Musculoskeletal pain and work absence – a 10 year follow-up study of Norwegian young adult twins
Authors: Ørstavik Ragnhild E. , Knudsen Gun Peggy , Tambs Kristian , Gjerde Line C. , Torvik Fartein Ask , Nielsen Christopher , Røysamb Espen , Reichborn-Kjennerud Ted 
Published: July 2016

Background and aims: Sickness absence (SA) and disability pension (DP) are increasingly recognized asmajor public problems. Musculoskeletal disorders are among the most common diagnoses set by physiciansgranting SA and DP. Results from recent twin studies have established that SA and DP are influencednot only by environmental and social factors, but also moderately to substantially by genes. The aim of thecurrent study was to examine to what degree musculoskeletal complaints in young adults predict SA andDP, including SA granted for other diagnoses. As the participants were twins, we were able to performwithin pair analyses, to see if the associations between musculoskeletal pain and later DP or SA were confoundedby unmeasured genetic and shared environmental factors.Materials and methods: The Norwegian twin registry includes a questionnaire conducted in 1998. Fromthis, we included three measures of recurrent pain (lower back, neck/shoulders and muscular) as well assymptoms of anxiety and depression (measured by the Symptom Checklist-5 (SCL-5)). The questionnairehas been linked to highly reliable official registries on SA and DP, as well as a range of sociodemographicvariables, for a ten-year follow up period. We applied logistic (DP as dependent variable) and binomialregression (SA as dependent variable) analyses to explore the relationship between musculoskeletal painand DP and SA. In the final models, we adjusted for sociodemographic factors and symptoms of anxietyand depression. Differences between twins in a pair were explored by applying fixed effect models. Allanalyses were conducted using STATA version 13.1.Results: The final sample of 7,626 twins included 3,055 complete pairs (488 monozygotic (MZ) male, 349dizygotic (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 sitewas significantly associated with DP in both sexes. Any increase in the number of pain sites reported wasassociated with about a 60% increased risk for receiving DP (OR 1.6, 95% CI 1.4-1.9), and the strength ofthe 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 fromgenetic and shared environmental effects. As for all cause SA, musculoskeletal pain predicted SA independentlyof all measured confounders, and the results remained significant in the within pair analyses (IncidenceRate 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-upperiod. Musculoskeletal pain was associated with higher levels of all cause SA, even within discordant MZtwin pairs. Our results indicate that interventions to prevent musculoskeletal pain in young adults canreduce levels of SA and DP.