Prediction of Outcome in Patients with Low Back Pain --
A Prospective Cohort Study Comparing Clinicians'
Predictions with those of the Start Back ToolThis section was compiled by Frank M. Painter, D.C.
Send all comments or additions to: Frankp@chiro.org
FROM: Manual Therapy 2016 (Feb); 21: 120–127 ~ FULL TEXT
Alice Kongsted, Cathrine Hedegaard Andersen,
Martin Mørk Hansen, Lise Hestbaek
Nordic Institute of Chiropractic and Clinical Biomechanics,
Odense, Denmark;
Department of Sports Science and Clinical Biomechanics,
University of Southern Denmark,
Odense, Denmark.
a.kongsted@nikkb.dk
The clinical course of low back pain (LBP) cannot be accurately predicted by existing prediction tools. Therefore clinicians rely largely on their experience and clinical judgement. The objectives of this study were to investigate
1) which patient characteristics were associated with chiropractors' expectations of outcome from a LBP episode,
2) if clinicians' expectations related to outcome,
3) how accurate clinical predictions were as compared to those of the STarT Back Screening Tool (SBT), and
4) if accuracy was improved by combining clinicians' expectations and the SBT.Outcomes were measured as LBP intensity (0-10) and disability (RMDQ) after 2-weeks, 3-months, and 12-months. The course of LBP in 859 patients was predicted to be short (54%), prolonged (36%), or chronic (7%). Clinicians' expectations were most strongly associated with education, LBP history, radiating pain, and neurological signs at baseline and related to all outcomes.
The accuracies of predictions made by clinicians (AUC .58-.63) and the STarT Back Screening Tool (SBT) (AUC .50-.61) were comparable and low. No substantial increase in the predictive capability was achieved by combining clinicians' expectations and the SBT. In conclusion, chiropractors' predictions were associated with well-established prognostic factors but not simply a product of these. Chiropractors were able to predict differences in outcome on a group level, but prediction of individual patients' outcomes were inaccurate and not substantially improved by the SBT. It is worth investigating if more accurate tools can be developed to assist clinicians in prediction of outcome.
From the FULL TEXT Article:
Introduction
A large number of prognostic factors have been identified in non-specific low back pain (LBP), but these generally have rather weak associations with outcome (Kent and Keating, 2008), and most investigated predictive models have not demonstrated adequate predictive value to be useful in relation to individual patients (Hayden et al., 2010). Still, clinicians need to make decisions about treatment plans every day and are repeatedly faced with patients wanting to know their most likely prognosis.
Lacking convincingly helpful predictive models, clinicians rely on experience and subjective judgement when establishing a patient's prognosis. The LBP prognosis established by general practitioners (GPs) has been consistently associated with outcome in studies investigating this, but although comparable to that of validated questionnaires (Jellema et al., 2007), the predictive accuracy of clinicians' prognostic estimation was quite low (Schiottz- Christensen et al., 1999; Jellema et al., 2007). Also, chiropractors were not able to accurately predict poor treatment outcomes when asked to register “whether they thought patients were less likely than average to report a good outcome following a course of care” (Newell et al., 2013). In addition, there is evidence suggesting that the prediction differs substantially between clinicians (Hill et al., 2010).
In elderly patients with musculoskeletal pain, GPs' prediction of outcome has been shown to improve if combining their subjective judgements with just three factors obtained from the patient history (Mallen et al., 2013). In non-specific LBP, the STarT Back Screening Tool (SBT) is an easily completed scale that combines potentially modifiable prognostic factors. It has shown promising for assisting GPs' decision about the treatment plan (Hill et al., 2008, 2011), and it may provide a simple tool to improve clinicians' prediction of outcome.
Clinicians' estimation of prognosis potentially differs from that of standardised screening if clinicians value other factors than those typically registered. It is not investigated to what extent clinicians' estimation of prognosis is based on established prognostic factors, but in one study factors such as pain intensity, level of disability, and number of previous episodes were associated with clinicians' prediction (Perrot et al., 2009). In a consensus process it was recognised that clinicians found issues such as ‘generally difficult life circumstances’ of importance for the prognosis and this construct is most likely not easily captured by screening tools (Hill et al., 2010). More accurate prognoses are essential to inform patients about their condition and to guide treatment, for instance by early identification of patients with more extensive treatment needs. Therefore, this study aimed to increase the understanding of clinicians' expectations of patient outcome in LBP.
