Measuring Bone Mass
- Several non-invasive techniques are now available for estimating skeletal mass or density. These include Dual-Energy X-ray Absorptiometry (DEXA), Single-Energy X-ray Absorptiometry (SXA), Quantitative CT, and Ultrasound
- DEXA is a highly accurate X-ray technique that has become the standard for measuring bone density in most centres
- Though it can be used for measurements of any skeletal site, clinical determinations are usually made of the lumbar spine and hip
- Portable DEXA machines have been developed that measure the heel (calcaneus), forearm (radius and ulna), or finger (phalanges)
- DEXA can also be used to measure body composition
- CT is used primarily to measure the spine and more recently the hip. Peripheral CT is used to measure bone in the forearm or tibia. The results obtained from CT are different from all others currently available since this technique is three dimensional and can provide a true density (mass of bone tissue per unit volume). CT can also specifically analyze trabecular bone and cortical bone content and volume separately
- Ultrasound is used to measure bone mass by calculating the weakening of the signal as it passes through bone or the speed with which it traverses the bone. It is unclear whether ultrasound assesses properties of bone other than mass (e.g., quality), but this is a potential advantage of the technique. Because of its relatively low cost and mobility, ultrasound is amenable for use as a screening procedure
Predicting fracture risk
- The Fracture Risk Assessment Tool (FRAX) is an International Osteoporosis Foundation certified tool
- It can be used as an assessment modality for the prediction of fractures on the basis of clinical risk factors, with or without the use of femoral neck bone mineral density
- The aim of FRAX is to provide an assessment tool for the prediction of fractures in men and women with use of clinical risk factors with or without femoral neck bone
- Mineral Density
- These clinical risk factors include age, sex, race, height, weight, body mass index, a history of fragility fracture, a parental history of hip fracture, and use of oral glucocorticoids, rheumatoid arthritis and other secondary causes of osteoporosis, current smoking, and alcohol intake of three or more units daily
- FRAX calculates the ten-year probability of a major osteoporotic fracture (in the proximal part of the humerus, the wrist, or the hip or a clinical vertebral fracture) and of a hip fracture calibrated to the fracture and death hazards
- The FRAX tool specific to India is available at Sheffield.ac.uk.
“Treatment of osteoporosis should be considered for patients with low bone mineral density (a T-score of between −1.0 and −2.5) or/and a ten-year risk of hip fracture of more than/equal to 3% or a ten-year risk of a major osteoporosis-related fracture of more than/equal to 20% as evaluated with FRAX tool”
