Comparison of Singh's index with Dual energy x-ray absorptiometry (DXA) in evaluating post-menopausal osteoporosis

Osteoporosis is a thinning of the bone that leads to fracture with minimum force. It affects postmenopausal women and elderly of both genders. Bone mineral density (BMD) is one of the parameter related to bone strength. Dual energy x-ray absorptiometry (DXA) is currently considered as the "gold standard" for measuring BMD. In India, DXA is very few in number and it is costly; on the other hand plain radiograph is cheaper and it is commonly taken even at rural health centre. The Sing's index (SI) is an inexpensive simple method to evaluate trabecular micro-architecture of the proximal femur, commonly used to assess osteoporosis. It is based on the radiological appearance of the trabecular bone structure of the proximal femur on a digital antero-posterior (AP) radiograph. A free medical camp for osteoporosis was conducted at SRM Medical College and Research Institute, Kattankulathur, Tamil Nadu, India during the months of June to August, 2010. 50 Indian women, aged 20-84 years were recruited. Out of which, 11 were pre-menopausal women, and the remaining 39 were post-menopausal women. BMD of the right proximal femur was measured in all women using a DXA, the total body bone densitometer. Also, digital radiograph of the right proximal femur was obtained in all the women whose diagnostic criteria for the disease was used in the study; Based on the femur neck DXA-BMD values, post-menopausal women were divided into the following subgroups: i) normal; ii) osteopenia; and iii) osteoporosis. The digital hip x-ray was visually assessed by an experienced radiologist and subsequently SI grading was done. All data was calculated as mean ± SD. Data analysis was carried out using SPSS/PC statistical software package. Student's t-test was used to find out the significance of the variables between the two groups. Pearson correlations were measured between the variables. In all post-menopausal women (n=39), the SI grading was correlated with total BMD by DXA, and it was statically significant (r2=0.168, p=0.05). In osteoporotic women, the mean values of femur neck BMD and SI were lesser by 33.7% and 30.0% respectively than in normal post-menopausal women, and these decrease were statistically significant (p=0.05). From this, it was found that, the percentage decrease was similar for both femur neck BMD measured by DXA and SI by simple visual assessment in osteoporotic women. SI can be used as a screening tool for the disease, particularly developing countries like India.