Osteoporosis is the most common metabolic bone disease, characterized by reduced bone mass and microarchitectural deterioration, leading to fragility fractures. Imaging plays a central role in diagnosis, fracture detection, and monitoring treatment response.
📌 Why Imaging in Osteoporosis?
- Detect early bone loss.
- Identify fragility fractures.
- Differentiate from other metabolic bone disorders.
- Guide treatment and follow-up.
🔍 Imaging Modalities
1. Plain Radiograph
- Not sensitive for early disease (changes appear after 30–40% bone loss).
- Findings:
- Generalized osteopenia.
- Cortical thinning, “pencil-thin” cortices.
- Increased radiolucency of vertebral bodies.
- Vertebral compression fractures: biconcave (“fish vertebrae”), wedge, or crush fractures.
- Useful in detecting fragility fractures in spine, hip, wrist.
2. Dual-Energy X-ray Absorptiometry (DEXA / DXA) – Gold Standard
- Measures Bone Mineral Density (BMD).
- Reported as:
- T-score: comparison with young adult mean.
- Z-score: age- and sex-matched comparison.
- WHO classification:
- Normal: T-score ≥ −1
- Osteopenia: T-score −1 to −2.5
- Osteoporosis: T-score ≤ −2.5
- Advantages: low radiation, reproducible.
3. Quantitative CT (QCT)
- Volumetric measurement of trabecular bone density (mg/cm³).
- More sensitive than DXA, but higher radiation.
- Useful for spine BMD, research, and problem-solving.
4. MRI
- Detects fracture vs. benign osteoporotic vs. pathological fractures.
- Findings:
- Osteoporotic compression fracture → low T1 signal, high T2/STIR, preserved posterior elements.
- Pathological fracture → soft tissue mass, involvement of posterior elements.
- No direct BMD measurement.
5. Nuclear Medicine (Bone Scan / PET)
- Increased uptake in acute osteoporotic fractures.
- Useful in differentiating old vs new fractures.
- Less specific for osteoporosis itself.
📍 Classic Imaging Findings in Osteoporosis
- Vertebral body collapse (wedge, biconcave, crush).
- Trabecular bone loss → “washed-out” appearance.
- Cortical thinning.
- Insufficiency fractures (pelvis, sacrum, proximal femur, distal radius).
📌 Teaching Pearls
- DXA = gold standard for diagnosis and follow-up.
- X-ray is useful for fractures, but not sensitive for early bone loss.
- MRI is best for differentiating acute osteoporotic fracture from malignancy.
- Always evaluate for secondary causes (hyperparathyroidism, renal osteodystrophy, steroids).
📊 Imaging in Osteoporosis – Modality Comparison
| Imaging Modality | Role | Key Findings | Limitations |
|---|---|---|---|
| X-ray | Screening, fracture detection | Osteopenia, cortical thinning, trabecular loss, vertebral compression fractures | Insensitive for early bone loss (needs >30–40% loss) |
| DEXA (DXA) | Gold standard for diagnosis & follow-up | Quantitative BMD, T-score, Z-score | Cannot differentiate fracture type, no structural detail |
| Quantitative CT (QCT) | Research, problem-solving | Volumetric trabecular bone density | Higher radiation, less widely available |
| MRI | Fracture characterization | Acute vs old fractures, marrow edema, benign vs pathological collapse | Cannot measure BMD directly |
| Bone Scan / PET | Detects active fractures, bone turnover | Increased uptake in acute insufficiency fractures | Non-specific, not diagnostic of osteoporosis itself |
✅ Takeaway:
- DXA = gold standard.
- X-ray = fracture detection (not early disease).
- MRI = fracture characterization.
- QCT = quantitative but high radiation.
- Bone scan = activity detection, not diagnosis.
