The stiffness and overall stability of the spine is greatly enhanced by the presence of the rib cage for all four physiologic motions (Click here to review a diagram depicting the role of the rib cage in determining spinal stiffness). Note the significant increase in stiffness during extension, and that removal of the sternum eliminates any gains that the ribs might have afforded.
The primary motion of ribs occurs during inspiration and expiration. The most common dysfunction that is associated with restriction of normal rib cage motion is restriction of respiration. During inspiration, the anteroposterior diameter of the thorax is increased when the ribs are raised. Because ribs slope downward, any elevation during inspiration results in an upward movement of the sternum at the manubriosternal joint and an increase in the anteroposterior diameter of the thorax. Movement at the costovertebral joints, through the long axes of the necks of the ribs, results in raising and lowering their sternal ends; pump-handle rib motion. The first to sixth ribs are the ones primarily involved in this movement.
During inspiration, the transverse diameter of the thorax is increased by the ribs swinging outward; bucket-handle rib motion. The seventh to tenth ribs are the ones primarily involved in this movement.
During expiration, the elastic recoil of the lungs and the weight of the thoracic walls cause the lateral and anteroposterior diameters of the thorax to return to the relaxed position.
Click here to view a simulation of pump-handle and bucket-handle motion mechanics of the ribs.
Join Dr. Philip E. Greenman, D.O., F.A.A.O., as he discusses pump-handle and bucket-handle motion mechanics of the rib cage during respiration.