A comparison of statistical associations between oedema in the lumbar fat on MRI, BMI and Back Fat Thickness (BFT)

PURPOSE: To compare the relationship between obesity markers Body Mass Index (BMI) and Back Fat Thickness (BFT) and oedema in the lumbo-sacral subcutaneous adipose tissue. PATIENTS AND METHODS: A retrospective study was performed of consecutive Magnetic Resonance Imaging examinations on 149 adults (95 females and 54 males) scanned at 1.5T between October 1 and December 31, 2010. The extent of oedema was graded from 1 to 8 based on the number of involved anatomical segments on the Fat Sat sequence. A vertebra and the disc immediately inferior or any of the upper, middle or lower third of the sacrum was assigned 1 unit. BFT was measured superiorly at the upper border of L1 (BFT L1) and inferiorly at the lower border of L5 (BFT L5) on the T1 weighted image. BMI was computed at the time of the examination. The data were analysed using StatPlus 2009. The association between variables was evaluated using univariate and multivariate regression. RESULTS: 68 patients (45.6%), 50 females (33.6%) and 18 males (12.0%) were found to have oedema. Weight (p = 0), BMI (p < 0.001), BFT L1 (p < 0.001), BFT L5 (p < 0.001) and age (p = .01) were significantly associated with oedema. On forward stepwise multiple regression significant independent variables predicting oedema were found to be BMI, BFT L1 and Age. ANOVA indicated that BMI explained 23.6% (F = 45.5, p = 0), BFT L1 22.7% (F = 43.2, p = 0) and age 4.7% (F = 7.4, p = 0.007) of the variance of oedema. CONCLUSIONS: Obesity markers BMI and BFT L1 are significant independent variables predicting oedema. Oedema is predicted to a variable extent by fat at different sites. The oedema may be, in part, a consequence of obesity.