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Intervertebral disc degeneration is characterised radiologically by the presence of osteophytes, disc space narrowing and endplate sclerosis. Various lifestyle factors including occupational and recreational physical activity, obesity and smoking have been reported to be associated with the occurrence of lumbar disc disease, although the results from studies are not always consistent, with few studies looking at associations with the component radiographic features of the disease.1–9 We studied a population-based sample of men and women to determine the association between weight, body mass index (BMI), regular levels of physical activity, smoking and radiographic features of lumbar disc degeneration.
Men and women aged ⩾50 years were recruited for participation in a screening survey of vertebral osteoporosis (European Vertebral Osteoporosis Study) in Aberdeen, UK. The sampling frame was a community health index based on primary-care registrants. Subjects were invited to attend for an interviewer-administered questionnaire and lateral spine radiographs. Height and weight were also assessed. Vertebral disc spaces from L1/2 to L4/5 were assessed by a single observer for anterior osteophytes, endplate sclerosis and disc space narrowing (each graded 0–3).10 For each feature, a total score was calculated by summing the grades across vertebral levels (range 0–12). Linear regression was used to determine the association between the total score for each of the radiographic features and the putative risk factors, with the radiographic feature as the dependent variable, results being expressed as β coefficients and 95% confidence intervals (CIs). All individuals gave written informed consent to take part in the study, which also received the approval of the local ethics committee.
A total of 286 men (mean (standard deviation (SD) age 65.3 (8.9) years) and 299 women (mean (SD) age 65.2 (8.9) years) were included in the analysis. The median (interquartile range) score for osteophytes was 4 (2, 5), endplate sclerosis 1 (0, 2) and disc space narrowing 1 (0, 3). After adjustment for age and sex, compared with those in the lowest tertile, those in the middle and upper tertiles of body weight had a higher total osteophyte score (table 1). Small positive associations were seen between weight and BMI and the scores for the other radiographic features although CIs around most estimates included unity. There was no association between any of the total scores and regular physical activity levels or smoking.
The response rate for participation in the study was 61%. Because the analysis of the influence of weight, BMI and lifestyle factors was based on an internal comparison of responders, non-participation is unlikely to have had a major effect on the observed results. Intraobserver agreement levels for assessment of the radiographic features were good (κ = 0.7–0.8), and it seems unlikely that random error in scoring the films importantly attenuated the associations. Finally, the results were derived from a predominantly Caucasian population in north-eastern Scotland, and the data should be extrapolated beyond this population with caution. Previous population-based studies examining the effect of regular levels of physical activity and smoking provide somewhat conflicting results.5,7–9 Our data suggest no important influence of these factors on the occurrence of the individual radiographic features of lumbar disc degeneration. By contrast, increased weight was associated with an increased risk of osteophytes.
We thank the Arthritis Research Campaign for support.
Competing interests: None.
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