Low back and neck-shoulder pain : work and heritability

Abstract

Low back pain (LBP) and neck-shoulder pain (NSP) represent a large public health problem being common disorders that often lead to negative consequences for the individual and large costs for Society. The main goal of the thesis is to explore how factors relating to aetiology, i.e. the influences of genetic factors and work-related physical load, as well as consequences in terms of sickness absence are associated with different combinations of LBP and NSP. This thesis is based on three different data materials; the MUSIC-Norrtälje study, the STAGE study, and the Swedish orchestra study.

Paper I used the MUSIC-Norrtälje study material to explore sickness absence during a 5-year period (1995-2001) for subjects with consistent Solely LBP, Solely NSP, and Concurrent LBP and NSP (n= 817). The results showed that the odds ratio for sickness absence was OR 1.69 (95% confidence interval 1.14-2.51) and for long-term sickness absence OR 2.48 (95% CI 1.32-4.66), for subjects with Concurrent LBP and NSP compared to those with Solely LBP or Solely NSP.

In paper II, the STAGE study material was used to estimate the heritability of Solely LBP, Solely NSP, and Concurrent LBP and NSP using classical twin study methodology (n= 20,946). The results showed that 60% of the total variance for Concurrent LBP and NSP could be explained by additive genetic effects, which was twice as large as for Solely LBP (30%) and more than twice as large as for Solely NSP (24%).

Paper III, also used the STAGE study material for investigating if the associations between high physical workload and different combinations of LBP and NSP are confounded by genetic and shared environmental factors (n= 16,107). Only for Concurrent LBP and NSP, genetic and shared environmental factors seemed to have an influence on the association with high physical workload. The results also showed that high physical workload was associated with having any combination of LBP and/or NSP even after adjusting for genetic or shared environmental factors (OR 1.44, 95% CI 1.06-1.95).

In paper IV, the association between exposure to work with elevated arms and the prevalence of NSP was investigated using orchestra musicians, an occupational group that share many other physical and psychosocial work-related exposures (n= 235). This was done using the Swedish Orchestra study material. The results showed an association between a work posture with an elevated arm position and NSP for both those that had a longer duration (OR 5.35, 95% CI 1.96 14.62) and those that had a short duration (OR 4.15, 95% CI 1.30 13.22) of active playing time during a work day, compared to those with a neutral arm position.

In conclusion, this thesis has identified that subjects with Concurrent LBP and NSP constitutes a group with higher prevalence of sickness absence and for which genetic factors seem to have a great influence compared to Solely LBP or Solely NSP. Further, having an occupation with an exposure to high physical workload was associated with the prevalence of LBP and/or NSP. Also, within an occupation there was an association between NSP and exposure to work with an elevated arm position.