Abstract
The incidence of osteoporotic fractures was estimated as nine million worldwide in 2000, with particular occurrence at the proximity of joints rich in cancellous bone. Although most of these fractures spontaneously heal, some fractures progressively collapse during the early post-fracture period. Prediction of bone fragility during progressive collapse following initial fracture is clinically important. However, the mechanism of collapse, especially the gradual loss of the height in the cancellous bone region, is not clearly proved. The strength of cancellous bone after yield stress is difficult to predict since structural and mechanical strength cannot be determined a priori. The purpose of this study was to identify whether the baseline structure and volume of cancellous bone contributed to the change in cancellous bone strength under cyclic loading. A total of fifteen cubic cancellous bone specimens were obtained from two 2-year-old bovines and divided into three groups by collection regions: femoral head, neck, and proximal metaphysis. Structural indices of each 5-mm cubic specimen were determined using micro-computed tomography. Specimens were then subjected to five cycles of uniaxial compressive loading at 0.05 mm/min with initial 20 N loading, 0.3 mm displacement, and then unloading to 0.2 mm with 0.1 mm displacement for five successive cycles. Elastic modulus and yield stress of cancellous bone decreased exponentially during five loading cycles. The decrease ratio of yield stress from baseline to fifth cycle was strongly correlated with bone volume fraction (BV/TV, r = 0.96, p < 0.01) and structural model index (SMI, r = − 0.81, p < 0.01). The decrease ratio of elastic modulus from baseline to fifth cycle was also correlated with BV/TV (r = 0.80, p < 0.01) and SMI (r = − 0.78, p < 0.01). These data indicate that structural deterioration of cancellous bone is associated with bone strength after yield stress. This study suggests that baseline cancellous bone structure estimated from adjacent non-fractured bone contributes to the cancellous bone strength during collapse.
Highlights
Osteoporosis is a common disease which is characterized by low bone mass and deterioration of bone tissue, resulting in an increased risk of fracture, at the proximity of the joint rich in cancellous bone (Riggs & Melton 3rd, 1995)
This study suggests that baseline bone structure estimated from the adjacent non-fractured bone side can contribute to the cancellous bone strength during clinical collapse
This bone fragility of cancellous bone during progressive collapse is only one part of the whole bone strength; medical institutions could more correctly evaluate the permissible pressure of the fracture area and more confidentially allow each osteoporosis patient to undertake the appropriate levels of rehabilitation without progressive collapse
Summary
Osteoporosis is a common disease which is characterized by low bone mass and deterioration of bone tissue, resulting in an increased risk of fracture, at the proximity of the joint rich in cancellous bone (Riggs & Melton 3rd, 1995). The occult fracture of the femur and the subchondral insufficiency fracture (SIF) of the femoral head are manifested in the cancellous bone region with rapid progression of the collapse, such as seen in rapidly progressive arthritis of SIF (Bangil et al, 1996; Yamamoto, 2012). Severe collapse of these areas can lead to chronic pain, depression, an inability to perform daily life activities, and in extreme cases can be life-threatening (Riggs & Melton 3rd, 1995; Poole & Compston, 2006; Ioannidis et al, 2009; Adachi et al, 2010). Prevention of the collapse in rich area of cancellous bone, especially proximal femur and spine fracture, is clinically critical
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