FR2802796A1 - Bolt for connecting vertebra to longitudinal member, e.g. spine - Google Patents

Abstract

The bolt or pedicle screw (1) includes a threaded rod (2) having a longitudinal axis (XX) and a head (4) in which there is a channel (5) adapted to receive a spinal support rod. The channel is formed such that its longitudinal axial plane (P) is inclined relative to the longitudinal axis of the threaded rod. The head of the screw being made up of two flanks (6,7), a threaded hole (11) is formed in one of them. An Independent claim is also included for an apparatus to support the spine.

Description

The present invention relates to instrumentation for shoring the spine, comprising at least one shoring rod sized to be able to extend along at least two vertebrae, at least two anchoring members comprising a body having a longitudinal axis and a head in which is arranged a channel having a longitudinal axial plane; this channel is adapted to receive the shoring rod, and the instrumentation comprises means for blocking the shoring rod in the channel, for example a threaded plug.

The anchoring members are either screws or hooks.

In the case of a screw, the longitudinal median plane of the channel containing the longitudinal axis of the threaded rod, channel extends along the axis of the threaded rod. As moreover it is necessarily inclined with respect to the edges of the spine incision in order to be anchored in a pedicle, the instruments used to position these screws come into contact with the flesh and tissue bordering the incision, during the screwing and other operations on the screw. The object of the invention is therefore to produce a bone anchoring member in such a way that the instruments associated with it can be used without coming into contact with the tissues delimiting the edge of the incision.

According to the invention, the channel is made so that its longitudinal axial plane is inclined relative to the longitudinal axis of the bone anchoring member.

Another object of the invention is to produce pedicle screws which are better suited than the usual bone screws to shoring rods of relatively small diameter. Indeed in the usual way the diameter of the core of the threaded rod of the screw increases with the diameter of the thread. However, it would not be satisfactory to use large diameter screws with shoring rods of relatively small diameter.

Another object of the invention to provide a solution to the following problem. It is found that shoring rods of relatively small diameter, for example 3 mm, give rise to an appreciable percentage of ruptures after a certain period of use on the patient. It is therefore desirable to increase the bending rigidity of these rods, but without increasing their diameter. One solution to this problem would be to use a pair of rods instead of just one. For a rod for example having a diameter of 3 mm, a pair of rods thus associated is equivalent for bending rigidity, to a rod with a diameter of 6 mm. But such a solution considerably increases the size and the cost price of the instrumentation, since it requires two rods instead of one.

The invention therefore aims to provide a satisfactory solution to this problem.

According to the invention, at least one longitudinal flat is formed on the shoring rod and extends over at least part of the length of the rod, so that the latter has in a longitudinal axial plane of the channel a different bending stiffness depending on whether its flat extends either perpendicularly or parallel to said longitudinal axial plane of the channel.

Thus, depending on whether the rod is oriented with its flat parallel to the longitudinal axial plane of the channel or, on the contrary, perpendicular to this plane, the bending stiffness of this rod is different. This rigidity is of course higher when the flat is parallel to the axial plane of the channel.

Such an arrangement therefore makes it possible to increase, if necessary, the bending stiffness of the rod by arranging one or two flats therein and by modifying its orientation. This has the advantage of avoiding the use of two identical rods, thereby reducing the size of the instrumentation and its cost price.

According to one embodiment of the invention, the rod has two flats parallel to one another and diametrically opposite, the rod having between its flats parts of circular cross section.

Other features and advantages of the invention will become apparent during the description which follows, made with reference to the accompanying drawings which illustrate several embodiments thereof by way of non-limiting examples.

Figure 1 an elevational view on an enlarged scale of a pedicle screw according to the invention, intended for instrumentation for shoring the spine.

The figure is a perspective view on an enlarged scale of the pedicle screw of Figure 1.

The figure is a top view of the head of the screw of Figures 1 and 2.

The figure is a view in a horizontal plane of two pedicle screws anchored in a vertebra, one of which is in accordance with the invention and the other of which is in accordance with the state of the prior art.

