WO2001097744A2

WO2001097744A2 - Expandable vertebral replacement prosthesis

Info

Publication number: WO2001097744A2
Application number: PCT/US2001/040847
Authority: WO
Inventors: M. Laine Mashburn
Original assignee: Sdgi Holdings, Inc.
Priority date: 2000-06-19
Filing date: 2001-06-05
Publication date: 2001-12-27
Also published as: AU2001267027A1; WO2001097744A3

Abstract

A vertebral prosthesis has a central body (8) with oppositely threaded holes (11a, 11b) in each end and smaller threaded apertures (19) around the side of the central body that open into them. A support member (9, 10) is threaded into each of the holes. Each support member has an oval-shaped plate with a complementary threaded shaft on one side to mate with the holes in the central body. The prosthesis operates like a turnbuckle, expanding when the central body is rotated in one direction and contracting when the central body is rotated in the opposite direction. Once the device is set at its proper length, a setscrew is tightly threaded into at least one aperture at each end of the central body to compress against the side of the shaft on the support members and hold device at a fixed length.

Description

EXPANDABLEVERTEBRALREPLACEMENTPROSTHESIS

This application claims priority to provisional application 60/139,666 filed 17 June 1999 in the United States Patent and Trademark Office.

This invention relates to a prosthesis for the replacement of a vertebra, and more particularly relates to such a prosthesis with oval-shaped support plates to contact adjacent vertebrae.

BACKGROUND

Anterolateral decompression by partially or totally resecting a vertebral body is a common technique to treat certain tumors, trauma and degenerative problems of the spine. But resection typically causes instability, and correcting the instability generally requires the spine to be reconstructed so that it is again capable of supporting the patient's weight and movement. One technique is to replace the damaged or diseased vertebra with a prosthesis. Such largely experimental prostheses, however, have proved to be clinically unworkable for this purpose or they are generally limited to use in the middle axial section of the vertebrae. What is needed is a vertebral prosthesis that can be used to reconstruct or replace an entire vertebral body and the following invention is one solution to that need.

SUMMARY OF THE INVENTION

In one aspect, this invention is a prosthetic device for stabilizing the spine where a portion of the spine has been removed. The prosthesis has a central body with oppositely threaded holes in each end, and smaller threaded apertures in its side that open into the threaded holes. A support member is threaded into each of the holes. Each support member has an oval-shaped plate with a threaded shaft on one side. The shafts have threads cut in opposite directions so that the device expands when the central body is turned in one direction and contracts when the central body is turned in the opposite direction, thusly operating similarly to a common turnbuckle. Once the device is set at its proper length, a set screw is threaded into at least one of the apertures opening to the shaft on each support member, which are then tightened against the shafts to hold the device at a fixed length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A is a side view of prosthesis in a typical installation according to one embodiment of the invention. FIG. 1 is a side exploded view of one embodiment of the invention.

FIGs. 2 and 3 are side views of one embodiment of the invention. FIGs. 4 and 5 are side and cross-sectional views of the central body according to one embodiment of the invention.

FIGs. 6, 7, 8 and 9 are side, bottom, top and cross-sectional views of the support plates according to one embodiment of the invention.

FIGs. 10 and 11 are end and side views of setscrews used in one embodiment of the invention.

FIGs. 12, 13, 14, 15, 16 and 17 are side views of successive steps in the use of one embodiment of the invention. FIGs. 18 and 19 are side views of the invention used with other supporting structures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated being contemplated as would normally occur to one skilled in the art to which the invention relates. Referring to FIGs. 1A and 1-3, there is shown a vertebral prosthesis 1 according to one embodiment of this invention. Prosthesis 1 includes a rigid, hollow central body 8, upper support platform 9, lower support platform 10, upper set screw 4, and lower set screw 5. Hollow central body 8 is generally cylindrical in shape and is preferably in the range of around twenty millimeters in diameter. And preferably, vertebral prosthesis 1 is entirely made of titanium for its strength, compatibility with human tissue, and its post-operative imaging properties.

