Influence of orthopaedic metal and high-density detection on body composition as assessed by dual-energy X-ray absorptiometry.

Abstract

We examined the influence of orthopaedic material and computerized high-density detection (HDD) on analysis of bone mass and soft tissue composition performed by dual-energy X-ray absorptiometry (DXA). Measurements of total and regional bone area, bone mineral content (BMC), areal bone mineral density (BMD), lean tissue mass (LTM) and fat tissue mass (FTM) were made using a Norland XR-26 DXA scanner with dynamically changing samarium filtration. Twenty-one subjects who were free of metal implants were measured without and with a Biomet femoral prosthesis (titanium) placed on the proximal part of the femoral region. Twenty-one women with an endogenous prosthesis in the proximal femur were measured once. Analyses of tissue composition were performed without and with HDD using software provided by the manufacturer. Measurements were considerably affected by exogenous metal with overestimation of LTM and underestimation of FTM and bone area. BMC and BMD were over- or underestimated depending on the anatomical region. Enabling the HDD mode, values of bone area and tissue mass came closer to the expected values (-metal/-HDD) but were in general still significantly different from these. For the total body, the following significant changes were found after application of metal (+metal/-HDD vs. +metal/+HDD, mean values): bone area -19.8% vs. -6.9%, BMC +1.1% vs. -2.1%, BMD +26.5% vs. +4.7%, LTM +12.4% vs. +3.7%, FTM -15.8% vs. -7.0%. A similar pattern of change in tissue composition and bone area was found for the subregions of the body. Changes in tissue composition after HDD were similar in subjects with exogenous and endogenous metal, indicating that the experimental model was appropriate. In conclusion, measurements of tissue composition were substantially influenced by orthopaedic metal. HDD partly corrected for the artefacts induced by the metal.