FR2817928A1 - Fixing for rod and spherical screw head e.g. for spinal stabilisation implant has lower and upper members shaped to grip screw head and rod - Google Patents

Abstract

The fixing consists of a lower member (14) and an upper member (15) shaped to grip the spherical head (10) of a pedicular screw. At least one of the two members also has a cavity (22) to receive a rod (12) connecting two or more fixings, and pressure on the screw head and rod is adjusted by a screw (42) inserted through holes in the opposite ends of the two members.

Description

<Desc / Clms Page number 1>

 The present invention relates to a fixing device intended to connect a rod and a screw head of spherical symmetry, said rod being located near said screw head.

 A field of application envisaged is in particular that of spinal surgery and more particularly the stabilization of the spine to overcome certain drawbacks linked to traumatic accidents or degenerative diseases.

 Stabilization devices comprising pedicle screws and a connecting rod capable of connecting the head of said screws to each other are well known. The pedicle screws of these devices generally have a U-shaped receiving head capable of receiving the rod and the internal wall of the head is tapped in the axis of said screw so as to allow the screwing of a piece of blocking against said rod. Thus, the rod is made integral with said screw by direct tightening of the blocking piece which forms a vice with the bottom of the receiving head.

 However, the bonding force between a receiving head and the rod passing through it is determined by the clamping force which has been transmitted to the locking piece. This blocking force is directly linked to the physical force of the operator, which is likely to vary depending on the individual.

 Furthermore, in these devices, the screw and the connecting rod are connected together and have relative directions determined by the shape of the receiving head.

 In order to overcome this last drawback, a U-shaped reception head has been devised having an external surface of spherical symmetry in which a threaded connecting rod engages so as to screw two nuts on each side of the head and to form a vice to hold the pedicle screw and the connecting rod in a fixed position. Thus, the screw head being of spherical symmetry, the rod is capable of being oriented in different positions relative to the screw, these different positions being

<Desc / Clms Page number 2>

 limited to the plane of symmetry containing the body of the screw and separating the two branches of the screw head in the shape of a "U".

 In addition, the two vice nuts also have the drawback of the tightening force since the nuts are directly screwed against the receiving head.

 The object of the present invention is to remedy these drawbacks by proposing a fixing device whose clamping force is increased.

 This object is achieved thanks to the fact that the device comprises a first longitudinal part having a first surface opposite to a second surface, the first end of said first surface being able to be applied against at least a portion of a first hemispherical part of said screw head and the middle part of said second surface being able to bear against at least a portion of a first part of said rod; a second longitudinal piece, capable of cooperating with said first longitudinal piece, the first end of which is capable of being applied, with respect to at least a portion of said first end of said first surface of said first piece, against at least one portion of the second hemispherical part of said screw head opposite to the first and the middle part of which is able to bear against at least a portion of a second part of said rod opposite to the first; and comprises securing and adjustment means able to hold the second ends of said first and second longitudinal pieces facing each other and to bring them closer to one another so as to pivot said second longitudinal piece around said rod relative to said first longitudinal piece for wedging simultaneously, said screw head between said first end of said first surface and said first end of said second longitudinal piece, and said rod between said middle part of said second surface of said first longitudinal piece and the middle part of said second longitudinal part, whereby said device connects said rod and said screw head and maintains them in a fixed position relative to one another.

<Desc / Clms Page number 3>

 Thus, a characteristic of the fixing device resides in the mode of immobilization and tightening of the reception head and of the rod by the pivoting of two longitudinal parts, one relative to the other around the rod so that the first ends of said longitudinal parts form a first clamp capable of wedging the head of a screw of spherical symmetry and that the median parts form a second clamp capable of wedging the rod simultaneously. The pivoting of the two longitudinal parts around the rod is achieved by means of securing and adjustment which allow to forcely bring the second ends of said longitudinal parts towards each other. In this way, by a leverage effect, the force exerted to bring the second ends towards each other allows the first ends of the longitudinal parts to form a vice and to simultaneously wedge the head of the screw and the rod with a force. much higher than that obtained by direct clamping of a blocking piece against the rod.

