8. A medical implant assembly comprising: a) first and second bone anchors each having a bone attachment structure on one end and a channel at an opposite end; b) an elongate core sized and shaped to be received in the bone anchor channels and extend therebetween; c) closures to secure the core in the bone anchor channels; and wherein d) the core is pretensioned and elastically stretched between the bone anchors so as to remain in tension and have an elongated stretched length between the bone anchors during usage.
8. A medical implant assembly comprising: a) first and second bone anchors each having a bone attachment structure on one end and a channel at an opposite end; b) an elongate core sized and shaped to be received in the bone anchor channels and extend therebetween; c) closures to secure the core in the bone anchor channels; and wherein d) the core is pretensioned and elastically stretched between the bone anchors so as to remain in tension and have an elongated stretched length between the bone anchors during usage. 9. The implant according to claim 8 , including a sleeve extending between the bone anchors and having a length that is greater than the length of the core between the bone anchor in a non-tensioned state such that the core is stretched to the length of the sleeve during assembly.