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The costal margin is the medial margin formed by the cartilages of the seventh to tenth ribs. It attaches to the body and xiphoid process of the sternum. [2] The thoracic diaphragm attaches to the costal margin. [3] The costal angle is the angle between the left and right costal margins where they join the sternum. [2]
In old age, the costal cartilages are prone to superficial ossification, particularly in women with age of 50 years and over. [3] In costochondritis and Tietze syndrome, inflammation of the costal cartilage occurs. [4] This is a common cause of chest pain. [5] Severe trauma may lead to fracture of the costal cartilage. [6]
Behind the posterior groove is a rough area for the attachment of the medial scalene. The under surface is smooth and without a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the serratus anterior.
Joints between costal cartilages of the sixth and ninth rib are plane synovial joints. Articulation between costal cartilage of the ninth rib and tenth rib is fibrous. [1] The lateral end of each costal cartilage is received into a depression in the sternal end of the rib, and the two are held together by the periosteum.
Above the costal margin [ edit ] Since the tendons of the internal oblique and transversus abdominis only reach as high as the costal margin , it follows that above this level the sheath of the rectus is deficient behind, the muscle resting directly on the cartilages of the ribs, and being covered only by the tendons of the external obliques.
In reference to the muscles of the thoracic wall, the intercostal nerves and vessels run posterior to the internal intercostal muscles: therefore, they are generally covered on the inside by the parietal pleura, except when they are covered by the innermost intercostal muscles, innermost intercostal membrane, subcostal muscles or the transversus thoracis muscle.
The pectoralis major arises from parts of the clavicle and sternum, costal cartilages of the true ribs, and the aponeurosis of the abdominal external oblique muscle; it inserts onto the lateral lip of the bicipital groove. It receives double motor innervation from the medial pectoral nerve and the lateral pectoral nerve.
Chest x-ray is the first test done to confirm an excess of pleural fluid. The lateral upright chest x-ray should be examined when a pleural effusion is suspected. In an upright x-ray, 75 mL of fluid blunts the posterior costophrenic angle. Blunting of the lateral costophrenic angle usually requires about 175 mL but may take as much as 500 mL.