Vertebral rods and methods of use

1. A vertebral rod comprising:

a first elongated rod section;

a second elongated rod section aligned along an axis with the first section;

an intermediate section positioned between the first and second sections, the intermediate section comprising a member with a turn and an upper section and a lower section, the intermediate section being open between the first and second sections opposite from the turn, each of the upper and lower sections including inner surfaces that intersect at the turn and overlap to form an interior portion;

an elastic member positioned in the interior portion of the intermediate section directly between the first and second sections along the axis; the elastic member distinct from the first, second, and intermediate sections and differing in material composition therefrom; the elastic member connected to the inner surfaces of both the upper and lower sections;

the intermediate section and elastic member configured to provide variable resistance to movement of the first and second sections, the elastic member being in compression during a first type of movement of the first and second sections and being in tension during a second type of movement;

wherein the elastic member is configured such that the axis exits the first section, enters the elastic member, passes through the elastic member, exits the elastic member, and enters the second section all without exiting the elastic member more than once.

2. The rod of claim 1 wherein the elastic member is adhesively secured to the intermediate section.

3. The rod of claim 1 wherein the elastic member engages the inner surfaces of the upper and lower sections of the intermediate section when the rod is in a neutral position free from applied loads acting thereon.

4. The rod of claim 1 wherein the elastic member is an elastically deformable block having external surfaces facing the first and second sections.

5. A vertebral rod assembly comprising:

a first elongated rod section;

a second elongated rod section spaced from the first rod section;

the first and second rod sections extending along a common centerline;

an intermediate section monolithically formed with the first and second rod sections and bridging therebetween; the intermediate section being offset from the centerline and convexly curved toward the centerline to form a pocket;

the first rod section having a first endface proximate the intermediate section;

the second rod section having a second endface proximate the intermediate section; the first and second endfaces generally facing toward each other;

an elastic bumper disposed in the pocket such that the centerline passes therethrough; the elastic bumper, with the rod assembly in a neutral position free from applied loads acting thereon, abutting the first endface along the centerline, the second endface along the centerline, and the intermediate section;

the elastic bumper formed of a different material than the first rod section, the second rod section, and the intermediate section;

the intermediate section and elastic bumper configured to provide variable resistance to movement of the first and second sections, the elastic bumper being in compression during a first type of movement of the first and second sections and being in tension during a second type of movement.

6. The vertebral rod assembly of claim 5 wherein the intermediate section has an interior surface bounding the pocket, the interior surface extending substantially all the way from the first rod section to the second rod section; wherein the elastic bumper, with the rod assembly in a neutral position free from applied loads acting thereon, abuts substantially all of the interior surface of the intermediate section.