Background Lumbar spine dual energy X-ray absorptiometry (DXA) scans are typically acquired with the patient's legs elevated on a positioning block thereby flattening the normal lumbar lordosis. With GE densitometers it is also possible to acquire lumbar spine scans with the legs down. BMD values obtained with legs down vs. legs elevated does minimally differ, however it is unknown if leg elevation affects trabecular bone score (TBS) results.
Objectives The purpose of this study is to assess the effect of leg position on TBS.
Methods Lumbar spine (L1-L4) DXA scans were acquired in legs up and legs down positioning using GE Healthcare Prodigy and iDXA densitometers. The “OneScan” feature mode was not used. These scans were analyzed with enCORE software v 12.3 or 14.1. All scans were re-processed using Medimaps TBS Calculator v2.3 or TBS iNsight v3.0.2 to obtain TBS results. Linear regression and Bland-Altman analyses were performed to compare TBS results in the legs up vs. legs down position.
Results Sixty-four women, mean age and BMI 65.1 years (range 28.2–86.6) and 26.4 kg/m2 (range 18.1–34.8) were studied on three Prodigy densitometers. Fifty women, mean age and BMI 68.6 years (range 15.2–92.5) and 26.2 kg/m2 (range 19.9–35.1) were studied on a iDXA densitometer. With Prodigy and standard legs up positioning, the L1-L4 BMD ranged from 0.738–1.549 g/cm2 and was highly correlated with legs down positioning, R2 =0.99. TBS results ranged from 1.072–1.632 and were also highly correlated, R2 =0.93 with a mean bias of -0.005 TBS units between leg positions (Figure). With iDXA and standard legs up positioning, the L1-L4 BMD ranged from 0.753–1.622 g/cm2 and was highly correlated with legs down positioning, R2 =0.97. TBS results ranged from 1.040–1.455 and were also highly correlated, R2 =0.90 with a mean bias of 0.00 TBS units between leg positions (data not shown).
Conclusions Leg positioning minimally affects TBS results with GE Healthcare Prodigy and iDXA densitometers but the difference from legs up to legs down is likely of no clinical significance.
Disclosure of Interest D. Krueger: None declared, E. Siglinsky: None declared, D. Tran Employee of: Medimaps, L. Del Rio: None declared, N. Binkley: None declared
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