10. A spine implant comprising: an anchor adapted to be inserted into the bone of a patient the anchor having a longitudinal axis; an anchor head extending from said anchor; said anchor head including a deflection cavity aligned with the longitudinal axis of the anchor; said deflection cavity having a deflection guide cavity wall, a first end which opens through the anchor head, and a second end internal to the anchor head; a deflection rod provided in said deflection cavity; said deflection rod having a distal portion secured within the deflection guide cavity and a proximal portion extending out of the opening of the deflection guide cavity; wherein the spine implant is configured such that, in the absence of a load applied to the proximal portion of the deflection rod, the deflection rod is aligned with the longitudinal axis of the anchor; wherein the spine implant is configured such that a load applied to the proximal portion of the deflection rod causes resilient deflection of the proximal portion of the deflection rod away from alignment with the longitudinal axis of the bone anchor; and wherein resilient deflection of the proximal end of the deflection rod is controlled by contact between the proximal portion of the deflection rod and the deflection guide cavity wall.
10. A spine implant comprising: an anchor adapted to be inserted into the bone of a patient the anchor having a longitudinal axis; an anchor head extending from said anchor; said anchor head including a deflection cavity aligned with the longitudinal axis of the anchor; said deflection cavity having a deflection guide cavity wall, a first end which opens through the anchor head, and a second end internal to the anchor head; a deflection rod provided in said deflection cavity; said deflection rod having a distal portion secured within the deflection guide cavity and a proximal portion extending out of the opening of the deflection guide cavity; wherein the spine implant is configured such that, in the absence of a load applied to the proximal portion of the deflection rod, the deflection rod is aligned with the longitudinal axis of the anchor; wherein the spine implant is configured such that a load applied to the proximal portion of the deflection rod causes resilient deflection of the proximal portion of the deflection rod away from alignment with the longitudinal axis of the bone anchor; and wherein resilient deflection of the proximal end of the deflection rod is controlled by contact between the proximal portion of the deflection rod and the deflection guide cavity wall. 12. The implant of claim 10 , wherein, said deflection guide cavity diminishes in diameter going from the first end toward the second end.