1. An adaptive spinal rod adapted to stabilize a spinal segment, wherein the spinal rod comprises: an elongated rod having a first end, a second end and a longitudinal rod axis; an aperture at the first end of the rod; a partially-spherical mount contained in the aperture, the partially-spherical mount can rotate and pivot within the aperture, wherein the partially-spherical mount has a central axis perpendicular to a base side of the partially-spherical mount; the partially-spherical mount having an elongated slot adapted to receive a post of a bone anchor, wherein the elongated slot has a first dimension perpendicular to the central axis of the partially-spherical mount and a second dimension parallel to the central axis of the partial-spherical mount, wherein the post is loosely coupled to the elongated slot such that the post can slide in the first dimension and the second dimension of the elongated slot, and rotate in the elongated slot; and wherein the bone anchor can be secured relative to the partially-spherical mount while permitting the bone anchor to change in angle relative to the longitudinal rod axis.
1. An adaptive spinal rod adapted to stabilize a spinal segment, wherein the spinal rod comprises: an elongated rod having a first end, a second end and a longitudinal rod axis; an aperture at the first end of the rod; a partially-spherical mount contained in the aperture, the partially-spherical mount can rotate and pivot within the aperture, wherein the partially-spherical mount has a central axis perpendicular to a base side of the partially-spherical mount; the partially-spherical mount having an elongated slot adapted to receive a post of a bone anchor, wherein the elongated slot has a first dimension perpendicular to the central axis of the partially-spherical mount and a second dimension parallel to the central axis of the partial-spherical mount, wherein the post is loosely coupled to the elongated slot such that the post can slide in the first dimension and the second dimension of the elongated slot, and rotate in the elongated slot; and wherein the bone anchor can be secured relative to the partially-spherical mount while permitting the bone anchor to change in angle relative to the longitudinal rod axis. 2. The adaptive spinal rod of claim 1 , in combination with a bone anchor, wherein the bone anchor comprises a threaded shaft adapted to engage a vertebra and a post adapted to mount relative to the partially-spherical mount in the elongated slot.