience Yes
70 % (403)
No in the past an year
11 % (61)
9 % (22)
20 % (84)
21 % (39)
Less than one time/month
73 % (180)
1 time/month
12 % (52)
14 % (26)
2–4 times/month
31 % (132)
18 % (32)
2–3 times/week
18 % (74)
12 % (22)
More than 4 times/week
5 % (21)
7 % (13)
15 % (82)
14 % (35)
No
0.025b
Spinal operation experience (patient history) Yes No
9 % (41) 91 % (416)
15 % (30) 85 % (172)
Length of hospital stay (day), mean (SD)
22.57 (11.59)
24.67 (11.96)
0.067b 0.002b
Proportion with duration of LBP (Month) \1 month
36 % (190)
23 % (56)
1–3 month
21 % (109)
25 % (62)
3–6 month
14 % (73)
15 % (38)
[6 month
29 % (151)
37 % (91)
Dominant pain categorya
\0.001c
Low back pain
50 % (261)
34 % (84)
Radiating pain
50 % (264)
66 % (163)
LBP
6.78 (1.53)
7.02 (1.63)
0.084b
Radiating pain
7.17 (1.34)
7.32 (1.59)
\0.001c
ODI (0–100), mean (SD)
54.51 (18.81)
46.50 (20.35)
\0.001c
Physical exam Straight leg raise test \60° (R)
12 % (64)
16 % (40)
0.057b
Straight leg raise test \60° (L)
16 % (82)
15 % (36)
0.537b
NRS (0–10), mean (SD)
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Table 1 continued
Satisfied group
Unsatisfied group
p value
Flexion
70.99 (28.76)
69.67 (28.98)
0.554b
Extension
16.76 (6.80)
15.88 (7.28)
0.14b
Rotation (R)
42.95 (8.09)
41.81 (10.37)
0.008b
Rotation (L)
43.24 (7.41)
41.87 (9.01)
0.055b
Lateral bending (R)
27.44 (6.50)
26.28 (7.34)
0.049b
Lateral bending (L)
27.66 (6.13)
26.53 (6.91)
0.243b
Lumbar ROM, mean (SD)
ODI Oswestry Disability Index, NRS Numeric rating scale, SD standard deviation a
Dominant pain category indicates that when NRS of low back pain is higher than NRS of radiating pain, the dominant pain is considered to be LBP
0.571d
Spinal disorder diagnosis herniated disc
85.93 % (397)
85.07 % (188)
Spondylolisthesis
1.08 % (5)
1.36 % (3)
Chi-square test were used for analysis
Stenosis
2.38 % (11)
3.62 % (8)
Scoliosis
0.22 % (1)
0.90 % (2)
c
Compression fracture
1.08 % (5)
1.81 % (4)
Sprain
6.71 % (31)
4.52 % (10)
Others
2.60 % (12)
2.71 % (6)
b
Student’s t test were used for analysis d
Fisher’s exact test were used for analysis Table 2 Discharge feature Satisfaction level
Number of subjects
ODI2
ODI2 (mean)*
ODI1– ODI$2
22.91
24.16
42.99
12.12
Satisfied group
Excellent
57
12.72
Satisfactory
470
24.14
Dissatisfied group
Poor
243
42.82
4
52.89
Extremely poor
ODI Oswestry Disablility Index, ODI1 ODI at the time of admission, ODI2 ODI at the time of discharge *,$
Both values are statistically significant at p value 0.05 (independent t test); p \ 0.0001
Although the two studies tested for different interventions, they both share similar results such consistency adds credibility to both studies. Another study by the same author reported that employment status and initial disability score greatly affected the effects of physical therapy and psychiatric treatment in a 1-year follow-up [18]. In this study, however, employment status does not seem to be any different between the two groups. Baseline ODI scores were, however, significantly different and thus was applied to a predictive model to find a cut-off ODI score. A core set of LBP evaluation criteria devised by experts in 2000 consists of 5 factors; pain intensity, LBP-specific disability, work disability, general functional status, and satisfaction with the process of care [19]. In this study, information on the patients’ age, gender, onset, NRS, baseline ODI, etc., was collected and each factor was tested for any correlation to satisfaction levels at the time of discharge.
