WO2003103519A2

WO2003103519A2 - Device

Info

Publication number: WO2003103519A2
Application number: PCT/GB2003/002465
Authority: WO
Inventors: Douglas Wardlaw
Original assignee: Grampian University Hospitals Nhs Trust
Priority date: 2002-06-06
Filing date: 2003-06-06
Publication date: 2003-12-18
Also published as: AU2003274778A8; WO2003103519A3; AU2003274778A1; GB0212948D0

Abstract

A device for supporting bones is described. The device includes a tensioning means adapted to pull a portion of a first bone towards a second bone. In preferred embodiments, a spacer device can be used in combination with the support device, to resist the tensioning action of the support device.

Description

"Device"

This invention relates to a device for supporting bones, and is particularly useful for supporting spinal vertebrae.

The deterioration of inter-vertebral discs is a common cause of back pain. Current solutions favour the attachment of pedicle screws or other fixings to the posterior surfaces of the pedicles of adjacent vertebrae, and the permanent inter-connection of the screws by means of a rigid metal frame, or by a braid. The connections between the screws are tensioned typically to a force of around 50N, and this locks the facets of the adjacent vertebrae, thereby stabilising the spine.

According to the present invention there is provided a device for supporting a bone, the device comprising a primary connector for attachment to a first bone, at least one secondary connector for attachment to a second bone, and a tensioning device for applying tension between the primary and secondary connectors, wherein at least one of the connectors has a hook for connection to its respective bone.

Typically the connectors are generally U-shaped, and can hook over the bones to be connected, typically without requiring a fixing means to be driven into the bone, although the device can be used with such fixings if desired. In preferred embodiments of the invention, at least one of the connectors has a connector formation for attaching the tensioning device, and preferably at least one of the connectors has a locking device such as a clamp for locking the tensioning device when the desired tension has been achieved.

The tensioning device can be a wire, braid, or similar, and is typically pre-stretched so as to maintain the tension applied to it.

In an especially preferred embodiment of the invention, the primary connector is generally in the form of a U-shaped hook that is adapted to hook around the bone, and at the apex of the hook, the first connector typically has a hinged portion to allow the two arms of the U-shaped hook to move towards and away from one another. The hinged portion can either be a mechanical hinge with an axle around which the two arms of the U-shaped hook are freely movable, or can simply be a passive hinge in the form of a part of the apex which is adapted to bend or flex slightly to allow the movement of the arms. The hinge may include another point on the device apart from the apex, for example, the arms of the hook may be inherently resilient. The movement of the arms of the U-shaped hook towards and away from one another enables the first connector to deform slightly to open the U-shaped hook when the primary connector is being fitted around the bone, so as to fit the primary connector more securely to the bone, and importantly, to deform slightly under the force applied by the tensioning device in order to close the hook around the bone, and to use the force applied by the tensioning device to grip the bone to prevent or restrict movement of the connector relative to the bone.

Certain preferred embodiments of the invention are designed for use in supporting spinal vertebrae. Typically, the primary connector is adapted to attach to a spinous process of a first vertebra and the secondary connector (s) is/are adapted to attach to the laminae of a second vertebra directly below and adjacent to the first vertebra. Alternatively, the secondary connector (s) is/are adapted to attach to the spinous process of the second vertebra. This may be done, for example, by forming the primary connector and the secondary connector as U-shaped hooks and hooking the primary connector over the upper surface of the first vertebra and hooking the secondary connector over the lower surface of the second vertebra. The ability to deform the U-shaped hook around the bone in order to grip it is particularly useful when the connectors are hooked around adjacent vertebrae, because the spinous process protrudes from the posterior surface of the spine at an angle of approximately 79°, and simple hooks adapted to fit around the spinous process without any means to maintain the hook in position can tend to be moved out of position on the spinous process when force is applied by the tensioning device.

