From the Guidelines
The Trabecular Bone Score (TBS) is calculated using specialized software that analyzes lumbar spine DXA images, providing a numerical score that typically ranges from 1.0 to 1.7, with higher scores indicating better bone microarchitecture and lower scores suggesting degraded microarchitecture and potentially higher fracture risk. To calculate TBS, a patient undergoes a standard DXA scan of the lumbar spine, and then the TBS software processes these images to evaluate the pixel gray-level variations in the bone texture 1. The software examines the trabecular microarchitecture patterns without directly visualizing individual trabeculae, providing a numerical score that reflects the three-dimensional structure of trabecular bone, which contributes significantly to overall bone strength beyond just density measurements 1. Some key points to consider when calculating TBS include:
- Proper positioning of the patient during the DXA scan and quality control measures to ensure accurate results
- TBS values can be used in conjunction with BMD and/or FRAX probability to enhance the accuracy of fracture risk assessment
- TBS can be applied retrospectively to previously obtained DXA scans without the need for repeated testing
- The presence of excess abdominal fat tissue may induce image noise that can artificially reduce TBS values, and it is recommended to perform TBS only in patients with a BMI of 15–37 kg/m² 1. The calculation of TBS requires specialized software and expertise, and the results should be interpreted in the context of the patient's overall clinical profile, including BMD measurements and other risk factors for fracture 1. In clinical practice, TBS can be a useful adjunct to DXA and other diagnostic tools, helping clinicians to better assess fracture risk and make informed treatment decisions, especially in patients with conditions like diabetes or those on glucocorticoid therapy where BMD alone might underestimate fracture risk 1.
From the Research
Calculation of Trabecular Bone Score
The trabecular bone score (TBS) is a texture index derived from standard lumbar spine dual energy X-ray absorptiometry (DXA) images, providing information about the underlying bone independent of the bone mineral density (BMD) 2.
Method of Calculation
- TBS is calculated from DXA images of the lumbar spine
- It is a grey-level textural measurement acquired from dual-energy X-ray absorptiometry lumbar spine images 3
- TBS reflects bone microarchitecture and can be used as a surrogate of bone strength
Applications of TBS
- TBS predicts hip and major osteoporotic fracture, at least partly independent of bone mineral density (BMD) and clinical risk factors 3
- TBS is potentially amenable to change as a result of pharmacological therapy
- TBS enhances fracture risk prediction in both primary and secondary osteoporosis, and can inform treatment initiation and the choice of antiosteoporosis treatment 3
Limitations of TBS
- Correlations between TBS and bone microarchitectural parameters vary widely across bone sites, microarchitectural parameters, and study designs 4
- TBS explains little of the variance in trabecular microarchitectural parameters in vivo
- Due to the lack of evidence, it is recommended not to use TBS for following patients treated by anti-osteoporotic drugs 4