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An analysis of baseline characteristics indicated that the higher the ODI1, the longer the duration of the pain and the older the patient, the higher the ODI2. Also, men and patients with radiculopathy as opposed to LBP alone reported higher ODI2. However, the absolute ODI2 was a more accurate pre-indicator than the relative ODId for determining the appropriate time for discharge. In evaluating treatment outcomes with ODI, minimally clinically important change (in most cases 10) is considered [20]. However, this is only a minimum difference, but probably not an appropriate guideline for the treatment of LBP patients. In this study, even the unsatisfied group experienced a 12.12 decrease in ODI2. ODI1–ODI2 was less accurate pre-indicator than ODI2 in differentiating between the more than 30/less than or equal to 30 groups. Because it is unrealistic to recheck ODI scores daily, various factors were examined to find ones that were most accurate pre-indicators for differentiating between the ODI [30 group and the ODI B30 group. T test results showed that five factors that were most significantly different between the two groups were coincidentally all a part of ODI2; questions number 3, 4, 6, 9, 10. The two groups responded most differently to question 6 (standing); there was a 50 % difference. Thus, it can be said that if a patient replies ‘‘Can stand for more than an hour’’ or longer, this patient will probably be included in the ODI B30 group. As for question 4 (walking), if the patient cannot ‘‘walk more than 500 m’’, it is very this patient will probably be included in the ODI [30 group. In clinical settings, if a patient can walk more than 500 m and/or stand for longer than an hour, it can be presumed that they will report an ODI score of less than 30 and be content with their current state, thus allowing them to be discharged.
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Fig. 2 Receiver operation Characteristic (ROC) curvature of predictive models, difference of ODI between admission/discharge, ODI at the time of discharge. ODI Oswestry Disablility Index, AUC area under the ROC curve, ODId the ODI score calculated by multivariate
Fig. 3 Correlation between response distribution of ODI question 4, 6 and two groups classified by cut-off value of ODI. ODI Oswestry Disability Index, 1–2, 3–6 indicate selected answer number of each ODI questions, ODI [30, ODI B30 indicate patient groups who have more than 30, equal or less than 30 of ODI score at the time of discharge
This study, however, has limitations. The interventions the patients received were non-surgical; different results may be observed with patients who have undergone surgery. Also, only 70.37 % of the patients participated in the follow-up at discharge. This could be because dissatisfied patients refused to respond. Trying to find a link between satisfaction levels, a subjective opinion and ODI, an objective score, may be inappropriate. The 40 patients (those who were satisfied at the time of discharge but reported an increased ODI score) excluded from this study, although a minority, may represent such limitations of this study. As for these 40 patients, we weigh in on the possibility that the 40 patients had either established a close rapport with the medical staff and therefore were satisfied with the overall treatment or failed to establish a close rapport with the medical staff, did not understand the questionnaire, or simply neglected to pay full attention to the process. The best possible treatment for LBP involves active participation in everyday life [16]. Because the patients have limited medical knowledge, the doctor needs to present an optimal time of discharge. For this type of
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regression model, ODI1 ODI at the time of admission, ODI2 ODI at the time of discharge, ODI1–ODI2 the change of ODI score between at the time of admission and discharge
decision-making, not only medical knowledge but satisfaction levels should be considered because it represents cost-effectiveness of the treatment as well as the net change in the patient’s condition. This study is meaningful in that if the cut-off value implements an agreed point between the patient who wishes to fully recover before discharge and the doctor who wants to encourage early return to normal life. Such objective cut-off value is not only valuable for clinical but also for research purposes; it can serve as a standard for evaluation of functional improvement. As any underlying spinal disorders may have negatively affected satisfaction rates, type of chief disease and satisfaction rates were screened for any correlation. Having spinal stenosis, spondylolisthesis, scoliosis, compression fracture, sprain, etc., did not affect satisfaction in any way. The ODI cut-off prediction model in this study that takes into account sex, age, ODI1, duration of pain, and presence of radiculopathy is relatively less significant that the model testing for ODI2 as shown by ROC curve analysis. Table 1 shows that acute/chronic states did not affect satisfaction levels. Duration of the onset did not affect satisfaction levels. Unsatisfied patients constituted a very small minority and most patients were diagnosed with herniated intervertebral discs; thus, it was difficult to find any statistical correlation. Further research with a larger pool of diverse patients is needed. Patients diagnosed with LBP accompanied by disability primarily undergo surgery or hospitalization, both of which incur steep medical costs. It is therefore important to identify an appropriate time for treatment and management. This study set a guideline for the evaluation of recovery in LBP patients with severe functional disability. This cut-off value is expected to serve as an important tool for the evaluation of treatment outcomes and for determining the type of treatment best suited for the patient.