Figure 5 is an elevational view of a pair of bone screws according to the invention, connected by a transverse connecting device. Figure 6 is a perspective view of an instrument which can advantageously be used in combination with a screw according to the invention. Figure 7 is a longitudinal partial sectional view on an enlarged scale of the head of a screw according to the invention and the lower end of the instrument of Figure 6, positioned on the head of the screw.

Figure 8 is a partial elevational view of two 'bone according to a second embodiment of the invention.

Figure 9 is a perspective view of a shoring rod for instrumentation of the spine, according to a third embodiment of the invention.

Figures 10 and 11 are elevational views in partial section showing head of a screw according to Figures 1 to 3 associated with shoring rod according to Figure 9, arranged in a first orientation in Figure 10 in a second orientation to Figure 11.

Figure 12 is an elevational view of spinal osteosynthesis instrumentation according to the invention.

Figure 13 is a partial perspective view on an enlarged scale second embodiment of the screw of Figures 1 to and its blocking means of the shoring rod.

FIG. 14 is a view in partial lateral elevation of the screw of FIG. 13. FIG. 15 is a view in longitudinal section of the means for locking the rod associated with the screw of FIGS. 13 and 14.

Figure 16 is a partial perspective view on an enlarged third embodiment of the screw of Figures 1 and its rod locking means.

FIG. 17 is a partial section view of the screw in FIG. 16.

FIG. 18 is a view in longitudinal section of the locking means of the screw of FIGS. 16 and 17.

Figure 19 is a partial perspective view on an enlarged scale of a fourth embodiment of the screw of Figures 1 to and its locking means of the shoring rod.

FIG. 20 is a partial section view of the screw in FIG. 19. FIG. 21 is a longitudinal section view of the locking means fitted to the screw in FIGS. 19 and 20.

FIG. 22 is an elevation view of the screw according to arrow K in FIG. 19.

Figure 23 is a side elevational view of a bone anchor hook according to the invention.

The pedicle screw 1 shown in Figures 1 to 3 is intended to be part of an instrumentation for the shoring of the spine not shown, known per se. This instrumentation comprises at least one shoring rod sized to be able to extend along at least two vertebrae, and at least two pedicle bone anchoring screws such as screw 1.

Each screw 1 consists of a threaded rod 2 provided with a bone thread 3 and having a longitudinal axis XX, and a head 4 in which is arranged a channel 5 having a U-shaped cross section and a longitudinal axial plane P. The channel 5, delimited by two sides 6, 7 of the head 4, is adapted to receive the shoring rod, generally cylindrical, and has for this purpose a bottom 8 of circular cross section. On its walls 9 are arranged tapped portions 10 intended to receive a screw, not shown, for blocking a shoring rod, not shown. This rod can be smooth or with roughness, or be of the type of rod 36 which will be described later.

The channel 5 in U is made so that its longitudinal axial plane P is inclined at an angle A relative to the longitudinal axis XX of the threaded rod 2. Thus the rectilinear walls 9 delimiting on either side of the parts taps 10 the channel 5 with its circular bottom 8, have an inclination A relative to the axis XX.

 This inclination A can vary between 0 degrees and about 65 degrees (see Fig. 19-20) in one direction or the other.

The sides 6 and 7 delimiting the channel 5 in a U can have respective widths 11, 12 different in a direction perpendicular to the longitudinal axial plane P. In addition, a tapped hole 11 is made in the side 7 whose width 12 is the most important. This hole 11 is intended to receive a threaded member whatever a screw 12 (Figure 7) for fixing a screw part 1, such as an instrument 13 (Figures 6-7).

The latter, known per se, has a generally tubular shape with a bent lower end 14 in which is arranged an orifice 15 for introducing the screw 12 into the tapped hole 11. In the instrument 13 is also arranged an axial bore 16 emerging at the opposite ends of the instrument 13, the end of which is provided with the elbow 14 is adapted to come to bear on the end faces of the branches 6, 7 while the screw 12 can be screwed into the hole 11, so that that the bore 16 is coaxial with the threaded portions 10 (Figure 3). The geometry of the head 4 of the screw 1 therefore makes it possible to position the instrument 13 in such a way that a tool can be introduced axially into the bore 16, exactly and with ease in the axis of the channel 5 to perform there conveniently the screwing of a threaded plug blocking the shoring rod crossing the channel 5.

