1. In a medical implant assembly having first and second bone attachment structures cooperating with a longitudinal connecting member, the improvement wherein the longitudinal connecting member comprises: a) an anchor member portion passing through and secured directly to the first bone attachment structure, the anchor member portion having a first width and having an integral core extension of reduced second width, the core extension extending from the anchor member portion along a substantially central axis of the longitudinal connecting member, the first and second widths being measured perpendicular to the central axis; b) a first elastic outer spacer, the core extension being received in the spacer, the spacer being positioned between the two bone attachment structures; c) a second elastic outer spacer, the core extension being received in the second spacer, the second spacer being more compressible than the first spacer, both the first and second spacers being pre-compressed prior to attachment of the assembly to the bone attachment structures; the second elastic outer spacer being located relative to the core extension so as to not be between the first and second bone attachment structures; and d) a substantially inelastic sleeve, the core extension being received through the sleeve and in slidable relationship therewith, the sleeve passing through and secured in the second bone attachment structure, the sleeve being disposed between the first and second pre-compressed spacers, the pre-compressed spacers exerting axial forces on the sleeve.
1. In a medical implant assembly having first and second bone attachment structures cooperating with a longitudinal connecting member, the improvement wherein the longitudinal connecting member comprises: a) an anchor member portion passing through and secured directly to the first bone attachment structure, the anchor member portion having a first width and having an integral core extension of reduced second width, the core extension extending from the anchor member portion along a substantially central axis of the longitudinal connecting member, the first and second widths being measured perpendicular to the central axis; b) a first elastic outer spacer, the core extension being received in the spacer, the spacer being positioned between the two bone attachment structures; c) a second elastic outer spacer, the core extension being received in the second spacer, the second spacer being more compressible than the first spacer, both the first and second spacers being pre-compressed prior to attachment of the assembly to the bone attachment structures; the second elastic outer spacer being located relative to the core extension so as to not be between the first and second bone attachment structures; and d) a substantially inelastic sleeve, the core extension being received through the sleeve and in slidable relationship therewith, the sleeve passing through and secured in the second bone attachment structure, the sleeve being disposed between the first and second pre-compressed spacers, the pre-compressed spacers exerting axial forces on the sleeve. 28. The improvement of claim 1 wherein the first spacer has a central compression member flanked by a pair of washers.