Does overgrowth of costal cartilage cause pectus excavatum? A study on the lengths of ribs and costal cartilages in asymmetric patients

Purpose The cause of pectus excavatum has been hypothesized to be overgrowth of the costal cartilage. According to this theory, the length of costal cartilages must be longer in the side of deep depression in asymmetric patients. To challenge this hypothesis, we measured the lengths of ribs and costal cartilages and investigated lateral differences. Subjects and methods Twenty-four adolescent and adult patients with asymmetric pectus excavatum (14-30 years of age) with no history of surgery were investigated in this study. The fifth and sixth ribs and costal cartilages were individually traced to measure their full lengths on 3-dimensional computed tomographic (CT) images. As an index of asymmetry, sternal rotation angle was measured in the chest CT images. Patients with a 21° or greater angle of sternal twist were designated as an asymmetric group and those with an angle of smaller than 20° as a symmetric group. Lateral differences in the fifth and sixth costal and costal cartilage lengths were compared between the groups. Results On comparison of the costal and costal cartilage lengths in the asymmetric group, the right fifth ribs and costal cartilages were significantly shorter than the left ( P = .02 and .03, respectively), and right sixth ribs were also significantly shorter than the left ( P = .004), but right sixth costal cartilages were not ( P = .31). In the symmetric group, the lengths of the left and right fifth ribs and costal cartilages were showing no significant difference ( P = .20 and P = .80, respectively), and those of the sixth ribs and costal cartilage were also showing no significant difference ( P = .97 and P = .64, respectively). Discussion The ribs and costal cartilages on the right side with severer depression were significantly shorter or not different than those on the contralateral side. Based on these findings, the theory of costal cartilage overgrowth is contradictory. The etiology of asymmetric chest deformity should be reevaluated.