Can bone quality be predicted accurately by Singh index in patients with rheumatoid arthritis?

The aim of this study was to evaluate Singh index as a simple and inexpensive means of estimation of bone quality in patients with rheumatoid arthritis. Singh index evaluation was made on digital pelvis radiographs in 50 consecutive patients by three observers. Bone mineral density T scores of the spine and left proximal femur were assessed using dual energy X-ray absorptiometry. Singh index was correlated with densitometry measurements after grouping the patients as normal, osteopenia and osteoporosis. Intra- and interobserver agreements were evaluated by kappa correlations. Sensitivity, specificity, positive and negative predictive values and likelihood ratio's of Singh index were calculated. Both intra- and interobserver agreements were 0.71 (range, 0.69 to 0.72) on average. Singh index proved highly sensitive for the diagnosis of osteopenia at the proximal femur (91%) and spine (90%), whereas the specificity of Singh index for identifying of osteoporosis at the femoral neck (93%) and spine (91%) was higher than sensitivity. Predictive values for osteoporosis at the proximal femur and spine were acceptable and positive likelihood ratios of Singh index for osteopenia and osteoporosis at the proximal femur were 2.4 and 10.1, respectively. Singh index can identify osteoporosis with a high specificity in patients with rheumatoid arthritis. However, the patients who are graded as osteopenia by the Singh index should undergo further evaluation with dual energy X-ray absorptiometry.