Leg Positioning During Lumbar Spine DXA

First Report from Clinical Osteoporosis 2017: A Joint Conference of the NOF & ISCD

Leg positioning during lumbar spine dual energy x-ray absorptiometry (DXA) does not impact patients’ trabecular bone scores (TBS), according to research presented at Clinical Osteoporosis 2017, A Joint Symposium of the National Osteoporosis Foundation (NOF) & the International Society for Clinical Densitometry (ISCD) in Orlando, Florida, April 20-22.

Study investigators conducted lumbar spine DXA scans (L1-L4) with both “legs up” and “legs down” positioning; analysis was performed to assess TBS.

Study participants were divided into 2 groups. The first group, scanned on 3 Prodigy densitometers, included 64 women (mean age, 65.1; mean body mass index [BMI], 26.4 kg/m²); the second group, scanned on iDXA densitometers (both densitometers, GE Healthcare; Little Chalfont, United Kingdom), included 50 women (mean age, 68.6; mean BMI, 26.2 kg/m²).

With standard “leg up” positioning on the Prodigy scanner, bone mineral density (BMD) ranged between 0.738 and 1.549 g/cm²; high correlation was noted with “legs down” positioning (R²=0.99). TBS results ranged from 1.072 to 1.632 and were also highly correlated (R²=0.93). A mean bias of −0.005 TBS units was noted between leg positions. Standard “leg up” scans on the iDXA scanner resulted in a BMD range of 0.735 to 1.622 g/cm² and a high correlation to “legs down” positioning (R²=0.97). TBS results ranged from 1.040 to 1.455 and were again, highly correlated (R²=0.90), with a mean bias of 0.00 TBS units.

“Leg positioning minimally affects TBS results with … Prodigy and iDXA densitometers,” the researchers concluded. “The difference from legs up to legs down is likely of no clinical significance.” 

Reference

Krueger D, Siglinsky E, Tran D, Del Rio L, Binkley L. Leg elevation does not substantially affect TBS results. Abstract 12. Presented at: Clinical Osteoporosis 2017: A Joint Symposium of NOF & ISCD. April 20-22, 2017; Orlando, FL.