Category: Central DXA: (DXA, TBS)

12 - Leg Elevation Does Not Substantially Affect TBS Results

Objective: 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. The purpose of this study is to assess the effect of leg position on TBS.


Methods:
Lumbar spine (L1-L4) DXA scans 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 an 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).


Conclusion:
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.

Neil Binkley

Professor of Medicine
University of Wisconsin School of Medicine and Public Health
Madison, Wisconsin

Luis Miguel Del Rio Barquero

Nuclear Medicine
CENTRE DE TECNOLOGÍA DIAGNÓSTICA
Barcelona, Not Applicable, Spain

Ellen Siglinsky

Research Specialist
University of Wisconsin Osteoporosis Clinical Research Program
Madison, Wisconsin

Doris Tran

Clinical Scientist
Medimaps SASU, Merignac, France
Merignac, Aquitaine, France

Diane Krueger

Research Program Manager
University of Wisconsin Osteoporosis Clinical Research Program
Madison, Wisconsin

Diane Krueger received her Bachelor of Science degree at the University of Wisconsin-Madison. She is an ISCD-certified clinical densitometrist and a certified clinical research coordinator through the Association of Clinical Research Professionals. She has been program manager of the University of Wisconsin Osteoporosis Clinical Research Program since its inception in 1993. Ms. Krueger has extensive clinical research experience in osteoporosis and bone densitometry, having coordinated multiple industry and investigator-initiated studies. In collaboration with the UW Osteoporosis Program, she has published over 70 manuscripts and authored or presented over 100 abstracts. Her service with ISCD has included chairing the Technologist Bone Densitometry Update and Annual Meeting Committees, participating on the Education Council, serving on the Executive Committee and Board as member and officer (Secretary and four Presidential seats). She has been Technologist Bone Densitometry Course faculty since 2006.