MECHANICAL-PROPERTIES OF OSTEOPENIC VERTEBRAL BODIES MONITORED BY ACOUSTIC-EMISSION

A microdamage event, either bone microfracture or microcrack propagati on, releases energy. Some of this energy is in the form of acoustic wa ves. We measured acoustic emission (AE) in normal and osteopenic verte bral bodies during compression loading to confirm the microdamage accu mulation. The 2nd to 4th lumbar vertebrae taken from the embalmed cada vers of a 37-year-old male and a 75-year-old female were used. Bone mi neral densities (BMDs) were measured by dual energy X-ray absorptiomet er (DEXA). The male vertebrae had normal BMDs, while the female verteb rae had lower BMDs than the normal range and were graded osteopenic. M echanical parameters (maximum load, maximum stress, stiffness, strain at maximum load, and apparent elastic modulus) and AE event count rate s in the load-deformation curve were measured during quasi-static comp ression loading (deformation rate 0.1 mm/min). For all mechanical para meters, the normal vertebrae had higher values than the osteopenic ver tebrae. Cumulative AE event counts until maximum load of the osteopeni c vertebrae were much greater than that of normal vertebrae. The verte brae which were well compressed to the plastic range in the load-defor mation curve displayed dome-shaped fracture lines just above the end p lates. These results are consistent with the hypotheses that microcrac ks of osteopenic vertebral bodies are generated and accumulate at lowe r strains than those of normal vertebrae at a specific site.