WO2008033457A2

WO2008033457A2 - Variable height vertebral body replacement implant

Info

Publication number: WO2008033457A2
Application number: PCT/US2007/019921
Authority: WO
Inventors: Ashok Biyani
Original assignee: The University Of Toledo
Priority date: 2006-09-14
Filing date: 2007-09-13
Publication date: 2008-03-20
Also published as: US8152852B2; US20090138083A1; WO2008033457A3

Abstract

A variable height vertebral body replacement implant used in corpectomy surgery to provide support in place of a removed or damaged vertebrae, and contain and compact bone graft material.

Description

VARIABLE HEIGHT VERTEBRAL BODY REPLACEMENT IMPLANT

Cross Reference to Related Applications

This application is based upon and claims the benefit of U.S. provisional application No. 60/844,887 filed September 14, 2006.

BACKGROUND OF THE INVENTION

This invention relates to the field of orthopedic surgery and more particularly to the area of spinal surgery. The present invention is a variable height vertebral body replacement implant and is designed to reconstruct the spinal column after part or all of a vertebral body has been removed. It consists of an open design, which is initially distracted and placed in the vertebral defect. Bone graft material is then placed in the cage like enclosure. Bone graft can be compacted within the cage as its open portion is completed.

SUMMARY OF THE INVENTION

The present invention is a variable height vertebral body replacement implant consisting of a top and bottom ring joined by telescoping rods. The variable length telescoping rods include a ratcheting mechanism for allowing the cage to be secured and released once implanted. Between the rings is a expandable mesh material that forms a three sided tubular cage. The mesh material has an opening on one side that allows for complete packing of the cage with bone graft material. After the bone graft is packed into the cage, a fourth lateral mesh wall is attached to the open side of the cage to form a completely contained cage structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the implant in its extended position. Fig. 2 shows the implant in its retracted position.

Fig. 3 is a sectional view taken through line 3-3 of Fig. 1 showing the removable cage wall. Fig. 4 is a view similar to Fig. 3 with the mesh insert in the installed position.

Fig. 5 is an expanded plan view of the mesh insert.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTfS)

Figs. 1-5 show the variable height vertebral body replacement implant of the present invention. The implant 10 has a first end ring 15 and a second end ring 19. A plurality of telescopically variable length rods 23 extend between the first end ring 15 and the second end ring 19. The telescoping rods 23 maintain the first and second end rings in generally parallel, spaced apart relationship. The first and second end rings are generally ovoid or rectangular in shape and are designed to engage the end plates of adjacent vertebrae. The first end ring 15 has a first engagement side 16 and the second end ring 19 has a second engagement side 20 wherein the first and second engagement sides are disposed to engage the adjacent vertebrae. A plurality of serrations or projections 27 can be positioned on the engagement sides of the first and second end rings to assist with securing the first and second end rings in the desired position with respect to the adjacent vertebrae. The end rings 15 and 19 as well as the telescoping rods 23 are made of titanium although other materials may be used for these components.

Four telescoping rods 23 maintain the first and second end rings in spaced apart relationship. As the first and second end rings are substantially rectangular in shape a telescoping rod 23 can be positioned at generally each corner of the first and second end rings. It should be understood that other shapes can be utilized for the first and second end rings. Shapes such as ovoid, trapezoid and other generally four sided shapes can be utilized for the end rings. The telescoping rods 23 are positioned on the end rings in a manner that allows the telescoping rods 23 to provide the necessary support for the end rings. This position for the telescoping rods will maintain the first end ring 15 and second end ring 19 in an aligned spaced apart relationship. A ratchet mechanism 31 is included on at least one of the telescoping rods 23 to allow the telescoping rod to be varied in length in finite increments and to maintain the telescoping rod in the desired position whereby the first and second end ring provide the desired spacing between adjacent vertebrae in the spine. It is desirable to include a ratchet mechanism 31 on at least two of the telescoping rods 23 to assist in maintaining the desired length of the implant or cage and to keep first and second end rings in an appropriate position. If two ratchet mechanisms 31 are utilized, it is preferable to place the ratchet mechanisms on telescoping rods 23 that are in diagonally opposed relationship in the implant 10. However, it should be understood that the number of ratchet mechanisms utilized in the implant 10 can be varied as long as the proper orientation for the first end ring 15 and second end ring 19 can be achieved and maintained to provide the proper spacing between the adjacent vertebrae in the spine. The ratchet mechanism 31 has a release feature to allow the telescoping rods 23 to be adjusted until just the proper length is achieved for providing the desired spacing between the adjacent vertebrae in the spine. A set screw 35 is provided on each telescoping rod 23 and the set screw 35 is utilized to releaseably lock the telescoping rod 23 in the desired position once the appropriate spacing has been achieved between the adjacent vertebrae.