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Eur Spine J (2014) 23:2090–2096 None.
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ORIGINAL ARTICLE
The dischargeable cut-off score of Oswestry disability index (ODI) in the inpatient care for low back pain with disability Sang-won Park • Ye-sle Shin • Hye-jin Kim Jin-ho Lee • Joon-Shik Shin • In-Hyuk Ha
•
Received: 14 February 2014 / Revised: 29 July 2014 / Accepted: 30 July 2014 / Published online: 7 August 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose The admission due to low back pain (LBP) became prevalent cause of international economic losses. Since LBP patients with disability are often subject to inpatient care, it is important to determine the appropriate time of discharge. The purpose of this study is to set the cut-off value of appropriate Oswestry Disability Index (ODI) at the time of discharge. Methods Of 1,394 LBP patients admitted in hospital specialized in spinal disease, 774 eligible patients with disability were included in this study. And several clinical variables including numerical rating score, ODI, satisfaction level were observed during the hospital stay. We considered satisfaction level as an important factor for discharge, categorized patients into satisfied group and dissatisfied group. Through the statistical analysis, appropriate factor for determining dischargeable patients satisfied with their current condition and its cut-off value of ODI were found. And proper predictors for the cut-off value were extracted statistically and logically from a pool of several clinical indexes. Results The ODI at the time of discharge was most accurate in determining dischargeable patients. The cut-off value of ODI was 30. Predictors were ODI questions 4 and 6. Conclusion We set the cut-off value of dischargeable ODI for LBP inpatient with disability and found its predictor.
S. Park Y. Shin H. Kim J. Lee J.-S. Shin I.-H. Ha (&) Jaseng Spine and Joint Research Institute, Jaseng Medical Foundation, Jaseng Hospital of Korean Medicine, 858 Eonju-ro, Gangnam-Gu, Seoul, Republic of Korea e-mail: [email protected]
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Keywords Oswestry Disability Index (ODI) Cut-off value Discharge Low back pain (LBP)
Introduction Low back pain (LBP) is an impending problem in the field of public health due to its high prevalence rate. The total prevalence rate of LBP was 31.0 % in a 2012 study and LBP is known to affect time off work more than any other medical condition [1, 2]. Despite the fact that LBP accompanied by functional disability is relatively less prevalent than LBP alone, patients with disability are responsible for the majority of the total medical expenses that go into LBP treatment [3]. As patients with functional disability cannot fully participate in everyday activities, they are often subject to inpatient care. In the USA, disorders associated with LBP were the 2nd and 4th most frequent causes of hospitalization in the 18–44 and 45–64-year-old population, respectively [4]. As for Korea, where a dual healthcare system (a system where both conventional medicine and Korean Medicine are legally recognized by the government) has been settled, LBP was the 7th most prevalent cause of inpatient care in conventional hospitals and 1st in Korean Medicine hospitals [5]. According to a 2012 study by a national institution in Korea that specializes in complementary alternative medicine (CAM), inpatients hospitalized for lumbar spinal disorders spent six times more total medical costs than outpatients [6]. This implies that inpatient care causes considerable socioeconomic losses. However, there are no guidelines for admission/discharge of patients with LBP. In clinical settings, decisions to admit/discharge patients tend to be based solely on subjective opinion of the doctor [7]. Not only is quick