 In addition, the spherical symmetry screw head having no indentation into which the rod would be introduced since it is kept close to the latter, it forms a real ball joint and the possibilities of orientation of the rod relative to the pedicle screw is no longer limited to one plane.

 According to a preferred embodiment, the first end of said first surface forms a spherical cap, the bottom of which has a hole opening into the end of the second surface of said longitudinal piece, said spherical cap being able to be applied to said screw head . Thus, the first end is perfectly wedged against the screw head since the end of the surface perfectly matches the surface of the head. Furthermore, the bore which is formed in the part at the bottom of the spherical cap provides access to the top of the screw head which has a hexagonal housing intended for the screwing of the pedicle screw. Thus, the adjustment of the tightening of the screw in the vertebra is made possible even if the fixing device is already mounted on the screw head.

<Desc / Clms Page number 4>

 Advantageously, the middle part of said second surface has a first housing in which said portion of a first part of said rod is able to bear. In this way, the rod is blocked in translation in the direction of the first longitudinal part and allows better locking of the rod relative to the head.

 According to a particularly advantageous arrangement, the second longitudinal piece has a portion located opposite said second surface of said first longitudinal piece and a curved portion forming said first end of said second longitudinal piece. In this way, the second longitudinal part, bearing on the rod is able to pivot around the latter within the limits of contact with the first longitudinal part. When the first longitudinal part is in abutment against a first hemispherical part of the screw head, the curved portion of said second longitudinal part is applied against the second hemispherical part of the screw head so as to wedge it.

 Advantageously, the first end of said second longitudinal part has a portion of truncated spherical cap capable of pressing against said portion of the second hemispherical part of said screw head. Thus, the shape of the end of said second longitudinal piece coincides perfectly with the surface of the screw head and allows better attachment.

 Preferably, said portion located opposite said second surface of said first longitudinal part has a through hole opening opposite said hole opening into the end of the second surface of said longitudinal part, whereby said screw head is accessible when said device has climbed.

 According to a particular embodiment, said middle part of said second longitudinal part has a second housing located opposite said first housing of said first longitudinal part, said second housing being able to receive said rod. Thus, said rod is also blocked in translation parallel to said second part

<Desc / Clms Page number 5>

 longitudinal. In this way, the rod is able to be wedged between the two longitudinal parts.

 Advantageously, said securing and adjusting means comprise a screw capable of passing through said second ends of said first and second longitudinal pieces, the head of which bears against said end of said second longitudinal piece and the body of which is screwed into a thread of the second end of said first longitudinal part. Thus, the tightening of the screw tends to bring together and hold the second ends of the longitudinal pieces, the middle parts of which bear to form a pivot, respectively, against at least a portion of a first part of said rod and against at least one portion of a second part of said rod opposite to the first so that the first ends of said longitudinal parts enclose the screw head to block the assembly.

 According to a first particular embodiment, the invention is applied to a spinal stabilization assembly comprising, two pedicle screws with a spherical head capable of being screwed each, in a pedicle of a vertebra; two fixing devices according to the invention mounted on said screw heads, said longitudinal parts being substantially parallel to each other and to the axis of the spine; a transverse rod capable of connecting said two devices together, said rod being substantially perpendicular to the axis of the spine; and, a connection system capable of connecting said transverse rod to a longitudinal rod substantially parallel to the axis of the spine.

 Thus, the stabilization assembly according to this first particular embodiment makes it possible to maintain between them the vertebrae of a portion of the spine when the anatomical organs capable of fulfilling this function are lacking. To do this, the fixing devices according to the invention mounted on each of the two pedicle screws fixed in a vertebra are connected together by a transverse rod forming a rung on the vertebra and the rungs are connected together by

<Desc / Clms Page number 6>

 longitudinal rods by means of a connection system capable of securing two substantially perpendicular rods.

