| Summary: | 博士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 103 === Background and Objective: Lumbar disc degeneration (LDD) has been related to heavy physical loading. However, the quantification of the exposure has been controversial and the dose-response relationship with the LDD has not been established. It is also unclear whether a specific threshold value exists in each lifting load, the accumulation above which best predicts lumbar disc protrusion, or on the other hand, all lifting load should be accumulated. In a clinical setting, the radiographic diagnosis of disc condition typically requires magnetic resonance imaging (MRI), which is less readily available than plain radiograph is in most primary care facilities. If the relationship between reduced disc height and disc bulging or protrusion was existed, useful insight can be obtained to guide further direction of patient evaluation. The purposes of this study are to investigate the dose-response relationship between lifetime cumulative lifting load and LDD; to determine the optimal threshold value of lumbar compression load in each lifting, which allowed for best prediction for disc protrusion while lifetime cumulative load was calculated; and to determine the association between disc morphology and disc bulging or protrusion.
Method: This is a cross-sectional study. Every participant received assessments with a questionnaire, MRI of the lumbar spine and lumbar disc compression load. MRI assessments included disc dehydration, annulus tear, disc height narrowing, bulging, protrusion, extrusion, sequestration, degenerative and spondylolytic spondylolisthesis, foramina narrowing, and nerve root compression on each lumbar disc level. The compression load was predicted by a biomechanical
software system. We sum up all lifting exposure to the calculation for examining the association between lifetime cumulative lifting load and LDD; and sum up only lifting load greater than proposed thresholds for determining the optimal threshold value of lumbar compression load in each lifting .For accumulation above different thresholds, predictive capabilities for disc protrusion were compared using four statistical values, (1) Area under the curve of a receiver operating characteristic curve, (2) R2, (3) Akaike information criterion, and (4) Bayesian information criterion. The intervertebral disc height and disc depth were measured. Logistic regression analysis was applied to identify the association between anthropometric factors, disc morphology factors, and disc bulging/protrusion. Model 1 was constructed using anthropometric variables to investigate the capacity for predicting disc bulging/protrusion. Model 2 was constructed using anthropometric variables and disc morphology variables. The ability of the models to discriminate between participants with and without disc bulging/protrusion was evaluated using a receiver operating characteristic curve.
Result: A total of 553 participants were recruited in this study and categorized into tertiles by cumulative lifting load, i.e., <4.0 × 105, 4.0 × 105–8.9 × 106, and >= 8.9 × 106 Newton× hours. The risk of LDD increased with cumulative lifting load. The best dose-response relations was found at the L5–S1 disc level, in which high cumulative lifting load was associated with elevated odds ratios of 2.5 (95% CI 1.5–4.1) for dehydration, and 4.1(95% CI 1.9–10.1)for disc height narrowing comparing to low lifting load. Participants exposed to intermediate lifting load had increased odds ratios of 2.1(95% CI 1.3–3.3) for bulging comparing to low lifting load. The tests for trend were significant. For men, 3000 Newton for each lifting
task was the optimal threshold value for predicting L4-S1 disc protrusion, whereas for women, 2800 Newton was optimal. Total of 452 MRI scans were analyzed for the morphology study. Age, body weight, body height, disc height, and disc depth were significantly associated with disc bulging/protrusion. The area-under-the-curve (AUC) statistics of Model 2 were significantly better than Model 1 at the L3-L4 (p<.05) and L4-L5 level (p<.05) but not at the L5-S1 level.
Conclusions: The results suggest a dose-response relationship between cumulative lifting load and LDD. Cumulative lifting load predicted L4-S1 disc protrusion best when the threshold value was set at 3000 Newton for men, and 2800 Newton for women. The results showed an association between disc morphology and disc bulging/protrusion at the L3-L4, L4-L5, and L5-S1 level. We also developed a model by using anthropometric factors and disc morphology to predict disc bulging/protrusion.
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