FR2761876A1 - INSTRUMENTATION OF LUMBAR OSTEOSYNTHESIS FOR CORRECTION OF SPONDYLOLISTHESIS BY POSTERIOR PATHWAY - Google Patents

Abstract

The disclosed apparatus comprises a first pair of sacral or pediculate screws (14), a second pair of pediculate screws (15) anchored in the vertebra to be corrected, as well as means for performing the correction. The apparatus further comprises a lever device (8) designed so as to be supported by the first pair of screws (14) and to be connected to the second pair of screws (15), so that displacement of the lever in a sagittal plane displaces the corresponding vertebra in a combined traction and rotation movement. The lever (8) includes an incline (13) and a manually prehensible handle; cross-span linking elements (19) are disposed so as to form a transverse link between the screws (14, 15). This apparatus enables spondylolisthesis to be corrected. The directional movement performed using the lever is transformed into a combined traction and rotation movement on the vertebra to be corrected. The link between the lever and the cross-span element allow the vertebra to be positioned freely in the sagittal plane during reduction, while avoiding any risk to the nerves.

Description

 The present invention relates to lumbar osteosynthesis instrumentation for the correction of spondylolisthesis by the posterior route.

 We know that spondylolisthesis is the forward movement of a lumbar vertebra with respect to its lower neighbor or the sacrum.

 Generally, this defect affects the fourth or fifth lumbar vertebra.

 Several devices have so far been proposed to correct spondylolisthesis.

 Thus, French patent 87 06 864 (2 615 095) describes a device with two rods fixed longitudinally in the spine by means of pedicle screws and which each serve as a support means for two double-threaded screws, linked to the vertebra corrected. These two double-threaded screws are connected transversely by a rigid plate which constitutes a bipedicular socket.

 It is this transverse plate which makes it possible to act on the corrected vertebra, thanks to a median hole for receiving a traction forceps thanks to which the surgeon can bring back in place, by posterior traction, the tilted vertebra.

 Such a device has the advantage of allowing triangulation of the screws and therefore symmetrical traction on the vertebra to be straightened. It also allows a real transverse connection and provides protection for the laminectomy.

 On the other hand, the correction obtained is in fact incomplete, since the traction is not accompanied by a tilting movement, so that the vertebra to be straightened abuts on the overlying or underlying vertebra or on the sacrum before reaching the target position by rotation.

 In addition, there is a risk of tearing of the pedicle screws by the axial traction which they undergo, as well as neurological risks.

 Finally, the screwing exerted results in a powerful reduction, without controlling the forces developed.

 French Patent No. 92 13 694 (2 697 991) describes an instrumentation comprising two pedicle screws with double thread, each connected to the neighboring vertebral rod by a connector. The surgeon makes the correction by screwing a nut on each double-threaded screw, alternately on one side and the other of the vertebra to be straightened.

 This instrumentation allows the surgeon to work only along the axis of each screw, by practically pure traction. This results in an incomplete correction of the spondylolisthesis, since the translational movement cannot be accompanied by a posterior tilting.

 In addition, the movement of the vertebra, by alternating displacements on each side by successive pulls, risks causing a loosening of a screw relative to the vertebra. It requires very large tensile forces, which the surgeon does not actually measure and which are likely to involve risks of rupture of the vertebra.

 Also known from European patent 0 528 177 is a spondylolisthesis correction instrumentation with which the correction is imposed.

 This instrumentation has a complex structure, the technique of implementation of which is delicate.

 The subject of the invention is an instrumentation which makes it possible to correct spondylolisthesis without having the drawbacks set out above.

 The instrumentation targeted by the invention comprises a first pair of sacral or pedicle screws intended to be anchored in a vertebra not affected by spondylolisthesis, a second pair of pedicle screws intended to be anchored in the vertebra affected by spondylolisthesis, these various screws being intended to receive vertebral longitudinal rods, the instrumentation also comprising means for carrying out the correction of spondylolisthesis.