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recovery and return to social life important for the patient’s quality of life, it is important for socioeconomic reasons as well. Therefore, for best effective inpatient care, an appropriate cut-off point is needed. The Oswestry Disability Index (ODI, version 2.0) has been validated in Korean and thus has proprietary [8, 9]. Because ODI is sensitive to continuous pain with severe disability [10], it is better than the Roland-Morris Disability Questionnaire for evaluating patients who have been considered for hospitalization. The ODI includes 1 question about pain and 9 questions about daily life. It is an easy-to-use, psychometric, practical tool [10]. The purpose of this study is to set a cut-off ODI score that represents a ‘‘satisfactory’’ condition; a condition appropriate for discharge. A cut-off value can provide objective guidelines to decisions that were once made by subjective judgment. Another purpose of this study is to identify any factors that can be examined to predict whether the patient’s ODI will exceed the cut-off.
Materials and methods 1,394 inpatients admitted to an integrative hospital specializing in spinal disorders between June 2012 and September 2013 were considered. Patients admitted multiple times were recognized once, only for their first admission. 849 patients responded to both ODI questionnaires (at admission and discharge) and a satisfaction level survey (at discharge). An ODI score greater than 12 is considered to be indicative of functional disability [16]. Therefore, 35 patients who reported an ODI score of less than 12 were excluded. 40 patients who reported increased ODI scores despite being ‘‘satisfied’’ were excluded because such responses were considered irrational. A total of 774 patients were included (Fig. 1) in the final study. Baseline characteristics, including the chief disease as diagnosed by a doctor, were tested for any significant differences between the satisfied and unsatisfied groups. This study was recognized by the IRB at Jaseng Hospital of Korean Medicine. Physicians interviewed the patient for baseline characteristics, current symptoms, and outcome measures numeric rating scale (NRS), ODI at the time of admission (ODI1), ODI at the time of discharge (ODI2), satisfaction level. They performed any necessary physical examinations and entered the information to an electronic medical data system devised for prospective research. The Korean version of the ODI, verified as reliable and valid by Kim et al. [9] was used. A 4-point Likert scale (excellent, satisfactory, poor, and extremely poor) was used to evaluate satisfaction levels at the time of discharge. While Likert scales usually include 5
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Fig. 1 Flow diagram of the study. ODI Oswestry Disability Index, ODI1 ODI at the time of admission, ODI2 ODI at the time of discharge. *In case of the patient who admitted several times, his/her first admission was only considered
or 7 points, a 4-point scale was used to avoid central tendency bias [11]. Patients who responded ‘‘excellent’’ and ‘‘satisfactory’’ were considered to be satisfied and ‘‘poor’’ and ‘‘extremely poor’’ to be unsatisfied. The difference in the ODI scores between the two groups was important for setting the cut-off value. Statistical analyses A Chi squared test was used to identify the differences in the baseline characteristics between the satisfied and unsatisfied groups that may affect satisfaction levels. For the individual items of each subgroup, the differences were validated by a t test. As for the distribution of different types of disorders, fisher’s exact test was used. To evaluate the accuracy of the tests intended to predict outcomes of either/or questions, sensitivity and specificity are commonly used. To determine the effectiveness of the analysis and to set a cut-off ODI value, a receiver operation characteristic (ROC) curve was used. The area under ROC curve (AUC) was observed to compare the three ODIs [ODI2, ODI1–ODI2, and derived ODI by a regression model (ODId)]. The accuracy of an ROC curve can be determined as uninformative (AUC B0.5), less accurate (0.5 \ AUC B 0.7), somewhat accurate (0.7 \ AUC B 0.9), very accurate (0.9 \ AUC \ 1) and perfectly accurate (AUC = 1) [12]. A cut-off value was set using an ROC curve where positive values represented the ‘‘satisfied’’ group. Based on clinical experience, five factors that were most likely to affect ODI2 (sex, age, ODI1, duration of pain, presence of radiculopathy) were selected. The statistical significance of the five factors was verified with a multivariate regression analysis (R-square 0.27) and ODId was
