FR2759894A1 - Spinal osteosynthesis implant - Google Patents

Abstract

The implant consists of a threaded section (1) designed to screw into a vertebra and a head (2) with a channel (5) to receive a rod (12) and a locking screw (10). The vertical axis (C - C') of the rod insert channel is offset to one side of the axis (A - A') of the implant's threaded section. The channel has a broad opening with a threaded inner surface to receive the locking screw and a semi-cylindrical trough-shaped base for the rod. In a variant of the implant the threaded section can be replaced by an open hook to engage with the vertebra.

Description

 The present invention relates to an implant for osteosynthesis of the spine for treating the various pathologies of the spine by fixing the vertebrae to each other using a cylindrical rod connecting the different implants.

 The invention relates more particularly to improvements to this type of implants. Several models of vertebral implants currently exist, and despite successive improvements developed by the manufacturers, no system of osteosynthesis of the spine gives full satisfaction.

 Generally the vertebral implants are provided with a channel intended to accommodate the connecting rod which connects the implants together and is fixed to the implant by a suitable locking screw. The main problem lies in the difficulty of aligning the vertebral implants with one another, and consequently the corresponding channels, during implantation because of the operating constraints and the irregularity of the human anatomy. This results in a difficulty of introducing the connecting rods into the different channels and untimely manipulation of the implants which can cause bone fractures in the vertebrae, or the subsequent fracture of the implant by fatigue.

 The implant according to the invention makes it possible to remedy this major drawback by virtue of a channel offset with respect to the axis of the implant making it possible to make up for alignment, while retaining optimal mechanical strength of the implant.

 This implant may consist of a pedicle screw or a hook, and in both cases has the same system for fixing the connecting rod.

 The implant therefore comprises, according to a first characteristic, two parts: a part attached to the bone and serving to hold the vertebra which will be called the intravertebral part, and a part fixed to the connecting rod which will be called the extra- vertebral.

 The intra-vertebral part is constituted by a bent metal blade in the case of a hook, and by a spongy thread in the case of pedicle screw.

 According to an advantageous arrangement, the intra-vertebral part of a pedicle screw has a spongy thread of cylindrical profile with a conical bottom of the net having no fracture initiator which can cause the implant to fracture. The angled blade of the hook can have different shapes to adapt to different parts of the vertebra.

 The extra-vertebral part of the implant, intended to fix the connecting rod, is formed by a channel used to house the rod and by a locking screw.

 To this implant can be added, in cases of large misalignments, an open hook terminated by a cylindrical rod and allowing the implant to be connected to the connecting rod.

 According to another characteristic of the implant, the channel intended to accommodate the rod is formed by two vertical walls open upwards, with a thread in their internal faces, making it possible to introduce a screw to block the connecting rod.

 According to an advantageous arrangement, the external, anterior and posterior faces of the vertical walls are flat to allow precise adaptation, and without play, of the various instruments intended to place the implant.

 According to an advantageous design, the channel is located in an offset position relative to the central axis of the implant, which allows in the case of pedicle screws to perform a rotation of 1800 of certain screws of the assembly and to catch up with the alignment of the different channels. In the case of hooks they will be of two types, one having a channel located on the left side, and the other a channel located on the right side. Using the correct hook will correct the alignment of the channels.

 According to an advantageous arrangement, the entrance to the channel is wide, allowing easy introduction of the rod, and ends in a gutter of the same diameter as that of the rod ensuring a firm fixing of the latter.

 According to an advantageous characteristic, a shallow groove is made at the bottom of the gutter.

This groove provides the rod with two clamping lines in its lower part, instead of a line in traditional systems, in order to combat its rotation or slipping.

 According to another advantageous design, an open hook, terminated by a cylindrical rod, can be fixed to the implant, and allows in cases of large gaps between the rod and the implant to connect the latter to the connecting rod.

 According to an advantageous characteristic, this hook open on the side has in its upper part an incorporated locking screw making it possible to firmly fix the connecting rod to the hook.

 According to an advantageous arrangement, this catching hook can be added at any necessary level, without dismantling the connecting rods, by performing a simple rotation of 900 of the pedicle screw, or by using a particular hook having a channel with horizontal axis.

 Other characteristics and advantages of the invention will emerge from the description which follows with reference to the appended drawings which are given only by way of nonlimiting examples.

 Figures 1 to 8 show the different parts of the system according to the invention.

Figure 1 is a front view of a pedicle screw.

Figure la is a side view of a pedicle screw.

Figure 1b is a top view of a pedicle screw.

Figure 2 is a front view of a hook.

Figure 2a is a side view of a hook.

Figure 2b is a top view of a hook.

FIG. 2c is a view of a hook having a channel with a horizontal axis.

Figure 3 is a view of the locking screw.

Figure 4 is a view of the connecting rod.