This study comprised a cross-sectional and a longitudinal part. The objectives of the cross-sectional part were to determine:(1) which individual patient characteristics were associated with chiropractors' expectations of outcome from a LBP episode, and
(2) how closely the chiropractors' expectations could be predicted by a combination of these patient characteristics.Since no empirical data could support the choice of investigated patient characteristics this part should be considered hypothesis generating.
The objectives of the longitudinal part were to determine:(1) the association between chiropractors' expectations of clinical course and outcome after 2 weeks, 3 months, and 12 months,
(2) how clinicians' expectations (3-level subjective judgement) performed compared to that of the SBT (3-level standardised tool), and
(3) to what extent combining clinicians' expectations with the SBT increased the amount of variation explained in outcome.
Method
The study is based on a cohort study which has previously been described (Eirikstoft and Kongsted, 2014), and consisted of patients visiting one of 40 chiropractors at 17 Danish chiropractic clinics due to a new episode of LBP. In Denmark, chiropractors belong to the public primary health care sector, patients can consult without referral and the expenses are partly covered (approximately 20%) by national health insurance. The participating clinics were members of a group of research clinics affiliated with the Nordic Institute of Chiropractic and Clinical Biomechanics. The chiropractors attended a one day course introducing study procedures and a research assistant visited all clinics prior to study start to repeat general information and ensure that clinical examination procedures (relevant for the main study) were adequately standardised. Collection of data on clinicians' expectations was not introduced from the beginning of patient recruitment and the present study therefore concerns a slightly smaller cohort than reported on before. According to the local ethical committee the study did not require ethical approval. (Danish National Commitee)
Procedures
Baseline questionnaires were completed in the reception area prior to the first consultation. Completed questionnaires were returned to the receptionist in a closed envelope and were not available to the chiropractor. There were no specific instructions to patients whether they could discuss the content of the questionnaire with the chiropractor. Clinicians obtained a patient history as they found appropriate and did a standardised clinical examination (Eirikstoft and Kongsted, 2014). Results from the clinical examination and the clinician's expectations were registered in a web based registration form. Treatment was unaffected by study participation and the chiropractors had no access to questionnaire data. Follow-up questionnaires were mailed to participants after 2 weeks, 3 months, and 12 months. Participants not responding were contacted by a research assistant to make sure they had received the questionnaire. All questionnaires were sent directly to the research department and patients were informed that their responses would not be revealed to the chiropractors and only reported in an anonymous form.
Participants
Consulters with non-specific LBP or lumbar nerve root involvement (based on usual clinical practice for diagnostic triage) aged 18–65 years who could read Danish and were able to respond to SMS-questions on a mobile phone (for reasons unrelated to this part of the study) were potential participants. Patient were not eligible if pregnant, if acute surgical referral was needed, or if having had more than one contact to a health care provider due to LBP within the preceding three months. In addition participants were excluded from the analyses if the clinician's expectation was missing.
Clinicians' expectations of clinical course
The final question of the clinical examination form was (translated from Danish) ‘What outcome do you expect for this patient?’ with four response options: 1) Short/uncomplicated course, 2) Prolonged but without lasting consequences, 3) Long-lasting/ sustained consequences (high risk of chronicity), or 4) Don't know. The expectation categories are hereafter referred to as short/ uncomplicated, prolonged, and long-lasting/chronic.
Baseline information
Table 1 Patient-reported baseline variables and their categorization are listed in Table 1. Body mass index was collected as weight and height. LBP and leg pain intensity were measured on 0e10 Numeric Rating Scales (Jensen et al., 1998), and activity limitation on the Roland Morris disability questionnaire (RMDQ) as a proportional score 0e100 (Kent and Lauridsen, 2011). Fear avoidance was measured by the physical activity section of the Fear Avoidance Beliefs Questionnaire (FABQ) (0e24) (Waddell et al., 1993), depression by the Major Depression Inventory (MDI) 0e50 (Bech et al., 2001),, and general health using the health thermometer of EQ-5D (0e100) (Rabin and de Charro, 2001).
