14. The improvement of claim 10 wherein one of the sleeve flanges includes an extension structure slidingly received over the cord and within the spacer.
10. In a medical implant assembly having a pair of bone anchors cooperating with a longitudinal connecting member having a tensioned cord and a spacer located between the first and second bone anchors, the cord extending through the spacer, each of the bone anchors having a first pair of opposed upstanding arms, the improvement wherein: a) one of the bone anchors is a polyaxial bone anchor having a shank pivotable with respect to a receiver and a compression insert engaging the shank, the compression insert having a second pair of upstanding arms forming a channel, each insert arm having a top surface; and b) a sleeve for attachment to the polyaxial bone anchor, the sleeve having a body and a pair of opposed outer flanges, a first through bore sized and shaped for slidably receiving the tensioned cord, a first aperture formed in the sleeve body substantially transverse to the first through bore, the first aperture sized and shaped for receiving a portion of an optional cord gripping closure top, the sleeve body sized and shaped for being closely received within the insert channel and the flanges sized and shaped to be received outside the bone anchor first pair of upstanding arms, the flanges each having a first substantially planar outer surface substantially perpendicular to the first through bore and a second substantially planar surface substantially perpendicular to the first planar surface, both the first and second surfaces sized and shaped for engagement with the spacer, preventing rotation of the spacer with respect to the sleeve.