 According to a second particular embodiment, the invention is applied to a spinal stabilization assembly comprising, two pedicle screws with a spherical head capable of being screwed into the pedicles of two superimposed vertebrae; two fixing devices according to the invention, mounted on said screw heads, said longitudinal parts being substantially parallel to each other and perpendicular to the axis of the spine; and, a longitudinal rod capable of connecting said devices to each other, said longitudinal rod being substantially parallel to the axis of the spine.

 In this way, the devices according to the invention are mounted on two pedicle screws fixed in two successive vertebrae, on the same side of the spine, and they are connected by a rod so as to keep the two pedicles in a fixed position. with respect to two successive vertebrae. In order to symmetrically strengthen the spine, a similar assembly is mounted on the other side of the spine.

 According to a third particular embodiment, the invention is applied to a spinal stabilization assembly comprising, at least two pedicle screws with spherical head capable of being screwed each, in a pedicle of a vertebra, two devices, conforming according to the invention, mounted on said screw heads, said second ends of said longitudinal pieces being directed towards one another, and, a transverse connecting piece capable of connecting said two devices to each other, said connecting piece being integral at least a second end of said parts of said two devices.

 As in the previous particular embodiment, the fixing device according to the invention makes it possible to connect superimposed pedicle screws with rods arranged parallel to the axis of the spine. However, the devices are, in this third particular mode, interconnected, transversely from one side to the other of the spine, by a transverse connecting piece.

<Desc / Clms Page number 7>

 Other features and advantages of the invention will emerge on reading the description given below of particular embodiments of the invention, given by way of indication but not limitation, with reference to the appended drawings in which: - Figure 1 is a schematic view in vertical section of the fixing device according to the invention connecting the rod in perpendicular section and the spherical head of symmetry; - Figure 2 is an exploded view of the invention showing the various means which constitute it; - Figure 3 is a schematic perspective view showing a stabilization assembly comprising a fixing device according to the invention; and - Figure 4 is a schematic view showing a stabilization assembly comprising a fixing device according to the invention, according to a particular embodiment.

 We will first refer to Figure 1 to describe the fixing device according to the invention and its mode of operation.

The fixing device according to the invention makes it possible to hold together in a determined relative position, a screw head 10 of spherical symmetry and a rod 12, located close to one another. The device comprises a first longitudinal part 14 and a second longitudinal part 15 arranged opposite the first. The first longitudinal part 14 has a first surface 16, or lower surface, against a first end 18 from which the screw head 10 is supported. It also has a second surface 20, or upper surface, against the middle part 22 of which the rod 12 is supported. At its second end 24, the first longitudinal part
14 includes a thread 26 in which a screw 28 is adapted to be screwed.

 The first end 18 of the first surface 16 forms a spherical cap in which at least a portion of a first hemispherical part 29 of the screw head is applied. This

<Desc / Clms Page number 8>

 particularity makes it possible to form a joint between the fixing device and the screw head. As will be explained in more detail in the following description, this articulation has an advantage for the mounting of this device.

 Furthermore, the bottom of the first end 18 forming a cap has a hole 30 passing through the first longitudinal part 14 right through to form a spherical ring so as to release the end of the screw head 10 which has an axial hexagonal housing 32 for screwing the pedicle screw into the vertebra.

 The middle part 22 of the first longitudinal part 14 forms a substantially semi-cylindrical housing in which the rod 12 is supported. This housing allows the rod 12 to be guided in the fixing device during mounting and better securing of the rod and the device.

 Said housing has dimensions and in particular a depth, relative to the second surface 20, less than the diameter of the rod 12 so that a portion 34 of rod 12 protrudes from the second surface 20. Thus, the second longitudinal part 15 located opposite the second surface 20 is capable of being applied against the portion 34 of rod 12 which forms a pivot for the second longitudinal part 15.

 The latter, applied opposite the second surface 20 of the first longitudinal part 14 has a first curved end 35, a middle portion 36 and a second end 37. The first curved end 35 is applied to at least a portion of a second hemispherical part 38 of the screw head 10, opposite the first part 29, facing at least a portion of the first end 18 of the first surface 16. In this way, the screw head 10 of spherical symmetry , ball joint form for the fixing device, the longitudinal parts of which have at least four support points, three of which are non-aligned and applied against the first hemispherical part 29 and the fourth of which is applied against the second hemispherical part 38 opposite the first.