The SBT was scored and categorised as recommended by the developers of the tool (Hill et al., 2008). Items on aspects that were not considered covered by other questionnaires (item 2: Shoulder or neck pain, item 7: catastrophising, and item 9: bothersome pain) were separately included in the cross-sectional analysis of factors associated with clinicians' expectations. The Quebec classification (Spitzer et al., 1987), was registered as part of the examination form completed by the clinician, and nerve root involvement and spinal stenosis were combined due to few observations.
Outcome measures
LBP intensity (NRS 0e10) and activity limitation (RMDQ 0e100) at 2-weeks, 3-months, and 12-months follow-up were outcome measures. The scales were used in their original forms and dichotomised to define poor outcome as LBP > 0 and RMDQ > 8 (RMDQ > 8 corresponded to >2 on the original 0e24 RMDQ (Kamper et al., 2010)).
Data analysis [can be omitted without loss of continuity]
Data were double entered into Epidata (Lauritsen, 2008), and analyses conducted in STATA SE/12.1.
To explore which patient characteristics were related to the clinicians' expectations of outcome, univariate associations were first tested by KruskaleWallis rank test (continuous variables) or Pearson's chi-squared test (dichotomous and categorical). We then did a multinomial multivariable regression with clinicians' expectations (4-level categorical) as the dependent variable to investigate which of the patient characteristics were associated with the clinicians' expectations of outcome independently of other measured factors. In this model all measured baseline factors were introduced simultaneously, and independent variables with p > .2 at all outcome levels were removed manually in a stepwise fashion without eliminating factors with a risk ratio above 1.5 or below .66.
Next, we calculated what the clinicians' expectation of outcome would be if this had been simply a product of the patient baseline characteristics. This was to understand how closely clinicians' judgements relate to measurable patient characteristics. To do that, we calculated the probability of belonging to each of the categories short/uncomplicated, prolonged and long-lasting when based on the full multinomial model described above. These predictions were compared to the actual expectations of the clinicians. If the expectations predicted from patient characteristics perfectly matched the clinicians' expectations of outcome, the predicted probability would be 100%, indicating that the clinicians' prediction was entirely based on the included characteristics. If, on the other hand, there was no match between predicted outcomes for a given category and the clinicians' expectations of outcome, the predicted probability would be 0%.
In the longitudinal part of the study patients in the ‘don't know’ category were excluded since we were interested in the predictive accuracy of clinicians' expectations only when they were able to come to a conclusion. Linear and logistic univariate regressions were performed to test for associations between prediction (clinicians' as well as prediction by the SBT) and outcome. Potential dependency between observations from the same clinics was taken into account using STATA's cluster option for robust variance estimation with clinics as cluster level.
The discriminative ability calculated as area under the curve (AUC) was compared between the clinicians' expectations and the SBT. Positive likelihood ratios (LHþ) for a poor outcome were calculated for each category of the clinicians' expectations and the SBT. The positive predictive value (PPV) for the short/uncomplicated category predicting a good 2-weeks outcome and for longlasting/ chronic predicting a poor 12-months outcome were calculated to represent the outcome that seemed to correspond best to the expectation categories provided to the clinicians. Similar PPVs were calculated for the SBT model. Finally, the amount of explained variance in continuous outcome measures (adjusted R-squared) was compared between the models and also used to quantify the effect of combining clinicians' expectations and the SBT.
For the multivariable analysis missing values on baseline factors were imputed by multiple imputations based on fully conditional specifications with five chained iterations without replacing missing values on outcome measures (Moons et al., 2006). No item had more than 7% missing values.
Results
Participants
Figure 1 Baseline information was available from 890 participants of which 31 (3%) were excluded from the analyses because there was no registration of the clinician's expectations. Characteristics of the study cohort (n = 859) and those excluded appear from Table 1. Patients with missing information had statistically significant less leg pain than the study cohort but otherwise no differences were detected. Follow-up questionnaires after 2 weeks, 3 months and 12 months were available from respectively 83%, 79%, and 74% of participants (Figure 1). Non-responders at the 12-months follow-up did not differ from responders regarding baseline LBP intensity, leg pain intensity, activity limitation, duration of LBP, sick leave, SBT risk group, or the clinician's expectations. However, nonresponders were on average 5.5 years younger and a larger proportion was male (63% vs. 54%), smoker (27% vs. 17%), and reported heavy physical workload (31% vs. 19%).