 According to the invention, the instrumentation comprises a lever device comprising a first part adapted to bear on the first pair of screws, and a second part adapted to be connected to the screws of the second pair, in order to exert on these last, and on the corresponding vertebra to be corrected, a combined movement of traction and rotation by tilting the lever in a sagittal plane.

 According to a possible embodiment of the invention, said first part of the lever device is an end adapted to bear on the screws of the first pair, and said second part is an area between its ends, adapted to bear on the screws of the second pair.

 The combined movement of traction and rotation in the sagittal plane, takes place without constraining the vertebra, which somehow finds its way itself to the corrected position.

 In fact, in the previous devices recalled above, all the movements are made by prestressing the ligaments of the soft tissues and sometimes the nerve roots, the final position of the vertebra being imposed.

 The end of the lever can rest on the lumbar vertebra L5, if the spondylolisthesis affects the lumbar vertebra L4, or on the sacrum if the spondylo listhesis affects the vertebra L5.

 This operating technique has the advantage of allowing neural decompression of the nerve roots pinched by spondylolisthesis and which cause pain in the subject. The invention therefore has a substantial neurological advantage.

 In addition, the combined movement of traction and rotation in the sagittal plane eliminates the "wedge" effect due to the instrumentations allowing only essentially traction and therefore almost pure translations.

 Indeed, the rotation accompanying the translation prevents the affected vertebra from coming into abutment on the overlying or underlying vertebra or the sacrum.

 According to an advantageous embodiment of the invention, the lever device comprises a fork with two parallel arms joined at one of their ends by a handle carrying a manual grip handle and the opposite ends of which form hooks; said device also comprises for each pair of screws, a transverse connection plate traversed by said screws, each plate being shaped to form articulated supports for the terminal hooks of the lever.

 Other features and advantages of the invention will appear during the description which follows, given with reference to the appended drawings which illustrate several embodiments thereof by way of nonlimiting examples.

- Fig.l is a schematic side elevational view of the lumbar part of a spine, illustrating a spondylolisthesis;
- Fig.2 is a schematic side elevational view showing the principle of the lever device according to the invention for the correction of spondylolisthesis;
- Fig.3 is a partial perspective view of a first industrial embodiment of the osteosynthesis instrumentation according to the invention;
- Fig.4 is a side elevational view of the instrumentation of Figure 3, illustrating the successive stages of the correction of a spondylolisthesis affecting a lumbar vertebra L5;
- Fig.5 is a partial end elevation view in an anteroposterior plane of the device of Figures 4 and 5;
- Fig.6 is an elevational view of the instrumentation lever of Figures 3 and 4;
- Fig.7 is a perspective view of one of the transverse plates of the instrumentation of Figures 3 to 5;
- Fig.8 is a longitudinal sectional view of the transverse plate of Figure 7;
- Fig.9 schematically illustrates a second embodiment of the lever device according to the invention;
- Figs.10, ll, 12 and 13 are schematic views of the lumbosacral part of a spine of a patient, illustrating the principle of four possible implementations of the instrumentation according to the invention depending the vertebra affected by spondylolisthesis;
- Fig.14 is an end elevation view of instrumentation according to a second industrial embodiment of the invention;
- Fig.15 is a side elevational view, in a sagittal plane, of the instrumentation of the
Fig. 14.

 We see in Figure 1, two lumbar vertebrae L4 and L5 as well as the sacrum S, the vertebra L5.1 being affected by a spondylolisthesis. The movement for correcting it, illustrated by arrow F, consists in bringing it back to position L5.2 by a combined movement of translation and rotation towards the rear. Spondylolisthesis can also affect the L4 vertebra.

 To correct this defect, the invention provides lumbar osteosynthesis instrumentation, the principle of a first embodiment of which is illustrated in FIG. 2.

