During respiration, motion occurs at both the costovertebral and costotransverse joints. Which of the following statements is true regarding the axis of motion and the type of motion that occurs at these joints?

a. The axis of motion of the upper ribs is close to the sagittal plane.
b. The axis of motion of the lower ribs is close to the frontal plane.
c. Motion of the upper ribs increases in the transverse (medial/lateral) diameter of the thorax.
d. The lateral end of the lower ribs is displaced laterally.

ANS: D
The kinematics of the ribs appears to vary; however, most investigators agree on a couple of
general motion activities. The axis of motion for the upper ribs lies nearly in the frontal plane, and
the axis of motion for the lower ribs, not including ribs 11 and 12, lies nearly in the sagittal plane.
During respiration, motion of the upper ribs tends to increase the anterior/posterior dimensions of
the rib cage, and the lateral ends of the lower ribs are displaced more laterally, causing a change in
the medial/lateral excursion of the rib cage.