Investigating the Effect of Combination Loading in Femur of Children

Literature Review

Different Computed Tomography (CT) Applications

            The introduction of CT in the clinical and biomedical is undoubtedly one of the critical milestones that have been achieved in the last forty years in the medical field. CT generally refers to a computerized X-ray imaging procedure where a narrow beam of X-rays is aimed at the affected body of a patient in order to in order to produce signals that are processed by computers to come up with cross-sectional images. The cross-sectional images produced by CT are known as topographic images and they have more detailed information in comparison to the traditional x-rays. Contrary to the traditional x-ray that uses fixed x-ray tubes, CT utilized motorized x-ray source that moves around a circular opening of a structure known as gantry. After a complete x-ray source rotation, the CT computer uses complex mathematical methods to construct a 2D image slice of affected person. The 3D image slices can be displayed by the CT computer to produce a 3D image of the patient in order to show the tissues, skeleton, tissue or organ in order to identify the abnormality in the body.

            CT helps in direct imaging of soft tissue structures in the human body such as liver and lung tissues. CT is particularly important in looking for large space that occupies lesions, tumors, and metastasis [1]. It can not only help in revealing the presence of tumor in the soft body organs, but also the sizes, location, and the extent of a tumor in various body parts. CT imaging in various body organs such as brain helps in detecting tumors, the presence of blood clot in the brain, and detects the enlarged ventricles in the brain. Since CT uses the short scan time of about 500 miles per second, it can be used to detect abnormalities in anatomic regions such as those susceptible patient’s motion and breathing [2]. Therefore, CT is more effective in imaging sensitive body organs such as the brain, heart, and lung in comparison to the conventional x-trays and it is able to provide excellent soft tissue resolution and spatial resolution.

            A CT scan is also extensively used to image complex bone fracture and severely eroded joints of the body. CT is used to image complex bone tumor due to its ability to produce detailed images that is not possible when the traditional x-ray is used [3]. Currently, physicians prefer to use CT scan in bone imaging because it enables them to access soft tissues in the bone such as cartilages, tendons, and muscles. In addition, CT offers more information related to fracture, injuries, or diseases of the bone. CT is also used in the cases of trauma and fracture of the cranium.

            Physicians use CT to diagnoses various diseases and abnormalities in the musculoskeletal system such as the diagnosis of orthopaedic disorders and incomplete ossification of the humeral condyle. CT helps in facilitating the examination of complex joint structures like elbow by removing superimposed structures [5]. It can also be used to detect and confirm the medial coronoid process fracture that occurs in the elbow. CT enables physicians to vie images in a number of image planes, which helps them to delineate fracture orientation and to effectively plan for the repair process.  

            Apart from brain, skeletal, and other soft organs in the body, CT is also used to identify the abnormalities and infections in the spine [6]. Physicians use CT to investigate spinal lesion in the case of doubtful radiographic findings. CT also enables heath providers to identify gas between vertebrae and vertebral canal, which is an indication of disc degeneration. The interpretation of spinal CT images is carried `out in both bone and soft tissue window.

            Therefore, CT is heavily applied in the medical field. It is used to detect the infections and tumor in soft organs such as brain, lungs and even the heart. CT is also applied in the musculoskeletal system, especially in the case of bone fracture, as it is able to provide 3D images that can help physicians to effectively plan for the repair process. In addition, CT can be used to diagnose abnormalities or infections in the spine.


Adult Femur

            The femur is the largest and the longest human bone that is found in the human anatomy. It is also one of the strongest bones in the human body, as it can be compared with the temporal bone of the skull. Because femur is one of the strongest bones in human anatomy, it takes a lot of force to break it and car crush is one of the forces that can break an adult femur. The average adult femur is about 48cm in length with a diameter of about 2.34cm. Studied have shown that adult femur can support up to thirty times the weight of a fully grown adult. The adult femur has four main parts that include the head, lower extremity, greater trochanter, and lesser trochanter. The parts gradually grow from the day a child is born to the adulthood. The lesser and greater trochanters act as muscles attachment site for the gluteal muscles.

