Device for the dynamic fixation of bones

Abstract

An intermediate element for a detachable, lockable, ball joint-like connection in a device for the dynamic fixation of bones has a longitudinal axis, an outer wall concentric with the longitudinal axis, and an inner wall forming a coaxial cavity. Either the outer wall or the inner wall comprises one of two contact zones that form the ball joint-like connection. The intermediate element is at least partly made of a super-elastic or visco-elastic material.

What is claimed is: 
     
         1 . A device for the dynamic fixation of bones or bone fragments, including segments of the spinal column, the device comprising:
 at least one bone fixation agent having a central axis, an anchoring segment operative to be anchored at or in a bone, and an axially adjoining head segment;   a connecting part having a longitudinal axis, a cavity coaxial with the longitudinal axis defining an inner surface, and a channel transverse to the longitudinal axis operative to accommodate a longitudinal carrier, the cavity having an upper portion and a lower portion, the inner surface of the lower portion having a shape, the connecting part suitable for the detachable connection of the bone fixation agent and the longitudinal carrier;   an at least partially deformable intermediate element operatively associated with the head segment for coupling the bone fixation agent and the connecting part, the intermediate element at least partially manufactured from a visco-elastic material and has an outer surface, the intermediate member being receivable within the lower portion of the cavity of the connecting part; and   a locking means operative to deform, either directly or indirectly, the intermediate element, wherein the outer surface of the visco-elastic portion of the intermediate element and the inner surface of the connecting part comprise contact zones A, B which are in contact with one another,   wherein in the unfastened state the outer surface of the contact zone A of the intermediate element has a shape that is non-corresponding and different than the shape of the contact zone B of the inner surface of the lower portion of the cavity of the connecting part in which the intermediate element is received, and a ball joint-like movement between the connecting part and the bone fixation agent is permitted, and in the fastened state the bone fixation agent is flexibly connected to the connecting part such that the bone fixation agent is permitted to move relative to the connecting part via elastic deformation of the intermediate member, and the intermediate element at least partially changes shape.