FIG. 4 shows a screw 1 according to the invention screwed into a pedicle of a vertebra V as well as a screw 17 according to the prior art, screwed into the other pedicle of the same vertebra. To allow the placement of the screws, the surgeon has previously made in the spine, posteriorly, an incision I delimited laterally by muscle tissue M. The screw 17 according to the prior art comprises head 18 secured to a rod threaded 19 and which has a channel 21 in a U whose axial plane contains the longitudinal axis of the rod 19. The sides 22 delimiting the channel 21 are thus similar in their dimensions and symmetrical with respect to this axial plane and to the axis of the rod 19. As the screw 17 is further inclined in the pedicle in the direction of the adjacent tissues M, it follows that a tool 23 for screwing the blocking plug of the shoring rod into the channel 21, necessarily placed in the axis of channel 21, undesirably interferes with muscle tissue M.

By cons, thanks to the inclination channel 5 on the axis X-X of the screw 1 according to the invention, the screwing tool 23 can be introduced into the channel 5 without coming into contact with the tissues M.

FIG. 5 illustrates the implementation of a transverse connection device 24 by virtue of the arrangement of the wider side 7 of the screw 1. The end face of this wide side 7 consists of a first flat part 25, located in the plane of the planar face 26 forming the end of the sidewall 6, and of a second planar part 27 forming with the planar part 25 an obtuse angle (FIG. 1). The transverse connection device 24 consists of a plate 28, the ends of which bear on the flat part of two screws 1, and of two locking members 29 of the plate 28 on the screws 1. Each member 29 comprises a threaded rod (not visible in FIG. 5), passing through a corresponding orifice in the plate 28 and coming to be screwed into the associated tapped hole 11. FIG. 8 shows two pedicle screws 31 and 32 for bone anchoring for instrumentation. shoring of the spine. Each screw comprises a 33 of diameter d, provided with a respective thread 34, 35 having an outside diameter d1, d2, and a head (not shown). The diameter d of the core 33 is identical for the two screws 31, 32, while the outside diameter of their respective thread 34, 35 increases from d1 to d2, for example from 5.5 to 7.5 mm. More generally, in the set of screws provided by the invention, each screw such as 31, 32 comprises a cylindrical core 33 whose diameter is constant for all the screws, while the outside diameters d1, d2 ... of their thread respectively 34, 35 ... increase from one screw to another, between determined limits. These screws may be of the conventional type such as the screw 17 shown in FIG. 4, or else in accordance with the invention such as the screw 1.

The isorigid screws 31, 32 ... of this set do not have too large a diameter compared to that of the shoring rods with which they can be associated, when these rods have a relatively small diameter, of the order of a few millimeters . The diameter of the core 33 is of course chosen so that all of the screws used in the spinal instrumentation under consideration have sufficient mechanical strength, while the height of their thread varies from one screw to another. In other words, the diameter of the core 33 of the screw remains identical from one screw to another whatever the outside diameter of its thread.

