Bone mineral density

Bone mineral density is the concentration of mineral matter in bone, commonly measured to estimate skeletal strength, diagnose osteoporosis, and track bone development or loss.

Dual-energy X-ray absorptiometry: An imaging method that estimates bone mineral content and areal density using two X-ray energy levels. It is the standard clinical method for measuring bone mineral density at common fracture sites.
Osteoporosis: A skeletal disorder characterized by reduced bone strength and increased susceptibility to fracture. Low bone mineral density is a central diagnostic indicator, though not the only determinant of fracture risk.
Hydroxyapatite: A calcium-phosphate mineral crystal that forms the main inorganic component of vertebrate bone and teeth. Its mineral content is what density measurements principally detect.
Bone mineral content: The total mass of mineral in a specified bone or region, rather than mineral concentration within an area or volume. DXA reports mineral content as well as areal density, and the quantities are not interchangeable.
Quantitative computed tomography: A CT-based method that measures volumetric bone mineral density in three dimensions. It distinguishes trabecular from cortical bone, unlike the projected measurement of standard DXA.
Osteopenia: A range of bone density below the young-adult reference average but not low enough to meet the densitometric threshold for osteoporosis. The term commonly describes intermediate T-scores on DXA.
Osteoblast: A bone-forming cell that produces the matrix on which bone mineral is deposited. Osteoblast activity builds the tissue whose mineral content contributes to measured density.
Bone quality: Structural and material properties of bone, apart from its mineral quantity, that affect resistance to fracture. Bone quality captures contributors to fracture risk that a density value does not measure.
T-score: A standardized comparison of a person's bone density with the average value of a healthy young-adult reference population. This score turns a DXA result into a category used to assess osteoporosis.
Fragility fracture: A fracture caused by trauma that would not ordinarily break healthy bone, such as a fall from standing height. Such fractures can signal skeletal weakness even when a density result is not in the osteoporosis range.

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