Anatomy of the anterior ribs and the composition of the costal margin: A cadaver study

Abstract

BACKGROUND Traditional rib anatomy and costal margin teaching contends that the costal margin consists of a combined costal cartilage made up of ribs 7 to 10. Variations in 9th and 10th rib anatomy have been observed. We sought to evaluate the variability of interchondral joints and the make-up of the costal margin. METHODS Cadaveric dissections were performed to evaluate the anatomy of the anterior ribs and the composition of the costal margin. Experienced chest wall surgeons evaluated this anatomy through a standardized dissection and assessment. Dissection videos were performed to allow for further review/assessment. RESULTS Bilateral chest wall anatomy of 30 cadavers was evaluated (15 male, 15 female). The average age was 78 ± 12 years, and all patients were Caucasian. In all patients, the first rib attached to the manubrium, the second rib attached to the manubriosternal junction, and ribs 3 to 6 attached directly to the sternum. Interchondral joints were present between ribs 4/5—3%, 5/6—68%, 6/7—83%, 7/8—72%. Ribs combining to form a common costal cartilage via cartilaginous unions were observed between 6/7—3%, 7/8—45%, 8/9—30%, and 9/10—20%. The 8th rib attached directly to the sternum without joining the 7th rib in 10% of cadavers. The 8th and 9th ribs had free tips in 45% and 60% of evaluations, respectively. The 10th rib was found to have a hooked tip in 25% of cases and was a floating rib without attachment to the 9th rib 52% of the time. Rib tip mobility was noted in ribs 8, 9, and 10 in 52%, 70%, and 90%, respectively. CONCLUSION Interchondral joints are common between ribs 5 and 8. Significant variability exists in the chest wall and costal margin compared with traditional teaching. It is important for chest wall surgeons treating diseases of the costal margin to appreciate this anatomic variability.