In some embodiments, the tensioning device can comprise several braids or wires etc, that can run between connection posts or other attachment means on the respective connectors, so that a separate wire or braid runs on each side of the spinous process. However, in other embodiments, a single wire or braid runs from a connection post on a secondary connector, optionally through a channel or notch on the primary connector, and back to a connection post or locking device on the same or different secondary connector, so that the force applied by the tensioning device is equalised between the two sides of the U-shaped connectors. In such embodiments, the notch typically extends along the length of the primary U-shaped connector, and is optionally smooth or coated with a low friction surface in order to permit the wire or braid to move freely relative to the first connector.

The invention further provides a bone support system comprising:

a device for supporting a bone, comprising a primary connector for attachment to a first bone, at least one secondary connector for attachment to a second bone, and a tensioning device for applying tension between the primary and secondary connectors, wherein at least one of the primary and secondary connectors has a hook for connection to the bone; and a spacer adapted to maintain the relative position of the first and second bones against the action of the tensioning device.

Typically, the spacer device is adapted to be inserted between the first and second bones.

Preferably, the spacer has co-operating surfaces profiled for engaging the first and second bones.

Preferably, the spacer has at least one retaining member adapted to hold the spacer between the first and second bones.

Preferably, the spacer is made from a resilient material such as silicon, polyurethane or another material with elastic or visco-elastic properties.

Typically, the first and second bones comprise adjacent spinal vertebrae and the spacer includes a spindle having a diameter substantially equal to the gap between adjacent spinous processes and a concave radial surface for co-operation with adjacent spinous processes of the first and second bones.

Preferably, two elongate retaining members are provided for attachment to both ends of the spindle, the end-to-end dimension of which is substantially the same as the width of the spinous processes, so that when the spacer is assembled and positioned between the spinous processes, the retaining members overlap and frictionally engage the spinous processes on each bone.

The invention also provides a method of supporting a bone comprising attaching a primary connector to a first bone, attaching at least one secondary connector to a second bone, and connecting a tensioning device between the primary and secondary connectors, wherein at least one of the primary and secondary connectors is hooked around the bone.

Typically, the method also includes the step of using a spacer device to maintain the relative position of the first and second bones against the action of the tensioning device.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

Fig 1 shows a posterior view of a spine with a first embodiment of a support device attached; Fig 2 shows a schematic side view of a spine with a second embodiment of a support device attached; Fig 3 shows a perspective view of a further embodiment of a support device; Fig 4 shows a plan view of a spacer device inserted between two adjacent spinous processes; Fig 5 shows a side view of the spacer device and spinous processes of Fig 4; Fig 6 shows a posterior view of a spine with another alternative embodiment of a support device attached; Fig 7 shows a side view of the arrangement of Fig 6 ; Fig 8 shows a posterior view of a spine with the support device of Fig 6 and the spacer device of Fig 4; and Fig 9 shows a side view of the arrangement of Fig 8.

Referring now to the drawings, a first embodiment of a support device has a U-shaped first connector 1 that is hooked over the upper surface of a spinous process SP. The first connector 1 has a pair of arms 2 extending from the apex of 3 of the connector. The arms 2 extend over the sides of the spinous process. The arms 2 extend laterally outwards from the spinous process SP and carry pegs 5 that extend perpendicular to the plane of the arms 2. The apex 3 of the first connector 1 has a weakened portion that facilitates flexing of the arms 2 towards and away from one another. The weakened portion can simply comprise a part at the apex 3 of reduced cross-section, or can comprise a notch or other such formation adapted to encourage flexing at that point and to act as a hinge. Alternatively, a structural hinge can be inserted at the apex to connect entirely separate arms together by means of an axle etc (not shown) .

The first embodiment has a pair of second connectors 10, each of which are in the form of a U-shaped hook with a pair of arms adapted to hook around the lower surfaces of each of the laminae of the vertebra below the vertebra to which the first connector 1 is attached. The second connectors 10 each have a peg 15 that extends away from the arms of each second connector 10 so that in use, the pegs 15 are generally parallel to the pegs 5.

