Reducing Cartilage Warp in Nasal Reconstruction: The Role of Collagen and Proteoglycans.

Background: Costal cartilage is commonly used in nasal reconstruction due to its strength and biocompatibility; however, warping of carved struts remains a challenge. Although proteoglycans (PGs) are known to generate internal swelling pressures contributing to warping, the role of collagen fiber orientation in modulating these stresses and the spatial interplay between PGs and collagen across costal cartilage remains poorly understood. This study compared regional variations in collagen alignment and PG distribution from 2 anatomical sites: one that when transversely cut demonstrates no warping, and one that has higher tendency to warp. Methods: Human costal cartilage samples were collected from the sixth/seventh rib costal bridge (autograft) and long rib (allograft). Collagen fiber orientation was assessed using diffusion tensor imaging/tractography and polarized light microscopy. Matrix composition was evaluated via histology. Fractional anisotropy and mean diffusivity maps were used to correlate structural and compositional patterns. Results: In the costal bridge and long rib cartilage, collagen fibers were predominantly aligned anterior-posterior in the mid and deep zones, with a tangential circumferential alignment near the surface. PG content was concentrated in the mid and deep zones and depleted superficially. Conclusions: These results suggest that cartilage warping arises from internal stress imbalances linked to regional variations in PGs and collagen. The elucidated microstructural geometry of struts sliced transversely from the costal bridge preserves matrix architecture and the circumferential tension band, preventing warping due to unresisted PG expansion. In contrast, disruption of the collagen fibers and unbalanced PG distribution in long cylindrical ribs leaves nonperfectly concentric carved struts, prone to deformation.