any structural anomaly of the hyaline cartilaginous joint (synchondrosis) between each rib and its costal cartilage; the articulation is between the cup-shaped depression in the sternal end of a rib and the lateral end of a costal cartilage; the rib and its cartilage are firmly bound together by the continuity of the periosteum of the rib with the perichondrium of the cartilage; no movement normally occurs at these joints