Figures 9 to 11 illustrate another embodiment of the invention, in which a pedicle screw 1 is associated with a shoring rod 36 on which is formed at least one longitudinal flat 37 over at least part of the length of the rod 36, the remaining part 38 of which is cylindrical. In the example illustrated in Figures 9 to 11, two longitudinal flats 37 are arranged on the rod 36 and positioned diametrically opposite over part of the length of the rod. In addition, these flats 37 are identical, that is to say that they are symmetrical with respect to the longitudinal axis YY of the rod 37. As a result, the latter has in the longitudinal axial plane P of the channel 5 of the head 4, a different bending stiffness depending on its orientation in this channel 5. More precisely, the flats 37 may extend, either perpendicular to said axial longitudinal plane P of channel 5 (FIG. 10), or parallel to this ( figure 11). Between the flats 37, the rod 36 has two diametrically opposite parts 39 with contours of circular cross section. The rounded bottom 8 of the channel 5 has a radius of curvature substantially equal to the radius of curvature of the circular parts 39. As a result, when the rod 37 is positioned so that its flats 37 are parallel to the axial plane P (FIG. 11), one of the circular contours 39 comes to bear on the circular bottom 8 by marrying the latter. Advantageously, the means for blocking the rod 36 in the channel 6, constituted for example by a threaded plug 40, has a bearing face coming into contact with the rod 37. When the rod 36 is oriented with its flats 37 perpendicular to the axial plane P of channel 5 (FIG. 10), its opposite circular contours 39 are supported on rounded fillets 43 connecting the bottom 8 to the flat walls of channel 5, and whose radius of curvature is substantially equal to that of circular contours 39. In this case, the flat end face cap 40 is applied tightly to one of the flats 37.

The arrangement of one or two flats such as 37 over at least part of the length of the shoring rod 36 therefore makes it possible to vary its bending stiffness in the axial plane P of the channel 5, depending on its orientation : when the flats 37 are perpendicular to the axial plane P (FIG. 10), its flexural rigidity in this plane is minimum, while when these flats 37 are arranged parallel to the axial plane P (FIG. 11), its flexural rigidity is clearly more important. Therefore, the ruptures that could occur so far with fully cylindrical rods can be reduced by the use of a rod of a larger diameter and with flat (s) such as 36, suitably oriented in the channel 5.

The flat (s) allow (s) to adapt the stiffness of the assembly to the patient's pathology, by varying the orientation of the rod 37 (Fig. 10 and 11).

As a non-limiting indicative numerical example, for a rod having a diameter of 4 mm, the flats 37 can be separated by a distance of 3 mm. As a possible variant, the sides 6, 7 ... of the screw 1 can have equal widths. Likewise, the function of the tapped hole 11 can be fulfilled by a threaded extension in the same place or else by a geometry on the sides such as holes 60 or grooves 107 (FIGS. 19 and 22), allowing the grip of the screw by an instrument.

FIG. 12 illustrates an instrumentation according to the invention, comprising two cylindrical vertebral rods 50 extending along a spinal segment of four vertebrae 51. These rods are equipped with pedicle screws 1 equipped with threaded plugs 53 for blocking the rods 50, as well as at the ends of said rods, hooks 52 for bone anchoring also provided with threaded plugs 53.

An instrumentation of this type is disclosed by US patent 5,005,562.

The pairs of screws 1 are connected by devices 24 of transverse connection.

Of course, the cylindrical rods 50 can be replaced by rods 36 with flats 37, as can the plugs 53 with plugs 40 or 41.

Figures 13 to 15 illustrate a second embodiment of the screw of Figures 1 to 3. In this embodiment, the screw 61 has a head 62 consisting of two sides 63, 64 of uneven width and which define between them a profiled channel 65 in a U. On one side of the body 62 is also provided a hole 66 for gripping the screw by an instrument not shown. The locking means of the shoring rod 50 is a threaded plug 67 provided with a flange 68 radially delimiting two threaded parts 41 and 69. In one of the flanks delimiting the channel 65, namely in the flank 63 most wide, is arranged a tapped hole 71 having an interruption 72 on its part contiguous to the channel 65, so as to communicate laterally with the latter. In this way, after screwing the plug 67 into the hole 71, the flange 68 comes into locking abutment on the rod 50 placed in the channel 65. The upper thread 41 projecting above the flange 68 can be associated with a plate of transverse connection such as 24 (Figure 12), to which it is fixed by a nut not shown.

In the threaded plug 67 is arranged a profiled imprint 73 for the reception of a corresponding screwing tool and not shown. Note that the flange 68 has an asymmetrical profile, consisting of a side 68a inclined so as to be able to bear on the rod 50 at the end of screwing the plug 67, and a second side 68b extending radially, approximately perpendicularly to the longitudinal axis of the plug 67.

