Vertebral connectors

Abstract

An apparatus is provided for correcting spinal disorders. The apparatus comprises: a flexible tether; at least two vertebral connectors, each comprising a base; an anchor capable of securing the base to an anterior segment of a vertebral body; and a cam cleat adapted to grip the tether and defining a direction in which said tether can be tightened through that cam cleat. The cam cleat is provided as part of or mounted on the base and comprises at least one pivotable cam-shaped member. The flexible tether extends through the cam cleat of a first of said at least two vertebral connectors and through the cam cleat of a second of said at least two vertebral connectors in the same direction defined by the respective cam cleats of the first and second vertebral connectors. The apparatus is adapted for use in vertebral body tethering in which the anchor of the first of said at least two vertebral connectors secures the base of that first vertebral connector to an anterior segment of the first vertebral body of a patient's spine, and in which the anchor of the second of said at least two vertebral connectors secures the base of that second vertebral connector to an anterior segment of a second vertebral body of the patient's spine, and the tether is tightened in the direction defined by the respective cam cleats of the first and second vertebral connectors, the arrangement allowing the patient's spine to remain flexible and able to grow. Also described is a vertebral connector for use with a flexible tether for correcting spinal disorders. The vertebral connector comprises: a base; an anchor for securing the base to an anterior segment of a vertebral body; and a cleat provided as part of the base or mounted on the base and adapted to grip a flexible tether extending through the cleat. The vertebral connector defines a channel through which a said tether may be passed. The channel commences at an entrance to the vertebral connector, and passes via the cleat to an exit from the vertebral connector. The vertebral connector further comprises an immovable restraining element fixed to or forming part of the base or the cleat and serving to prevent dislodgement of a said tether passing through the channel from said entrance to said exit in a direction generally perpendicular to the direction from the entrance to the exit.

Description

[0001] VERTEBRAL CONNECTORS

[0002] This disclosure relates to vertebral connectors. In particular, it relates to vertebral connectors and apparatus incorporating vertebral connectors for use in correcting spinal disorders, such as scoliosis.

[0003] Scoliosis is a three-dimensional deformity which occurs in the spine. Scoliosis is often progressive and tends to be particularly problematic in growing children, where the deformity may progress quickly. The traditional surgical procedure for treating scoliosis deformity and preventing its progression has been fusion surgery. This procedure involves fusing multiple vertebrae of the spine with a rigid structure, such as a titanium rod, to restrict movement between the fused vertebrae, thereby lowering the risk of irritation or compression of nearby nerves and reducing pain and related symptoms. However, fusion surgery presents severe drawbacks, particularly in younger children. By restricting spinal growth, fusion surgery can significantly stunt a growing child’s height and can lead to complications associated with restricting spinal growth, such as the crankshaft phenomenon, or limited truncal or chest growth.

[0004] In recent years, vertebral body tethering (VBT) has attracted considerable attention as a promising new paediatric procedure that might overcome the above- mentioned drawbacks. In VBT, pedicle screws are anchored into different vertebral bodies from an anterior approach. A strong, flexible tether is laid within the tulip head of each pedicle screw and, after securing the tether at one end, a tensioning device is used to tighten the tether through the pedicle screws so as to sequentially reduce the spinal deformity. A staple is often incorporated as part of anchoring the screw into the vertebral body to prevent any ploughing of the pedicle screw resulting from the tensile and compressive forces involved in reducing the spinal deformity. Once tightened, the tether is then secured within the tulip head of each pedicle screw by compressing the tether into the tulip head with a blocker / set screw. The flexibility of the tether allows the patient’s spine to remain flexible and able to grow.

[0005] However, Dr Kenneth M.C. Cheung recently demonstrated at the Scoliosis Research Society (SRS) 57thAnnual Meeting (Stockholm, Sweden, 14-17 September 2022) that the use of a blocker / set screw to secure the tether within the pedicle screw causes considerable damage to the tether. A tether having a tensile strength on the order of 10,000 N / m2(Newtons per meter squared), equivalent to the tensile strength of stainless steel, demonstrates a drastically reduced tensile strength when damaged, only then being capable of withstanding tensile forces on the order of 650 N / m2. Unsurprisingly, tether breakage after surgery has been and remains a significant issue in the successful long-term execution of VBT.

[0006] The present inventors have found inspiration for solving this medical problem from a most unlikely source, namely, at sea. In sailboats, ropes or sheets are normally used to raise the sails. This involves placing the ropes or sheets under significant tension. It is, of course, crucial to be able to make quick adjustments to the sail, so the tensioning mechanism used to maintain tension in the ropes or sheets must be relatively simple. The mechanism most usually employed is some form of cleat. A fairlead cleat, for example, has grooves that direct a rope in one direction opposite to the direction of the forces that would be applied to the rope as wind filling the sail pulls on that rope. A further example is a cam cleat, which is a mechanical device that usually involves two pivoting cams having serrated faces for gripping and engaging a rope, the cams serving to directly resist pulling of the rope out of the cam cleat in one direction while allowing the rope to be easily pulled into the cleat in the other direction. This allows successive and progressive forces to be maintained through a rope.

