¹National Research Centre for the Working Environment, Copenhagen, Denmark

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Introduction: Painful knee disorders are highly prevalent and disabling among the working population. Research on ergonomic risk factors is limited and conflicting, and mostly rely on self-reported measures of physical behaviours, which have been suggested to be imprecise and biased. Studies applying technical measures of occupational physical behaviours are therefore warranted.

Methods: We performed a prospective study among 377 eldercare workers employed across 20 Danish nursing homes. Occupational physical behaviours were measured using thigh-worn accelerometers over one to four working days. Workers reported intensity of and days with non-specific knee pain in a questionnaire at baseline and after one year. We explored associations between compositions of occupational physical behaviours, i.e. sedentary, standing, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA), and knee pain, adjusting for potential confounders.

Results: No significant associations were found. Trends were found for increased occupational time spent in MVPA and decreased risk of days with knee pain (RR (95% CI): 0.58 (0.32 - 1.05), p=0.07) in main analyses, and for decreased risk of knee pain intensity among non-pain-cases (0.36 (0.12 - 1.13), p=0.08) in sensitivity analyses.

Discussion: Previous research, primarily based on self-reported measures of occupational physical activity, has shown conflicting results; some studies have found an increased risk of knee disorders related to increased self-reported occupational standing, walking, or climbing, whereas other similar studies have not found any associations. Thus, our findings possibly suggesting a decreased risk of knee pain with increasing occupational MVPA could seem in contrast to the literature showing an increased risk of knee disorders with higher exposure to occupational walking and stair climbing. However, given the statistical uncertainty of these findings, further research with larger sample sizes and longer and repeated follow-ups is warranted.

Notable study limitations include

1. the lack of repeated exposure measurements,
2. a possible healthy worker effect, and
3. a larger sample could have increased the precision of the estimates.

In addition, potentially co-occurring knee-straining activities previously been linked to increased risk of knee disorders, such as kneeling, squatting, and lifting at work, were not considered or adjusted for.

Prominent study strengths include

1. 24-hour accelerometer measurements previously shown high sensitivity and specificity, and conducted over several consecutive days,
2. the longitudinal design, and
3. the reliance on compositional data analysis, addressing some methodological shortcomings associated with other more often-used methods.

Conclusion: These findings suggest that specific occupational physical behaviours may be associated with knee pain among eldercare workers. Particularly, increasing occupational MVPA might be a protective factor for knee pain, though more research with larger samples is warranted.