Final answer:
Routine positions for the left tenth posterior rib pertain to the anatomical structure and articulations with the thoracic vertebrae and include the head, tubercle, angle, and costal groove of the rib.
Step-by-step explanation:
Routine positions for the left tenth posterior rib involve understanding its anatomical structure and articulations. Each rib is a curved, flattened bone that contributes to the thoracic cage. The ribs are numbered 1-12 in correspondence with the thoracic vertebrae they articulate with. The posterior end of the rib, known as the head of the rib, articulates primarily with the costal facet on the corresponding thoracic vertebra, and secondarily with the costal facet on the body of the adjacent higher vertebra.
The tubercle of the rib, which is a small bump on the posterior surface, articulates with the facet located on the transverse process of the same numbered vertebra. Lateral to the tubercle is the angle of the rib, which is the point at which the rib has its greatest curvature and forms the most posterior extent of the thoracic cage. The angle aligns with the medial border of the scapula in the anatomical position. A costal groove for the passage of blood vessels and nerves is found along the inferior margin of each rib.