[0007] Very few attempts have been made to take advantage of this useful mechanism of nautical cleats in the correction of spinal deformities. Those attempts that have been made present themselves with a number of deficiencies, as outlined below.

[0008] US 8,403,958 (Warsaw Orthopedic, Inc.) discloses a system for correcting or treating spinal deformity through a non-fusion procedure. This system involves anchoring vertebral connectors, each comprising a cam cleat, to different vertebrae of a patient’s spine. The connectors are arranged in one or more opposing pairs, so that each respective pair of cam cleats runs in opposing directions, as shown in Figure 6 of US 8,403,958. A pair of connectors are connected by first passing a tether forward through the cam cleat of the first connector and then back through the cam cleat of the second connector. The tether may then be pulled through either side to slide the tether between the cam cleats without disconnecting it from either connector until the desired corrective tension is applied to the anchored vertebrae. However, in practice, the opposed arrangement of the connectors makes it quite tricky to pass the tether through those connectors without causing a lot of bending of the tether or without often needing to manually block the action of the cam cleats. Moreover, the use of more than one opposed pair of connectors, for example, as shown in Figure 9 of US 8,403,958, is problematic because the tether would, as a result of some cam cleats running towards each other, inadvertently accumulate and bunch up between some opposed pairs of connectors. The consequence of these issues is a greater risk of complications arising during or after surgery, and an installation and uninstallation process that is overly intricate and complicated. Moreover, there is no mechanism provided that secures the tether in place in the cleats, so that this system presents a real risk of dislodgement of the tether from the vertebral connector. No suggestion is made by the Patentee for seeking to mitigate this risk.

[0009] US 11,304,730 (OrthoPediatrics Corp.) discloses a vertebral connector suitable for correcting or treating a spinal deformity through a non-fusion procedure. The vertebral connector comprises a clam cleat, which is a form of cleat adapted to grip a tether between two opposing walls, the walls having grooves that direct said tether when pulled in one direction towards the base of the clam cleat. The clam cleat is adapted to anchor to the vertebral body of a patient’s spine. A tether passes through the clam cleat, and a threaded cap is received at the top of the clam cleat to secure the tether within the clam cleat. One end of the tether is fixed, and the tether is tensioned across multiple vertebral connectors to correct and address the spinal deformity. While the threaded cap need not be tightened to compress the screw, in practice, there is still the risk that the threaded cap may be inadvertently secured too tightly by the operator, causing damage to the tether. Perhaps worse, the threaded cap may be secured too loosely, presenting a real danger of the tether slipping out of the clam cleat and causing complications during or after surgery.

[0010] Thus, all of the prior proposals of which the present Inventors are aware suffer from one or more drawbacks. The present disclosure has arisen from our work seeking to improve upon the prior proposed methods. In particular, we have addressed the risk of dislodgement of the tether in a cam cleat system. We also provide a general cleat solution that circumvents the risk of surgical and postoperative complications associated with the under- / over-tightening of the tether into a vertebral connector.

[0011] According to one aspect of this disclosure, there is provided an apparatus for use in correcting spinal disorders, comprising: a flexible tether; at least two vertebral connectors, each comprising a base, an anchor capable of securing the base to an anterior segment of a vertebral body, and a cam cleat adapted to grip the tether and defining a direction in which said tether can be tightened through that cam cleat; the cam cleat being provided as part of or mounted on the base and comprising at least one pivotable cam-shaped member; the flexible tether extending through the cam cleat of a first of said at least two vertebral connectors and through the cam cleat of a second of said at least two vertebral connectors in the same direction defined by the respective cam cleats of the first and second vertebral connectors; the apparatus being adapted for use in vertebral body tethering in which the anchor of the first of said at least two vertebral connectors secures the base of that first vertebral connector to an anterior segment of the first vertebral body of a patient’s spine, and in which the anchor of the second of said at least two vertebral connectors secures the base of that second vertebral connector to an anterior segment of a second vertebral body of the patient’s spine, and the tether is tightened in the direction defined by the respective cam cleats of the first and second vertebral connectors, the arrangement allowing the patient’s spine to remain flexible and able to grow.

[0012] Advantageously, the tether is tightenable through each cam cleat in the same respective direction defined by those cam cleats, which considerably simplifies the installation / uninstallation of the apparatus, thereby reducing the risk of surgical and postoperative complications.

[0013] Preferably, the cam cleat has serrated edges to allow for a stronger grip on the tether. Preferably, the anchor comprises at least one screw for securing the base to the anterior segment of a vertebral body. The screw may be formed as part of the base. The screw may have a denser thread pitch towards the tip of the screw to act as a bicortical fix, and a less dense thread pitch at the body of the screw to better grip cancellous / medullary bone. The screw may also be coated with hydroxyapatite to encourage bonding with the vertebral body. The anchor may further comprise a staple comprising at least one opening through which the screw may be received for securing the base on the staple to the anterior segment of a vertebral body, the staple further comprising spiked feet that embed within the vertebral body to minimise torsion of the vertebral connector in relation to that vertebral body when anchored. The staple may be treated to encourage bonding with the vertebral body, for example, by coating the surface of the staple with hydroxyapatite or by roughening the surface of the staple. The staple may include one or more stops limiting how far a given cam-shaped member may pivot. One or more blocker screws screwed through the staple may be partially unscrewed from the staple to provide the one or more stops.

