Musculoskeletal pain and work absence – a 10 year follow-up study of Norwegian young adult twins

Sammendrag

Background and aims: Sickness absence (SA) and disability pension (DP) are increasingly recognized as
major public problems. Musculoskeletal disorders are among the most common diagnoses set by physicians
granting SA and DP. Results from recent twin studies have established that SA and DP are influenced
not only by environmental and social factors, but also moderately to substantially by genes. The aim of the
current study was to examine to what degree musculoskeletal complaints in young adults predict SA and
DP, including SA granted for other diagnoses. As the participants were twins, we were able to perform
within pair analyses, to see if the associations between musculoskeletal pain and later DP or SA were confounded
by unmeasured genetic and shared environmental factors.
Materials and methods: The Norwegian twin registry includes a questionnaire conducted in 1998. From
this, we included three measures of recurrent pain (lower back, neck/shoulders and muscular) as well as
symptoms of anxiety and depression (measured by the Symptom Checklist-5 (SCL-5)). The questionnaire
has been linked to highly reliable official registries on SA and DP, as well as a range of sociodemographic
variables, for a ten-year follow up period. We applied logistic (DP as dependent variable) and binomial
regression (SA as dependent variable) analyses to explore the relationship between musculoskeletal pain
and DP and SA. In the final models, we adjusted for sociodemographic factors and symptoms of anxiety
and depression. Differences between twins in a pair were explored by applying fixed effect models. All
analyses were conducted using STATA version 13.1.
Results: The final sample of 7,626 twins included 3,055 complete pairs (488 monozygotic (MZ) male, 349
dizygotic (DZ) male, 747 MZ female, 589 DZ female, and 882 opposite sex twin pairs) and 1,516 singletons.
By the end of follow up, 181 subjects (44 men and 137 women) received DP, and 63.7% of the sample
(47.4% of males and 76.0% of females) had at least one period of SA extending 16 days. Pain at any site
was significantly associated with DP in both sexes. Any increase in the number of pain sites reported was
associated with about a 60% increased risk for receiving DP (OR 1.6, 95% CI 1.4-1.9), and the strength of
the association was only marginally reduced when adjusted for symptoms of mental disorders (1.4, 1.2-
1.7). In the within pair analyses the effect was no longer significant, indicating possible confounding from
genetic and shared environmental effects. As for all cause SA, musculoskeletal pain predicted SA independently
of all measured confounders, and the results remained significant in the within pair analyses (Incidence
Rate Ratio (IRR) 1.12, 95% CI 1.03-1.23).
Conclusion: In young adults, musculoskeletal pain strongly predicted SA and DP for a 10 year follow-up
period. Musculoskeletal pain was associated with higher levels of all cause SA, even within discordant MZ
twin pairs. Our results indicate that interventions to prevent musculoskeletal pain in young adults can
reduce levels of SA and DP.