The effect of region of interest selection on dual energy X-ray absorptiometry measurements of the calcaneus in 55 post-menopausal women.

Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA) in four different regions of the calcaneus in 20 pre-menopausal and 55 post-menopausal women, none of whom were on treatment or suffering from conditions affecting bone. The total body option in the small animal software package of a Lunar DPX-L bone densitometer was used. The precision of the technique (%CV) varied from 0.7 to 2.2% depending on the region scanned. For post-menopausal women, BMD results in the mid and posterior parts of the calcaneus varied by < 7% while BMD in the anterior region was about 20% lower. DXA of the calcaneus was compared with measurements at the spine (L2-L4) and hip (femoral neck) and changes with age were estimated from cross-sectional data. BMD of the calcaneus was significantly reduced in 28 post-menopausal women with low lumbar spine BMD (-2SD) compared with women with normal spine BMD. Calcaneal BMD was significantly correlated to axial BMD (r = 0.45-0.77) and to age (r = 0.45 to -0.63). For a subgroup of 33 post-menopausal women measured twice after approximately 1 year, calcaneus BMD decreased by between 1.2% and 2.5% while axial BMD showed no significant change. Unlike spine or femoral neck BMD, the decrease in calcaneus BMD was significantly greater in women with low spine BMD than in normal women, possibly indicating improved detection of skeletal changes. The optimum measurement sites for BMD in the calcaneus were within the mid or posterior part of the calcaneus or enclosing the whole posterior calcaneus. The calcaneus was shown to be a precise, sensitive and simple measurement site suitable for the assessment of osteoporosis, especially in the elderly where degenerative changes in the spine and hip can complicate BMD assessment.