Biomechanics of Thorax

The contribution of thorax about 20 percent to the overall length of the body comparison to 12 percent of the lumbar spine and 8 percent of the cervical spine.1 The thoracic wall is bounded anteriorly by the sternum laterally by the ribs and posteriorly by the thoracic vertebrae as well as superiorly by the suprapleural membrane and inferiorly by the respiratory diaphragm.2 functions of thoracic cage is 1) provides a base for the muscle attachment of the upper extremities, the head and neck, the vertebral column and the pelvis. 2) this provides protection for the heart, lungs and viscera.3 The anterior chest wall sternum include the thick manubrium, The most superior portion of the manubrium is called jugular notch, and it is also the first to form during embryogenesis. Anatomically, the manubrium is located at the level of thoracic vertebral bodies T3 and T4, the manubrium is also the widest and thickest segment of the sternum, the middle long part is called body of the sternum, and inferior part of sternum called xiphoid process. The sternal body is located at the level of vertebral bodies T5 to T9, covers a significant portion of the mid-chest, and is very strong. The xiphoid process is a thin and very small bone, this may appear bifid, oval, or curve inward or outward and the bone’s size may vary from 2 to 5 cm.2 The ribs are the bony framework of the thoracic cavity, there are twelve pairs of ribs. According to their attachment to the sternum, the ribs are classified into three groups: true, false, and floating ribs. the first seven ribs are called true ribs as they are ribs that directly articulate with the sternum with their costal cartilages. the eighth, ninth, and tenth ribs are called false ribs, these ribs are indirectly articulate with the sternum, as their costal cartilages connect with the seventh costal cartilage. 11th and 12th ribs are called floating ribs as the ribs that do not articulate with the sternum at all. 4