Each peg 15 is attached to the peg 5 on the same side of the spinous process by means of a braid 20 that is tensioned before being fixed by a crimp so as to exert a force of around 50N between the first and second connectors 1,10.

Referring now to fig 2, a modified embodiment of a support device is shown having a first connector 30 in the form of a U-shaped hook that is hooked over the upper surface of a spinous process. The first connector 30 has a pair of arms 32 extending from the apex 33 of the first connector 30 and over the sides of the spinous process. The first connector 30 has a notch 30n running over one arm 32, over the apex 33 and over the other arm 32. The apex 33 of the first connector 30 has a part with reduced . cross-section to provide a weakened portion to facilitate flexing of the arms 32 towards or away from one another.

A pair of second connectors 10 similar to those described for the first embodiment are also used in the second embodiment shown in fig 2, and will not be described further.

A tensioning device in the form of a braid 35 extends from the peg 15 on one of the second connectors 10, over the surface of one arm 32 of the first connector 30, over the apex 33 of the first connector 30, and over the other arm 32, before being attached to the peg 15 on the other second connector 10. While the braid passes over the first connector 30, it is located in the notch 3 On. Tensioning of the braid 35 before attachment to the peg 15 of the second connector 10 draws the two vertebrae together and as before, it is preferred that a force of around 5ON is applied by the braid 35 before it is tied off. In addition to applying the force to stabilise the vertebrae in relation to one another, the force applied by the braid 35 also pulls the two arms 32 of the first connector 30 towards one another so as to grip the spinous process between the two arms 32, and prevent or restrict movement of the first connector 30 on the spinous process as a result of the force applied to it by the braid 35. If desired, the inner surface of the first or second connector can be provided with a high friction material so as to reduce slippage of the connector relative to the bone.

Referring now to fig 3, a further embodiment of a support device has a first connector 40, again in the form of a U-shaped hook that is adapted to be hooked over the upper surface of a spinous process as described for the previous embodiments. The first connector 40 has a pair of arms 42, an apex 43 with a weakened portion adapted to promote flexing of arms 42, and a notch 40n for guiding a braid 35 as previously described. In the fig 3 embodiment, the second connectors are rather different from those previously described, in that they comprise U- shaped hooks having arms 52, 54, and respective apexes 53. One of the second connectors 50 has an anchor 50a for anchoring the braid 35 which passes through a conduit in the upper arm 52 before terminating in an anchor (not shown) that is trapped within the conduit. The braid 35 extends from the connector 50 over the first connector 40, with the braid 35 being guided over the first connector 40 by the notch 4On as previously described, before passing to the other of the second connectors 51, on which it is anchored by a clamp plate 55 that is secured in position by means of a bolt 56 after the braid 35 has been tensioned to the appropriate extent (typically 50N) . The braid can be passed around the bolt in a clockwise direction before the bolt is tightened so that tension on the braid in use will tighten rather than loosen the bolt. In a similar manner to previous embodiments, the tensioning of the braid 35 draws the vertebrae together to lock the facets and support the vertebrae relative to one another. In addition, the tensioning of the braid also pulls the arms 42 of the first connector 40 tighter together around the spinous process, thereby preventing or resisting slippage of the first connector 40 relative to the spinous process .

Referring now to Figs 6 and 7, a yet further embodiment of support device has a first connector 80, second connectors 90, 91 and braid 35. The first connector 80 is similar to the connector 40 from the Fig 3 embodiment, comprising a U-shaped hook having arms 82, apex 83 and a weakened portion to promote flexing of arms 82. Respective eyelets 84 are provided in each arm 82 and apex 83, dimensioned to accommodate braid 35. Second connectors 90, 91 are also similar to connectors 50, 51 of the Fig 3 embodiment, comprising U-shaped hooks having arms 92, 94 and respective apexes 93. Second connector 90 has an interior bore linking apertures in arm 92 and apex 93 for insertion of braid 35. Optionally, one end of braid 35 may be provided with an anchor of greater dimension than the diameter of the interior bore of second connector 90. However, braid 35 can be permanently connected to second connector 90 by any suitable attachment means, e.g. braid 35 may be attached inside the interior bore. The other second connector 91 has a first interior bore connecting apertures 97, 98 in arm 92 and apex 93 respectively. Connector 91 also has a substantially cuboid extension 100, which extends out of apex 93, the longitudinal axis of which being approximately aligned with the first interior bore.

