The Trabecular Bone Score (TBS) is a diagnostic tool used to assess bone health, providing information that complements the traditional measurement of Bone Mineral Density (BMD). While BMD measures the quantity of bone mass, the TBS evaluates the quality of the internal bone structure, specifically the microarchitecture of the spongy, or trabecular, bone. Bone strength and fracture resistance depend not only on bone quantity but also on how well that bone is organized. The TBS helps healthcare providers gain a more complete picture of a man’s skeletal health beyond density measurement.
Understanding the Trabecular Bone Score
The Trabecular Bone Score is not a separate imaging test but is an advanced computer analysis performed on images from a standard dual-energy X-ray absorptiometry (DXA) scan of the lumbar spine. This software extracts information about the texture of the gray-level pixels in the DXA image, which serves as an indirect index of bone quality. The score is essentially a measure of the density and connectivity of the trabeculae—the delicate, interconnected rods and plates that form the honeycomb-like structure inside the bone.
A high TBS value suggests a strong, well-connected microarchitecture, which is more resistant to fracture. Conversely, a lower TBS reflects a degraded microarchitecture, characterized by thinner, less connected bone structures, which increases bone fragility. This index relates to three-dimensional bone characteristics, such as the number and separation of trabeculae. The ability of TBS to discern differences in bone structure, even when two people have the same BMD, makes it a valuable addition to bone health assessment.
Interpreting TBS Score Ranges for Men
The TBS provides a numerical value categorized into three main risk levels for men to help determine their fracture risk profile. These classifications are based on the degree of trabecular microarchitectural degradation. The specific numerical cutoffs for these categories can vary slightly depending on the reference population and software version used, but general ranges are consistently applied to men over the age of 50.
For a man, a TBS score of approximately 1.310 or higher typically indicates optimal or normal bone microarchitecture, suggesting a low risk for fragility fractures. This high score reflects a healthy, well-connected internal bone structure. When the score falls between roughly 1.230 and 1.310, the microarchitecture is considered partially degraded, placing the man in an intermediate fracture risk category.
A score of 1.230 or lower generally indicates a degraded microarchitecture, which is associated with a significantly higher risk of fracture. Cutoffs around 1.230 are commonly cited in clinical use. These numerical ranges help healthcare providers move beyond BMD alone to quantify the level of structural deterioration.
Clinical Significance and Fracture Risk Assessment
The primary clinical value of the Trabecular Bone Score lies in its ability to enhance the accuracy of fracture risk prediction, independent of standard BMD measurements. Research shows that TBS predicts fragility fractures in men over 50 years old, with each standard deviation decrease in TBS correlating to an increased risk of incident fracture. This is important because a significant number of fragility fractures occur in individuals who do not meet the criteria for osteoporosis based on BMD T-scores alone.
Integrating the TBS into fracture risk models, such as the FRAX algorithm, provides a more personalized risk estimate. By adjusting the FRAX probability based on the TBS value, physicians can more accurately identify men who are at high risk of fracture despite having borderline BMD results. This improved risk stratification helps guide therapeutic decisions, ensuring that men who need bone-strengthening treatments are identified and treated, even if their BMD is not severely low.
Factors Influencing TBS
Several medical conditions and lifestyle elements are known to negatively affect bone microarchitecture, resulting in a lower TBS score, sometimes disproportionately to the loss of BMD. Type 2 Diabetes is a notable example, as it is associated with a degraded TBS score, even in cases where the BMD measurement may appear normal. Chronic kidney disease and certain rheumatic diseases also contribute to a lower TBS, reflecting damage to the internal bone structure.
The long-term use of specific medications, such as glucocorticoids (steroids used to treat inflammation), is strongly associated with a reduced TBS. Lifestyle factors can also play a role. For men, the following are linked to a lower TBS:
- Older age
- Higher weight
- Low physical activity during childhood
- Smoking
- Larger waist circumference