<Desc / Clms Page number 9>

 However, although the fixing device and the screw head 10 are capable of forming a joint, and this characteristic has an advantage, the device must be able to be locked on the head 10.

 Thus, the middle part 36 of the second longitudinal part 15 is in abutment on the portion 34 of rod 12 and the second end 37 is located opposite the second end 24 of the first longitudinal part 14. In addition, the second longitudinal part 15, in accordance with FIG. 1, has no other point of contact with the first longitudinal part 14, than the portion 34 of rod 12, capable of blocking the pivoting of this second longitudinal part 15 around the rod 12. By moreover, the second longitudinal part 15 has a bore 40 made in its second end 37 capable of coming into view with the internal thread 26 formed in the second end 24 of the first longitudinal part 14. Thus, the head 42 of the screw 28 which is inserted in the bore 40 and screwed into the internal thread 26 so that the head 42 is pressed against the end 37 of the second longitudinal part 15.

 In this way, the screwing of the screw 28 in the thread 26 tends to bring the second ends 24 and 37 closer to the longitudinal parts, 14 and 15. When the head 10 of the pedicle screw is housed between the end 18 of the first surface 16 and the curved end 35 of, that the rod 12 is inserted between the housing of the middle part 22 of the first longitudinal part 14 and the middle part 36 of the second longitudinal part 15, and that the two ends 24 and 37 of the two longitudinal parts 14 and 15 are maintained at a fixed distance, from each other by the screw 42 without the latter exerting a force capable of bringing them together, the device provides the connection between the screw head 10 and the rod 12.

 As long as the screw 42 is not tightened in the internal thread 26 and that it does not compress the two longitudinal parts, the device is capable of turning around the screw head 10 since the end 18

<Desc / Clms Page number 10>

 of the first surface 16 and the end 35 of the second longitudinal part 14 do not enclose the screw head 10.

 The main object pursued by the present invention is to maintain a rod in a fixed position with respect to a screw head of spherical symmetry, with a holding force greater than the holding force obtained with the devices of the prior art, all by exerting the same clamping force on a screwed element.

 Thus, when the screw 42 is rotated, the end 37 and 24 of the two longitudinal parts 14 and 15 are brought towards each other in a direction D1, and if the first longitudinal part 14 and the rod 12 are considered as a fixed reference, the second longitudinal part will pivot around the rod 12 and the end of this part 35 will compress the head 10, according to F1, against the first end 18 of the first longitudinal part 14. Simultaneously, the rod 12 is compressed between the middle parts 22 and 36 of the longitudinal parts 14 and 15.

 When the screw 42 is tightened with a first intensity, the articulation formed by the device integral with the rod and the head of the screw 10 is partially blocked and it is possible, manually, to give another orientation to the rod 12 relative to the head 10. This feature allows prior adjustment of the rod and has an advantage during the mounting of the fixing device as will be explained in the following description.

 When the final position is determined, a tightening of the screw 42 with a second intensity, greater than the first, is capable of locking the joint with sufficient force so that the rod 12 and the screw head 10 are in the fixed position despite the functional constraints to which the joint is subjected.

 It is understood that the leverage effect provided by the device according to the invention allows greater clamping of the rod 12 and the screw head 10 together than does direct clamping of a part against the other.

<Desc / Clms Page number 11>

 Reference will now be made to FIG. 2 to describe more particularly the second longitudinal part 15 of which the sectional view of FIG. 1 illustrates only a part.

 Found in Figure 2, the pedicle screw surmounted by a spherical head 10, above which the first end 18 of the first longitudinal part 14 is adapted to be applied. The second longitudinal part 15 forms a cowling in which the first longitudinal part 14 is able to be embedded and whose lateral recesses 44 allow the passage of the rod 12. Thus, the two longitudinal parts 14 and 15 are integral in translation along an axis parallel to the rod 12.