A second interior bore in second connector 91 is provided along the longitudinal axis of cuboid extension 100, connecting apertures 102, 104 in each end of extension 100. First and second interior bores are dimensioned to accommodate braid 35. Optionally, at least one of the first and second interior bores of second connector 91 is provided with a locking device, such as an internal cleat in the second bore (not shown) , which allows braid 35 to pass through the bore in one direction only and locks braid 35 against reverse movement. Typically, the locking device is self-locking. Optionally, the locking device comprises a crimp, although an external crimp can be applied to the braid in addition to an internal locking cleat in the bore of a connector.

In use, braid 35 is anchored into second connector 90 and threaded through eyelets 84 in first connector 80, typically before the support device is attached to the patient's spine. This eases insertion of the support device and reduces the time needed for the surgery.

Then, a hole is formed through the interspinous ligament just above a first vertebra 81, to which the first connector 80 will later be attached. The end of braid 35 which has been threaded through eyelets 84 in first connector 80 is then pulled through the hole in the interspinous ligament and first connector 80 is positioned astride the hole with arms 82 arranged on opposite sides of the spinous process of first vertebra 81, as shown in Figs 6 and 7. Second connectors 90, 91 are then hooked around the laminae of a second vertebra 99 directly below first vertebra 81. Braid 35 is then tensioned and threaded through the first interior bore in second connector 91 from aperture 97 to aperture 98 and then threaded through the second interior bore from aperture 104 to 102. The jagged interior edges of the cleat in the second interior bore grip the braid 35 to prevent reverse movement of braid 35 back through the second interior bore. Due to the first and second bores being aligned with one another, braid 35 is doubled back on itself when threaded through connector 91, which helps to secure braid 35 against further movement in the bores.

Figs 4 and 5 show an interspinous process spacer 60 having a spindle 62 and two retaining wings 64. The interspinous process spacer 60 is positioned between two adjacent spinous processes SP. The spindle 62 is generally cylindrical but with an oval cross- section. The outer radial surface of spindle 62 is preferably concave; i.e. the radius of spindle 62 is narrowest in the middle and widens towards both ends, so that spindle 62 resembles a pulley wheel. Elongate retaining wings 64 attach to each flat end of spindle 62, with the longer sides of each wing 64 rotationally aligned with one another, so that in the Fig 5 view, one retaining wing 64 is completely obscured by the other. The longer sides of the oval cross-section of spindle 62L are orientated perpendicular to the longer sides of the retaining wings 64L.

The spacer 60 is shaped so as to closely engage adjacent spinous processes SP, as best shown in Fig 4. The concave radial surface of the spindle 62 is shaped to co-operate with the front and back ends of the spinous processes SP and the length of spindle 62 (and hence the distance between the retaining rings 64) is just slightly greater than the width of spinous processes SP.

In this embodiment, one of the retaining wings 64 is permanently attached to spindle 62, whereas the other is provided with an aperture for insertion of a screw (not shown) to attach it to spindle 62, which has a co-operating axial aperture.

Spacer 60 is typically made of a visco-elastic material such as silicon, polyurethane or another material with elastic or visco-elastic properties that is able to compress or deform slightly under a compressive force.

In use, spindle 62 and the attached retaining wing 64 are attached to an introducer and inserted between two adjacent spinous processes SP, typically via a small hole made with a trochar through the base of the interspinous ligament 66 . The spindle 62 and retaining wing 64 are oriented so that the longer sides of elongate retaining wing 64 (and therefore also the shorter sides of the oval cross- section of the spindle 62) are parallel to the spinal column. The other retaining wing 64 is then attached to the opposite side of spindle 62 by a screw device 70.