Cross-sectional part investigating clinicians' expectations
The chiropractors expected a short/uncomplicated course in 54% of the cohort, a prolonged course in 36%, a long-lasting/chronic course in 7%, and did not know what to expect in 3%. Patient characteristics are compared between these groups in Table 1. Gender, education, number of previous episodes, LBP last year, duration of the present episode, leg pain, activity limitation, SBT items, depression, general health, the Quebec classification, and whether the patient had previously visited a chiropractor were all associated with the expected prognosis in the univariate analyses (p < .05) (Table 1).
Table 2 A multivariable model demonstrated that independently of other measured factors, clinicians more often expected a prolonged or a long-lasting course than a short/uncomplicated in patients with higher BMI, more previous LBP, long duration of the present episode, more disability, radiating pain, and neurological signs and of female sex (Table 2). Having more than five years of education after finishing public school was associated with the clinicians predicting a short/uncomplicated course. Clinicians felt more often unable to predict the clinical course in patients with long duration, shoulder/neck pain or nerve root involvement whereas a long education, having light physical workloads, and age between 35 and 45 years reduced the likelihood of the clinician choosing the ‘don't know’ option (Table 2).
We used information from the baseline questionnaire to calculate which category (short/uncomplicated, prolonged or longlasting) the clinicians would be expected to assign each patient to if that decision could be explained as a product of just the factors registered in the questionnaire. When averaging across all categories, the probability that the outcome predicted by the combination of patient-reported baseline factors matched the clinicians' expectation of outcome was 62% (95% CI: 60e65%). The outcome category with the lowest probability for matching between the prediction from patient-reported baseline factors and the clinicians' expectation of outcome was for the long-lasting/chronic group at 18% (95% CI: 8e34%). These results imply that clinicians' expectations were likely based on other, and possibly more complex, factors than those registered in the baseline questionnaire.
Longitudinal part
Table 3
Figure 2
Table 4
Table 5
Table 6
Associations between chiropractors' expectations and outcome Clinicians' expectations were significantly associated with all outcome measures at all follow-up points. Table 3 shows the differences in mean LBP intensity and RMDQ scores between the short/uncomplicated group and the other groups (b-values), and the odds ratios for poor outcome in the prolonged and long-lasting/ chronic groups as compared to the short/uncomplicated group. LBP intensity and activity limitation in the expectation groups during the follow-up period are illustrated in Fig. 2.
Clinicians' expectations compared to the STarT Back Tool
The abilities of the clinicians' expectations and the SBT to discriminate patients with a poor outcome from others are presented in Tables 4 and 5. AUC values quantify the ability to discriminate between patients with good and poor outcome and range from .5 (no better than tossing a coin) to 1 (perfect discrimination). The discriminative ability of the clinicians' expectations (AUCs .58 to .63) and the SBT (AUCs .50 to .61) were of similar magnitudes and generally low. Because the number of patients in some categories was low some of the estimated likelihood ratios in Tables 4 and 5 are subject to uncertainty as apparent from the wide confidence intervals.
In the group expected by the clinicians to have a short/uncomplicated course, 11% were pain free (LBP = 0) after two weeks (PPV = .11; 95% CI: 8e15%), and similarly in the group predicted to be in low risk of poor prognosis by the SBT, 10% (95% CI: 6e14%) were pain free. The group expected to have long-lasting LBP by clinicians, 83% (95% CI: 67–93%) actually had a poor 12-months outcome, whereas this was only true for 60% (95% CI: 44–74%) in the high risk SBT group.
The clinicians' expectations as well as the prediction of outcome by SBT explained only little of the variation in the continuous outcomes, meaning that patient outcomes differed substantially within each prediction category. Clinicians' expectations and the SBT combined were slightly better than each of the two by themselves when predicting activity limitation after 3 and 12 months, but the proportions explained remained low (Table 6).
