The Singh Index (SI), a classification system by which the severity of osteoporosis is assessed based on plain radiographs, is a renowned, simple and inexpensive form of evaluating osteoporosis. The aim of this study was to evaluate the correlation between the SI and bone mineral density (BMD) as measured by dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). The SI was evaluated in 128 cadaveric femora (64 patients, mean age 66.7 years, range 24-89 years) by three independent observers, all blinded to plain radiographs. BMD was also analysed by means of DXA and pQCT in the cadaveric femora. The mean interrater correlation was found to be 0.629. The correlation of the mean BMD measured by DXA (DXA-BMD) and SI was found to be poor, with r = 0.49. The corresponding sensitivity of 45.2 % and specificity of 92.3 % were even poor. The BMD measured by pQCT (pQCT-BMD) also revealed a poor correlation with SI, such that r = 0.337 and r = 0.428 for the trochanteric and neck regions, respectively. Due to the poor correlation of the SI with BMD and the poorer interrater correlation, the SI should be rejected as a tool for evaluating osteoporosis. The SI was found to be too imprecise and is therefore unsuitable for diagnosing osteoporosis and osteopenia.