The spacer 60 will thus be held in position by the elongate retaining wings 64 engaging the sides of spinous processes SP, and the longer, flatter sides of the oval cross-section of spindle 62 engaging the ends of the spinous processes SP. Spacer 60 maintains the relative spacing of the spinous processes SP and prevents them from being pulled too closely together. The elastic properties of spacer 60 allow it to deform slightly when compressed between the spinous processes SP.

Spacer 60 is especially useful when used in conjunction with spinal support devices such as those of Figs 1 to 3 and Figs 6 and 7, as these support devices will tend to pull the adjacent spinous processes together, which locks the spinal segment in extension. Figs 8 and 9 show two different views of a part of a spinal column with spacer 60 positioned between two spinal vertebrae in addition to the support device of the Figs 6 and 7 embodiment. The addition of spacer 60 will hold the spinal segment in a neutral position against the tensioning action of a support device. This can avoid the unfortunate effects of locking the spinal segment in extension, which include narrowing the spinal canal, root irritation and root compression. Although the spinal segment is not locked in extension (which would block all rotational movement), the braids 20, 35 will resist rotation and protect the spinal segment from rotational stresses. The spacer will also support the posterior annulus, thereby reducing loading on the posterior annulus; this will reduce pain and promote healing.

Modifications and improvements can be incorporated without departing from the scope of the invention. For example, the secondary connectors do not necessarily have to be attached to the laminae of the vertebra below the vertebra to which the first connector is attached; instead there could be only one secondary connector adapted to attach to (e.g. hook around) the spinous process of that lower vertebra. In such an embodiment, the primary and secondary connectors could be of the same design as connector 80.

The support device may be used without the spacer device. The design of spacer device is not limited to the pictured embodiment. For example, the spacer device could be formed to fit very closely between the upper and lower surfaces of adjacent spinous processes so as to engage therewith by friction alone, thereby obviating the need for any retaining wings .

In the Fig 6 and Fig 7 embodiment, the particular design shown of apertures and extension 100 is not fundamental. For example, apertures 95, 96 are not necessary, provided that braid 35 is attachable by some means to connector 90. The interior bore of connector 90 could extend through a different part of connector 90, e.g. through arm 92 alone and not through any part of apex 93. Similar considerations apply to the interior bores of connector 91.

In the Fig 6 and Fig 7 embodiment, as an alternative to the locking device, a fixing device of greater diameter than the second interior bore of connector 91 could be attached (e.g. screwed) to the end of braid 35 after it has been threaded through the first and second interior bores and suitably tensioned. As the fixing device has a greater diameter than the second interior bore, this would prevent reverse movement of braid 35 back through the bore.

Claims

"Claims "

1. A device for supporting a bone, the device comprising a primary connector for attachment to a first bone, at least one secondary connector for attachment to a second bone, and a tensioning device for applying tension between the primary and secondary connectors, wherein at least one of the connectors has a hook for connection to its respective bone.

2. A device as claimed in claim 1, wherein all of the primary and secondary connectors have hooks for connection to their respective bones.

3. A device as claimed in claim 1 or claim 2, wherein at least one of the primary and secondary connectors is U-shaped to hook over its respective bone.

4. A device as claimed in any preceding claim, wherein the primary connector is adapted to deform around the first bone to grip the bone.

5. A device as claimed in any preceding claim, wherein the primary connector comprises a U-shaped hook adapted to hook around the bone, and wherein at least one part of the hook is adapted to flex to allow relative movement of the hook arms.

6. A device as claimed in claim 5, wherein the apex of the hook has a hinged portion to allow relative movement of the hook arms .

7. A device as claimed in claim 5 or claim 6, wherein the tensioning device is adapted to pull the hook arms into gripping contact with the bone to prevent or restrict relative movement of the primary connector and the bone .

