Correlation of plain radiographic indices of the hip with quantitative bone mineral density

Radiographic parameters of the hip can be useful as an indication of bone mineral density at the femoral neck. Measurements available from routine hip radiographs were correlated with DXA values. Although radiographs are not a test for osteoporosis, measurements of cortical thickness provide information useful for referral for osteoporosis assessment.

Plain hip radiographs are widely used for evaluation of hip pathology in osteoarthritis. A purpose of this study was to determine whether there are relationships between radiographic parameters of bone structure and bone mineral density T-scores, as assessed by dual energy x-ray absorptiometry (DXA).

Pre-operative radiographs of 32 postmenopausal, osteoarthritic women undergoing hip arthroplasty were evaluated. Radiographic parameters including the Singh index, Dorr classification, canal-to-calcar ratio, and cortical thickness indices (CTI) were measured and compared with T-score, serum 25 hydroxyvitamin D levels, body mass index (BMI), and body weight.

The T-score at the femoral neck for type C bone was significantly lower than that of type A (p = 0.041). The CTIs were correlated positively with T-scores for anteroposterior radiographs (r = 0.5814, p = 0.0005), and for lateral radiographs (r = 0.571, p = 0.0006). A threshold for lateral CTI set at a value of < or =0.40 results in sensitivity of 0.85 and specificity of 0.79 to segregate the osteoporotic and non-osteoporotic patients.

Femurs with small radiographic cortical thickness indices had lower T-scores. Finding a radiographic hip cortical thickness index (LAT) with a value of < or =0.40 should be an alert for referral for osteoporosis evaluation and bone mineral density testing.