The instrumentation comprises a lever device 1 comprising a ramp 2 which can be rectilinear as shown, equipped with a manual handle 3 for gripping by the surgeon. The end of the ramp 2 is constituted by a curved hook 4 bearing on a transverse connecting element B between the screws 5 of a first pair schematically represented and anchored, in this embodiment, in the sacrum
S.

 The ramp 2 also rests on a transverse connecting element A secured to the two pedicle screws 7 schematically shown, anchored in the lumbar vertebra L5 affected with spondylolisthesis, at a point between the ends of the ramp 2.

 Once the mechanical connection has been made between the transverse elements A, B and the screws 5, 7, the correction of the spondylolisthesis can be obtained by tilting the whole of the lever 1 around the hook 4.

 During this movement, the connection with the screws 7 drives the vertebra L5 backwards, to its location L5.2. This translational and rotational movement in the sagittal plane is accompanied by a sliding of the transverse element A on the ramp 2 in the direction of the transverse element B.

 Thus, the element A comes in Al and the lever comes in 1.1 at the end of this combined movement.

 The principle of embodiment illustrated in FIG. 2 corresponds to the case of spondylolisthesis represented in FIG. 10.

 In the case of FIG. 11, the spondylolisthesis affects the vertebra L4 and the lever 1 is supported on transverse elements integral with screws anchored in the vertebra L5, to raise the vertebra L4.

 In the case illustrated in Figure 12, the spondylolisthesis affects the L4 vertebra, but the lever 1 is supported on the sacrum S.

 Finally, in the case of FIG. 13, the L5 vertebra is affected by a spondylolisthesis. The lever 1 is supported on the sacrum S and its end exerts a traction-rotation on the vertebra L4, which drives in its displacement the vertebra L5.

 A description will now be given with reference to FIGS. 3 to 8, an embodiment of the instrumentation targeted by the invention constituting an application of the principle illustrated in FIG. 2.

 The lever 8 comprises a handle 9 carrying a handle 11 for gripping and the opposite end of which is extended by a fork 12. The latter comprises two parallel arms 13 having a directed concavity, when the lever is in the use position, of the opposite side to two pairs of screws 14 and 15 respectively anchored in the sacrum S and in the vertebra L5 affected by a spondylolisthesis.

 The arms 13 are joined at one of their ends by a connection fitting with the handle 9, while their free ends are constituted by rounded hooks 18, the concavity of which is oriented opposite that of the arms 13. The radius of curvature R of the arms 13 is chosen at an appropriate value, for example between 50 and 150 mm. The curvature R of the lever conditions the amplitudes of the translational movements. The smaller R is, the greater the share of rotation relative to translation.

 For each pair of screws 14 and 15, the instrumentation also comprises a respective plate 19 for transverse connection between the two screws 14 and between the two screws 15. Each plate 19 is pierced at its two ends with two eyelets or oblong holes 21 for the passage of the corresponding sacred 14 or pedicular 15 screws. The end portions in which the eyelets 21 are pierced, are connected by a central portion 22 in the form of a bridge, on each side of which the end portions extend in a widely divergent manner.

 In this central part 22 are formed, symmetrically with respect to the center C of the plate 19, two threaded holes 23 in which can slide the corresponding threaded pins 24 provided at the ends of rollers 25 U-shaped, in the form of a tuning fork (Figure 5) whose inner walls 26 are tapped.

 In each roller 25 can be screwed a corresponding plug 27, the spacing between the two branches 28 of a roller 25 being adjusted to allow the sliding introduction of an arm 13 of the lever 8 between the branches 28 (Figures 3 and 4), the plug 27 preventing the exit of the arm 13 from the roller 25.

 The introduction of the arms 13 between the branches 28 provides a mechanical connection of the lever 8 with the rollers 25, the transverse plate 19 and the associated screws 15.

 On either side of each tapped hole, each plate 19 has a rounded fillet 29, the curvature of which is congruent with the internal curvature of the hooks 18, in order to allow them to be articulated and to slide easily on these fillet 29.

