Back disorder incidence and occupation in Denmark: a cross-sectional register-based study

Tip of the iceberg: unveiling the impact on back disorders from cumulative physical job exposure and evaluating bias from the healthy worker effect using a nationwide longitudinal cohort study

PURPOSE

Longitudinal studies across various sectors with physically demanding jobs are notably absent in back disorder risk research. This study aimed to investigate the relationship between cumulative physical job exposure (PJE) and hospital-diagnosed back disorders among individuals in Denmark. To assess the healthy worker effect, we compared the cumulative risk estimate with results from a naive cross-sectional model ignoring PJE history.

METHODS

A nationwide longitudinal cohort study was conducted using Danish registers, encompassing individuals born between 1975 and 1978 and working in 1996. Cumulative PJE was measured with a 10-year look-back period for each year 2006-2017. PJE consisted of lower-body occupational exposures, including the total weight lifted, stand/sit ratio, and the frequency of lifting more than 20 kg per day from a job exposure matrix. Odds ratio for back disorders was estimated for each year and all years combined.

RESULTS

The results unveiled a significant 31% increase in the risk of hospital-diagnosed back disorders after 4 years of cumulative PJE. The lowest risk (7%) was observed for incident back disorders with 1 year of exposure, suggesting a healthy worker effect. Nevertheless, this risk is still significantly elevated. This cumulative estimate is fourfold the estimate from the 2006 naive cross section model.

CONCLUSION

Our study clearly demonstrates an 31% increase in the risk of hospital-diagnosed back disorders with just 4 years of PJE over a 10-year period. Further, we find that cross-sectional studies strongly underestimate the risk of back disorders due to the healthy worker effect.

The clinical back pain courses described by information available in Danish central registries

BACKGROUND

Patients with back pain are often in contact with 2-4 hospital departments when receiving a back pain diagnosis and treatment. This complicates the entire clinical course description. There is, currently, no model that describes the course across departments for patients with back pain. This study aims to construct an interdisciplinary clinical course using the central register's information.

METHODS

All patients with back pain referred for diagnosis and treatment at the Spine Center of Southern Denmark from 1 January 2011 until 31 December 2017 were included. By means of information available in central registers, we described the interdisciplinary clinical course for the individual patient, including information on all contacts at different departments, and proposed three different models to define the index and final date. The index date was defined as the first visit without a previous contact to the Spine Center for 6 months for model I, 1 year for model II, and 2 years for model III. The final date was defined as the last visit without following contacts for 6 months, 1 year, and 2 years, respectively, for models I, II, and III.

RESULTS

A total of 69,564 patients (male: n = 30,976) with back pain diagnosis were identified. The three models all leave the information on the entire course at the hospital. In model I (64,757 clinical back pain courses), the time span to a possible previous clinical course is too short to secure the start of a new course (14% had two or more). With at least 1 year between a possible previous contact, model II (60,914 courses) fits the everyday clinical practice (9% had two or more clinical back pain courses). In model III (60,173 courses) it seems that two independent courses might be connected in the same course as only 5% had two or more clinical back pain courses.

CONCLUSIONS

Despite contact with different departments, the clinical course for back pain patients can be described by information from the central registers. A one-year time interval fits best the clinicians' everyday observations.