[0014] A given vertebral connector may define a channel through which the tether passes, the channel commencing at an entrance to that vertebral connector, and passing via the cleat to an exit from that vertebral connector, that vertebral connector further comprising a restraining element fixed to the cleat or forming part of the base or of the cleat and serving to prevent dislodgement of the tether passing through the channel from said entrance to said exit in a direction generally perpendicular to the direction from the entrance to the exit.

[0015] Preferably, the restraining element comprises a loop-shaped barrier and / or a bridge running over the channel. The restraining element may comprise a cap which additionally serves to reinforce the structural integrity of the vertebral connector. The cap may comprise a rigid bubble providing structural rigidity to the vertebral connector without limiting the action of the cam cleat or the tether. The bubble may be formed of titanium or any other suitably rigid material. The cap may be deformable. The cap may include a plurality of feet adapted to removably fix the cap to the staple. Preferably, the feet of the cap are resilient and formed with corresponding end portions that are slidable through corresponding slots in the staple to lock the cap to the staple, the cap being deformable to allow the end portions to subsequently unlock and pass back out through the slots. More preferably, the end portions are fin-shaped or hook-shaped. The restraining element may be removable, and may be tightenable towards the base without causing compressive forces that would otherwise damage the tether, to further prevent dislodgement of the tether while retaining the tether’s integrity. Alternatively, the restraining element may be immovable to mitigate the risks associated with over- or under-tightening of the tether. The restraining element may provide a buttress for supporting the use of a tensioning device.

[0016] According to a second and alternative aspect of this disclosure, there is provided a vertebral connector for use with a flexible tether for correcting spinal disorders, the vertebral connector comprising: a base, an anchor for securing the base to an anterior segment of a vertebral body, and a cleat provided as part of the base or mounted on the base and adapted to grip a flexible tether extending through the cleat; the vertebral connector defining a channel through which a said tether may be passed, the channel commencing at an entrance to the vertebral connector, and passing via the cleat to an exit from the vertebral connector; and further comprising an immovable restraining element fixed to or forming part of the base or the cleat and serving to prevent dislodgement of a said tether passing through the channel from said entrance to said exit in a direction generally perpendicular to the direction from the entrance to the exit.

[0017] The immovable restraining element presents no risk of over- or undertightening of the tether by the operator, thereby addressing the risk of dislodgement of the tether while simultaneously reducing the risk of surgical and postoperative complications.

[0018] Preferably, the anchor comprises at least one screw for securing the base to the anterior segment of a vertebral body. The screw may be formed as part of the base. The screw may have a denser thread pitch towards the tip of the screw to act as a bicortical fix, and a less dense thread pitch at the body of the screw to better grip cancellous / medullary bone. The screw may also be coated with hydroxyapatite to encourage bonding with the vertebral body. The anchor may further comprise a staple comprising at least one opening through which the screw may be received for securing the base on the staple to the anterior segment of a vertebral body, the staple further comprising spiked feet that embed within the vertebral body to minimise torsion of the vertebral connector in relation to that vertebral body when anchored. The staple may be treated to encourage bonding with the vertebral body, for example, by coating the surface of the staple with hydroxyapatite or by roughening the surface of the staple.

[0019] Preferably, the cleat is a fairlead cleat, and the immovable restraining element is formed as part of the fairlead cleat. Two fairlead cleats may be provided as part of the base or mounted on the base. The presence of two fairlead cleats allows two flexible tethers to be passed through a single vertebral connector, which allows for a considerably higher tensile force to be applied across multiple vertebral connectors without causing as much wear or damage to the individual tethers or vertebral connectors. The two fairlead cleats may run parallel or in opposite directions.

[0020] The vertebral connector may further comprise a further restraining element comprising a loop-shaped barrier and / or a bridge running over the channel. The further restraining element may comprise a cap which additionally serves to reinforce the structural integrity of the vertebral connector. The cap may comprise a rigid bubble providing structural rigidity to the vertebral connector without limiting the action of the cleat or the tether. The bubble may be formed of titanium or any other suitably rigid material. The cap may be deformable. The cap may include a plurality of feet adapted to removably fix the cap to the staple. Preferably, the feet of the cap are resilient and formed with end portions that are slidable through corresponding slots in the staple to lock the cap to the staple, the cap being deformable to allow the end portions of the feet to subsequently unlock and pass back out through the slots. More preferably, the end portions are fin-shaped or hook-shaped. The further restraining element may be removable, and may be tightenable towards the base without causing compressive forces that would otherwise damage the tether, to further prevent dislodgement of the tether while retaining the tether’s integrity. Alternatively, the further restraining element may also be immovable to mitigate the risks associated with over- or under-tightening of the tether. Either restraining element may provide a buttress for supporting the use of a tensioning device. Reference may now be made, by way of example only, to the accompanying drawings, in which:

[0021] Fig. 1 is a perspective view of an assembled vertebral connector incorporating a cam cleat;

[0022] Fig. 2 is a similar view to Fig. 1 showing a tether passed through the cam cleat;

[0023] Fig. 3 is an exploded perspective view of the vertebral connector shown in Figs. 1 and 2;

[0024] Fig. 4 is a plan see-through view of the vertebral connector shown in Figs. 1 to 3, the staple being omitted for illustrative purposes;

[0025] Fig. 5 is a side elevation view of part of a spine showing a pair of anchored vertebral connectors incorporating cam cleats that run in the same direction;

[0026] Fig. 6 is a longitudinal sectional view of the vertebral connector as shown in Fig. 4 fitted with a cap;

[0027] Fig. 7 is a perspective view showing a tether passed through a fairlead cleat;

[0028] Fig. 8 is a plan view of the fairlead cleat shown in Fig. 7 without the tether;

[0029] Fig. 9 is a rear elevation view of the fairlead cleat shown in Fig. 8;

[0030] Fig. 10 is an exploded perspective view of a vertebral connector incorporating the fairlead cleat shown in Figs. 7 to 9;

[0031] Fig. 11 is a side elevation view of part of a spine showing a pair of anchored vertebral connectors incorporating fairlead cleats that run in the same direction;

[0032] Fig. 12 is a similar view to Fig. 11 showing a pair of anchored vertebral connectors each incorporating two fairlead cleats that run in the same direction;

[0033] Fig. 13 shows a similar view to Fig. 12 wherein the two fairlead cleats of each vertebral connector run in opposite directions;

[0034] Fig. 14 is a schematic plan view of a further embodiment of a vertebral connector incorporating a cam cleat;

[0035] Fig. 15 is a schematic perspective view of a cap for fitting to the vertebral connector shown in Fig. 14;

[0036] Fig. 16 is a side elevation view of cap shown in Fig. 15 fitted on the vertebral connector shown in Fig. 14, the staple being shown as see-through for illustrative purposes;

[0037] Fig. 17 is a plan view of yet a further embodiment of a vertical connector incorporating a cam cleat; Fig. 18 is a front elevation view of the vertebral connector of Fig. 17 showing a tether passed through the cam cleat and fitted with a cap formed with a bubble;

[0038] Fig. 19 shows a plan view of yet a further embodiment of a vertebral connector incorporating a cam cleat and a pair of blocker screws, shown with a tether passing through the cam cleat; and

[0039] Fig. 20 is a perspective view of the vertebral connector of Fig. 19 shown without a tether passing through the cam cleat.

[0040] A vertebral connector 1 includes a cam cleat. The cam cleat has a pair of cams 2 pivotably mounted on pins 3. Pins 3 extend from a base, in this case, the head of a cylindrical hex female screw 4, and are formed as part of that screw 4. Screw 4 is driveable by a standard hex screwdriver. Each of pins 3 is welded with a top cap 5 wider than the respective pin 3, as best shown in Fig. 3. This serves to prevent cams 2 from inadvertently slipping out from pins 3 when mounted.

[0041] The cam cleat defines a direction DI in which a flexible tether 6, of the kind previously suggested for vertebral body tethering, can be tightened through the cam cleat, as shown in Fig. 2. Cams 2 have opposed serrated faces 7 that grip and engage said flexible tether 6 when passed through the cam cleat. As tether 6 is passed through the cam cleat in direction DI, the friction between tether 6 and serrated faces 7 causes cams 2 to pivot outwardly and move opposed serrated faces 7 apart to disengage tether 6, thereby allowing tether 6 to be passed through the cam cleat in direction DI with relative ease. As tether 6 is passed through the cam cleat opposite to direction DI, the friction between tether 6 and serrated faces 7 causes cams 2 to pivot inwardly and move opposed serrated faces 7 towards each other to engage and grip tether 6 by friction, thereby restricting tether 6 from passing through the cam cleat opposite to direction DI. In this way, when tether 6 is secured at its end opposite direction DI, the cam cleat allows progressive tension applied in direction DI to be maintained through tether 6.

[0042] Cams 2 may be biased by an internal spring (not shown) to pivot inwardly and cause the opposed serrated faces 7 to meet each other at rest. At rest, the biased serrated faces 7 also partially obstruct the drive of screw 4, as shown in Fig. 4, where cams 2 are shown as see-through to illustrate this obstruction. The bias of cams 2 must therefore be overcome and opposed serrated faces 7 must be moved apart from each other to make accessible the drive of screw 4 to be able to drive screw 4 into a vertebral body.

[0043] As shown in Fig. 3, screw 4 is blunt-tipped and has a denser thread pitch towards the tip of screw 4 to act as a bicortical fix, and a less dense thread pitch at the body of the screw 4 to better grip cancellous / medullary bone. Screw 4 may be coated with hydroxyapatite to encourage bonding with a vertebral body.

