Assessment of Cortical Bone Mechanics Technology (CBMT) Fracture Discrimination Capability

Osteoporosis is a disease characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility (i.e., weakness), and an increased risk for fracture. The incidence of osteoporosis related fragility fractures (i.e., low energy fractures resulting from a fall from standing height or less) increases with age and is highest in post-menopausal women. In the United States, there were approximately 2.3 million fragility fractures in 2020. The total annual expense of providing direct and indirect care for osteoporotic fractures among Medicare beneficiaries was estimated at $57 billion in 2018, with an expected increase to over $95 billion by 2040.

Bone strength is a critical factor in a bone's ability to resist fracture and is clearly an important outcome in studies of osteoporosis. The current standard for assessing bone health and diagnosing osteoporosis is to use dual-energy x-ray absorptiometry (DXA) to quantify the areal bone mineral density (BMD), typically at the hip and spine. However, DXA-derived BMD has relatively poor discriminatory accuracy to distinguish individuals who will fracture from those who will not.

One well known limitation of BMD is that it does not adequately assay bone strength. As with any complex structure, bone strength depends on the interplay between a variety of factors, including the amount or mass of bone present and the structural organization and quality of the material. BMD primarily indicates bone mass but does not adequately assess the contributions of bone structure or quality to bone strength.

Reflecting the limitations of DXA, BMD explains less than half of the variation in whole bone strength, and when bone strength is improved and fracture risk reduced via bisphosphonate drug therapy, less than 18% of the observed reductions in vertebral fracture risk can be attributed to increases in BMD. These findings clearly suggest that the current standard care is insufficient for identifying those who might benefit most from early intervention to improve bone health, as well as for assessing the effect of new therapies targeted at increasing bone strength. A potential new diagnostic approach to address this critical unmet need and improve osteoporosis diagnosis is the use of Cortical Bone Mechanics Technology (CBMT).

CBMT leverages multifrequency vibration analysis to conduct a noninvasive, dynamic 3-point bending test that makes direct, functional mechanical measurements of ulnar cortical bone (e.g., flexural rigidity). Because CBMT is a whole bone test, its measurements reflect the combined influences of bone quantity, structure, and quality at all hierarchical levels. Its validity in accurate measurements of ulna flexural rigidity and estimations of quasistatic ulna bending strength have been demonstrated. CBMT-derived flexural rigidity yielded a near perfect estimate of cadaveric bone strength (R2=0.99). Additionally, flexural rigidity has been reported to decrease 21% following potassium hydroxide-induced collagen degradation whereas BMD was not altered. Thus, current data indicates that CBMT-derived ulnar flexural rigidity accurately estimates ulnar whole bone strength and provides information about cortical bone that is unique and independent of BMD. Assessing cortical bone, in particular, is important because after ~65 years most bone loss is cortical, and the cortical bone loss is associated with increased incidence of fragility fractures. However, the clinical utility of CBMT-derived flexural rigidity has not yet been demonstrated.