Discussion
Chiropractors expected a short uncomplicated course for about half of their LBP patients and a severe long-lasting course for less than 10% when asked to choose one of three prognostic categories. The clinicians' expected outcomes were associated with a number of previously identified prognostic factors. Long duration, radiating pain, and nerve root involvement were factors strongly associated with clinicians' expectations of a severe long-lasting course, whereas the registered psychological factors had no independent association with the expected prognosis. This is in contrast to the SBT in which identification of the 'high risk' category is based on psychological factors. Long duration and nerve root involvement also increased the probability of the clinician stating that he/she did not know which prognosis to expect. Despite individual associations with previously identified prognostic factors, combining the patient-reported baseline characteristics mathematically in a regression model did not accurately predict clinicians' expectations, especially when considering the long-lasting/chronic outcome category. These findings suggest that the clinicians' may have used other pieces of information to make their prognostic estimates. The clinical process of establishing a prognosis ought to be further elucidated in qualitative or mixed methods studies which may inform future development of prediction models.
The prognosis expected by the clinicians was significantly associated with the observed clinical course. The mean outcome in the expectation groups differed by a sufficient magnitude that we believe the groups were truly clinically different. However, prediction on an individual level was not accurate (as discrimination between patients with good and poor outcome was low), at least not when the clinical course was defined by the applied outcome measures. Compared to these outcome measures the expectations about outcome were generally overoptimistic as observed also in a recent study investigating GPs' prediction of outcome in musculoskeletal pain (Mallen et al., 2013). One possible explanation for the lack of accurate prediction is that the clinicians may have thought of expected ‘course’ as for instance expected number of treatments, whereas we tested if their predictions were in line with recovery from pain and activity limitation. The SBT was not helpful as a tool for increasing the accuracy of the prediction. That finding was in line with a previous study that did not find the SBT very useful as a prognostic tool in chiropractic practice (Field and Newell, 2012). It seems that the relatively low prognostic ability of the SBT in this cohort is related to many patients presenting with short duration of LBP (Morso et al., 2015), and it can be speculated that psychological factors may not be very influential in chiropractic patients as indicated by the only prospective study that we know of investigating this (Leboeuf-Yde et al., 2009), conceivably because psychological distress appears to be infrequent in chiropractic patients (Bolton, 1994; Leboeuf-Yde et al., 2009; Kongsted et al., 2011).
The main limitation of this study was that the measure of clinicians' expectations was not validated and it is uncertain to what extent the expectation question could be anticipated to match the outcome measures. It is possible that clinicians define ‘short and uncomplicated’ differently than being pain free and likewise it is unknown what clinicians would define as ‘prolonged’ or ‘longlasting’ since this was not specifically defined in the question. It may not be problematic that the positive predictive valuewas low if clinicians' definition of the prognostic categories is different from what was captured by our outcome measures; as long as they make sure that their patients have the same understanding when informed about prognosis. Future studies should use an expectation question that aligns closely with outcome as demonstrated by Mallen et al. (2013).
Still, the study provided new insights based on a large study sample with quite complete data and an acceptable drop-out rate that we did not suspect to influence conclusions. A further strength was the relatively large number of participating chiropractors which increased the generalizability of the results. The number of patients included by each clinician was not sufficient to investigate potential individual differences between clinicians.
In summary, chiropractors' expectations of the clinical course was associated with well-established prognostic factors but was not simply a product of these. Chiropractors were able to predict differences in outcome up to one year after the initial visit on a group level but did not predict individual patients' outcome precisely although as well as the SBT. Therefore it is worth investigating if more accurate tools can be developed to assist clinicians in prediction of outcome. Although subject to uncertainty, chiropractors identified a group with markedly increased risk of a poor outcome more precisely than the SBT and the development of prediction rules may benefit from understanding better how clinicians predict poor long-term outcome. In short, chiropractors cannot rely solely on their gut feeling when telling LBP patients what to expect, but they have an insight that may help researchers in the development of improved prediction tools.
Acknowledgements
The authors would like to thank the clinics that took part in the data collection. The Danish Foundation for Chiropractic Research and Post-graduate Education funded the study through an unrestricted grant (Grant No. 01/1624).
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