Losing Radial BMD: Forearmed is forewarned

Introduction

Forearm BMD measurement has been critical to our understanding of osteoporosis epidemiology, fracture risk, and response to treatment in clinical trials (1-3). The ISCD have embraced understanding densitometric techniques, identified research needs and advancing standards for appropriate use in clinical practice. Central DXA today has supplanted many older methods and is used predominantly to measure hip and lumbar spine BMD, and occasionally other sites. The ISCD clearly outlines acceptable levels of measurement error for measurements at the hip and spine, with official positions for measuring and monitoring changes in place but has neglected an acceptable threshold for distal 1/3 radius and whole-body BMD. The Practice: Empirically centres usually have no L.S.C. for forearm/ distal 1/3 radius, despite repeating DXA measurements of that site in practice. Increasingly we note centres are less familiar with forearm measurement today, sometimes lack confidence in their knowledge, skill and competency for measurement or interpretation.

Objectives

The Problem: Forearm measurements are sometimes reported in clinical trials, and in practice the forearm may be the only suitable site such as when hips have been replaced, there have been fractures or surgery to the lumbar spine, or the patient is unable to mount or lie on the DXA table. Consistency and excellence in clinical practice suggest the same standards apply irrespective of which site is being measured. We aimed to calculate the L.S.C. for distal radial BMD as recommended by the ISCD.

Methods

We calculated the L.S.C. for our centre as part of a cross-calibration exercise when our DXA machines (G.E. Lunar Prodigy) were re-located from the radiology department to the rheumatology department in 2018 and new staff were trained in DXA technology. We scanned 30 patients twice on the same day repositioning between each scan, as we did for lumbar spine and total hip.

Results

We obtained an L.S.C. of 0.046g/cm2 for the 13 distal radius. While our spine and total hip BMD LSC values fell under the ISCD recommended acceptable threshold, we could not find Official Position guidance as to where the radial LSC value sits on the spectrum of acceptability. However, our results fall within the range published by Krueger et al in 2013 which included some technical errors when images were reviewed.

Conclusions

Diagnostic excellence suggests standards and consistency apply for clinical metrology. The ISCD should include and define acceptable forearm L.S.C. in their official positions.

References

PMID: 1150873, 2008103, 10527181, 15159268, 16234965.