Chronic low back pain in patients with systemic lupus erythematosus: prevalence and predictors of back muscle strength and its correlation with disability

Objective To determine the prevalence of Chronic Low Back Pain (CLBP) and predictors of Back Muscle Strength (BMS) in patients with Systemic Lupus Erythematosus (LES). Methods Cross‐sectional study. Ninety‐six ambulatory patients with LES were selected by non‐probability sampling and interviewed and tested during medical consultation. The outcomes measurements were: Point prevalence of CLBP, Oswestry Disability Index, Tampa Scale of Kinesiophobia, Fatigue Severity Scale and maximal voluntary isometric contractions (MVIC) of handgrip and of the back muscles. Correlation coefficient and multiple linear regression were used in statistical analysis. Results Of the 96 individuals interviewed, 25 had CLBP, indicating a point prevalence of 26% (92% women). The correlation between the Oswestry Index and maximal voluntary isometric contraction of the back muscles was r = ‐0.4, 95% CI [‐0.68;‐0.01] and between the MVIC of handgrip and of the back muscles was r = 0.72, 95% CI [0.51;0.88]. The regression model presented the highest value of R² being observed when MVIC of the back muscles was tested with five independent variables (63%). In this model handgrip strength was the only predictive variable (ß = 0.61, P = 0.001). Conclusions The prevalence of CLBP in individuals with LES was 26%. The MVIC of the back muscles was 63% predicted by five variables of interest, however, only the handgrip strength was a statistically significant predictive variable. The MVIC of the back muscles presented a linear relation directly proportional to handgrip and inversely proportional to Oswestry Index i.e. stronger back muscles are associated with lower disability scores.