The implementation of the instrumentation which has just been described, is carried out as follows, within the framework of the correction of a spondylolisthesis affecting the L5 vertebra (Fig. 10)
Before being anchored in the sacrum S and in the pedicles of the vertebra L5, the four screws 14,15 are introduced into the oblong holes 21 of the two associated plates 19.

 Then, the surgeon puts in place in the sacrum S and in the vertebra L5 to be straightened, shown in phantom in FIG. 4, the two pairs of respective screws 14 and 15. These screws can be of the U-type head 31 adapted to receive, after correction, in the channel 41 delimited by this U, a rod 32.

 The surgeon then screws the threaded end pieces or pins 24 of two rollers 25 without a plug 27 into the holes 23 of the plate 19 connecting the pedicle screws 15. I1 then places the hooks 18 on the leaves 29 of the plate 19 connecting the sacred screws 14 and introduces the arms 13 between the branches 28.

 The caps 27 are screwed onto the rollers 25. They are adjusted as a function of the initial position of the vertebra to be corrected.

 At this moment, the lever 8 is in the low position, shown in dashed lines in FIG. 4.

The surgeon then exerts in the sagittal plane, on the handle 11, a force F which causes the arms 13 and the hooks 18 to tilt on the leaves 29 by driving in the posterior direction the screws 15 and the vertebra L5, by a combined movement of traction and rotation. During this maneuver, the instrumentation allows the surgeon to control and control the forces applied to the spine. The vertebra
L5 gradually returns to its correct position (solid line, Fig. 4) at the end of this maneuver, without coming into abutment against L4 or against the sacrum S, the lever 8, the screws 15 and the rollers 25 arriving in the corresponding position .

 During this movement, the two plugs 27 progressively slide over the arms 13, the concavity of which, turned away from the screws 14, 15 and the vertebrae, facilitates this sliding.

 Once the spondylolisthesis L5 has been corrected, and while maintaining this correction, the surgeon sets up the vertebral rods 32 and fixes them appropriately, for example by plugs screwed inside the heads 31 in a manner known per se.

The lever 8 and roller 25 assembly is removed, starting with the unscrewing of the plugs 27. The transverse elements 19 are left in place.

 The operating technique which has just been described is similar for the cases illustrated in FIGS. 11, 12 and 13.

 In the diagram of Figure 11, the screws 14 are anchored in the vertebra L5 instead of the sacrum, and the screws 15 are anchored in L4.

 In the diagrams of Figures 12 and 13, the screws 14 are anchored in the sacrum S, while the screws 15 are anchored in the vertebra L4.

 FIG. 9 illustrates another embodiment of the invention in which the directional movement of the lever 33 is a push towards the sacrum by the handle 11. The direction of application of the forces on the vertebrae and the sacrum is identical to the previous achievement.

 The fixed support is provided to the transverse element B linked to the screws 14 anchored in the sacrum S.

To subject the L5 vertebra to the combined traction-rotation movement necessary in the sagittal plane, the surgeon presses the handle 11 towards the sacrum (arrow G). The lever 33 rocks on the transverse element B and causes a traction-rotation on the vertebra L5 via the transverse element
Linked to screws 15.

 In addition to the advantages set out above, the instrumentation according to the invention has the following.

 - The rotation combined with traction, prevents the vertebra to be corrected from coming into abutment against the underlying or underlying vertebra or the sacrum, so that the vertebra can carry out the entire correction movement sought.

 - These displacements of the vertebra to be instrumented require only controlled efforts, which constitutes a very significant advantage compared to the known prior devices.

 - The instrumentation according to the invention allows the channels 41 of the heads 31 of the screws 14, 15 to be left free during the correction.

 - The fact that the holes 21 of the plates 19 are oblong, in a direction substantially perpendicular to the general direction of the lever 8, advantageously allows angulation of the screws in a horizontal plane, as illustrated in FIG. 5 by the two positions represented by a screw 14 and allows a variation of center distance during the installation of the screws.