The telescoping rods 23 can be straight or have a slight curvature depending on the configuration of the area of the spine that is being repaired. The objective is to have the implant generally conform with the shape of the spine in the area that is being repaired and to maintain the adjacent vertebrae in a position that is consistent with the normal location of the adjacent vertebrae in the spine before the injury. The telescoping rods 23 usually have a range of expansion up to 20 mm. If more expansion is needed, an implant with longer telescoping rods should be utilized.

An expandable mesh wall 41 is positioned to extend between the first end ring 15 and the second end ring 19. The mesh is usually made of titanium similar to the telescopic rods. The expandable mesh wall 41 defines an opening 45 for providing access to the interior of the implant 10. The mesh wall is interconnected with the four telescoping rods 23 to structurally support and assist in locating the mesh wall 41. To provide for expansion for the mesh wall, it may be desirable to secure one portion of the mesh wall to the first end ring 15 and to secure a second portion of the mesh wall 41 to the second end ring 19. The first and second portions of the mesh wall will extend to be in an overlapping relationship generally in the center of the implant 10. The overlap 43 (Fig. 2) for the first and second portions of the mesh wall is sufficient to allow for any expansion of the implant due to the extension of the telescoping rods 23. Usually, the mesh wall 41 extends substantially around three sides of the generally rectangular first and second end rings. The opening 45 defined by the mesh wall 41 is, therefore, usually one side wall that extends between the first end ring 15 and the second end ring 19.

A mesh insert 51 is releaseably secured to the two telescoping rods 23 on opposite sides of the opening 45 to cover the opening 45. The mesh insert 51 is made of the same general material as the mesh wall 41. The mesh insert 51 has a channel 52 positioned on each side of the insert. The channels provide strength to the mesh insert and the channels are designed to fit over and engage the telescoping rods 23. The mesh insert 51 has two holes 53 positioned at one end of the mesh insert and two slots 57 positioned in the opposite end of the mesh insert 51. The holes 53 and slots 57 are preferably located in the channels 52 located on each side of the mesh insert. A threaded projection 17 is positioned on each of the two telescoping rods 23 on opposite sides of the opening 45 adjacent the first end ring 15 so that the threaded projections extend in a direction that is substantially perpendicular to the telescoping rods 23. A threaded projection 21 is positioned on each of the two telescoping rods 23 on opposite sides of the opening near the second end ring 19 so that the threaded projections 21 extend in a direction that is substantially perpendicular to the telescoping rods 23. The threaded projections 17 are disposed to be in alignment with and engage the holes 53 in the mesh insert 51. The threaded projections 21 on rods 23 adjacent the second end ring 19 are disposed to be in alignment with and engage the slots 57 in the opposite end of the mesh insert 51. Nuts 25 can be threadingly positioned on the threaded projections 17 and the threaded projections 21 to releaseably secure the mesh insert 51 over the opening 45 in the mesh wall 41. The slots 57 in one end of the mesh insert 51 allow the mesh insert to accommodate expansion and contraction of the implant due to changes in the length of the telescoping rods 23. The lengths of the slots 57 are at least as long as the anticipated range of movement for the telescoping rods 23 and preferably are a little bit longer than the range of motion for the telescoping rods 23. The end of the mesh insert 51 that contains the slots 57 has section 59 that extends into the second end ring 19 a distance that is also sufficient to accommodate the range of motion for the telescoping rods 23. In this manner the mesh insert will be able to accommodate the expansion and contraction anticipated for the implant 10. It is also anticipated that slots could be positioned on each end of the mesh insert 51 to allow the mesh insert to accommodate variations in length of the implant 10 on either end of the mesh insert. If desired, the mesh insert 51 could be connected to the first and second end rings 15 and 19 rather than to the telescoping rods 23.