Figure 5 is a view of the connecting rod fixed to the implant using the locking screw.

Figure 6 is a side view of the catch hook.

Figure 7 is a top view of the catch hook attached to the implant and the connecting rod.

Figure 7a is a side view of the catch hook attached to the implant and the connecting rod.

Figure 8 is a view of an assembly made with screws, hooks, connecting rods, and catch hooks.

 The accompanying drawings illustrate the invention. The mechanism for mounting a connecting rod on the different implants will be described below, with reference to FIGS. 1 to 8. Depending on the number and location of the vertebrae involved, an assembly can be made up of a variable number of screws and hooks, and is almost always carried out on either side of the midline formed by the spinous processes.

 According to a characteristic of the invention, the implants (fig.l, fig.2), as well as the connecting rods (12) and the catching hooks (fig.6), are machined with a biocompatible and resistant metal alloy which can be, for example, a titanium alloy.

 The implant according to the invention is made up of two parts: - An intra-vertebral part with spongy thread (l) in the case of pedicle screw (fig. 1), or in the form of a bent blade (9) in the case of '' a hook (fig.2a). The intra-vertebral part is intended to fix the implant in the bone and to oppose the tearing forces. The spongy thread (1), with cylindrical profile, has a cylindrical thread bottom at its distal part, then becomes progressively conical, thus reducing the depth of the thread. This form of threading is resistant, and devoid of breaking points.

- An extra-vertebral part intended to house the connecting rod (12) and to fix it thanks to a locking screw (10) exerting a vertical force. This extra-vertebral part constituting the system for fixing the connecting rod (12) is formed of four parts: - a horizontal wall (2), - two vertical walls open from above (3,4) - a channel (5 ) delimited by the two vertical walls and intended to house the connecting rod (12), - a locking screw (10) ensuring the fixing of the rod (12).

 According to a characteristic of the invention, the channel (5) has a wide opening from the top in order to facilitate the entry of the rod (12), and ends in its lower part by a semicircular gutter (6) having the same diameter as that of the connecting rod (12) and used to obtain optimal contact with the latter.

 According to an advantageous design, and in order to obtain a better clamping efficiency and to fight against the rotation and the sliding of the connecting rod (12), a shallow groove (7) is made at the bottom of the gutter (6) .

The purpose of this groove (7) is to provide two clamping lines on the lower part of the rod (12), instead of one in traditional fastening systems.

 According to an advantageous characteristic, the channel (5) with axis CC '(fig.l, fig.2) intended to accommodate the connecting rod (12), is located in an offset position relative to the central axis (AA') of the screw (fig.l) constituted by the threaded part (l), and to the axis (BB ') of the hook (fig.2) constituted by the bent blade (9). This latter arrangement results in two types of hook; one with channel (5) located on the right side of the axis (BB '), and the other with channel (5) located on the left side of the axis (BB').

 Thanks to this important characteristic, it is possible, by rotating certain screws (fig. 1) of the assembly, to make up for the correct alignment of the different channels (5), and to facilitate the introduction of the connecting rod therein. (12), main concern during spinal osteosynthesis.

 At the level of the hooks (fig. 2), it suffices to choose a hook having a channel (5) on the side corresponding to the alignment of the other channels.

 The vertical walls (3,4) of the channel (5) will be designated by proximal wall (3) for the wall closest to the axis of the implant (AA ', BB'), and distal wall (4) for the most distant wall. Each vertical wall (3 and 4) has four faces - an internal threaded face into which the locking screw (10) will be screwed, - a flat external face (fig.lb, fig.2b), - a flat front face (fig. lb, fig. 2b), - a flat rear face (fig.lb, fig.2b).

The external, anterior and posterior faces are flat and are used for the precise adaptation, and without play, of the instrumentation of installation on the walls of the implant (fig.l, fig.2).

 According to an advantageous arrangement of the invention, the upper part of the distal vertical wall (4) carries a milling mark (8) making it possible to identify it during the implantation by looking at the implant from above.

 The locking screw (10) is a threaded cylinder with identical and flat upper and lower walls. It is pierced over its entire height with a hexagonal profile hole (11), or other profile, making it possible to introduce an instrument used to screw it.

 Once all the implants are in place, the connecting rod (12) is bent according to the desired alignment, then introduced into the different channels (5) and fixed with the locking screws (10).

The locking screw (10) is screwed onto the internal threaded faces of the two vertical walls (3,4) and ensures tightening from the top of the connecting rod (12). The rod is thus subjected to three clamping zones, an upper zone provided by the locking screw (10) and two lower zones separated by the groove (7) at the bottom of the gutter (6). One of the most effective and stable clamps is three-zone tightening. Note the impossibility of rotation of the implant (fig.l, fig.2) during the tightening of the locking screw (10) thanks to the contact between the vertical walls (3,4) and the connecting rod (12 )
In extreme cases where the connecting rod (12) is very far from the channel (5) of the pedicle screw (fig. 1) or the hook (fig. 2), and where the offset channel alone does not allow catch the alignment of the channels, a catch piece (fig. 6) can be used.