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derived using this model. Although the adjusted R-square value was a low 0.27, the purpose of this modeling was not to pinpoint a specific ODI score but to derive ODI scores reflecting the individual characteristics of the patient. Thus, this modeling seems to be appropriate. Of the three ODIs, the one with an AUC value closest to 1 was considered to be the most acceptable. The best fit classifier was used to set a cut-off value. To identify any pre-indicators for differentiating patients below the cut-off value from the patients above it, t tests were conducted for 30 factors. The five that showed the most significant differences were considered to be possible pre-indicators. SPSS software (Version 18.0, SPSS Corp., Chicago, IL, USA) was used.
Results The study population was 43.13 years old and 48 % male. Mean hospital day was 23.26 days, and the mean ODI1 was 49.63. The mean NRS of LBP was 5.99 whereas NRS of radiating pain was 5.36. 32 % had experienced LBP for less than 4 weeks, 21 % for 4–12 weeks, 15 % for 13–24 weeks, and 32 % for more than 24 weeks. The majority of the patients had acute LBP (onset \4 weeks ago) or chronic LBP (onset [24 weeks ago). 55 % had LBP with radiculopathy. The factors that were significantly different between the satisfied/unsatisfied groups were age, presence of any radiculopathy, and ODI scores. Distributions of chief diseases were not significantly different. Preexisting degenerative conditions such as spinal stenosis did not affect satisfaction levels. Even baseline characteristics that were significantly different between the two groups were not greatly different; all the above-mentioned factors have been put under consideration for our prediction model (Table 1). The mean ODI2 was 22.91 (n = 527) and 42.99 (n = 247) in the satisfied and unsatisfied group, respectively (p \ 0.0001). The differences in the ODI scores were notable as well; satisfied patients reported a 24.16 decrease in their ODI scores while unsatisfied patients reported a 12.12 decrease (p \ 0.0001) (Table 2). Based on such results, satisfaction levels were hypothesized to be a valid pre-indicator for discharge and thus a subsequent ROC analysis was conducted. Regression analysis showed that the five factors considered were significantly correlated with actual ODI scores at discharge (p \ 0.05). The regression model was then used to predict ODI2, taking into account the individual characteristics of the patient. A comparison of AUC values on the ROC curve showed that the difference in ODI scores (ODI1–ODI2) and the
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ODId were not any better than the ODI2. The AUC of ODId was 0.679 and the ODI1–ODI2 was 0.692, the ODI2 was 0.88 (Fig. 2). The cut-off ODI at 78 % sensitivity and 82 % specificity was 30. Then, any pre-indicators that could be used to differentiate between the ODI [30 group and the ODI B30 group were looked for. For this, 30 factors (The NRS of LBP and radiating pain, the difference of the NRS scores at baseline and discharge, the difference in total ODI, responses to individual questions of the ODI1 and ODI2, SLR, ROM) were tested for any correlation with ODI2 scores. The two groups were significantly different for all 30 factors. The 5 factors that were most different were questions 3, 4, 6, 9, and 10; lifting, walking, standing, social activities, and traveling. Of the 5 questions, those that the patients in the ODI [30 group and the ODI B30 group replied most differently to were searched for. Questions where (1) 80 % or more of the ODI B30 group chose 1 or 2 or (2) the difference between the percentage of respondents choosing 1–2 was greater than 40 % in the two groups were questions 4 (walking) and 6 (standing) (Fig. 3).