[0044] The vertebral connector 1 also includes a rectangular staple 8 which has a central opening 9 that receives screw 4. Screw 4 has a flat top that is wider than the central opening 9, so that the head of screw 4 rests on top of the staple 8 when the shaft of screw 4 is passed through opening 9 of staple 8. Staple 8 has at its four comers four corresponding spiked feet 10 that embed within a vertebral body to minimise torsion of the vertebral connector 1 in relation to that vertebral body when anchored. The underneath surface of staple 8 that contacts a vertebral body is roughened and coated with hydroxyapatite to encourage bonding with the vertebral body.

[0045] There are also a pair of loop barriers 11, each consisting of an arch 12, and a pair of feet 13 that are welded to fix the loop barrier 11 to the staple 8. When fixed, the loop barriers 11 act as immovable restraining elements. One loop barrier 11 is located near where tether 6 enters into the cam cleat, and the other loop barrier 11 is located near where tether 6 exits from the cam cleat. The tether 6 passes into the first loop barrier 11 and then passes via the cam cleat out from the second loop barrier 11 , as shown in Fig. 2. The fixed arches 12 of loop barriers 11 prevent dislodgement of the tether 6 in a direction generally perpendicular to direction DI.

[0046] As an addition to or an alternative for use of fixed loop barriers to serve as restraining elements to prevent dislodgement of a tether in a direction generally perpendicular to the direction of its passage through the cleat, a removable cap 14 may then be fitted over the cam cleat and the head of screw 4, which serves as a base. The material from which cap 14 is formed is preferably deformable either by hand or by use of tools to fit the cap 14 closely over and around the cleat and the head of the screw 4, as shown in Fig. 6. The top caps 5 of pins 3 prevent cap 14 from contacting the top of cams 2, and the undeformed cap 14 is wide enough to surround cams 2 without contacting them. Thus, movement of cams 2 remains unrestricted. The cap 14 must, however, have openings that enable a tether to extend into the cam cleat, and again out of the cam cleat in the direction DI. The tight fit of cap 14 prevents dislodgement of tether 6 and reinforces the structural integrity of the vertebral connector 1.

[0047] As will be appreciated, the described restraining elements may be used with other embodiments, such as with the vertebral connector incorporating a fairlead cleat (described further below) shown in Figs. 7 to 10. Whichever restraining element is used, the secure nature of the restraining element allows the restraining element to provide a buttress for supporting a tensioning device when used to apply tension to the tether 6.

[0048] In operation, a pair of vertebral connectors 1 are each anchored to a different vertebral body of the spine of a patient suffering from spinal deformity. The vertebral connectors 1 are aligned so that flexible tether 6 extends through both the cam cleat of the first vertebral connector and the cam cleat of the second vertebral connector in the same direction DI as defined by the respective cam cleats of the first and second vertebral connectors, as shown in Fig. 5. This allows flexible tether 6 to be passed through the respective cam cleats with relative ease. Flexible tether 6 is secured at the end towards which the tether 6 cannot be tightened through the cam cleats, i.e., the tether 6 is secured at its end opposite direction DI. A tensioning device (not shown), of the kind normally used in vertebral body tethering, can then be used, preferably using the buttress provided by the restraining element as a support, to apply tension to tether 6 at the other end to sequentially reduce the spinal deformity.

[0049] Should tension be required across more than two vertebrae, further vertebral connectors may be employed in a similar fashion.

[0050] Figs. 7 to 10 show an alternative embodiment of a vertebral connector incorporating a different form of cleat, namely a fairlead cleat (sometimes referred to as a monoblock cleat), where the same reference numerals are used for like features to those of the embodiment of Figs. 1 to 6. In this embodiment, the vertebral connector 1 includes a fairlead cleat 15, which has a base in the form of a plate 16, a pair of opposing side walls 17 and a bridge 18 running above the base plate 16 and between the opposing side walls 17 to form a closed arch, as shown in Fig. 6. Opposing side walls 17 and bridge 18 are both formed integrally with the base plate 16 as a single moulding.

[0051] The fairlead cleat defines a direction D2 in which a flexible tether 6 can be tightened through the fairlead cleat, as shown in Fig. 7. Each of the opposing side walls 17 forms a side of a generally V-shaped groove 19, the side wall being formed with a series of ridges 20 running downwardly and from top to bottom of the groove 19 angled in a direction opposite to direction D2, as best shown in Figs. 8 and 9. At the open mouth of the groove 19, the flexible tether 6 can be passed under the bridge

[0052] 18 freely in either direction. As flexible tether 6 is pushed downwardly into the groove

[0053] 19 and is pulled opposite to direction D2, ridges 20 increasingly grip the flexible tether 6 and direct it further along the line of the ridges 20 down towards the bottom of groove 19 and opposite direction D2. Thus, the flexible tether 6 is firmly jammed in groove 19 by friction and any further pulling of flexible tether 6 opposite to direction D2 will only cause the tether 6 to jam more tightly in groove 19. As flexible tether 6 is pulled within groove 19 in direction D2, individual ridges 20, grip the flexible tether 6 and direct it along the line of the ridges 20, namely, upwardly and in the direction D2, to a position where the sidewalls 17 are sufficiently far apart for tether 6 to disengage from the grip of ridges 20. In this way, when tether 6 is secured at its end opposite direction D2, the fairlead cleat allows progressive tension applied in direction D2 to be maintained through tether 6.