In operation the implant 10 is positioned in the body of a patient to provide the desired spacing when one or more vertebrae have been removed from the spine of the patient. The first end ring 15 and the second end ring 19 are positioned in a not completely extended orientation to allow the implant 10 to be more readily inserted into the proper location in the spine of the patient. Once the implant 10 is positioned between the adjacent vertebrae, the telescoping rods 23 can be advanced to engage the adjacent vertebrae and to position the adjacent vertebrae in the desired spatial relationship. The ratchet mechanism 31 is utilized to advance the telescoping rods 23 in small increments until the desired spacing between the adjacent vertebrae is achieved. Once the desired positioned for the first ring 15 and second ring 19 has been achieved, the set screws 35 on each telescoping rod 23 can be engaged to lock the telescoping rods in the desired position. Bone or bone graft material can then be positioned in the implant 10 through the opening 45 in the mesh wall 41. The bone or bone graft material normally completely fills the interior of the implant 10. Once the appropriate amount of bone or bone graft material is positioned in the implant 10, the mesh insert 51 is positioned on the threaded projections 17 and 21 and secured in position with nuts 25 to close the opening 45 in the mesh wall 41. The mesh insert 51 presses against the bone or bone graft material and acts to compact the bone or bone graft material in the interior of the implant 10. Compaction of the bone or bone graft material assist in the fusing of the bone or bone graft material with the adjacent vertebrae to complete the surgical repair of the spine.

The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications other than those cited can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims.

Claims

CLAIMSI claim:

1. A variable height vertebral implant comprising: a first end ring and a second end ring positioned in spaced apart relationship, the first and second end rings being disposed to engage adjacent spaced apart vertebrae; a plurality of telescopically variable length rods extending between the first and second end rings, the plurality of rods being adjustable in length to provide the desired spacing between the first and second rings to engage the adjacent spaced apart vertebrae, at least one of the telescopically variable length rods including a ratchet mechanism for releasably securing the at least one telescopically variable length rod in a fixed position; an expandable mesh wall extending between the first and second rings, the mesh wall defining an opening for providing access to the interior of the vertebral implant; and a mesh insert that is releasably secured to the variable length rods or the first and second rings whereby the mesh insert covers the opening in the mesh wall.

2. The implant of claim 1 wherein bone material is positioned through the opening in the mesh wall into an interior chamber defined by the wall of the implant whereby the bone material extends between the spaced apart adjacent vertebrae.

3. The implant of claim 2 wherein the mesh insert is secured to the variable length rods or the first and second rings after the bone material is positioned in the interior chamber of the implant, the mesh insert being disposed to engage the bone material and to compact the bone material.

4. The implant of claim 1 further including projections extending from said first and second rings for engagement with said spaced apart vertebrae.

5. The implant of claim 1 wherein said mesh insert is releasably secured to the variable length rods by means comprising (a) projections extending outwardly from said rods and (b) openings in said mesh insert positioned to receive said projections, at least two of said openings defining elongated slots to accommodate movement of said variable length rods.

6. A method for performing vertebrae surgery comprising the steps of:

(a) providing an implant member having a variable length wall, said wall defining a part of chamber and extending from a first end to a second end, said wall having an opening for receiving bone graft material;

(b) expanding said wall lengthwise to lengthen the distance between said first end and said second end whereby said first and second ends will engage spaced apart portions of said vertebrae;

(c) introducing bone graft material into partial chamber; and (d) engaging an insert to said wall member to complete the encircling of said bone graft material.