Radix grafts are grafts placed in the superior portion of the nose, aka where the nose meets the forehead. The purpose of radix grafts to change the angle that the dorsum so that it is not too low on the face. This allows for a longer more elegant nose in some instances.
Radix grafts can be from a few materials including crushed cartilage, perichondrium, costal cartilage, etc. Cartilage radix grafts swell less than perichondrium but have a higher chance of being visibile later. One key element of using a radix graft is a tight periosteal pocket to make sure graft is secure and does not move around.
Figure demonstrating low radix (top view) which is augmented in (bottom view) to provide balance to nose. If radix graft was not used nasal dorsum would be too low resulting in a saddle nose deformity.