[0054] As will also be evident from Fig. 7, bridge 18 acts as an immovable restraining element that serves to prevent complete dislodgement of the flexible tether 6 from the cleat in a direction generally perpendicular to direction D2.

[0055] As shown in Fig. 10, the vertebral connector 1 also includes a blunt-tipped hex female screw 21, which has a denser thread pitch towards the tip of the screw 21 to act as a bicortical fix, and a less dense thread pitch at the body of the screw 21 to better grip cancellous / medullary bone. Screw 21 is also coated with hydroxyapatite to encourage bonding with a vertebral body. Screw 21 is received by an opening 22 in the base plate 16.

[0056] Screw 21, together with a staple 8, serves as an anchor for the vertebral connector 1. As in the embodiment of Figs. 1 to 3, staple 8 takes a generally rectangular form with a central opening 9 that aligns with the opening 22 in the base plate 16 to receive screw 21. Screw 21 has a flat top that is wider than the central opening 9, so that the head of screw 19 rests on top of the staple 8 when the shaft of screw 21 is passed through opening 9 of staple 8. Staple 8 has at its four comers four corresponding spiked feet 10 that embed within a vertebral body to minimise torsion of the vertebral connector 1 in relation to that vertebral body when anchored. The underneath surface of staple 8 that contacts a vertebral body is roughened and coated with hydroxyapatite to encourage bonding with a vertebral body.

[0057] In operation, a pair of vertebral connectors 1 incorporating the fairlead cleats are anchored each to a different vertebral body of the spine of a patient suffering from spinal deformity. The vertebral connectors 1 are aligned so that flexible tether 6 extends through the fairlead cleat of the first vertebral connector and the fairlead cleat of the second vertebral connector in the same direction D2 defined by each of the respective fairlead cleats, as shown in Fig. 11. The aligned direction of the fairlead cleats allows for flexible tether 6 to be passed straight through those fairlead cleats with relative simplicity. Flexible tether 6 is secured at the end towards which the tether 6 cannot be tightened through the fairlead cleats, i.e., the tether 6 is secured at its end opposite direction D2. A tensioning device (not shown) can then be used, preferably using the buttress provided by the restraining element as a support, to apply tension to the tether 6 at the other end to sequentially reduce the spinal deformity.

[0058] Optionally, each vertebral connector 1 may be provided with two fairlead cleats, as shown in Figs. 12 and 13. Each of the cleats will have a respective screw 21 passing through a respective opening 22 in its base plate 16 and is received by a respective opening 9 of a common staple 8 for the two cleats having two such openings 9. Thus, operationally, two flexible tethers 6 extend from a particular vertebral connector to other connectors. The two fairlead cleats on each vertebral connector 1 may define directions D2 that run parallel in the same direction, as shown in Fig. 12. Alternatively, one of the two fairlead cleats on a vertebral connector 1 may define a direction running in direction D2, and the other of the two fairlead cleats on that vertebral connector 1 may define a direction parallel to but in the opposite direction to direction D2, as shown in Fig. 13. In this bi-directional arrangement, each vertebral connector 1 should be aligned to allow one flexible tether 6 to run from connector to connector in the same direction D2 on one side, and should also allow a second flexible tether 6 to run from connector to connector in a parallel direction opposite to direction D2 on the other side. In this way, the situation where some fairlead cleats run towards each other is avoided, thereby preventing accumulation and bunching up of the tether 6 between vertebral connectors 1.

[0059] In any of the above embodiments, should there be any over-correction of the patient’s spine resulting from over-tightening of the flexible tether 6, tension can be removed from the tether 6 manually with a minimally invasive procedure.

[0060] While the cap 14 of the embodiment shown in Fig. 6 and described above is fitted over the head of screw 4, the cap 14 may, in alternative embodiments, be fitted onto the staple 8 itself, as described below.

[0061] In the embodiment shown in Figs. 14 to 16, the cap 14 is generally cuboidal and includes at its four lower comers four corresponding resilient feet 23. Each resilient foot 23 extends straight down from the corresponding lower comer of cap 14 for a small distance before forming an end portion 24, which, in this embodiment, is in the shape of a downwardly directed fin. The four fin-shaped end portions 24 formed at the bottom of the corresponding four feet 23 are pushed to enter into four corresponding slots 25 present on and passing through the staple 8. Slots 25 are misaligned relative to the transverse plane of the corresponding fin-shaped end portion 24. As the end portions 24 are pushed into the slots 25, the curvature of the end portions 24 causes the resilient feet 23 to bend and move the end portions 24 to slide into alignment with and pass through the slots 25. Once an end portion 24 has passed through to the other side of a slot 25, the resilience of the corresponding foot 23 brings the fin-shaped end portion 24 back out of alignment from the slot 25, thereby preventing the end portion 24 from coming out of the slot 25 and locking the cap 14 onto the staple 8 (as shown in Fig. 16). Thus, the cap 14 is fixed to the staple 8, so that dislodgement of the tether 6 is prevented, and vertebral connector 1 is made more structurally secure. The cap 14 is deformable to bring the fin-shaped end portions 24 back into alignment with the corresponding slots 25 of staple 8 to allow the end portions 24 to pass through the slots 25, so that cap 14 may be removed from the staple 8. As will be appreciated, the cap 14 may have more or less feet 23, and the feet 23 need not necessarily be at the comers of the cap 14. For example, Figs. 17 and 18 show an embodiment wherein the cap 14 incorporates only two feet 23 with two corresponding fin-shaped end portions 24 passing through two corresponding slots