 The first end 35 of the second longitudinal part 15 has a portion of truncated spherical cap capable of being applied against a portion of the second hemispherical part 38 of the screw head.

 In addition, advantageously provision is made for specific machining of the first end 35 of the second longitudinal part 15 so that, when the device is mounted on the rod 12 and the screw 42 is partially screwed into the thread 26, the device can 'force fit on the screw head 10. This arrangement allows to partially mount the device and then fix it on the screws secured to the vertebrae.

 Furthermore, we find in Figure 2 the bore 30 which passes through the first longitudinal part 14 to access the hexagonal housing for screwing the pedicle screw. In order to access this housing when the complete fixing device is mounted on the screw head 10, the second longitudinal part 15 also has a hole 46 located opposite the hole 30.

 We will now refer to Figure 3 to describe a spinal stabilization assembly comprising a fixing device according to the present invention.

<Desc / Clms Page number 12>

 Figure 3 illustrates a portion of spine having two vertebrae, V1 and V2 in each of which two pedicle screws whose heads 50,52, 53,54 appear. On each of the screw heads 50.52, 53.54, a fixing device 58.60, 62.64 according to the invention is fitted and two transverse rods 66 and 68 connect the devices 58 and 64 and the devices 60 respectively. and 62, perpendicular to the axis of the spine.

 Furthermore, the transverse rods 66 and 68 are interconnected by two longitudinal rods 70 and 72 arranged on each side of the spinous processes. The longitudinal rods 70,72, are secured to the transverse rods 68,66 by connection devices 74,76, 78, 80. Each connection device comprises a connection member capable of holding the transverse rods 66,68 against the rods longitudinal and, adjustable locking means, adapted to be applied against the longitudinal rods 70,72 to form a lever and compress the transverse rods so as to block the rods and the connection devices together.

 This set allows optimal stabilization of the portion of spine that is equipped with it.

 Furthermore, during assembly of the stabilization assembly, the pedicle screws are inserted into the vertebrae and then the devices are nested in pairs with a transverse rod in each of the screw heads of the vertebrae of the portion of the spine to be stabilized, without excessive tightening of the devices so as to cause the joint to play during assembly. It is only after mounting the longitudinal rods by means of the connection devices that the devices are tightened so that the assembly adapts perfectly to the morphology of the spine or to the shape that is wish to give it to him.

 According to a particular embodiment of the invention, the spinal stabilization assembly comprises: two pedicle screws with a spherical head capable of being screwed into the pedicles of two superimposed vertebrae and two mounting devices according to the invention mounted

<Desc / Clms Page number 13>

 on said screw heads, said longitudinal parts being substantially parallel to each other and perpendicular to the axis of the spine. Furthermore, a longitudinal rod connects said devices to each other, said longitudinal rod being substantially parallel to the axis of the spine.

 Reference will now be made to FIG. 4 to describe another set for stabilizing the spine comprising at least two pedicle screws 82, 84 with spherical head each capable of being screwed, in a pedicle of a vertebra and two devices 86, 88, in accordance with the present invention, mounted on said screw heads 82, 84, the second ends, 90 and 92 of the devices 86 and 88 being directed towards each other so that the rods are parallel to the axis of the spine . In addition, the second ends 90 and 92 are interconnected by a transverse connecting piece 94 perpendicular to the axis of the spine.

Claims (11)

