Relative value of femoral and lumbar bone mineral density assessments in patients with ankylosing spondylitis.

The objective of this study was to examine the relative sensitivity of femoral and lumbar bone mineral density (BMD) measurements in patients with ankylosing spondylitis (AS) and to identify the most appropriate test site for detection of osteopenia in these patients. Fourteen patients with ankylosing spondylitis had femoral and lumbar bone mineral density studies using dual energy x-ray absorptiometry. Significant osteopenia was found in 93% of patients when the femoral hip was examined and in 29% of patients when the lumbar region was examined. Moreover, femoral measurements exhibited greater severity of osteopenia than lumbar measurements when average T and Z scores were compared. Bone loss was most marked at Ward's triangle and the neck of the femur. When the lumbar measurements are insensitive and inappropriate, femoral neck and Ward's triangle measurements provide a more reliable indication of the presence and severity of osteopenia in patients with AS. Interpretation of BMD at the trochanter and intertrochanter, as well as total hip BMD, yielded no additional information in the diagnosis of osteopenia.