[0062] 25, the feet 23 and slots 25 being located towards the middle of the cap 14 and staple 8, respectively. Although the present embodiment employs fin-shaped end portions 24, any suitable shape, such as a hook-shape, may be employed, so long as the end portions 24 can be slid through the slots 25 with relative ease to lock the cap 14 to the staple 8, following which deformation of cap 14 allows them to be slid back out through the slots 25.

[0063] In the embodiment shown in Fig. 18, the cap 14 further includes a rigid bubble

[0064] 26, preferably of titanium, formed centrally on the surface of the cap 14 facing in towards the cam cleat and positioned between the cams 2. The rigidity and positioning of the bubble 26 provides structural rigidity to the vertebral connector 1 without limiting the action of the cam cleat or the tether 6.

[0065] In the embodiment shown in Figs. 19 and 20, there is a pair of blocker screws 27 screwed through the staple 8, each of which are positioned slightly outboard of the cams 2. The blocker screws 27 do not interfere with the camming action of the cam cleat when fully screwed into the staple 8. However, blocker screws 27 may be partially unscrewed from the staple 8, whereby they act as a stop limiting how far the cams 2 of the cam cleat may pivot outwardly. This ensures a minimum level of engagement of the tether 6 by the cam cleat, and offers further structural integrity to the vertebral connector 1.

[0066] It will be readily appreciated by a person skilled in the art that various modifications to the above embodiments are possible. For example, the loop barriers 11 may be screwed at their feet 13 to the staple 8 instead of being welded. A loop barrier 11 may be provided on the fairlead cleat 15 itself, for example, the feet 13 of a loop barrier 11 are formed as part of the fairlead cleat base 16, so that the loop barrier arch 12 extends between the fairlead cleat side walls 17. Additional screws can be passed through further openings in staple 8 for additional anchoring of the vertebral connector 1 to a vertebral body. This is particularly useful for larger vertebrae, such as those in the lumbar spine, to which greater tension may need to be applied to correct spinal deformity. In the fairlead cleat arrangement, the additional screws may also pass through further aligned openings in the base plate 16 of the fairlead cleats. The cams 2 of the cam cleat may be formed sufficiently deep for a single cam cleat to be capable of accommodating two or more flexible tethers 6. Similarly, a fairlead cleat may be formed with a groove 19 that is sufficiently deep to accommodate two or more flexible tethers; but since the respective flexible tethers will need to jam within the groove 19 at different depths where the ridges 20 have different separations, the tethers will need to have correspondingly differing thicknesses.

[0067] While the above embodiments describe anchoring vertebral connectors to different vertebrae, it is contemplated that some vertebral connectors may be anchored to the same vertebra.

[0068] A cam cleat having a single pivotable cam, instead of two, could also function adequately for gripping a tether.

[0069] While the above-described staple and screw combination works well for anchoring a vertebral connector to a vertebral body, it will readily be appreciated that other suitable combinations of anchoring elements, including screws, staples, teeth, bolts, spikes, wedges, grooves, etc., are feasible.

[0070] Other treatments or compounds that encourage bonding with a vertebral body may also or alternatively be applied to surfaces of the screws, staples and / or other anchoring elements.

Claims

Claims1. An apparatus for use in correcting spinal disorders, comprising: a flexible tether; at least two vertebral connectors, each comprising a base, an anchor capable of securing the base to an anterior segment of a vertebral body, and a cam cleat adapted to grip the tether and defining a direction in which said tether can be tightened through that cam cleat; the cam cleat being provided as part of or mounted on the base and comprising at least one pivotable cam-shaped member; the flexible tether extending through the cam cleat of a first of said at least two vertebral connectors and through the cam cleat of a second of said at least two vertebral connectors in the same direction defined by the respective cam cleats of the first and second vertebral connectors; the apparatus being adapted for use in vertebral body tethering in which the anchor of the first of said at least two vertebral connectors secures the base of that first vertebral connector to an anterior segment of the first vertebral body of a patient’s spine, and in which the anchor of the second of said at least two vertebral connectors secures the base of that second vertebral connector to an anterior segment of a second vertebral body of the patient’s spine, and the tether is tightened in the direction defined by the respective cam cleats of the first and second vertebral connectors, the arrangement allowing the patient’s spine to remain flexible and able to grow.

