In 2012 the FDA approved a new diagnostic tool for assessing fracture risk in people with osteoporosis. Since that time, Trabecular Bone Score (TBS) has rapidly made its way into the clinical setting. For years we have relied on dual-energy X-ray absorptiometry (DXA) exams to assess bone health, or lack-there-of. But DXA analysis looks solely at bone quantity irrespective of quality. TBS is obtained from the lumbar spine portion of the DXA exam, and is an assessment (at least to a certain extent) of bone quality. When used together, the DXA and TBS enhance our ability to more-accurately predict fracture risk.
TBS measures the grey-level texture [kind of like looking at a 3-dimensional pixel (voxel) and assessing its texture inhomogeneity] of the inner part of the vertebral vertebrae. This cancellous bone is where the trabeculae measured in the TBS are found. It is in this central part of the spinal vertebrae where the bone marrow is located.
|Cross section of normal bone (left), osteoporotic bone (right)|
Individually, the trabeculae are somewhat fragile but together they form a lattice of three-dimensional structural beams that add strength and lightness to bones. When bone density declines, these trabeculae thin and become weaker. Eventually they can become completely disconnected looking not like strong sturdy rods, but like microscopic stalactites and stalagmites with no ability to withstand compressive forces. It is under these circumstances of skeletal architectural disintegration that TBS decreases and fracture risk increases.
When assessing TBS, values greater than 1.350 are considered normal. Scores between 1.200 and 1.350 are from “partially degraded” bone and when the score is 1.200 or less the trabeculae are considered “degraded” or severely weakened. A good example of why TBS can be so helpful in determining fracture risk is when we look at the DXA scans of a person with type 1 diabetes. DXA scores can actually be slightly elevated in these patients but their bone quality is poor and they have a higher risk for fracture than their DXA results would predict. When assessed by TBS the results would be low indicating poor bone quality and heightened risk for breaking a bone.
TBS values decrease with the following circumstances/conditions:
– Long-term glucocorticoid use (greater than 5 mg a day for more than 3 months)
– Ehlers-Danlos syndrome
– Rheumatoid arthritis
– The use of estrogen-deprivation therapy in women with breast cancer
Make sure you ask your doctor to include a TBS on the requisition the next time he or she orders a DXA for you. The requisition has to have TBS on the form for the lab to do this analysis.
EVENT REMINDER: Don’t forget to sign up for the one day seminar on osteoporosis we are hosting in Florida. Please join Irma Jennings (Bone-Health Coach) and me on March 9th, 2019 from 1 to 6 p.m. in Hollywood, Florida. Go to https://MyBones.Me for more info and to sign up. Hope to see you there!