Prevalence of gluteus medius weakness in people with chronic low back pain compared to healthy controls

Clinical observation suggests that hip abductor weakness is common in patients with low back pain (LBP). The purpose of this study is to describe and compare the prevalence of hip abductor weakness in a clinical population with chronic non-specific LBP and a matched sample without LBP. One hundred fifty subjects with chronic non-specific LBP and a matched cohort of 75 control subjects were recruited. A standardized back and hip physical exam was performed. Specifically tensor fascia lata, gluteus medius, and gluteus maximus strength were assessed with manual muscle testing. Functional assessment of the hip abductors was performed with assessment for the presence of the Trendelenburg sign. Palpation examination of the back, gluteal and hip region was performed to try and reproduce the subject's pain complaint. Friedman's test or Cochran's Q with post hoc comparisons adjusted for multiple comparisons was used to compare differences between healthy controls and people with chronic low back pain for both the affected and unaffected sides. Mann-Whitney U was used to compare differences in prevalence between groups. Hierarchical linear regression was used to identify predictors of LBP in this sample. Gluteus medius is weaker in people with LBP compared to controls or the unaffected side (Friedman's test, p < 0.001). The Trendelenburg sign is more prevalent in subjects with LBP than controls (Cochran's Q, p < 0.001). There is more palpation tenderness over the gluteals, greater trochanter, and paraspinals in people with low back pain compared to controls (Cochran's Q, p < 0.001). Hierarchical linear regression, with BMI as a covariate, demonstrated that gluteus medius weakness, low back regional tenderness, and male sex were predictive of LBP in this sample. Gluteus medius weakness and gluteal muscle tenderness are common symptoms in people with chronic non-specific LBP. Future investigations should validate these findings with quantitative measures as well as investigate the effect of gluteus medius strengthening in people with LBP.