2. An apparatus according to Claim 1, wherein the cam cleat has serrated edges to allow for a stronger grip on the tether.

3. An apparatus according to any of Claims 1 or 2, wherein one or more of the at least two vertebral connectors define a channel through which the tether passes, the channel commencing at an entrance to that vertebral connector, and passing via the cleat to an exit from that vertebral connector, the said one or more vertebral connectors each further comprising an auxiliary restraining element fixed to the cleat or forming part of the base or of the cleat and serving to prevent dislodgement of the tether passing through the channel from said entrance to said exit in a direction generally perpendicular to the direction from the entrance to the exit.

4. A vertebral connector for use with a flexible tether for correcting spinal disorders, the vertebral connector comprising: a base, an anchor for securing the base to an anterior segment of a vertebral body, and a cleat provided as part of the base or mounted on the base and adapted to grip a flexible tether extending through the cleat; the vertebral connector defining a channel through which a said tether may be passed, the channel commencing at an entrance to the vertebral connector, and passing via the cleat to an exit from the vertebral connector; and further comprising an immovable restraining element fixed to or forming part of the base or the cleat and serving to prevent dislodgement of a said tether passing through the channel from said entrance to said exit in a direction generally perpendicular to the direction from the entrance to the exit.

5. A vertebral connector according to Claim 4, wherein the cleat is a fairlead cleat, and the immovable restraining element is formed as part of the fairlead cleat.

6. A vertebral connector according to any of Claims 4 or 5, wherein the two fairlead cleats are provided as part of the base or mounted on the base.

7. A vertebral connector according to Claim 6, wherein the two fairlead cleats run parallel or in opposite directions.

8. A vertebral connector according to any of Claims 4 - 8, further comprising an auxiliary restraining element comprising a loop-shaped barrier and / or a bridge running over the channel.

9. An apparatus or vertebral connector according to any preceding Claim, wherein the anchor comprises at least one screw for securing the base to the anterior segment of a vertebral body.

10. An apparatus or vertebral connector according to Claim 9, wherein the screw is formed as part of the base.

11. An apparatus or vertebral connector according to any of Claims 9 or 10, wherein the screw has a denser thread pitch towards the tip of the screw to act as a bicortical fix, and a less dense thread pitch at the body of the screw to better grip cancellous / medullary bone.

12. An apparatus or vertebral connector according to any of Claims 9 - 11, wherein the screw is coated, for example with hydroxyapatite, to encourage bonding with the vertebral body.

13. An apparatus or vertebral connector according to any of Claims 9 - 12, wherein the anchor further comprises a staple comprising at least one opening through which the screw may be received for securing the base on the staple to the anterior segment of a vertebral body, the staple further comprising spiked feet that embed within the vertebral body to minimise torsion of the vertebral connector in relation to that vertebral body when anchored.

14. An apparatus or vertebral connector according to Claim 13, wherein the staple is treated by coating the surface of the staple, for example with hydroxyapatite, or by roughening the surface of the staple to encourage bonding with the vertebral body.

15. An apparatus according to any of Claims 13 - 14 as dependent on any of Claims 1 - 3, wherein the staple includes one or more stops limiting how far a given cam-shaped member may pivot.

16. An apparatus according to Claim 15, wherein one or more blocker screws screwed through the staple are partially unscrewed from the staple to provide the one or more stops.

17. An apparatus or vertebral connector according to Claims 3, 8 or any Claim dependent thereupon, wherein the auxiliary restraining element comprises a loopshaped barrier and / or a bridge running over the channel.

18. An apparatus or vertebral connector according to Claim 17, wherein the auxiliary restraining element comprises a cap which additionally serves to reinforce the structural integrity of the vertebral connector.

19. An apparatus or vertebral connector according to Claim 18, wherein the cap comprises a rigid bubble providing structural rigidity to the vertebral connector without limiting the action of the cleat or the tether.

20. An apparatus or vertebral connector according to any of Claims 18 - 19, wherein the cap is deformable.

21. An apparatus or vertebral connector according to any of Claims 18 - 20, wherein the cap includes a plurality of feet adapted to removably fix the cap to the staple.

22. An apparatus or vertebral connector according to Claim 21, wherein the feet of the cap are resilient and formed with corresponding end portions, preferably fm- shaped or hook-shaped, that are slidable through corresponding slots in the staple to lock the cap to the staple, the cap being deformable to allow the end portions to subsequently unlock and pass back out through the slots.

23. An apparatus according to any of Claims 3 - 22, wherein the auxiliary restraining element is removable, and is tightenable towards the base without causing compressive forces that would otherwise damage the tether, to further prevent dislodgement of the tether while retaining the tether’s integrity.

24. An apparatus or vertebral connector according to any of Claims 3 - 23, wherein the auxiliary restraining element is immovable to mitigate the risks associated with over- or under-tightening of the tether.

25. An apparatus or vertebral connector according to any of Claims 3 - 24, wherein the auxiliary restraining element and / or the immovable restraining element provides a buttress for supporting the use of a tensioning device.

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