Radiolucent casting tape allows for accurate measurement of forearm bone mineral density using dual-energy X-ray absorptiometry

The ability to perform dual-energy X-ray absorptiometry (DXA) while a patie nt is in a cast would give investigators the opportunity to follow early ch anges in bone mineral density (BMD, g/cm(2)) during fracture healing or to evaluate bone changes related to immobilization. The objective of this stud y was to determine if accurate and precise DXA scans could be obtained thro ugh polyester-based radiolucent casting tape (Delta-Cast Elite [DCE], Johns on & Johnson, Inc., Raynham, MA) and standard fiberglass casting tape (Delt a Lite [DL], Johnson & Johnson, Inc.). DXA scans were performed using a Lun ar DPX-L densitometer. Standard forearm regions of interest were analyzed. Ten normal volunteers had three consecutive scans of their dominant arm wit h no cast, with a radiolucent (DCE) cast, and with a fiberglass (DL) cast. Precision was calculated using data from three volunteers (three scans each ; no cast, DCE, DL). Results of DCE and DL were compared with results with no cast. In a second series, a spine phantom was placed inside rice-filled forearm casts and repetitively scanned; results with DCE and DL were compar ed with the mean BMD values for the phantom alone. Analyses of the scans th rough the DL casts were difficult because the radiodensity of the fiberglas s interfered with edge detection. This problem was exacerbated by low BMD ( i.e., scans for women). Edge detection was not a problem with the DCE scans . Although the group mean BMD values with in vivo no cast, DCE, or DL scans were similar for all regions of interest, the data obtained for ultradista l regions of interest with DL scans were less precise. BMD values for the f iberglass-encased phantom were significantly lower compared with no cast or DCE scans (p = 0.0002). This study demonstrates that it is possible to per form accurate and precise forearm DXA scans through polyester-based radiolu cent DCE casting tape.