Journal of Biomechanics 41 (2008) 438–446 Dependence of mechanical compressive strength on local variations in microarchitecture in cancellous bone of proximal human femur E. Perilli, M. Baleani à , C. O ¨ hman, R. Fognani, F. Baruffaldi, M. Viceconti Laboratorio di Tecnologia Medica, Istituti Ortopedici Rizzoli, Via di Barbiano 1/10, 40136 Bologna, Italy Accepted 10 August 2007 Abstract Human cancellous bone is a heterogeneous material. Despite this, most of the published studies report correlations between mechanical properties and morphometric parameters averaged on the whole specimen. This work investigated whether local variations in morphometric parameters were linked to the localized failure regions of cancellous bone. Additionally, it was examined whether local values of morphometric parameters can predict the ultimate stress better than the average bone volume fraction (BV/TV). Cylindrical cancellous bone specimens extracted along the primary compressive group of human femoral heads were studied. These were microCT-imaged to assess the morphometric parameters, compressed to determine the ultimate stress, and rescanned by microCT to visualize the failure region. Failure involved slightly less than half of the free height of the specimens. Significant differences were found in the morphometric parameters calculated in the failure and in the non-failure regions. The cross-sections containing minimum BV/TV values were those most often located inside the failure region (83%, po0.001). Regression analysis confirmed that variations in BV/TV best describe variations in ultimate stress (R 2 ¼ 0.84) out of the averaged morphometric parameters. The prediction of ultimate stress increased when minimum or maximum values of the morphometric parameters were taken, with the highest prediction found by considering the minimum BV/TV (R 2 ¼ 0.95). In conclusion, due to the heterogeneity of cancellous bone, there may exist regions characterized by a different microarchitecture, where the bone is weaker and consequently is more likely to fail. These regions mostly contain minimum values in BV/TV, which were found to predict ultimate stress better than average BV/TV. r 2007 Elsevier Ltd. All rights reserved. Keywords: Cancellous bone; Trabecular architecture; Morphometric parameters; Mechanical testing; Bone strength 1. Introduction Bone fractures represent a major health problem in the increasingly elder population. The World Health Organi- zation (WHO) recommends the use of bone mineral density (BMD) measurements to determine fracture risk (WHO, 1994). However, while BMD is correlated to fracture risks, using it to identify individuals who will suffer a fracture is not always reliable (Marshall et al., 1996; McCreadie and Goldstein, 2000). Furthermore, BMD measurements alone neither allow to differentiate between cortical and cancel- lous bone, nor to determine structural changes within the cancellous bone microarchitecture. Apart from density, cancellous bone microarchitecture has an important effect on bone strength (McCalden et al., 1997; Gibson, 2005). Spatial resolution is one of the key- parameters for the morphometric quantification of cancel- lous bone microarchitecture (Mu¨ller et al., 1996b). The development of high resolution 3D imaging techniques, such as microtomography (microCT) or high resolution magnetic resonance imaging, has made it possible to assess cancellous bone structure in three dimensions non destruc- tively (Mu¨ ller etal., 1996a; Majumdar, 1998). A number of studies have found significant correlations between me- chanical properties and morphometric parameters (Goulet ARTICLE IN PRESS www.elsevier.com/locate/jbiomech www.JBiomech.com 0021-9290/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbiomech.2007.08.003 à Corresponding author. Tel.: +39 051 6366864; fax: +39 051 6366863. E-mail address: baleani@tecno.ior.it (M. Baleani).