Published May 14, 2021
Editor’s note: This story first appeared on the IASP Pain Research Forum and has been lightly edited for RELIEF.
How common is the transition from acute to chronic low back pain (LBP)? And what are the risk factors behind it? It’s been difficult to answer these questions, in part because of the absence of a standardized definition of both acute and chronic LBP.
Now, Joel Stevans, University of Pittsburgh, US, and colleagues use standardized definitions in a new clinical study and find that more than a third of patients with acute LBP transition to chronic LBP within six months.
The researchers also show that early exposure to care that is inconsistent with recommended guidelines for back pain treatment increases the likelihood of the transition.
Finally, the study also found that a prognostic tool called the Subgroups for Targeted Treatment (STarT) Back tool (SBT) did a good job in predicting who would go on to have chronic LBP.
The study was published February 16, 2021, in the journal JAMA Network Open.
Stopping the problem before it starts
Acute LBP is an extremely common condition, but most cases of it are presumed to have a favorable prognosis. But once it becomes chronic, LBP is an expensive and highly disabling condition to manage, highlighting the urgency of preventing the transition.
Previous reports have varied with respect to the proportion of patients who transition from acute to chronic LBP. A 2010 review of 20 studies reported that a median of 26% of patients (a range of 2%-48%) with acute LBP in primary care settings transition to chronic LBP.
Much of this wide variability can be attributed to inconsistent definitions of acute and chronic LBP used in such studies. To combat this problem, the National Institutes of Health (NIH) Pain Consortium previously convened a Research Task Force to develop a standardized definition of chronic LBP, which the researchers would use in the current study.
The Task Force also recommended the study of tools like the SBT. This tool had previously been found to perform well in predicting poor functional outcomes. However, it had not been tested as a potential prognostic tool for the transition from acute to chronic LBP. So the current research explored that aspect as well.
Recent clinical guidelines for acute LBP have highlighted that non-pharmacologic interventions, such as heat, massage, acupuncture, or spinal manipulation should be first-line treatment options. Importantly, treatments such as the initial use of diagnostic imaging, specialist consultation, and opioids (in the absence of warning signs like fever, fracture, or cancer) are not recommended. Using treatments that are not recommended – so-called non-concordant care – can be harmful, but it was unclear how non-concordant care affects the transition from acute to chronic LBP, thus providing another matter the current study would take on.
“In response to a call from the Patient-Centered Outcomes Research Institute, we formed a team of experienced LBP investigators representing four geographic areas across the US,” wrote study author Anthony Delitto, University of Pittsburgh, US, in an email to RELIEF. “[We wanted to] undertake a study that would investigate strategies to prevent acute LBP from transitioning to chronic LBP.”
The study design
The researchers undertook what is known as an inception cohort study that would look at people at an early stage of their back pain (an inception cohort study is a type of study where researchers observe patients over time but do not subject them to an experimental manipulation, in contrast to a randomized clinical trial, in which researchers do intervene). This study took place alongside the Targeted Interventions to Prevent Chronic Low Back Pain in High-Risk Patients (TARGET) randomized clinical trial. The TARGET trial was testing whether the addition of psychologically informed physical therapy to usual care was better than usual care alone.
Adults with acute LBP were stratified at the start of the study according to their SBT risk. Those at high risk took part in the randomized trial and cohort studies, while those with low or medium risk took part only in the cohort study.
Tasha Stanton, who studies back pain at the University of South Australia in Adelaide but was not involved in the new study, said the authors’ research design was “really innovative.”
“In addition to the people they followed as part of the randomized trial component, they also invited anyone who didn’t meet the randomized trial criteria to participate in an observational cohort study,” said Stanton. “This is perfect, because clinical trials exclude so many people. In this case, the researchers have used this to their advantage. People who want to participate and who met some, but not all of the eligibility criteria could still be studied.”