In the third embodiment of the screw 75 shown in FIGS. 16 18, the head of the screw 75 is made up of a short flank 76 which is not very thick, and of a second flank 77 which is wider and extending beyond sidewall 76. These two sides delimit a channel 78 whose bottom has an axial plane P having a certain inclination on the longitudinal axis XX of the bone anchoring member 75, and whose end walls 79, 81 have an axial plane Z more inclined with respect to the axis XX as the axial plane P.

These walls 79, 81 delimit an inlet for the shoring rod which is thus guided as far as the bottom of the U-shaped channel 78. In the wide flank 77 there is provided a tapped hole 82 whose lower, truncated part opens into the channel 78 and in the area between the inlet walls 79 and 81 (Figure 17). In other words, the tapped wall of the hole 82 is interrupted in its part contiguous to the channel 78. The screw 75 is completed by a threaded plug 83 provided with a screw-in recess 84. The rod 50 being previously placed in the channel 78, the terminal cone 42 of the plug 83 comes into locking abutment on the rod 50 (FIG. 16), thus blocked in the channel 78 when the screwing is sufficient. The upper part of the thread of the plug 83 can, as for the plug 67 in FIG. 13, be used with a transverse connection plate not shown and a locking nut.

In the fourth embodiment illustrated in FIGS. 19 to 22, the screw 85 comprises a channel 86 for receiving a shoring rod 50, delimited by two flanks 87 and 88. The flank 88 ends in a straight part which tangents the cylindrical bottom 86a of the channel 86. This rectilinear part is extended by a flat surface 89 delimiting a second flank 91 of the screw head, strongly inclined on the longitudinal axis XX of the screw 85, namely in the example shown d 'around 60. The bottom 86a is therefore connected to a flat surface 88, 89, in which a tapped hole 92 is arranged.

Side grooves 107 are arranged on the sides of the sides 88, 91, to allow the grip of the screw 85 by an instrument not shown.

The screw 85 is equipped with a threaded plug 93 with preferably a reverse pitch and which is provided with a head 94 constituted by a collar projecting radially. The flange 94 delimits an end bearing 95 inclined on the longitudinal axis of the plug 93 and turned towards the outside of the hole 92 when the plug 93 is screwed into the latter (FIG. 19). The bearing surface 95 is connected to a radial surface 96 completing the flange 94. The plug is preloaded in the factory, the plug being delivered pre-mounted on the screw. To implement this embodiment, the surgeon screws in melts the plug 93 in the hole 92, then it sets up the rod 50 in the channel 86. The screwing of the plug 93 is carried out by turning it in the opposite direction to the usual direction in the case of its pitch being reversed. After the rod 50 has been put in place, the surgeon again proceeds to screw the plug 93 in the opposite direction to the previous one, that is to say clockwise. Therefore, the plug 93 begins to come out of the hole 92 until its range 95 comes to bear on the rod 50 and blocks it against the circular inner wall of the channel 86 (Figure 19).

The plug 93 can also be fitted with a normal pitch, and in this case the rotations of this plug are reversed.

FIG. 23 illustrates a bone anchoring member 97 constituted by a hook formed by a body 98, having a longitudinal axial plane XX, and a head 99 delimiting a channel 101 in U shape, between two sides 102 and 106. The latter are provided with an internal thread allowing the screwing of a member for locking the rod 50 in the channel 101. The axial plane P of the channel 101 is inclined on the axial longitudinal plane of the body 98 by a variable angle A, as for the screw 1 previously described. Of course it is the same for the other screws described above (Figures 10-11) which can be replaced in the same way by a hook. In general, the arrangement aimed by the invention is applicable to all types of bone anchoring hooks: thus the embodiments of FIGS. 13 to 21 can be implemented on hooks.

