Euler(strut.cavity), a new histomorphometric parameter of connectivity reflects bone strength and speed of sound in trabecular bone from human os calcis.

The amount of bone and the trabecular microarchitecture are two determinants of bone strength which can be quantified by bone histomorphometry. Among the parameters of bone microarchitecture, the Euler number developed in our laboratory (E( strut.cavity )) and trabecular bone pattern factor (TBPf) evaluate the connectivity and complexity independently of the bone quantity, and the speed of sound (SOS) measured by quantitative ultrasound (QUS) corroborates E( strut.cavity ). The aim of the present study was to validate E( strut.cavity ), TBPf, and SOS as parameters of bone microarchitecture and their contribution to bone strength. We examined 20 right os calcis taken after necropsy in 11 males and 9 females, aged 52-95 years. At the same anatomic location, we measured SOS and broadband ultrasound attenuation (BUA) using a Hologic Sahara device and bone mineral density (BMD) using a Hologic QDR 1000W. At this site a transcortical cylinder was cut for both apparent density measurement (Ap.Dens) and biomechanical tests (maximum compressive stress (sigma(max)) and Young's modulus (E)), and histomorphometry was performed with an automatic image analyzer (Visiolab, Explora Nova, France). E and sigma(max) were significantly correlated with the parameters of bone quantity, microarchitecture, and QUS. However, after adjustment for the bone quantity, E correlated only with E( strut.cavity ), TBPf, and SOS, and sigma(max) with BUA. In conclusion, the bone connectivity and complexity evaluated by E( strut.cavity ) and TBPf contribute to bone strength, independently of the bone quantity. The bone mechanical properties may be assessed, in os calcis, in the elastic domain by SOS and in the plastic domain by BUA.