The present application is directed to vertebral rods constructed for vertebral movement in first and second planes, and to prevent or inhibit vertebral movement in a third plane. The vertebral rod may include one or more notches. The notches change the cross section shape of the rod and thus the structural characteristics. The notches may be shaped, sized, and positioned to facilitate vertebral movement in the first and second planes, and prevent or inhibit movement in the third plane. A fill material may be positioned within the notches to strengthen the rod and/or provide durability.