Discussion This study reported that satisfaction levels of patients hospitalized for LBP can be predicted using the ODI2. The AUC value was 0.88, making this an appropriate approach. The cut-off point of ODI2 was 30. Of the many clinical variables, those best suited for the prediction of cut-off scores were questions 4 and 6 of the ODI questionnaire. Tonosu et al. [13] reported that the mean ODI of patients experiencing more than one day of job loss was 22.07 whereas the mean ODI score of patients with no disability was 11.88. The cut point between the two was 12. On the other hand, the results of this study showed that the mean ODI of satisfied patients were 24.13 and the cut point between satisfaction and dissatisfaction was 30. Such a difference may be because Tonosu et al. study defined functional disability as a day or more of job loss but such patients may not consider inpatient care. Only 20–30 % of LBP patients seek medical care [14, 15]. Because there is not a notable difference between the normative score (8) and the cut-off score (12), this does not seem to be an appropriate way to filter out LBP patients with severe problems. The patients included in this study are patients in more severe conditions and are therefore more interesting subjects for research. The cut-off values presented in this study was close to the cut-off ODI value presented in a previous study that reported 29 to be a cut-off ODI score for somewhat satisfied patients who had undergone surgery [17].
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Table 1 Basic demographics at admission
Satisfied group
Unsatisfied group
Sex, male (%)
50 (266)
43 (105)
Age (years), mean (SD)
41.09 (13.89)
47.12 (14.97)
0.039b \0.001c 0.328b
Exercise Regular exercise
p value
43 % (206)
39 % (82)
Frequency (days/week), mean (SD)
3.65 (1.79)
3.82 (1.85)
0.419c
Time (min/day), mean (SD)
62.20 (47.30)
66.50 (53.30)
0.394c
57 % (277)
61 % (130)
Irregular exercise or no
0.063b
Job distribution Manager or professional
24 % (106)
22 % (47)
Clerks
23 % (104)
16 % (34)
Service or sales
12 % (55)
11 % (24)
Skilled agricultural, forestry and fishery
3 % (12)
5 % (11)
Craft or equipment operation and assembling
2 % (9)
2 % (4)
Elementary
3 % (14)
4 % (9)
33 % (149)
41 % (88)
Housewife or student (not specific) Smoking status Yes
0.955b 32 % (170)
32 % (78)
Average smoking year
14.94 (7.21)
16.53 (11.46)
0.297b
Average smoking cigarettes/day
13.65 (7.21)
14.96 (10.05)
0.571b
58 % (306)
58 % (144)
No
0.418b
Drinking experience Yes
70 % (403)
No in the past an year
11 % (61)
9 % (22)
20 % (84)
21 % (39)
Less than one time/month
73 % (180)
1 time/month
12 % (52)
14 % (26)
2–4 times/month
31 % (132)
18 % (32)
2–3 times/week
18 % (74)
12 % (22)
More than 4 times/week
5 % (21)
7 % (13)
15 % (82)
14 % (35)
No
0.025b
Spinal operation experience (patient history) Yes No
9 % (41) 91 % (416)
15 % (30) 85 % (172)
Length of hospital stay (day), mean (SD)
22.57 (11.59)
24.67 (11.96)
0.067b 0.002b
Proportion with duration of LBP (Month) \1 month
36 % (190)
23 % (56)
1–3 month
21 % (109)
25 % (62)
3–6 month
14 % (73)
15 % (38)
[6 month
29 % (151)
37 % (91)
Dominant pain categorya
\0.001c
Low back pain
50 % (261)
34 % (84)
Radiating pain
50 % (264)
66 % (163)
LBP
6.78 (1.53)
7.02 (1.63)
0.084b
Radiating pain
7.17 (1.34)
7.32 (1.59)
\0.001c
ODI (0–100), mean (SD)
54.51 (18.81)
46.50 (20.35)
\0.001c
Physical exam Straight leg raise test \60° (R)
12 % (64)
16 % (40)
0.057b
Straight leg raise test \60° (L)
16 % (82)
15 % (36)
0.537b
NRS (0–10), mean (SD)
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Table 1 continued
Satisfied group
Unsatisfied group
p value
Flexion
70.99 (28.76)
69.67 (28.98)
0.554b
Extension
16.76 (6.80)
15.88 (7.28)
0.14b
Rotation (R)
42.95 (8.09)
41.81 (10.37)
0.008b
Rotation (L)
43.24 (7.41)
41.87 (9.01)
0.055b
Lateral bending (R)
27.44 (6.50)
26.28 (7.34)
0.049b
Lateral bending (L)
27.66 (6.13)
26.53 (6.91)
0.243b
Lumbar ROM, mean (SD)
