Arthritis Care Res. 2014 Oct;66(10):1496-505. doi: 10.1002/acr.22326.

Total hip replacement due to primary osteoarthritis in relation to cumulative occupational exposures and lifestyle factors: a nationwide nested case-control study.

Rubak TS, Svendsen SW, Søballe K, Frost P.

Slagelse Hospital, Slagelse, Denmark.

 

Abstract

OBJECTIVE: To investigate the risk of total hip replacement (THR) due to primary osteoarthritis in relation to cumulative occupational mechanical exposures and lifestyle factors.

METHODS: Using register information, we identified first-time THR cases within the Danish working population in 2005-2006. For each case, 2 age- and sex-matched controls were drawn. Persons within 2,500 randomly selected case-control sets received a questionnaire about job history, weight at age 25 years, present weight and height, smoking, and sports activities at age 25 years. The job history was combined with a job exposure matrix. Cumulative exposure estimates were expressed according to the pack-year concept of smoking (e.g., cumulative lifting was expressed as ton-years). We used conditional logistic regression for statistical analyses.

RESULTS: In total, 1,776 case-control sets (71%) were available for analysis. The adjusted odds ratio (OR) for exposure to ≥20 ton-years was 1.35 (95% confidence interval [95% CI] 1.05-1.74) for men and 1.00 (95% CI 0.73-1.41) for women. Standing/walking and whole body vibration showed no associations. The adjusted OR for body mass index (BMI) ≥30 kg/m(2) at age 25 years was 2.44 (95% CI 1.38-4.32) for men and 5.12 (95% CI 2.30-11.39) for women. The corresponding adjusted ORs for an increase in BMI of ≥10 kg/m(2) since age 25 years were 2.16 (95% CI 1.25-3.70) and 2.46 (95% CI 1.47-4.13). Sports participation showed weak positive associations, while pack-years of smoking showed no associations.

CONCLUSION: The results indicated a modest increase in risk of THR in relation to cumulative lifting among men and an increased risk in relation to a high BMI at age 25 years and to a gain in BMI in both sexes.

PMID: 24664794

 

Supplements:

Osteoarthritis has a long latency and one of the major hypothesis is that cumulative and sustained exposures are of importance for the onset of disease. This is difficult to study, as there are very few records of specific physical exposures for different job types.

In this study we tried to overcome one of these problems by using a job exposure matrix (JEM) to obtain information on different exposures in different job, and assigning these to approximately 5400 persons. Thus we created knowledge of cumulative and sustained exposures for the entire study population, using their self-reported job titles, but not self-reported exposures. This is important as it has been shown that people with i.e. pain tends to remember differently about their exposures from non-symptomatic persons.

The JEM was constructed specifically to study exposures toward the lower extremities(1) and have been used in other studies of i.e. inguinal hernias(2) with success.

We cannot fully explain the difference between men and women, but a possible explanation could be that women in the Danish labour market do not have jobs, which entail the same amount of heavy lifting as men. And thus they might not cumulate exposure enough to show the small, but statistically significant, increase for men.

This study does not show if heavy lifting causes OA, or makes OA symptomatic. But either way it is important to investigate possible preventive initiatives in order to lower the burden on society and avoid unnecessary surgeries for the patients. The study also shows a possible way to study relationship between exposures and outcomes in larger populations without having to rely on self-reported exposure estimates.

 

References:

(1) Rubak TS, Svendsen SW, Andersen JH, Haahr JP, Kryger A, Jensen LD, et al. An expert-based job exposure matrix for large scale epidemiologic studies of primary hip and knee osteoarthritis: the Lower Body JEM. BMC Musculoskelet Disord 2014;15:204.

(2)  Vad MV, Frost P, Bay-Nielsen M, Svendsen SW. Impact of occupational mechanical exposures on risk of lateral and medial inguinal hernia requiring surgical repair. Occup Environ Med 2012 Nov;69(11):802-9.

 

 

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