            The adult femur has high level of robusticity and dense because it is the main supporting limp. The adult femur is also heavily surrounded with muscles. Contrary to humerus, femur has a direct ligament attachment that is found between femoral bone and acetabulum. The long and straight part of the femur is known as femoral shaft. The femoral shaft is slender and almost cylindrical in shape. The lower extremity of adult femur is larger than the upper extremity. The extremities consist of two eminence called condyles. Since it is the only bone in the thigh, femur acts as an attachment point for the muscles that exert their force around the hip and the knee joints of the human body. About 22 individual muscles originates insert onto the adult femur, which makes it a very important bone.

Children Femur

            Unlike adult femur where only the metaphysic and diaphysis are present, children femur has four main parts that include diaphysis, metaphysic, physis, and epiphysis. The epiphysis is mainly cartilaginous among children. Before it fully develops, epiphysis consists of both articular cartilages and growth cartilage. However, with time, the two cartilages are differentiated by the development of secondary ossification center. The physis, on the other hand, is responsible for the longitudinal growth of children femur. The circumferential growth of children femur is due to periosteal growth. Physis also plays important role in children femur, as it acts as barrier to blood flow, which is important during healing that takes place after physeal separation. It is not possible to see physis on x-ray because it is radiolucent.

            Studies have shown that femur fractures in children heal faster than those of adults due to the biological active periosteum and high level of vascularity. In addition, the development and remodeling of the callus are rapid among children who have femora fractures, which make them to heal faster than adults. The presence of ossification centers in children femur changes the internal fixation in the case of femoral fractures in children [7]. Child abuse is the leading cause of femoral fracture in children, especially those aged between 1 and 4 years. Other major causes of femoral fracture in children include falling hard on the playground and motor vehicle accidents. Therefore, there is difference between adult femur and children femur in terms of structure and healing process in the case of fracture.

4 Point Bending FEA Test

            Bend or flexure testing is common in brittle materials such as concretes, glasses, plastics and bones [13]. Therefore, bend test is always used to assess the strength of brittle materials. However, bend test is not suitable for ductile materials because it is difficult to determine the yielding point of the material that is put under bending. In addition, bending test is most appropriate for testing brittle materials whose stress-train curves indicate that they posses linear elastic behavior before they fail [11].

            According to Coni et al, 4 point bending FEA test is a technique that is used to determine the strength of brittle materials [10]. In addition, 4 point bending FEA test is used to investigate the properties of pavement materials such as stiffness and fatigue [12]. The 4 point bending FEA test is preferred over other tests because of some of its advantages such as simple test fixtures, simple sample geometries, and the requirement of minimum sample machining. However, it has more complex stress distribution in the sample.

Bone Mechanics

            Bone is a complex tissue that is found in the human body and other mammals. The two types of bone tissue include cortical and trabecular bones and they have important task of withstanding substantial stress during locomotion and other strenuous activities [14]. Cortical bone is the outer shell of bone while trabecular is the interior meshwork of bone. Because bones are loaded cyclically and statically, fatigue and creep are some of the important aspects of their mechanical behaviors [15]. The core stimulus for bone remodeling is the repair of damage. However, the ability to repair and remodel bones decreases with an increase in age of humans.

            The bone consists of organic and inorganic materials. Based on its weight, 60% of the bone is inorganic while 30% is organic [14]. The remaining 10% of the bone is water. The organic part of the bone consists of crystalline-type mineral whereas the organic part of the bone is mainly a type I collagen. Therefore, the bone consists of organic and inorganic materials, including water. In terms of mechanical properties, cortical bone is stronger and stiffer when it is loaded longitudinally.

            Human cortical bone is a linearly elastic object that can easily fail when exposed to smaller strains after experiencing a marked yield point [14]. On the other hand, trabecular bone is nonlinearly elastic at small strain. Trabecular can also absorb significant energy on mechanical failure. In addition, it has anisotropic mechanical features that rely on porosity of the specimen [8]. The anisotropy of trabecular bone strength rises with an increase in age.  



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