IWH study finds 7 in 10 injured workers still experience pain more than a year after injury

Key messages

  • In a study of lost-time workers’ compensation claimants in Ontario, 70 per cent said they continued to experience pain 18 months after a work-related injury.  
  • Of those interviewed, 45 per cent had mild pain, and 25 per cent had severe pain which impeded their ability to return to work. 
  • Compared with injured workers with no pain, those with mild pain were three times more likely to be on workers’ compensation benefits for at least a year. Those with severe pain were nine times more likely. 

Link between pain severity and time off work also found in study of Ontario injured workers, conducted 18 months post-injury

Published: September 30, 2022

A high proportion of injured workers in Ontario experience persistent pain for well over a year after their work-related injury.

In a study that interviewed Workplace Safety and Insurance Board (WSIB) lost-time claimants, a research team at the Institute for Work & Health (IWH) found 70 per cent of workers said they continued to experience pain 18 months after their injury.

This percentage included 45 per cent who said they had mild pain that interfered with some of their normal activity, and 25 per cent who said their pain was so severe that it resulted in substantial impairment.

The prevalence of severe persistent pain among this group of workers is about six times higher than among Canadian and U.S. adult populations, where this level of pain is reported by about four per cent of adults, says Dr. Kathleen Dobson, an IWH associate scientist and lead author of a paper on the study, which was published in the journal Occupational and Environmental Medicine in July 2022 (doi:10.1136/oemed-2022-108383). She also shared findings in November 2022, in an IWH Speaker Series webinar.

The study found a relationship between pain severity and time off work. Compared with injured workers with no pain, those with mild pain were three times more likely to be on workers’ compensation benefits for at least a year. Those with severe pain were nine times more likely.

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A similar pattern was found for other health-related outcomes explored in the study. The more severe the pain, the more injured workers reported taking prescription opioids, using sedatives and experiencing poor physical and mental health.

Among the injured workers in the study who had no pain, only six per cent were still receiving health-care services for their injury at 18 months. That’s compared to 28 per cent with mild pain and 56 per cent with severe pain.

Our findings show that persistent pain of severe intensity arising from work-related traumatic injury impedes the ability to return to work, says Dr. Cameron Mustard, former senior scientist and president of the Institute, and principal investigator of the study. Among the population of individuals who experience persistent pain, most are unable to work, yet express a desire to do so.

18 months post-injury

The study draws on a longitudinal cohort (meaning a group that was followed over time) of injured workers who had a lost-time compensation claim with the WSIB.

The sample of 1,100 workers comprised three groups of workers in roughly equal numbers: those with short-duration claims (between five days and three months), those with medium-duration claims (three to 12 months) and those with long-duration claims (12 to 18 months). To obtain this sample, the team had to “oversample” or focus its recruitment on injured workers with year-long claims, as they represent only six per cent of WSIB claimants.

Study participants were interviewed 18 months after their work-related injury. The interviews included questions on a range of topics, including participants’ work, claim experience, injury-related health-care use and current health profile. Participants were also asked how much pain interfered with their normal activity over the past four weeks and how they would rate the severity of that pain. The team also drew on the WSIB administrative data of those participants who consented to its use to get information about participants’ time off work and health-care benefits. Results were later “weighted” to reflect the actual makeup of the three groups among WSIB claimants at large.

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While previous research has shown a high prevalence of pain in the early stages of recovery after a work injury, few studies have examined the prevalence of persistent pain beyond the acute period of injury recovery, Dobson says.

She notes that the persistent pain observed in the study is reported both by injured workers who had returned to work and by those who remained off work. As only six per cent of WSIB claimants remain off work 18 months after an injury, the prevalence of persistent pain we see in this study—70 per cent—means that many injured workers are experiencing some level of pain even after they’ve returned to work.

Noting that the research literature suggests people should not wait for full recovery to return to work, Dobson adds that the high prevalence of some level of pain among claimants reinforces the importance of modified duties (if necessary) and return-to-work planning. Involving the injured worker in consultative return-to-work planning becomes especially important to enable the worker to feel engaged, and stay at work.