13. A spinal rod anchoring system comprising: a rod adapted to extend along a spine of a patient, the rod forming a chase feature having a non-circular cross-section; and a first rod anchor adapted to be fixed to a vertebra of the spine, the first rod anchor comprising: a housing forming a receptacle portion having a substantially concave inner surface; and a sleeve having a passage forming a chase receiving the rod chase feature such that the rod is secured against substantial lateral translation relative to the sleeve while allowing the rod to slide axially relative to the sleeve through a first pivot point and substantially preventing the rod from changing in roll relative to the sleeve, the sleeve having a substantially convex mating surface adapted to mate with the concave surface of the housing such that the sleeve is adapted to rotate relative to the housing to change in pitch and yaw relative to the housing.
13. A spinal rod anchoring system comprising: a rod adapted to extend along a spine of a patient, the rod forming a chase feature having a non-circular cross-section; and a first rod anchor adapted to be fixed to a vertebra of the spine, the first rod anchor comprising: a housing forming a receptacle portion having a substantially concave inner surface; and a sleeve having a passage forming a chase receiving the rod chase feature such that the rod is secured against substantial lateral translation relative to the sleeve while allowing the rod to slide axially relative to the sleeve through a first pivot point and substantially preventing the rod from changing in roll relative to the sleeve, the sleeve having a substantially convex mating surface adapted to mate with the concave surface of the housing such that the sleeve is adapted to rotate relative to the housing to change in pitch and yaw relative to the housing. 18. The system of claim 13 , wherein the first rod anchor limits axial sliding of the rod relative to the first rod anchor to a predefined range.