The recovery patterns of back pain among workers with compensated occupational back injuries

Objectives

To investigate the longitudinal patterns of recovery among workers with compensated occupational back injuries.

Methods

A longitudinal cohort study, with one‐year follow‐up via structured telephone interviews, among respondents off work because of “new” back injuries. Self‐reported pain intensity was recorded at baseline and at four follow‐up time points over the course of one year. Workers who answered the questionnaire on at least three occasions (n = 678) were classified into clusters according to their patterns of pain intensity over time using a two‐step cluster analysis.

Results

Four pain recovery patterns were identified: workers with high levels of pain intensity showing no improvement over time (43%); those experiencing recovery in the first four months with no further improvement or possibly even some deterioration, in the second half year (33%); those experiencing a slow consistent recovery but still with considerable back pain at the end of the follow‐up (12%); and those quickly progressing to low level of pain or resolution (12%). Trajectories of average Roland‐Morris Disability scores and SF‐36 Role of Physical scores for above clusters mapped consistently with the corresponding patterns in pain. However, individuals with fluctuating, recurrent pain patterns showed the shortest cumulative duration on 100% benefit and the earliest return‐to‐work among other clusters.

Conclusions

Four clinically sensible patterns were identified in this cohort of injured workers, suggesting inter‐individual differences in back pain recovery. The results confirm that recurrent or chronic back pain is a typical condition in respondents with new back injuries. Pain intensity and disability scores are good measures of recovery of back pain at the individual level. After initial return‐to‐work, or cessation of benefits, administrative measures of percentage of respondents back at work, or no longer on benefits, may not accurately reflect an individual''s condition of back pain.Low back disorders are the most common, costly and disabling of musculoskeletal health problem.¹ They are one of the most common reasons for visits to primary care,² and the single largest category of workers'' compensation claims in most compensation systems.³ While some cases of low back pain are transient and resolve or considerably improve over several weeks,^4,5 symptoms can often be recurrent or chronic.^6,7 Studies have shown that over 65% of back pain patients in primary care continued to experience at least mild pain one month after seeking care, and approximately 33% reported continuing pain of at least moderate intensity after 12 months.^5,8The course of back disorders can be characterised using measures of different aspects of health,⁹ such as pain, disability, activity limitations and/or participation.¹⁰ For instance, the course has been studied by assessing the prevalence of back pain at different time points, or by evaluating changes in the amount of pain across time in pre‐classified patient groups.^10,11,12 Transitions between different states such as resolution, improvement, aggravation and recurrence have also been used to study courses.¹³Participation in work is also a key outcome in studies of back pain. Duration of claim in workers'' compensation systems^10,14,15 and time to return to work^10,16 have also been used as end‐points in studies evaluating the duration of back‐pain episodes, or to identify prognostic factors or effective interventions. However, measures based on first return to work may underestimate the percentage of people impaired^17,18 because workers may continue to experience pain after returning to work, or may experience recurrent episodes of pain and disability. While some studies have shown a relation between pain and disability and time to claim closure,¹⁹ other factors also may influence the decision to return to work.¹⁰Von Korff described the course of back pain as highly variable, occurring in transient, recurrent, and chronic phases.⁷ Few longitudinal studies have been carried out to classify the different pathways of back pain.^13,20 Dunn et al used longitudinal latent class analysis to identify four groups of back pain patients with distinctive recovery patterns in a primary care setting.²⁰ It would be of interest to explore the course of back pain in a population of injured workers to determine similarities and differences to those among the general population.The purpose of this study is (1) to identify and summarise the course of pain in a cohort of injured workers off work because of back pain and (2) to describe the distribution of the patterns across other commonly used proxy measures of recovery.