Cross-sectional circularity: a new tomographic variable validates a biomechanical analysis of human distal tibia for diagnosing bone fragility and selective trabecular osteopenia.

GUSTAVO ROBERTO COINTRY; SARA FELDMAN; PABLO ANDRÉS MORTARINO; IVAN YELIN; PAOLA REINA; JOERN RITTWEGER; JOSÉ LUIS FERRETTI; RICARDO FRANCISCO CAPOZZA

Toronto

Congreso; XXXII ANNUAL MEETING, American Society for Bone & Mineral Research (ASBMR).; 2010

American Society for Bone & Mineral Research

This study evaluates the structural efficiency of the distal tibia to resist compression stress employing pQCT (XCT-2000, Stratec), assuming that the adapted optimal cross-sectional design would show both a minimal cortical mass and a maximal circularity (Circ). To show that association in the heel, we measured Circ = 2 ã(area/perimeter), and correlated it with the total BMC (ToC) of scans taken at every 5% of the tibia length from the heel throughout the bone (C5-C95) in 21 healthy volunteers (10 men) of 20-40 yr. The ToC, higher in men (p<0.001), felt 1/3 from C5 to C15 (the lowest observed value) and then grew up to C95. Circ varied opposite to ToC throughout the bone, showing a maximal value at C15.The dispersion observed for both variables was also the lowest (CVs 8.2 & 8.5%) at C15 in both genders. Data confirmed the existence of an almost pure compression stress pattern between C15, where bone structure is almost purely cortical, and C5, where structure is combined trabecular/cortical. A separate study of the correlation between ToC at the standard 4% (close to C5, y) and 14% (close to C15, x) sites in 300 healthy men and pre- and post-MP women showed a linear relationship with a slope close to 1.5 and a very low SEE, with no gender-related differences. Results support using the 4/14 ToC ratio from a standard pQCT study of the leg as a specific indicator of trabecular bone mass with reference to cortical mass, following a simple biomechanical criterion. 1. If only a compression stress occurs at those sites (for which only the mass of bone material in the cross-section accounts), then the 3:2 ratio between C4/C14 ToC would express the natural relationship between both the masses and structural abilities of both bone structures. 2. As long as trabecular bone tends to be lost faster than cortical bone, the C4/C14 ToC ratio would evaluate the lost in mechanical efficiency of the trabecular structure with reference to the cortical mass of the same individual, avoiding comparison with younger subjects as required by DXA. Thus, a Z-scored version of the C4/C14 graph obtained can be used as a standard reference for comparative diagnoses as well as for comparison with the muscular status of the individual. This simple study offers a non-invasive, biomechanical diagnosis of osteoporosis as an "osteopenic fragility" in agreement with the NIH criteria, based in relevant features of the same individual, and independent of age, gender, or anthropometric traits.