 1. A fixing device intended to connect a rod and a screw head of spherical symmetry, said rod being located near said screw head, characterized in that it comprises: - a first longitudinal part (14) having a first surface (16) opposite a second surface (20), the first end (18) of said first surface (16) being capable of pressing against at least a portion of a first hemispherical part (29) of said head screw (10) and the middle part (22) of said second surface (20) being able to bear against at least a portion of a first part of said rod (12); - A second longitudinal part (15), capable of cooperating with said first longitudinal part (14), the first end (35) of which is capable of being applied, with regard to at least a portion of said first end (18) of said first surface (16) of said first part (14), against at least a portion of the second hemispherical part (38) of said screw head (10) opposite to the first (29) and of which the middle part (36 ) is able to bear against at least a portion (34) of a second part of said rod (12) opposite the first; - And in that it comprises securing and adjusting means (26,28) capable of holding the second ends (24,37) of said first (14) and second (15) longitudinal pieces facing each other and bringing them closer together. 'from each other so as to pivot said second longitudinal piece (15) around said rod (12) relative to said first longitudinal piece (14) to wedge simultaneously, said screw head (10) between said first end (18) of said first surface (16) and said first end (35) of said second longitudinal part (15), and said rod (12) between said middle part (22) of said second surface (20) of said first part longitudinal (14) and the middle part (36) of said second longitudinal piece (15), whereby said <Desc / Clms Page number 15>  device connects said rod (12) and said screw head (10) and keeps them in a fixed position relative to each other.  2. Fastening device according to claim 1, characterized in that said first end (18) of said first surface (16) forms a spherical cap whose bottom has a hole (30) opening into the end of the second surface ( 20) of said longitudinal piece (14), said spherical cap being able to be applied to said screw head (10).  3. Fastening device according to claim 1 or 2, characterized in that said middle part (22) of said second surface (20) has a first housing in which said portion of a first part of said rod is able to bear. .  4. Fastening device according to any one of claims 1 to 3, characterized in that said second longitudinal part (15) has a portion located opposite said second surface (20) of said first longitudinal part (14) and a curved portion forming said first end (35) of said second longitudinal part (15).  5. Fastening device according to any one of claims 1 to 4, characterized in that said first end (35) of said second longitudinal part (15) has a portion of truncated spherical cap adapted to be applied against said portion of the second hemispherical part (38) of said screw head (10).  6. A fixing device according to claim 4, characterized in that said portion located opposite said second surface (20) of said first longitudinal part (14) has a through hole facing said hole opening into the end of the second surface (20) of said longitudinal piece (14), whereby said screw head (10) is accessible when said device is mounted.  7. Fastening device according to any one of claims 1 to 6, characterized in that said middle part (36) of said second longitudinal part (15) has a second housing (44) <Desc / Clms Page number 16>  located opposite said first housing, said second housing (44) being able to receive said rod (12).  8. Fastening device according to any one of claims 1 to 7, characterized in that said securing and adjusting means comprise a screw (28) capable of passing through said second ends (24,37) of said first (14) and second (15) longitudinal pieces, the head (42) of which presses against said end (37) of said second longitudinal piece (15) and the body of which is screwed into a thread (26) of the second end (24) of said first longitudinal part (14).  9. Stabilization assembly of the spine characterized in that it comprises: - two pedicle screws with spherical head (50,56) capable of being screwed each, in a pedicle of a vertebra (V1); - two devices (58,64), according to any one of claims 1 to 8, mounted on said screw heads (50,56), said longitudinal parts being substantially parallel to each other and to the axis of the spine; - A transverse rod (66) capable of connecting said two devices (58,64) to each other, said rod (66) being substantially perpendicular to the axis of the spine; and, - a connection system (74,80) capable of connecting said transverse rod (66) to a longitudinal rod (70,72) substantially parallel to the axis of the spine.  10. Spinal stabilization assembly characterized in that it comprises: - two pedicle screws with a spherical head capable of being screwed into the pedicles of two superimposed vertebrae; - Two fixing devices according to any one of claims 1 to 8, mounted on said screw heads, said longitudinal parts being substantially parallel to each other and perpendicular to the axis of the spine; and, <Desc / Clms Page number 17>  - A longitudinal rod capable of connecting said devices together, said longitudinal rod being substantially parallel to the axis of the spine.  11. Spinal stabilization assembly characterized in that it comprises: - at least two pedicle screws (84,82) with a spherical head capable of being screwed each, in a pedicle of a vertebra; - two devices (86,88), according to any one of claims 1 to 8, mounted on said screw heads (84,82), said second ends (90,92) of said longitudinal parts being directed one towards the 'other; and, - a transverse connecting piece (94) capable of connecting said two devices (86,88) to each other, said connecting piece being integral with at least one second end (90,92) of said pieces of said two devices (86 , 88).