ODI Oswestry Disability Index, NRS Numeric rating scale, SD standard deviation a
Dominant pain category indicates that when NRS of low back pain is higher than NRS of radiating pain, the dominant pain is considered to be LBP
0.571d
Spinal disorder diagnosis herniated disc
85.93 % (397)
85.07 % (188)
Spondylolisthesis
1.08 % (5)
1.36 % (3)
Chi-square test were used for analysis
Stenosis
2.38 % (11)
3.62 % (8)
Scoliosis
0.22 % (1)
0.90 % (2)
c
Compression fracture
1.08 % (5)
1.81 % (4)
Sprain
6.71 % (31)
4.52 % (10)
Others
2.60 % (12)
2.71 % (6)
b
Student’s t test were used for analysis d
Fisher’s exact test were used for analysis Table 2 Discharge feature Satisfaction level
Number of subjects
ODI2
ODI2 (mean)*
ODI1– ODI$2
22.91
24.16
42.99
12.12
Satisfied group
Excellent
57
12.72
Satisfactory
470
24.14
Dissatisfied group
Poor
243
42.82
4
52.89
Extremely poor
ODI Oswestry Disablility Index, ODI1 ODI at the time of admission, ODI2 ODI at the time of discharge *,$
Both values are statistically significant at p value 0.05 (independent t test); p \ 0.0001
Although the two studies tested for different interventions, they both share similar results such consistency adds credibility to both studies. Another study by the same author reported that employment status and initial disability score greatly affected the effects of physical therapy and psychiatric treatment in a 1-year follow-up [18]. In this study, however, employment status does not seem to be any different between the two groups. Baseline ODI scores were, however, significantly different and thus was applied to a predictive model to find a cut-off ODI score. A core set of LBP evaluation criteria devised by experts in 2000 consists of 5 factors; pain intensity, LBP-specific disability, work disability, general functional status, and satisfaction with the process of care [19]. In this study, information on the patients’ age, gender, onset, NRS, baseline ODI, etc., was collected and each factor was tested for any correlation to satisfaction levels at the time of discharge.
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An analysis of baseline characteristics indicated that the higher the ODI1, the longer the duration of the pain and the older the patient, the higher the ODI2. Also, men and patients with radiculopathy as opposed to LBP alone reported higher ODI2. However, the absolute ODI2 was a more accurate pre-indicator than the relative ODId for determining the appropriate time for discharge. In evaluating treatment outcomes with ODI, minimally clinically important change (in most cases 10) is considered [20]. However, this is only a minimum difference, but probably not an appropriate guideline for the treatment of LBP patients. In this study, even the unsatisfied group experienced a 12.12 decrease in ODI2. ODI1–ODI2 was less accurate pre-indicator than ODI2 in differentiating between the more than 30/less than or equal to 30 groups. Because it is unrealistic to recheck ODI scores daily, various factors were examined to find ones that were most accurate pre-indicators for differentiating between the ODI [30 group and the ODI B30 group. T test results showed that five factors that were most significantly different between the two groups were coincidentally all a part of ODI2; questions number 3, 4, 6, 9, 10. The two groups responded most differently to question 6 (standing); there was a 50 % difference. Thus, it can be said that if a patient replies ‘‘Can stand for more than an hour’’ or longer, this patient will probably be included in the ODI B30 group. As for question 4 (walking), if the patient cannot ‘‘walk more than 500 m’’, it is very this patient will probably be included in the ODI [30 group. In clinical settings, if a patient can walk more than 500 m and/or stand for longer than an hour, it can be presumed that they will report an ODI score of less than 30 and be content with their current state, thus allowing them to be discharged.