The study participants were enrolled in 77 primary care practices in four US health systems, in Pennsylvania, Massachusetts, Utah, and Maryland and assessed for whether they had or did not have chronic LBP at baseline and then six months later.
The NIH Task Force definition of chronic LBP adapted in this study defined it as pain lasting more than three months and interfering with regular daily activities on at least half the days over the past six months.
The study made use of electronic medical records to examine LBP-related care that patients had received. These processes of care were categorized as pharmacologic therapies, diagnostic imaging, or medical subspecialty referrals. Each process of care was further categorized as concordant or non-concordant with clinical guidelines.
The results are in
Overall, about one in three patients (1,666 of 5,233 who completed the follow-up) had transitioned from acute to chronic LBP at the six-month mark. Nineteen percent (333 of 1,788) of low-risk patients transitioned to chronic LBP at the six-month mark. This figure increased to 33% (703 of 2,152) and 49% (630 of 1,293) in the medium- and high-risk groups, respectively.
“[The] overall transition to chronic LBP at six months was higher than published estimates,” Delitto noted.
The association between risk according to the SBT and the transition to chronic LBP at six months was also one of the key findings from the study.
“This result suggests that as a prognostic screening tool, the SBT has some validity in understanding the trajectory and course of acute LBP,” Stanton said.
When the researchers looked across risk levels, they saw that many study participants had received non-concordant care, including 1,544 (30%) who had been given prescriptions for non-recommended drugs (65% of whom received opioid prescriptions). About 25% received X-ray or computed tomography/magnetic resonance imaging (CT/MRI) orders, and 6% were referred to a medical specialist.
Each type of non-concordant care increased the risk of the acute to chronic LBP transition, with transition rates increasing the more non-concordant care processes there were.
Next, using a statistical model in which the researchers controlled for variables that could affect the results, the researchers found that patients in the medium-risk group at baseline had 1.59 times the odds of developing chronic LBP at the six-month mark compared to the low-risk group. Patients in the high-risk group had 2.45 times the odds of developing chronic LBP compared to the low-risk group.
Other factors associated with the transition from acute to chronic LBP included baseline disability, health insurance, obesity, smoking status, and psychological conditions that patients also had. Further, patients exposed to one, two, or three non-concordant care processes had 1.39, 1.88, and 2.16 times the odds of developing chronic LBP at six months, respectively, compared to patients who were not exposed to any non-concordant processes of care.
“Observing that smoking, obesity, and depression/anxiety were predictors of the transition to chronic LBP was not surprising,” Delitto wrote to RELIEF. “However, when these factors were controlled for, non-concordant care predicted the transition to chronic LBP.
“Non-concordant care in patients who initially present with acute LBP is common, particularly in primary care settings. In most cases, non-concordant care is deemed wasteful. However, in this study, we provide evidence of its potential harm,” Delitto continued.
While the results add to the understanding of risk factors for the acute-to-chronic LBP transition, Stanton highlighted that a cautious interpretation of the data is needed.
“This study used the definitions for acute and chronic LBP as recommended by the NIH. But it’s important to acknowledge that the way they’ve defined this [acute-to-chronic transition] doesn’t allow for easy comparisons with other study populations and results. If the definitions used in the study are different, then you have an inherently different population.”
Stanton also warned of confusing correlation with causation.
“It’s tempting to interpret these results as a causal effect, [where] receiving non-concordant care results in the increased transition to chronic LBP,” she said. “However, with this type of study design, it’s not possible to say that getting non-concordant care is causal. It’s associated with an increased transition, but we can only conclude that the ‘type’ of people who received non-concordant care were more likely to transition to chronic LBP.”
Still, the new research documents the large scope of the problem of the transition from acute to chronic LBP, adding urgency to efforts to prevent it. It also highlights the need to better implement guideline-concordant care successfully in primary care settings and understand why many patients don’t yet receive it.
Lincoln Tracy, PhD, is a researcher and freelance writer based in Melbourne, Australia. Follow him on Twitter @lincolntracy.