Referring to FIG. 4, the superior face 101 and the inferior face 102 of central body 8, respectively contain threaded holes 11A and 11B that preferably extend about ten millimeters into central body 8. Notably, threaded holes 11A and 1 IB are threaded in opposite directions, that is, one is cut with right-hand threads and the other is cut with left-hand threads. The waist section 12 of central body 8 preferably has a hexagonally shaped cross-section to provide flat surfaces on which, if necessary, a surgeon may engage an instrument.

Support platforms 9 and 10 are respectively attached to superior face 101 and inferior face 102 of central body 8. Referring to FIGs. 7 and 8, each platform is preferably oval shaped so that it may reside within the lateral limits or footprint of the vertebrae located above and below prosthesis 1. By residing within the perimeter of these vertebrae, support platforms 9 and 10 avoid injuring surrounding blood vessels and other soft tissue. The distal face 103 of platforms 9 and 10 is covered with teeth 14 to accomplish a controlled biting action that provides a secure attachment to vertebrae and provides shear resistance without compromising the vertebrae. Preferably, each tooth 14 is cut at a 90° angle and a 1.7 millimeter depth. Referring to FIG. 9, optionally either or both of platforms 9 and 10 may have a posterior-to-anterior elevation 15 to accommodate varying anatomies, preferably between 0.5 and 4.5 degrees from the horizontal, but more preferably about 2.5 degrees from the horizontal. Referring to FIGs. 6 and 7, the proximal face 104 of platforms 9 and 10 is integrally attached to a cylindrical central shaft 16, the exterior of which is covered with complementary threads 17 to engage holes 11 A and 1 IB. Particularly, one set of threads is left-handed and the other is right-handed. In one preferable arrangement, shaft 16 is perpendicularly mounted to each platform (FIG. 6) as well as centrally located on each (FIG. 7). An arrangement commonly called a turnbuckle is formed when the left- hand threaded platform and the right-handed threaded platform are respectively threaded into the left and right-handed threaded holes in central body 8. When central body 8 is rotated in one direction with respect to platforms 9 and 10, the shaft 16 of each platform simultaneously move axially outward to extend the overall height of vertebral prosthesis 1. When central body 8 is rotated in the opposite direction, the shaft 16 of each platform simultaneously retracts into the central body 8 to shorten the overall height of vertebral prosthesis 1. This mechanism enables prosthesis 1 to be expeditiously inserted into the spine and adjusted to correct kyphotic deformities and to replicate physiological support and load transmission against adjacent vertebrae.

Referring to FIGs. 4 & 5, multiple small threaded apertures 19 are provided around the sides of central body 8. These apertures open into either hole 11A or 11B. After rotating central body 8 and setting vertebral prosthesis 1 to the desired height, hexagonal setscrews 4 and 5 are threaded into apertures 19 at each end of central body 8. Set screws 4 and 5 compress against shaft 16 and thereby lock vertebral prosthesis 1 to a desired height. Set screws 4 and 5 are preferably of the socket type (FIGs. 10 and 11) to securely engage the screw driver and help prevent the screw driver from inadvertently slipping from the set screw. Referring back to FIGs. 1 and 4, a third group of apertures 20 are located through hexagonal waist section 12. These apertures are adapted to accept instrument 21 (FIGs. 14 and 15) to rotate central body 8 about its axis. Instrument 21 has an extended tip to insert into apertures 20, and thereby generate a vertical movement when central body 8 is rotated by pulling or pushing instrument 21 around the axis of central body 8. Optionally, apertures 20 are also threaded to accept a threaded tipped instrument, not shown, to engage and retrieve vertebral prosthesis 1 after it has been positioned.

The use of the present invention is shown in FIGs. 12-19. In a first step (FIG. 12), the pathologic vertebral body is removed. While in the contracted position, vertebral prosthesis 1 is inserted in the spine where the pathologic vertebral body was previously located (FIG. 13). In a third step, vertebral prosthesis 1 is vertically expanded by engaging instrument 21 into a waist aperture 20 and thereby rotating central body 8 about its axis. In a next step, the expansion height is verified with special calipers 3 (FIG. 16), and when properly extended, vertebral prosthesis 1 is locked by tightening set screws 4 and 5 against the cylindrical shaft 16 at each end of central body 8 (FIG. 17). In a final intraoperative step, an anterior plate 6 or a posterior rod assembly 7 is fastened onto the adjacent superior and inferior vertebrae (FIGs. 18 and 19).

