A dynamic fixation medical implant for attachment to at least two bone anchors includes a longitudinal connecting member assembly having first and second rigid sections, at least one section having a convex or frusto-conical surface held in spaced relation with the other section by an elastic spacer. The spacer may be an over-mold that connects the first and second rigid sections. Some embodiments include an inner, tougher spacer and a separate over-molded spacer.