Fracture risk in the femoral hip region: A finite element analysis supported experimental approach Alexander Tsouknidas a,n , Kleovoulos Anagnostidis b , Georgios Maliaris c , Nikolaos Michailidis d a Laboratory for Machine Tools and Manufacturing Engineering, Mechanical Engineering Department, Aristoteles University of Thessaloniki, 54124 Thessaloniki, Greece b 3rd Orthopaedic Department ‘‘Papageorgiou’’ General Hospital, Aristoteles University of Thessaloniki, Greece c Department of Electrical and Computer Engineering, Democritus University of Thrace, Xanthi, Greece d Physical Metallurgy Laboratory, Mechanical Engineering Department, Aristoteles University of Thessaloniki, Greece article info Article history: Accepted 9 May 2012 Keywords: Femoral hip FEA Dual-energy X-ray absorptiometry Fracture risk indicator abstract The decrease of bone mineral density (BMD) is a multifactorial bone pathology, commonly referred to as osteoporosis. The subsequent decline of the bone’s micro-structural characteristics renders the human skeletal system, and especially the hip, susceptible to fragility fractures. This study represents a systematic attempt to correlate BMD spectrums to the mechanical strength characteristics of the femoral neck and determine a fracture risk indicator based on non-invasive imaging techniques. The BMD of 30 patients’ femurs was measured in vivo by Dual-energy X-ray absorptiometry (DXA). As these patients were subjected to total hip replacement, the mechanical strength properties of their femurs’ were determined ex-vivo using uniaxial compression experiments. FEA simulations facilitated the correlation of the DXA measurements to the apparent fracture risk, indicating critical strain values during complex loading scenarios. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Osteoporosis is a multifactorial bone disease concerning roughly 4% of the human population (Melton et al., 1992). As an asymptomatic condition, osteoporosis fails to exhibit noticeable symptoms, particularly at early stages and thus is usually under- diagnosed. Untreated however, this clinically silent disease is likely to increase the risk of fragility fractures (Ettinger, 2008; Rockwood et al., 1990; Cooper et al., 1992). Due to its high morbidity and global nature, osteoporosis is considered a pathology with a significant socioeconomic impact (Ray et al., 1997). The affected patients’ bone mineral density (BMD) is drastically reduced, deteriorating the bones’ micostructural characteristics as a result of excessive bone resorption followed by insufficient bone formation during remodelling (Frost and Thomas, 1963; Raisz, 2005). The pathogenesis has been associated to dietary aspects (Hackett et al., 2009), immobilisation (Minaire, 1989), hyper-para- thyroidism (Dupree and Dobs, 2004), vitamin D deficiency (Holick, 2004), alteration of biochemical markers like hormones (Parfitt et al., 1995; Black et al., 2003) and aging (Newton-John and Morgan, 1970). Regardless of aetiology, decreased bone mineral density renders the skeletal system susceptible to fracture, predominantly occurring at the hip (Bohr and Schaadt, 1985), the vertebral column (Old and Calvert, 2004) and wrist (Dempster, 2011). According to the World Health Organisation, osteopenia and osteoporosis are defined by the patient’s bone mass deviation, when compared to that of an average, young and healthy adult (World Health Organisation, 1994) when measured by DXA. Even though DXA can accurately determine the minerals and lean soft tissue of the examined area, the overall accuracy of the measurement is impaired by the subtraction of the indirectly calculated fat mass (St-Onge et al., 2004). Furthermore, DXA results are represented as mass per area, thus not considering the anisotropy of the bone tissue and are hence a qualitative and not quantitative index of the bone structure (Lochmuller et al., 2000). Several other methods have been recently introduced to determine bone mineral density (Genant et al., 1996; Braun et al., 1998); DXA nevertheless is still widely considered as the method of choice. Other techniques like peripheral quantitative computed tomography (pQCT) may be accurate in measuring BMD at peripheral skeletal sites; however they exhibit restric- tions that prohibit measurements at the proximal femur (Augat et al., 1996, 1998). The aim of this investigation is to determine the correlation of the bone mineral density in the femoral neck, as measured by DXA, to experimentally determined strength characteristics of the bone. This, followed by the introduced FEA simulation, will facilitate the use of DXA as an indicator of fragility fracture risk Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics 0021-9290/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jbiomech.2012.05.011 n Corresponding author. Tel.: þ30 2310 995940; fax: þ30 2310 996059. E-mail address: alextso@auth.gr (A. Tsouknidas). Journal of Biomechanics 45 (2012) 1959–1964