Claims (15)

1. Instrumentation for shoring the spine, comprising at least one shoring rod (36) sized to be able to extend along at least two vertebrae, at least two organs (1) for bone anchoring comprising a body having a longitudinal axis (XX) and a head (4) in which is arranged a channel (5) having a longitudinal axial plane (P) and adapted to receive the shoring rod, and means (40 ...) for blocking of the shoring rod in said channel, characterized in that the channel is produced so that its longitudinal axial plane (P) is inclined relative to the longitudinal axis (XX) of the bone anchoring member. 2. Instrumentation according to claim 1, characterized in that the longitudinal axial plane (P) is inclined relative to the longitudinal axis (XX) by an angle (A) between O degree and 65 degrees approximately. 3. Instrumentation according to claim 1, characterized in that the rod locking means (50, 36) is a threaded plug (67) provided with a flange (68) projecting radially from the thread (69), and in a sidewall (63) bordering said channel (65) is arranged a tapped hole (71) communicating laterally with the channel, so that after screwing the plug into the hole the flange comes into locking abutment on the shoring rod. 4. Instrumentation according to claim 1, characterized in that the locking means is a threaded plug (83) adapted to be screwed into a tapped hole (82) formed in a sidewall (77) bordering said channel (78) and opening laterally in the channel, so that after screwing the plug into the hole, a terminal cone (42) of said plug comes into locking abutment on the shoring rod (50). 5. Instrumentation according to claim 1, characterized in that the channel (86) is delimited by two sides (87, 88) one of which (88) is extended by a surface (89) in which is arranged a tapped hole (92 ), and in that there is provided a threaded plug (93) and provided with a head constituted by a collar (94) projecting radially by delimiting a bearing surface (95) for supporting and blocking the shoring rod (50) by screwing the plug, the shoring rod coming to rest on this bearing surface after screwing the plug, which is then screwed to lock the rod in place in the channel. 6. Instrumentation according to claim 5, characterized in that the pitch of the threaded plug (93) is reverse. 7. Instrumentation according to claim 1, characterized in that the bone anchoring member is a pedicle screw (1; 61; 75; 85). 8. Instrumentation according to claim 1, characterized in that the bone anchoring member is a hook (97). 9. Instrumentation according to claim 1, comprising at least two bone anchoring members (1, 17) each comprising a head in which is arranged a channel (5, 21) for receiving the shoring rod, and means ( 40) for locking said rod in said channel, characterized in that on the shoring rod (36) is formed at least one longitudinal flat (37) extending over at least part of the length of the rod, such that the latter has in a longitudinal axial plane (P) of the channel (5) a different bending stiffness depending on whether its flat extends either perpendicularly or parallel to said longitudinal axial plane of the channel. 10. Instrumentation according to claim 9, characterized in that the rod (36) has two flats (37) parallel to each other and diametrically opposite, the rod having between these flats parts (39) of circular cross section . 11. Instrumentation according to claim 10, characterized in that the channel (5) has a bottom (8) for supporting the rounded rod with a cross section having a radius of curvature substantially equal to the radius of curvature of the circular parts (39 ) of the rod (36) between the flats (37). 12. Instrumentation according to claim 11, characterized in that the bottom (8) of the channel (5) is connected to its walls by rounded fillets (43) whose radius of curvature is substantially equal to that of the circular parts (39) of the rod (36) between its flats (37). 13. Instrumentation according to claim 12, characterized in that the means (40) for locking the rod (36) has a flat bearing face (44) on the rod so as to be able to bear on one (37) flats. 14. Instrumentation according to one of claims 3 and 4, characterized in that the threaded plug (67 or 83) comprises a threaded part (41) projecting from the bone anchoring member (61, 75) after screwing, and which can be associated with a transverse connection plate (24) to which it is fixed by a nut. 15. Bone anchoring member (1; 97) intended for instrumentation for propping up the spine, comprising a body having a longitudinal axis (XX) and a head (4) in which a channel (5; 101) is arranged. .) having a longitudinal axial plane (P) and adapted to receive a shoring rod (50), means (12) for blocking the rod in the channel being provided, characterized in that the channel is designed so that its longitudinal axial plane (P) is inclined at an angle (A) determined relative to the longitudinal axis (XX) of the bone anchoring member.