Bone-health glossary
The words you'll meet on a scan report, in a study, or at an appointment — in plain language. Nothing here is a diagnosis; it's meant to help you read your own record and ask sharper questions.
- Fragility fracture
- A broken bone from a fall at standing height or less — a force that shouldn't break a healthy bone. It's one of the strongest signs that bone is fragile, and one of the strongest predictors of the next fracture.
- Osteopenia
- Bone density that is lower than normal but not low enough to be called osteoporosis. It is not a disease so much as a description — and many fractures happen to people in this range.
- Osteoporosis
- A condition of reduced bone strength that raises fracture risk. By density, it's usually defined as a T-score of −2.5 or lower — but that number is a definition for counting the disease, not the whole story of who breaks.
- BMD (bone mineral density)
- How much bone mineral is packed into an area of bone, measured in grams per square centimeter (g/cm²). The raw number behind a T-score.
- T-score
- Your bone density compared with a healthy young adult, expressed as standard deviations. 0 is average; −1 to −2.5 is osteopenia; −2.5 or lower is osteoporosis.
- Z-score
- Your bone density compared with people of your own age and sex. More useful than the T-score in younger adults and when looking for a secondary cause.
- DXA (often called DEXA)
- Dual-energy X-ray absorptiometry — the low-dose X-ray scan that is the standard tool for measuring bone density and diagnosing osteoporosis.
- TBS (Trabecular Bone Score)
- A texture index calculated from an existing lumbar-spine DXA image. It hints at bone microarchitecture (quality) and can refine fracture-risk estimates. An adjunct that refines risk — not a standalone diagnosis.
- REMS (Radiofrequency Echographic Multi-Spectrometry)
- A radiation-free ultrasound method (e.g. Echolight) that estimates bone density and a Fragility Score. A complementary tool, useful where DXA struggles — not yet a replacement for DXA.
- Fragility Score
- REMS's 0–100 estimate of bone quality / fracture risk, separate from density.
- FRAX
- An online tool that estimates your 10-year probability of a major fracture from clinical risk factors (age, prior fracture, smoking, steroids, and more), with or without a bone-density value.
- LSC (least significant change)
- The smallest change between two scans that is real rather than measurement noise — specific to each machine and facility. Essential for judging whether your bone density has truly changed over time.
- VFA (vertebral fracture assessment)
- A low-dose image of the spine, often taken on the DXA machine, to look for spine fractures — which are frequently silent and can change the diagnosis.
- Osteoblast
- The bone-building cell. The '+' crew that lays down new bone.
- Osteoclast
- The bone-removing cell. The '−' crew that clears old bone. Bone loss is largely these cells out-pacing the builders.
- Remodeling
- The lifelong cycle of removing old bone and laying down new bone. Nearly every cause of osteoporosis works by tipping this balance toward removal.
- Ferroptosis
- A form of cell death driven by iron and oxidative damage. In bone, excess iron can push bone-building cells toward it — one way iron overload harms the skeleton.
- Secondary osteoporosis
- Bone loss caused by another identifiable condition or medication (for example steroids, an overactive thyroid or parathyroid, celiac disease, or iron overload) rather than by aging and menopause alone.
- Gonadal
- Relating to the ovaries or testes and the sex hormones they make (estrogen, testosterone) — hormones that strongly influence bone.
- Anabolic (bone)
- A treatment that actively builds new bone (for example teriparatide, abaloparatide).
- Antiresorptive
- A treatment that slows bone breakdown (for example bisphosphonates, denosumab).
Educational, not medical advice. Definitions are simplified for understanding and can't capture every clinical nuance. Your clinician and your own results govern your care.