The facet of the tubercle of the rib forms an articulation with the adjacent transverse process of a thoracic vertebra. This is a plane type synovial joint called the costotransverse joint. This articulation is present in all but the eleventh and twelfth ribs. Ribs 1 to 10 have two joints in close proximity posteriorly; the costovertebral joints and the costotranseverse joints. This arrangement restrains the motion of the ribs allowing them to work in a parallel fashion during breathing. If a typical rib had only one joint posteriorly the resultant swivel action would allow a rib to be non-parallel with respect to the neighboring ribs making for a very inefficient respiratory mechanism. The ventral rami innervate the costotransverse joints. Therefore, therapeutic medial branch blocks are ineffectual. The ligaments of the joint are: Articular capsule Posterior costotransverse Anterior costotransverse Ligament of the neck of the rib Ligament of the tubercle of the rib. [ http://en.wikipedia.org/wiki/Costotransverse_joint ]