20. The implant of claim 17 , wherein said deflection rod has a first resistance to deflection over a first zone of deflection and a second resistance to deflection over a second zone of further deflection and wherein the second resistance is more than double the first resistance.
17. An implant adapted to be implanted in a spine of a patient comprising: a body including a shield with a shield cavity, the shield cavity having a first end and a second end and a shield cavity axis; a deflection rod having a fixed end and a free end and a longitudinal axis, the deflection rod mounted in said shield cavity such that the fixed end is secured in the first end of the shield cavity, the free end extends out of the second end of the shield cavity, and the longitudinal axis is aligned with the shield cavity axis; an gap defined between said deflection rod and said shield, said gap extending from the second end of the shield cavity at least partway along the shield cavity towards the first end of the shield cavity; said gap being configured to allow bending of the deflection rod within the shield cavity to thereby allow deflection of the free end of the deflection rod away from alignment with the shield cavity axis in response to a load applied to the free end of the deflection rod; and wherein said deflection of the free end of the deflection rod away from alignment with the shield cavity axis is limited by contact between the deflection rod and the shield.