 According to another characteristic of the invention, this catching piece consists of a hook (13) with lateral opening machined as a single piece with a cylindrical rod (15), of different lengths, intended to be fixed in the channel (5) of the implant (fig.l, fig.2). The catching hook (13) has in its upper part an incorporated screw (14), with internal hexagon, making it possible to fix the connecting rod (12) in the hook (13) (fig.7a).

 In the case of a pedicle screw (fig. 1), it suffices to perform a rotation of 900 of the screw (fig. La) making its channel in a horizontal position.

 In the case of the vertebral hooks (fig.2), it is necessary to use a different model (fig.2c) having a channel (5) with horizontal axis therefore oriented at 90 "with respect to a channel (5) of a normal hook (fig.2a).

 The catching hook (13) is mounted on the connecting rod (12) at the desired height without fully tightening the incorporated screw (14). The connecting rod (12) is placed in the different channels (5) and the cylindrical rod (15) of the hook (13) is introduced and fixed in the channel (5) adjusted in horizontal position (fig.2c). Then proceed to tighten the incorporated screw (14), and the various locking screws (10) (fig.8).

 According to an advantageous arrangement, the catching hook (13) can be added, even after the end of the assembly, in the case of persistence of a large gap between the connecting rod (12) and one of the implants (fig. l, fig. 2). The hook (13) is mounted on the connecting rod (12) through its lateral opening, and by a simple rotational movement from top to bottom, its cylindrical rod (15) is introduced into the channel (5) of the implant placed in horizontal position (fig.2a, fig.2c).

 The tightening of the locking screw (10) on the rod (15) of the hook (13), and of the incorporated screw (14) on the hook (13) on the connecting rod (12) makes the system rigid and integral in catching up with the space between the implant and the connecting rod (12) (fig. 8).

Claims (10)

 1) Implant for spinal osteosynthesis intended to attach on one side to the vertebrae by a thread or an angled blade, and on the other to a rod thanks to a channel (5) open upwards, and characterized in that this rod insertion channel is located in an offset position (CC ') relative to the axis of the implant (AA', BB ') with a locking screw (10) exerting a vertical force.  2) Implant according to claim 1, characterized in that the rod to which the implant is attached by its channel (5) is a connecting rod (12) which connects all the implants together.  3) Implant according to claim 1, characterized in that the rod to which the implant is attached by its channel (5) is a cylindrical rod (15) terminating a hook (13) open laterally and intended to connect the implant to a connecting rod (12) when there is too great a gap between the implant and this connecting rod (12).  4) Implant according to any one of claims 2 or 3, characterized in that the channel (5) intended to accommodate the connecting rod (12) or the cylindrical connecting rod (l5), has a wide inlet opening (5) which ends in a semicircular gutter (6) having the same diameter as that of the rod (12) (15).  5) Implant according to claim 4, characterized in that the bottom of the semicircular groove (6) has a shallow groove allowing, after screwing the locking screw (10), to obtain two clamping lines at level of the lower face of the rod (12) (15).  6) Implant according to any one of claims 2 or 3, characterized in that the channel (5), intended to accommodate the rod (12) (15) is delimited by two vertical walls, a proximal (3) and the another distal (4) relative to the axis of the implant (AA 'and BB') and having internal faces threaded in order to screw the locking screw (10) serving to hold the connecting rod (12) or the cylindrical connecting rod (15).  7) Implant according to any one of claims 1, 2 or 3, characterized in that the channel (5), intended to accommodate the rod (12) (15), is located in an offset position (CC ') relative to the axis of the implant (AA 'and BB') in order to correct the alignment, and allows to exert on the rod (12) (15) a vertical force by the introduction of a locking screw (10 ) cylindrical with a large vertical axis.  8) Implant according to claim 6, characterized in that the proximal (3) and distal (4) vertical walls have external, anterior and posterior flat faces to facilitate the adaptation of the placement instruments to the implant.  9) Implant according to any one of claims 6 or 8, characterized in that the distal vertical wall (4) of the channel (5) has on its upper face a groove (8) making it possible to identify it during implantation by looking at the implant from above.  10) Implant according to claim 3, characterized in that the hook (13) of the cylindrical connecting rod (15) has a lateral opening and in its upper part an incorporated fixing screw (14) for tightening the connecting rod (12). This hook (13) is machined in one piece with the cylindrical rod (15) having the same diameter as that of the connecting rod (12) and which is inserted into the channel (5) of the implant while the hook (13) is fixed to the connecting rod (12) to form an integral assembly.