18. A spine implant comprising: an anchor adapted to be inserted into the bone of a patient; an anchor head extending from said anchor; said anchor head including a deflection cavity; the deflection cavity having an open end, a closed end, a longitudinal axis, and a cavity wall; a deflection rod provided in said deflection cavity; a distal end of the deflection rod secured in the closed end of the deflection cavity; a proximal end of the deflection rod extending out of the open end of the deflection cavity; the deflection rod being spaced from the wall of the deflection cavity at the open end by a gap which diminishes in size toward the closed end; wherein said spine implant is configured such that the deflection rod is resiliently held in alignment with the longitudinal axis of the deflection cavity and the proximal end of the deflection rod can resiliently deflect in response to a load applied to the proximal end of the deflection rod; and wherein contact between the deflection rod and the cavity wall limits resilient deflection of the proximal end of the deflection rod in response to a load applied to the proximal end of the deflection rod.
18. A spine implant comprising: an anchor adapted to be inserted into the bone of a patient; an anchor head extending from said anchor; said anchor head including a deflection cavity; the deflection cavity having an open end, a closed end, a longitudinal axis, and a cavity wall; a deflection rod provided in said deflection cavity; a distal end of the deflection rod secured in the closed end of the deflection cavity; a proximal end of the deflection rod extending out of the open end of the deflection cavity; the deflection rod being spaced from the wall of the deflection cavity at the open end by a gap which diminishes in size toward the closed end; wherein said spine implant is configured such that the deflection rod is resiliently held in alignment with the longitudinal axis of the deflection cavity and the proximal end of the deflection rod can resiliently deflect in response to a load applied to the proximal end of the deflection rod; and wherein contact between the deflection rod and the cavity wall limits resilient deflection of the proximal end of the deflection rod in response to a load applied to the proximal end of the deflection rod. 19. The implant of claim 18 , wherein the deflection rod comprises an inner metal rod and an outer polymer shell.