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Fig. 2 Receiver operation Characteristic (ROC) curvature of predictive models, difference of ODI between admission/discharge, ODI at the time of discharge. ODI Oswestry Disablility Index, AUC area under the ROC curve, ODId the ODI score calculated by multivariate
Fig. 3 Correlation between response distribution of ODI question 4, 6 and two groups classified by cut-off value of ODI. ODI Oswestry Disability Index, 1–2, 3–6 indicate selected answer number of each ODI questions, ODI [30, ODI B30 indicate patient groups who have more than 30, equal or less than 30 of ODI score at the time of discharge
This study, however, has limitations. The interventions the patients received were non-surgical; different results may be observed with patients who have undergone surgery. Also, only 70.37 % of the patients participated in the follow-up at discharge. This could be because dissatisfied patients refused to respond. Trying to find a link between satisfaction levels, a subjective opinion and ODI, an objective score, may be inappropriate. The 40 patients (those who were satisfied at the time of discharge but reported an increased ODI score) excluded from this study, although a minority, may represent such limitations of this study. As for these 40 patients, we weigh in on the possibility that the 40 patients had either established a close rapport with the medical staff and therefore were satisfied with the overall treatment or failed to establish a close rapport with the medical staff, did not understand the questionnaire, or simply neglected to pay full attention to the process. The best possible treatment for LBP involves active participation in everyday life [16]. Because the patients have limited medical knowledge, the doctor needs to present an optimal time of discharge. For this type of
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regression model, ODI1 ODI at the time of admission, ODI2 ODI at the time of discharge, ODI1–ODI2 the change of ODI score between at the time of admission and discharge
decision-making, not only medical knowledge but satisfaction levels should be considered because it represents cost-effectiveness of the treatment as well as the net change in the patient’s condition. This study is meaningful in that if the cut-off value implements an agreed point between the patient who wishes to fully recover before discharge and the doctor who wants to encourage early return to normal life. Such objective cut-off value is not only valuable for clinical but also for research purposes; it can serve as a standard for evaluation of functional improvement. As any underlying spinal disorders may have negatively affected satisfaction rates, type of chief disease and satisfaction rates were screened for any correlation. Having spinal stenosis, spondylolisthesis, scoliosis, compression fracture, sprain, etc., did not affect satisfaction in any way. The ODI cut-off prediction model in this study that takes into account sex, age, ODI1, duration of pain, and presence of radiculopathy is relatively less significant that the model testing for ODI2 as shown by ROC curve analysis. Table 1 shows that acute/chronic states did not affect satisfaction levels. Duration of the onset did not affect satisfaction levels. Unsatisfied patients constituted a very small minority and most patients were diagnosed with herniated intervertebral discs; thus, it was difficult to find any statistical correlation. Further research with a larger pool of diverse patients is needed. Patients diagnosed with LBP accompanied by disability primarily undergo surgery or hospitalization, both of which incur steep medical costs. It is therefore important to identify an appropriate time for treatment and management. This study set a guideline for the evaluation of recovery in LBP patients with severe functional disability. This cut-off value is expected to serve as an important tool for the evaluation of treatment outcomes and for determining the type of treatment best suited for the patient.
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Eur Spine J (2014) 23:2090–2096 None.
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