Forearm Bone Mineral Density: A Comparison Study of Positioning and Side

Abstract

Background: The scanning position for measure forearm bone mineral density (BMD) is recommended by the International Society for Clinical Densitometry (ISCD) to scan at the non-dominant forearm in the sitting position. However, this position may be uncomfortable for the patients. Especially for those who are elder or cannot easily move. Pragmatically, the supine position is more comfortable than the sitting position for patients to measure forearm BMD.

Objective: The purpose of this study was to estimate the difference of forearm BMD between the standard sitting and supine position as well as between the non-dominant and the dominant side.

Methods: One hundred and fifty two female patients who gave written informed consent underwent 3 acquisitions of dual X-ray absorptiometry (DXA) altogether: 2 on the non-dominant forearm--one in the sitting and the other in the supine position; 1 on the dominant forearm in the sitting position. 

Results: All patients were right forearm dominant. The 33% radius BMD difference between the sitting and supine position was -0.005 g/cm² (95% CI, -0.03 to 0.02) while that between the dominant and non-dominant side was -0.011 g/cm² (95% CI, -0.06 to 0.04). When classified by World Health Organization (WHO) classification into 3 groups as normal, low bone mass, and osteoporosis, the agreement between the sitting and supine position of the non-dominant at this site was perfect (Kappa = 0.85) while that between the dominant and non-dominant side in the sitting position was moderate (Kappa = 0.64).

Conclusions: Measurement of BMD by DXA at non-dominant forearm in the sitting position can be scanned in the supine position without a change in diagnosis. Then the dominant forearm can be used instead the non-dominant if the non-dominant forearm is not properly done due to the presence of historical fracture or congenital deformities.