This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The ribs are frequently fractured, sometimes they become affected with caries, and in operating the chest is frequently opened between them or portions of them are excised. They are both elastic and movable, and difficult to break; hence fracture is almost always due to direct violence, and this violence may be so great as sometimes to cause death. Normally there are twelve ribs on each side, but sometimes there is an extra cervical or lumbar rib. These are both rare, the latter the more so.
The seven upper ribs are called true ribs because they articulate with the sternum. The remaining five are called false ribs, the eleventh and twelfth being floating ribs. The eighth, ninth, and tenth ribs each articulate by their cartilages with the rib above. The tenth forms the lower margin of the thorax. The eleventh and twelfth ribs are attached only by their posterior extremities, their anterior portion being imbedded in the soft parts; hence they are called floating ribs. The ribs slope downward and forward. This obliquity increases until the ninth rib, after which it decreases. The first rib in front corresponds to the fourth behind, the second, third, fourth, fifth, sixth, and seventh in front correspond each to the fourth rib lower behind. The first rib is the nearest horizontal in regard to its surface and, being well protected by the clavicle, is rarely broken. The intercostal spaces are broader in front than behind and broader above than below. The third is the largest.
The groove on the lower surface of the ribs holds the intercostal artery, but only as far back as the angle, from which point it occupies the middle of the space.
The extent of the intercostal spaces is considerably influenced by position - flexion of the body brings the ribs together, extension and bending to the opposite side separates them. This point is of importance in reference to the operations of paracentesis and empyema.
The first costal cartilage unites directly with the sternum, there being no joint present. The second and sometimes the third cartilage is joined to the sternum by a ligament with a synovial joint above and below it. The other costal cartilages are united by a joint with a single cavity. These joints may be the seat of metastatic abscesses in pyaemic infections.
Cervical ribs spring from the body and transverse process of the seventh cervical vertebra. They may be long enough to reach to the sternum, but usually are much shorter. One case of this affection was seen by the writer in a man twenty-seven years of age. There was an abnormal fulness above the scapula posteriorly, and above the clavicle anteriorly, just to the inner side of the external jugular vein, a distinct bony process could be felt. This did not move with the scapula or clavicle but did move somewhat with respiration. A skiagraph showed it to be attached to the spine. The patient was seen again five years later, when the same condition of affairs existed, with the exception that movement on respiration was not so marked. A knowledge of the possible presence of a cervical rib is important in diagnosis, otherwise it may be thought to be a bony or malignant new growth and treatment advised accordingly. The subclavian artery may pass over the cervical rib above and may have its circulation seriously interfered with.
Fig. 198. - A cervical rib attached to the right side of the seventh cervical vertebra.
The ribs are almost always broken by direct violence; fractures from indirect force, as from coughing, sneezing, and other forms of muscular exertion, are rare. Fracture from compression of the chest is also rare. The site of the fracture is most frequently on the anterior portion of the chest and not the sides or back. The fourth, fifth, sixth, and seventh ribs are most often broken. The first rib is well protected from direct blows by the clavicle. Lane, however, has shown that it can be broken by pressure of the clavicle when the shoulder is depressed. The eleventh and twelfth, being floating ribs, are rarely broken. The twelfth rib is the least frequently so. In one case we saw the eighth, ninth, tenth, eleventh, and twelfth all broken by the passage of a wheel. The soft parts attached to the fragments prevent much displacement, but there is always some, due to the respiratory movements. Hence callus is always present and it may be so abundant as to join adjacent ribs (see Fig. 199). As already stated, death frequently follows fracture of the ribs and is due to wounding of the chest contents. Rarely the intercostal arteries may be wounded and produce haemothorax. Wounding of the lung is frequent.
Fig. 199. - Fractured ribs; fusion of callus.
Emphysema of the surface of the body may ensue, but is not dangerous. Pneumothorax, which may be accompanied by infiltration of air into the lung tissue, is more dangerous, favoring collapse of the lung. The object of treatment is to keep the chest-walls from moving. This is accomplished by strapping the chest with adhesive plaster, which is usually laid on almost in the direction of the ribs; but as the chest moves with respiration, the ribs rising, and as they slope downward and forward, I have preferred to lay the straps on from in front downward and backward, this tends to prevent the ribs from rising in inspiration.