8. A device as claimed in any preceding claim, adapted for use in supporting spinal vertebrae.

9. A device as claimed in claim 8, wherein the primary and secondary connectors are adapted to attach respectively to the spinal process and laminae of adjacent spinal vertebrae.

10. A device as claimed in claim 8, wherein the primary and secondary connectors are adapted to attach to the spinous processes of adjacent spinal vertebrae.

11. A device as claimed in any preceding claim, wherein the tensioning device comprises at least one elongate member adapted to run between attachment means on the connectors, and wherein the elongate member comprises a braid or a wire.

12. A device as claimed in claim 11, wherein two secondary connectors are provided, and a separate elongate member attaches each secondary connector to the primary connector.

13. A device as claimed in claim 11, wherein two secondary connectors are provided and a single elongate member is adapted to run from a first attachment means on the first secondary connector, to the primary connector and back to a second attachment means on the second secondary connector, so that the force applied by the tensioning device is equalised between the two sides of the primary connector.

14. A device as claimed in any of claims 11 to 13, wherein the elongate member is disposed in a passage extending along the length of the primary connector, the passage comprising a notch or a groove.

15. A device as claimed in claim 14, wherein the passage is smooth to facilitate relative movement of the tensioning device and the primary connector.

16. A device as claimed in claim 15, wherein the passage is coated with a low friction surface.

17. A device as claimed in any preceding claim, wherein the tensioning device is pre-stretched.

18. A device as claimed in any preceding claim, wherein at least one of the connectors is provided with a locking device for attaching and locking the tensioning device when the desired tension has been achieved.

19. A device as claimed in claim 18, wherein the locking device is self-locking to automatically lock the tensioning device against reverse movement on engagement of the tensioning device with the locking device.

20. A device as claimed in claim 18 or claim 19, wherein the locking device comprises a cleat.

21. A device as claimed in any preceding claim, wherein at least a portion of the- primary connector is inherently resilient.

22. A method of supporting a bone comprising attaching a primary connector to a first bone, attaching at least one secondary connector to a second bone, connecting a tensioning device between the primary and secondary connectors, and tensioning the tensioning device; wherein at least one of the primary and secondary connectors is hooked around the bone.

23. A support system for a bone comprising:

a device for supporting a bone, comprising a primary connector for attachment to a first bone, at least one secondary connector for attachment to a second bone, and a tensioning device for applying tension between the primary and secondary connectors, wherein at least one of the primary and secondary connectors has a hook for connection to the bone; and a spacer device adapted to maintain the relative position of the first and second bones against the action of the tensioning device.

24. A support system as claimed in claim 23, wherein the spacer device is adapted to be inserted between the first and second bones.

25. A support system as claimed in claim 23 or claim 24, wherein the spacer has co-operating surfaces profiled for engaging the first and second bones.

26. A support system as claimed in claim 25, wherein the co-operating surfaces of the spacer are adapted to fit closely with the respective surfaces of the first and second bones, so that when in position, the spacer is retained between the first and second bones by friction.

27. A support system as claimed in any of claims 23 to 26, wherein the spacer has at least one retaining member adapted to hold the spacer between the first and second bones.

28. A support system as claimed in any of claims 23 to 27, wherein the spacer is made from an elastic or visco-elastic material.

29. A support system as claimed in any of claims 23 to 28, wherein the first and second bones comprise adjacent spinal vertebrae and the spacer includes a spindle having a diameter substantially equal to the gap between adjacent spinous processes and a concave radial surface for co-operation with adjacent spinous processes of the first and second bones.

30. A support system as claimed in claim 29, wherein two elongate retaining members are provided for attachment to both ends of the spindle, the end- to-end dimension of which is substantially the same as the width of the spinous processes, so that when the spacer is assembled and positioned between the spinous processes, the retaining members overlap and frictionally engage the spinous processes on each bone .