 - the fact that each plate 19 is provided with both two oblong holes 21 and two tapped holes 23, makes it possible to use either one or the other, to associate them with the screws anchored to the fixed support (screws 14 in FIG. 3) or with the screws 15 anchored in the vertebra to be corrected. This also makes it possible to limit the number of plates required.

 Furthermore, the plates 19 retain the advantages of known interpedicular plates: transverse connection between the implants, symmetrical action between the vertebrae, and triangulation of the screws, which very significantly increases their resistance to tearing.

 The rolled-up shape of the rollers 25 advantageously allows the arms 13 of the lever 8 to be inserted.

 The threaded plugs 27 allow the rollers 25 to be closed and above all an anteroposterior adjustment adapted to the sliding of the vertebra. These plugs 27 also allow, by a final tightening, to complete the correction and to keep the correction in place.

 The second industrial embodiment of the invention illustrated in FIGS. 14 and 15 comprises, like the previous one, a lever 8 with curved arms 13, but the screws 14 and 15 are here connected by a system of two pairs of pliers 35, 36 and of two cross bars 37.38.

 More specifically, each screw 14.15 has a head consisting of a body 31 defining a U-shaped channel 41 for the passage of the associated rod 32, and on the walls of which are formed lateral holes 39. The latter can receive bosses complementary (not visible in FIG. 15) formed on the spouts 35a, 36a of the pliers 35, 36, which thus tighten the bodies 31 laterally, leaving the channels 41 free. The two pliers of each pair 35 and 36 are connected by a transverse turnbuckle 37, 38, of which the two threaded rods 51, 52, of opposite pitch, are each articulated on a cylindrical bush 42 fixed to the corresponding clamp 35, 36. Each bush 42 is provided with a nut 45 for locking in the chosen angular position of the clamp relative to the turnbuckle 37, 38, the rotation of the central tube 53 of which spreads or brings the rods 51, 52 apart, therefore the clamps 35, 36, according to the direction of rotation.

 The clamps 35, 36 are of known type and do not require a more detailed description.

 Once mounted on the screws 14,15, they are in alignment with them. The two clamps 35 mounted on the screws 14, anchored on the fixed support part (sacrum or vertebra L5) are connected by the turnbuckle 38.

 The arms 13 of the lever 8 are introduced under the turnbuckle 37 and the hooks 18 come to bear on the turnbuckle 38.

 The operation of the lever 8 makes it possible to raise the turnbuckle 38, which drives the screws 15 and the vertebra to be corrected, by a combined traction-rotation movement in the sagittal plane as before.

 The articulated and lockable connection between the transverse turnbuckles 37-38 and the clamps 35-36 makes it possible to maintain the initial angulation of the screws 14, 15 to maintain the triangulation during the application of the forces.

 Once the correction has been made and the rods 32 have been put in place, the complete instrumentation (8, 35, 36, 37 and 38) is removed, which has, compared to the previous embodiment, the advantage of not leaving in place on the patient, the transverse connecting elements 37, 38.

 As a variant, the lever 8 may have only one arm or ramp 13 associated with a single roller 25.

Likewise the arm (s) 13 can (can) be rectilinear (s).

Claims (14)

