Dual-energy X-ray absorptiometry (DXA) continues to be the gold standard for evaluating bone mineral density (BMD), a key component of bone strength. But while DXA provides critical insight, its focus on bone density alone can sometimes fall short in predicting who will experience a fracture. In fact, many suffer fractures despite having BMD values above the osteoporosis threshold. To fill this gap, clinicians now rely on two valuable tools: Fracture Risk Assessment Tool (FRAX®) and Trabecular Bone Score (TBS). Both enhance fracture risk assessment using information already collected during a routine DXA scan, making them efficient, non-invasive, and cost-effective additions to traditional bone health evaluations.

What DXA Measures, and What It Doesn’t

DXA measures bone mineral density at key skeletal sites, like the lumbar spine and hip. The results are typically reported as T-scores, which compare the patient’s bone density to that of a healthy young adult. According to WHO guidelines:

• A T-score ≥ -1.0 is considered normal.
• A T-score between -1.0 and -2.5 indicates osteopenia.
• A T-score ≤ -2.5 is diagnostic for osteoporosis.

But here’s the catch: BMD only accounts for about 60–70% of bone strength. The other major contributor, bone quality, is not captured in a standard DXA scan. That’s where FRAX and TBS come in.

FRAX: Expanding Risk Assessment Beyond Density

Developed by the World Health Organization, FRAX estimates a patient’s 10-year probability of hip fracture or major osteoporotic fracture. It combines clinical risk factors (like age, sex, prior fracture, steroid use, smoking, and alcohol consumption) with or without BMD data to produce an individualized risk estimate. There is an option to allow inclusion of femoral neck BMD to further refine the estimate.

One of the major motivations behind FRAX was due to a significant number of fractures occurring in people whose BMD doesn’t fall within the osteoporotic range. FRAX addresses this by being able to quantify fracture risk even in those with normal or osteopenic BMD. This helps better identify high-risk patients and allows us to implement preventive strategies before fractures occur.

FRAX scores help guide treatment decisions by categorizing patients into low, intermediate, or high-risk groups. For example, in the United States, pharmacologic treatment is typically recommended for patients whose FRAX-calculated 10-year probability of hip fracture is ≥3%, or whose probability of major osteoporotic fracture is ≥20%. Those with lower scores may be managed through lifestyle changes such as calcium and vitamin D supplementation, weight-bearing exercise, and fall prevention strategies. In cases where FRAX scores are borderline or unclear, additional tools like TBS can provide further insight.

Why FRAX matters:

• It contextualizes BMD results by factoring in non-skeletal risk variables.
• It guides treatment decisions by providing risk thresholds (e.g., a 10-year hip fracture risk >3% or major osteoporotic fracture risk >20% may trigger pharmacologic treatment).
• FRAX can be used even without a DXA scan but combining it with BMD data gives a more refined risk profile.

TBS: Quantifying Bone Quality

Trabecular Bone Score (TBS) is a textural analysis of the DXA lumbar spine image. It evaluates pixel-level variations that reflect the underlying trabecular microarchitecture, an important component of bone strength. A high TBS score indicates better bone quality. A low score points to deteriorated microarchitecture and greater fracture risk, even when BMD appears normal.

TBS was developed in response to the need for a tool that could capture bone quality, something that BMD alone cannot assess. Bone quality, particularly at the microstructural level, plays a significant role in determining fracture risk. TBS has been shown to predict fracture risk independently of BMD and has been used to reclassify patients who might otherwise be considered low risk based on density alone.

TBS adds an important dimension to fracture risk evaluation. For instance, a postmenopausal woman with osteopenic BMD but a low TBS may be at higher risk of fracture than suggested by her BMD alone. In these cases, physicians may choose to initiate pharmacologic treatment or increase monitoring. TBS is also useful for tracking changes in bone quality over time, making it valuable in treatment follow-up and adjustment.

Key points about TBS:

• It uses existing DXA images…no additional scan required.
• TBS is especially useful in populations with secondary osteoporosis, like individuals with diabetes, glucocorticoid use, or certain endocrine disorders.
• A low TBS can reclassify fracture risk in patients with osteopenia, helping clinicians make more aggressive treatment decisions when appropriate.

Integrating FRAX and TBS for Enhanced Precision

One of the most effective applications of TBS is its integration with the FRAX model. TBS-adjusted FRAX allows clinicians to fine-tune the calculated 10-year fracture probability based on trabecular bone quality. A lower TBS value increases the estimated risk, while a higher TBS can reduce it. Adjustment tools or built-in software within modern DXA systems can apply these corrections automatically or via published conversion tables.

This approach improves decision-making, especially for patients in the intermediate-risk category. For example, a patient with borderline FRAX scores and a degraded TBS may move into a treatment-eligible range when TBS is factored in. Conversely, a patient with modest risk and a strong TBS score might be managed conservatively. This helps ensure that treatments are matched to true fracture risk, avoiding both undertreatment and overtreatment.

While DXA remains a foundational tool for osteoporosis diagnosis and monitoring, its predictive power is significantly enhanced by incorporating FRAX and TBS. FRAX broadens the risk assessment beyond bone density by incorporating clinical risk factors, while TBS adds a measure of bone quality through microarchitectural analysis. Together, they provide a more complete, personalized evaluation of fracture risk. This combined approach enables earlier interventions, better-targeted therapies, and more effective strategies for preventing fragility fractures, ultimately leading to improved patient outcomes in the management of osteoporosis.