| 摘要 |
<p>A bone fixation device has a housing on the exposed head of a screw mounted in a bone part from which it projects. A clamp for a fixation rod is mounted on a plate extending from each of opposite lateral sides of the housing in such a manner that allows the plate to rotate about a lateral axis relative to the housing. Each clamp is itself rotatable on its plate about an axis perpendicular to its respective lateral axis, and thereby provides universal movement relative to the housing. Mechanisms are provided for closing the clamps, for locking each plate against rotation about its lateral axis, and blocking each clamp against rotation about its perpendicular axis. In this way rods can be fixed in the clamps and relative to the device. In a particular embodiment, the plates are supported for pivotal movement about their lateral axes, on part-cylindrical surfaces on opposite lateral sides of the housing. Each clamp is mounted on a boss extending through its respective plate to a locking element in a groove beneath the part-cylindrical surfaces. Each clamp has jaws forming a groove for receiving a fixation rod and a clamping element over the rod. The groove depends into the boss such that a rod received in the groove engages the plate at either end of the groove. Activation of the clamping element thereby locks the rod and clamp relative to the plate, and the plate relative to a housing bracket, to prevent any movement of the rod relative to the head of the screw. In an alternative embodiment of the invention the housing on the head of the screw has jaws defining adjacent grooves for receiving fixation rods, and a split ball element for clamping a rod in the groove. Each groove has a central section in which the base has a part-spherical surface, and opposed end sections in which the base has a surface divergent from the central section base. The split ball element has a diametrical bore therethrough, and a clamping element is provided for compressing each ball element to clamp the rod in the ball element, and the element against the part-spherical surface of the groove central section.</p> |
