Abstract
Osteoporosis is chronic disease affecting most postmenopausal females and 30% of males with biological, behavioral and financial consequences. A non invasive method to assess bone structural integrity is presented, based on in-vitro or in-vivo measurement of bone dynamic characteristics (Modal Damping Factor) by applying vibration excitation in the range of acoustic frequencies, in the form of an acoustic sweep signal. This method has been applied on metallic structures and composites, including bones, and is supported by analytical and arithmetic tool based on model's theory. Experimental MDF results are compared to results acquired with conventional methods for bone quality assessment and show impressive correlations between damping factor and indices of bone quality in an advantageous manner. Evaluation of these research findings strengthens the potential of the proposed method to consist a valuable assessment tool for diagnosis and monitoring of bone integrity, in metabolic bone diseases, especially osteoporosis.
TopBackground
Bone is a composite formed by the mineralization of an organic matrix (largely collagen type I) by the deposition and growth of a carbonated calcium phosphate mineral (bio apatite), highly resembling hydroxy-apatite, Ca10(PO4)6(OH)2, within the matrix. Bioapatite provides the biomechanical properties needed for body support and movement, enabling it also to withstand stresses. Failure of mineralization of newly formed or bone remodeling results in an excess of unmineralized bone matrix (called osteoid tissue) comprising the clinical entity of osteomalacia. Main causative mechanisms are vitamin D deficiency and phosphate depletion (Mundy, 1995). In contrary, the decrease in the amount of normally mineralized bone and the disturbance in bone micro architecture (which increases the risk of fractures occurring in the absence of trauma or in response to trivial trauma) are known as osteoporosis (Melton, 1998). Some clinicians use the generic term osteopenia, which describes decreased mineralized bone mass with no reference in particular bone pathology responsible for the decrease in bone mineral density (Mundy, 1995). Osteopenia may be due to osteomalacia, primary hyperparathyroidism or malignant diseases, all of which may cause generalized bone loss.
Bone Mineral Density (BMD) is recognized as the most important single determinant of fracture risk in populations with bone disease (Cumings, 1990, 1993). Accordingly, measurement of bone density is currently the mainstay for the diagnosis and monitoring of osteoporosis, osteomalacia or osteopenia in general. However, many other skeletal and extraskeletal factors and conditions may influence the risk of developing a fracture, as in particular, a hip fracture (Cumings, 1995). Therefore, the ability of bone to withstand traumatic insults is the result of both the amount of mineralized tissue per unit of volume (density), and many other factors that are commonly referred to as bone quality. Loss of trabecular connectivity is considered one of the critical factors that weaken bone strength in osteoporosis (Parfitt, 1987). Although data are still limited, this architectural abnormality may independently constitute an important factor for predicting fracture risk (Kleerekoper, 1985).
Key Terms in this Chapter
Structural Integrity: Term used for the performance characteristic applied to a component or a structure and expresses the item ability to hold together under a load, resisting breakage. It assures that the construction will perform its designed function, for its designed life. Items are constructed with structural integrity excluding catastrophic failure, which can result in injuries, severe damage, death, or monetary losses.
Dynamic Characteristics: Physical properties of a structure under variable loading.
Bone Structural Integrity: Term refers to the ability of a bone to function as component of the whole body, sustaining anticipated loads. Any change in bone architecture, i.e. mineral losses, deteriorates the overall bone quality and may result in injuries, fractures, death, life quality deterioration and monetary losses.
Osteoporosis: Bone is a composite formed by mineralization of an organic matrix by nucleation and growth of bioapatite, which provides the biomechanical properties needed for body support and movement, enabling it also to withstand stresses. Decrease in the amount of normally mineralized bone and bone micro architecture disturbance constitute osteoporosis.
Structural Integrity and Failure: Engineering aspect dealing with the ability of a structure to support a designed load without failure.
Damping: Materials or structural members dissipating energy under cyclic loading present stress-strain curve with hysteretic loop. The area between loading-unloading branches is proportional to the energy absorbed, is called damping and constitutes a dimensionless physical property accounting for structural changes.
Structural Failure: Loss of structural integrity, which is the loss of the structure's load-carrying capacity. Structural failure is initiated when the material is stressed beyond its strength limit, thus causing excessive deformations or fracture. In a well-designed system, a localized failure should not cause immediate or even progressive collapse of the entire structure.