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

The claimed invention is:

1. A prosthetic device for stabilizing the spine where vertebral bodies have been removed comprising: a cylindrical central body having a longitudinal surface and first and second ends, said first end having a right-handed threaded hole therein and said second end having a left-handed threaded hole therein; said longitudinal surface having a first threaded aperture opening into the right-handed threaded hole and a second threaded aperture opening into the left-handed threaded hole; a first support member having a proximal face and a distal face, the proximal face having a right-handed threaded shaft laterally projecting therefrom, said right-handed threaded shaft threadedly coupled to the right-handed threaded hole in said central body; a second support member having a proximal face and a distal face, the proximal face having a left-handed threaded shaft laterally projecting therefrom, said left-handed threaded shaft threadedly coupled to the left-handed threaded hole in said central body; at least one of the distal face of said first support member and the distal face of said second support member having an oval shape; and a first set screw threadedly engageable into said first threaded aperture and a second set screw threadedly engageable into said second threaded aperture.

2. The prosthetic device of claim 1, wherein the distal faces of said first and second support members have pyramid-shaped teeth uniformly placed over the entire surface.

3. The prosthetic device of claim 2, wherein each of said pyramid- shaped teeth has an apex angle between the opposite sides of each tooth ranging from 80 degrees to 100 degrees.

4. The prosthetic device of claim 3, wherein the apex angle is about 90 degrees.

5. The prosthetic device of claim 1, wherein at least one of the distal face of said first support member and the distal face of said second support member is between from 0.5 to 4.5 degrees from being perpendicular to the axis of the threaded holes in the first and second ends of said cylindrical body.

6. The prosthetic device of claim 5, wherein at least one of the distal face of said first support member and the distal face of said second support member is about 2.5 degrees from being perpendicular to the axis of the threaded holes in the first and second ends of said cylindrical body.

7. The prosthetic device of claim 1, wherein said prosthetic device is made of titanium.

8. A prosthetic device for stabilizing the spine where vertebral bodies have been removed comprising: a cylindrical central body having a longitudinal surface and first and second ends, said first end having a right-handed threaded hole therein and said second end having a left-handed threaded hole therein; said longitudinal surface having a first threaded aperture opening into the right-handed threaded hole and a second threaded aperture opening into the left-handed threaded hole; a first support member having a proximal face and a distal face, the proximal face having a right-handed threaded shaft laterally projecting therefrom, said right-handed threaded shaft threadedly coupled to the right-handed threaded hole in said central body, said distal face of said first support member having an oval shape; a second support member having a proximal face and a distal face, the proximal face having a left-handed threaded shaft laterally projecting therefrom, said left-handed threaded shaft threadedly coupled to the left-handed threaded hole in said central body, said distal face of said first support member having an oval shape; a first set screw threadedly engageable into said first threaded aperture and a second set screw threadedly engageable into said second threaded aperture; and the distal faces of said first and second support members have pyramid- shaped teeth uniformly placed over at least 80% of the surface area of each distal face, and wherein each of said pyramid-shaped teeth has an apex angle between the opposite sides of each tooth ranging from 80 degrees to 100 degrees.

9. The prosthetic device of claim 8, wherein the apex angle is about 90 degrees.

10. The prosthetic device of claim 8, wherein at least one of the distal face of said first support member and the distal face of said second support member is between from 0.5 to 4.5 degrees from being perpendicular to the axis of the threaded holes in the first and second ends of said cylindrical body.

11. The prosthetic device of claim 10, wherein at least one of the distal face of said first support member and the distal face of said second support member is about 2.5 degrees from being perpendicular to the axis of the threaded holes in the first and second ends of said cylindrical body.

12. The prosthetic device of claim 8, wherein said prosthetic device is made of titanium.