 1. Lumbar osteosynthesis instrumentation for the correction of spondylolisthesis posteriorly, comprising a first pair of sacral or pedicle screws (14) intended to be anchored in a vertebra not affected by spondylolisthesis, a second pair of pedicle screws (15) intended to be anchored in the vertebra (L5 or L4) affected by the spondylolisthesis and means for carrying out the correction, characterized in that it comprises a lever device (1; 8) comprising a first part adapted to be linked to the first pair of screws (14), and a second part adapted to be connected to the screws (15) of the second pair in order to exert on the latter and on the corresponding vertebra to be corrected, a combined movement (F) of traction and rotation by tilting the lever in a sagittal plane.  2. Instrumentation according to claim 1, characterized in that said first part of the lever device (1; 8) is an end (18) adapted to bear on a transverse element (19) connecting between the screws (14) of the first pair, and said second part is a ramp (13) adapted to bear on a transverse element (19) connecting between the screws (15) of the second pair.  3. Instrumentation according to claim 1, characterized in that said second part of the lever device (33) is one of its ends adapted to bear on a transverse element (19) connecting between the screws (15) of the second pair , and said first part is an area between its ends and adapted to bear on a transverse element (19) connecting between the screws (14) of the first pair.  4. Instrumentation according to claim 1, characterized in that the lever device (8) comprises a ramp (13) with a single arm or two parallel arms (13) joined at one of their ends by a handle (9) carrying a handle (11) for manual gripping and the opposite ends of which form hooks (18), and said device also comprises, for each pair of screws (14,15), a transverse connection plate (19) traversed by said screws, each plate being shaped to form articulated supports for the terminal hooks (18) of the lever (8).  5. Instrumentation according to claim 4, characterized in that at least the transverse connecting plate (19) between the screws of the second pair of screws is equipped with means (25) for securing with the arms (13) of the lever ( 8), authorizing a sliding of the arms on the lever.  6. Instrumentation according to claim 5, characterized in that said securing means comprise threaded holes (23) provided in the central part of the plate (19), adapted to receive corresponding threaded pins (24) of rollers (25) U-shaped, whose internal walls (26) are tapped and inside which threaded plugs (27) can be screwed, the spacing between the branches (28) of these rollers allowing the passage between them of a respective arm lever (8), between the plug and the bottom of the U in order to link the lever to the rollers, to the transverse plate and to the associated screws, the arms of the lever thus being able to slide in the rollers during combined movements of traction and rotation of the lever.  7. Instrumentation according to one of claims 4 to 6, characterized in that each transverse plate (19) is pierced with two oblong holes (21) for the passage of the pedicle or sacral screws (14,15) corresponding.  8. Instrumentation according to claim 6, characterized in that each plate (19) has rounded leaves (29) complementary to the end hooks (18) of the arms (13) of the lever (8), in order to facilitate the support and the rotation of these.  9. Instrumentation according to claims 6 and 9, characterized in that the rounded leaves (29) extend on either side of each tapped hole (23) in a direction transverse to the plate (19).  10. Instrumentation according to one of claims 4 to 6, characterized in that the arms (13) of the lever (8) have a concavity directed on the side opposite the screws.  11. Instrumentation according to one of claims 1 and 2, characterized in that the lever device (8) comprises a ramp with one or two parallel arms (13) joined by a handle (9) and whose free ends constitute hooks (18) of the clamps (35,36) adapted to be mounted on each screw (14,15) in the extension thereof, leaving free channels (41) for passage of associated longitudinal vertebral rods (32), arranged in the heads (39) of the screws, two transverse bars (37,38) connecting between the two pairs of respective pliers, the hooks of the lever being able to bear on one (37) of the transverse bars while the arms of the lever pass below the second transverse bar (38), in order to allow the lifting thereof and the associated screws (15) anchored in the vertebra to be corrected.  12. Instrumentation according to claim 11, characterized in that the heads (31) of the screws (14,15) being formed of U-shaped bodies, the ends (18) of the clamps (35,36) are provided with bosses adapted for s '' introduce into corresponding holes (39) formed on the sides of the U-shaped bodies, leaving free the channels (41) delimited by said U-shaped bodies.  13. Instrumentation according to claim 2, characterized in that each transverse connecting element is a turnbuckle (37, 38) provided with two opposite adjustable rods (51, 52), articulated on respective clamps (35, 36) mounted on the screws (14, 15) and can be locked in the chosen position.  14. Instrumentation according to any one of the preceding claims, characterized in that the lever (1) comprises at least one rectilinear ramp (2).