Anatomy of the interchondral joints and the effects on mobility of ribs

Abstract

BACKGROUND Variations in the anatomy of the anterior rib cage and costal margin have been observed. We sought to evaluate the location of interchondral joints and evaluate their effect on mobility of the rib cage. METHODS Cadaveric dissections were performed to evaluate the anatomy of the anterior ribs and the composition of the costal margin. Experienced chest wall surgeons and anatomists evaluated this anatomy through a standardized dissection and assessment. The presence of interchondral joints, and morphology and mobility of ribs were quantified. In addition, the movement and interactions of the ribs with upward pressure on the costal margin at the tip of the 10th rib were assessed. RESULTS Twenty-eight cadavers were evaluated bilaterally. In all patients, the first rib attached to the manubrium, the second rib attached to the sternal/manubrial junction, and ribs 3 to 6 attached directly to the sternum. Interchondral joints were present between ribs 4/5 in 0%, 5/6 in 35%, 6/7 in 96%, and 7/8 in 96%. The eighth/ninth ribs had free tips in 58% and 92%, respectively, and 10th rib was floating in 46%. Upward pressure on the costal margin resulted in compression of the ribs up to, on average, the 5.7 ± 0.6 rib with no compression above this level. This level corresponded to the rib interspace just above the most superior interchondral joint in 98% of evaluation. The transmission of these upward forces demonstrated an articulation of the ribs at the costal cartilage-sternal junction in the lower ribs. CONCLUSION Bridging interchondral joints are common between ribs 5 to 8 and participate in distributing forces from the costal margin across the chest wall. Upward forces at the costal margin are transmitted across the lower rib cage and result in increased mobility of the lower half of the ribs. The eighth/ninth ribs often have mobile tips, and the 10th is often a floating rib. LEVEL OF EVIDENCE Diagnostic Test; Level II.