The chest wall is formed from the sternum anteriorly, 12 pairs of ribs, costal cartilages and intercostal muscles laterally, and the thoracic vertebrae posteriorly. The palpable midline sternum is variable in size and shape; it is made up of the manubrium superiorly, the body and the xiphisternum (figure 1). The manubrium has an upper central depression, the suprasternal notch. This has the attachments of the sternomastoid muscles and articulations of the medial ends of the clavicles on each side. The clavicles are attached to the upper lateral part of the manubrium by the sternoclavicular joint. This is a synovial joint, its bony surfaces are covered by fibrocartilage and it has a fibrocartilaginous disc. The first costal cartilage is attached to the manubrium just below this joint. The entry from the neck to the thorax (thoracic inlet – figure 2), is surrounded by the first thoracic vertebra, the first ribs and the manubrium.
- Tubercle of first rib
- Neck of first rib
- Head of first rib
- Suprasternal notch
- Acromioclavicular joint
- Sternoclavicular joint
- Costosternal junction of first rib
- Sternal Split; approach to mediastinum
- Manubriosternal Joint
- Second costal cartilage (an important landmark)
- Body of sternum
- Fourth interspace
- Anterolateral thoractomy incision
- Xiphisternal joint
- Seventh costal cartilage ( lowest of true ribs)
- Eighth( floating) rib
- Ninth floating) rib
- Tenth (floating) rib
- Lower costal margin
The joint between the manubrium and body of the sternum (manubriosternal joint) is a symphysis and has slight mobility. The two bones are joined at a slight angle that protrudes anteriorly (sternal angle, angle of Louis). This is an important landmark, as the second costal cartilage is attached to it laterally, and from here the ribs can be easily seen and counted in thin subjects. This is more difficult in the female, on account of the breasts, and is also a problem with generalised obesity.
The manubriosternal joint is at the level of the lower border of the body of the fourth thoracic vertebra and the xiphisternal joint at the level of the ninth. The xiphisternum is of variable length and covered by the attachments of the rectus muscles. It is important to feel the xiphisternum of patients, and be aware of its variations, as not infrequently a patient needs reassurance that the xiphisternum they have just felt is not an abdominal tumor. The first seven ribs are attached directly by their costal cartilages to the sides of the sternum and are termed true ribs. The eighth to tenth (false) ribs are attached via their costal cartilages to the costal cartilage of the rib above. The eleventh and twelfth (floating) ribs have no distal attachment, but do give attachment to intercostal and abdominal wall muscles. In the male the nipples lie approximately in the fourth intercostals space and the liver rises to this level underneath the central dome on the right side of the diaphragm.
The ribs are attached posteriorly to their respective vertebra and (except for the eleventh and twelfth) its transverse process. The heads of the second to the ninth ribs also articulate with the intervertebral disc and the body of the vertebra above. The shape of these articulations contributes to respiratory expansion of the chest: the upper part of the chest expands primarily in an anteroposterior direction and the lower half from side to side; in the latter, the ribs moving in a ‘bucket handle’ fashion. These different directions of rib movement are reflected in the shape of their articular surfaces.
Posteriorly, the thorax merges with the neck and lumbar regions (figure 3). The vertebra prominens (C7) and the spine of the first thoracic vertebra are easily palpable. The remaining thoracic spines lie subcutaneously, but the downward angled spines are less easily defined. The upper ribs are covered by the powerful muscles of the shoulder girdles. The scapulae overlie the second to the seventh ribs. The eleventh and twelfth ribs are usually palpable inferiorly; they overlie the kidneys. On the left side the tenth rib overlies the longitudinal axis of the spleen. With the arms abducted to 180 degrees, the lower medial border of the scapula approximates to the line of the oblique fissure of the lung on each side.
1. Transverse process of seventh cervical vertebra (angled downwards)
2. Transverse process of first thoracic vertebra (angled upwards)
3. Spine of first thoracic vertebra
4. First rib
5. Line of angle of ribs; also lateral limit of erector spinae muscles
6. Posterolateral thoracotomy incision
8. Spinous process of seventh thoracic vertebra (angled downwards for morethan a vertebra in depth)
9. Eleventh and twelfth (floating) ribs
10. Eleventh and twelfth (floating) ribs
11. Iliac crest
12. Spine of fourth lumbar vertebra (supracristal plane – through the two iliac crests)