Implant having a shaft and a holding element connected therewith for connecting with a rod

Abstract

An implant is described having a shaft (1) and a holding element (3; 30) connected therewith for connecting with a rod (100). A recess is provided in the holding element. The recess has a U-shaped cross section for accommodation of the rod and two free legs (7, 8; 32, 33) at one end which include an inner thread (9; 34). A closure element (20; 36) fixes the rod inserted into the U-shaped recess. The closure element has an outer thread cooperating with the inner thread of the legs. An abutment is provided at or in the holding element (3; 30) to limit tilting of the closure element about the rod at the time of final tightening of the closure element in the holding element. As a result thereof it is possible to keep the wall thickness of the receiver member small in spite of the large forces acting at the time of final tightening. The invention is applicable to both monoaxial screws and polyaxial screws as well as bone hooks.

Description

FIELD OF THE INVENTION[0001]The invention relates to an implant to be used in spine or trauma surgery, the implant having a shaft and a holding element connected therewith for connecting with a rod, wherein the holding element comprises a recess having a U-shaped cross section for receiving the rod and two free legs at one end which have an inner thread and a closure element for fixation of the rod inserted into the U-shaped recess, the closure element comprising an outer thread cooperating with the inner thread of the legs.BACKGROUND OF THE INVENTION[0002]EP 0 614 649 B1 describes a polyaxial bone screw with a receiver member with a nut to be screwed onto the receiver member for securing a rod.[0003]If the thread of the receiver member and of an inner screw is a metric thread, force components in radial direction of the cylindrical receiver member occur when screwing in the inner screw, which could cause splaying of the legs of the receiver member resulting in a loosening of the in...

AI Technical Summary

Benefits of technology

The present invention provides an implant for fixing a rod to a bone, which includes a holding element and a shaft connected with the holding element. The holding element has a U-shaped recess for receiving the rod and two free legs with inner threads. A closure element with outer threads is used to fix the rod in the implant. A securing device is provided to prevent tilting of the closure element during final tightening. The implant can be used for polyaxial or monoaxial bone screws and is suitable for use with rods having circular cross section. The method for fixing the rod involves connecting the implant to the bone, positioning the rod, and fixing the rod by tightening the closure element. The securing device prevents tilting of the closure element and ensures stability of the rod.

Problems solved by technology

If the thread of the receiver member and of an inner screw is a metric thread, force components in radial direction of the cylindrical receiver member occur when screwing in the inner screw, which could cause splaying of the legs of the receiver member resulting in a loosening of the inner screw.

Such implants that have thin side flanks of the receiver member, however, encounter a problem when using only an inner screw for fixation without an additional securing via a nut to be screwed on or a cap covering the legs of the receiver member at the outside or a ring or the like.

To avoid this, the inner screw should be tightened with reduced torque which, however, impairs the retention force.

Further, the problem also can be reduced, if a wall of the receiver member is very thickly dimensioned, which is, however, an obstacle to the requirement of a compact implant design.

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