US20020068973A1 - Threaded interbody device - Google Patents

Abstract

An interbody device having upper and lower surfaces that are sized and shaped to be operably positioned between a pair of adjacent vertebrae for support and/or fusion. The upper and lower surfaces have a generally convex curvature. The upper and lower surfaces are joined by a pair of side surfaces that are arcuate and semi-circular, when viewed from the front, so as to be generally concave. The interbody devices are used in pairs between two vertebrae and joined by a bar that is received in a recess in each of the devices so as to resist rotation of the devices relative to the bar subsequent to installation.

Description

BACKGROUND OF THE INVENTION
• The present application is directed to a threaded interbody device for implantation between a pair of adjacent vertebrae in order to provide support to the vertebrae and/or promote fusion between the vertebrae.[0001]
• In the human spine the pad or disc between vertebrae is sometimes damaged or deteriorates due to age, disease, injury or congenital defect. The vertebrae themselves may also become compressed or otherwise damaged. Because of this, surgery is often utilized to place spacers or interbody devices between the vertebrae which provide proper spacing of the vertebrae and which often are also utilized to promote fusion between the vertebrae. When a device of this type is utilized for purposes of promoting fusion, it is often referred to as a fusion cage or an intervertebral fusion device. When utilized to promote fusion, the interbody devices often are windowed and packed with bone so as to promote growth of the bone between the vertebrae. Sometimes bone is packed between a pair of devices that are placed in close proximity to one another between the vertebrae so as to promote growth of bone and, therefore, fusion between the vertebrae.[0002]
• Interbody devices are typically either generally rectangular in shape or generally cylindrical in shape. The cylindrical devices have an advantage that they can be threadably received between and into the bones themselves. For this purpose, the vertebrae are typically first spaced and then a drill is utilized to create a partial bore in each vertebrae which allows the interbody device to be received between the vertebrae. Because of the space between the bones, the interbody device usually engages the bone's only along an upper surface and a lower surface thereof. When the cage is of a cylindrical threaded type, the upper and lower surfaces are curved and essentially designed to engage the portion of the vertebrae whereat bone is unremoved during boring to create an opening for the device.[0003]
• When interbody devices of this type are used, it is desirable that the device support as much surface of bone as possible to provide strength and reduce the likelihood of subsidence of the device into the bone, especially as part of the bone is spongy by nature. The remainder of the structure mainly functions to support the two surfaces, unless the device is also used as a cage within which to pack bone. Because it is also desirable in such structures to maintain weight and volume as low as possible, in order to make the device more compatible with the body, it is also desirable to make the entire device as small and lightweight as possible, while maintaining strength.[0004]
• Still further, the cylindrical devices are most often threaded in order to bite into the bone of the vertebrae in order to resist inadvertent removal of the devices from between the vertebrae. Therefore the upper and lower surfaces are threaded for this purpose. In the past flat sided segments have been removed and a tool which saddles over the device has been used that slides along the sides thereof to at least partially complete the threads and that can be rotated to allow the device to be screwed between the vertebrae. Consecuently, it is desirable to have a side structure that reduces volume, maintains strength and allows for mating engagement with a tool that can both rotate the device and complete the thread during installation.[0005]
• Finally, devices of this type that have sectors in the sidewalls missing are essentially taller than wide. This leads to a potential for instability in that the device can inadvertently rotate 90° during use and partly collapse. In order to avoid this, an additional structure is needed to prevent inadvertent rotation of the device once it is installed.[0006]
SUMMARY OF THE INVENTION
• An interbody or intervertebral spacer device for placement between a pair of spaced but adjacent vertebrae. The device has upper and lower surfaces that are threaded so as to have a helically wound threadform pattern thereon that is discontinuous between the two surfaces, but mateable with a similar threadform on a tool for completion of the thread for use during insertion of the device.[0007]
• The device has an elongate body that extends along an axis of rotation. The upper and lower surfaces of the body are convex and the two side surfaces are concave in shape. That is, a cross-section of the upper surfaces and lower surfaces and the side surfaces have edges which are generally semi-circular in shape, except that the upper and lower surface are convex or bowed outwardly, whereas the side surfaces are concave or bowed inwardly. Preferably the radii of generation of each of the side surfaces, the upper surface and the lower surface are approximately the same. The side surfaces join together the outer edges of the upper and lower surfaces on respective sides of the device. In this manner the device has a profile from the front which approximates a double-headed ax.[0008]
• The devices are utilized in pairs between two adjacent vertebrae. The devices are preferably joined by a bar. Each of the devices has a recess located on the front thereof within which the bar snugly fits such that the bar resists rotation of each device subsequent to installation. This prevents the devices from inadvertently rotating to a non-supporting configuration during use. A set screw joins the bar to each device.[0009]
OBJECTS AND ADVANTAGES OF THE INVENTION
• Therefore, the objects of the present invention are: to provide an interbody spacer or fusion cage device that is threaded on upper and lower surfaces thereof and can be screwed between a pair of vertebrae in order to support the vertebrae and/or to promote fusion between the vertebrae; to provide such a device having concave arcuate side surfaces that join the upper and lower surfaces on opposite elongate sides of the device; to provide such a device wherein the structure provides strength while reducing volume and weight; to provide such a device wherein the device easily mates with an insertion tool having external threads that align with the threads of the device to allow screwing of the device between a pair of vertebrae; to provide such a device that can be either solid or partly hollow in order to allow packing with bone chips or the like; to provide such a device allowing a relatively close spacing of a pair of devices in side by side relationship; to provide such a device that allows a substantial opening between a pair of devices in side by side relationship to facilitate packing with bone chips and subsequent fusion between the vertebrae associated with the devices; to provide such a device utilized in a pair in conjunction with a bar connecting the pair to resist inadvertent rotation of the devices during use; to provide such a device that includes feathering or reduced thread depth near the front or anterior end of the device to provide an even surface for engagement with a harder bony region near the anterior end of the vertebrae in order to reduce the likelihood of subsidence of the device into the vertebrae after installation; and to provide such a device that is relatively easy to construct, inexpensive to produce and especially well suited for the intended usage thereof.[0010]
• Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.[0011]
• The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.[0012]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of an interbody device and a bar for linking the interbody device with a second such device in accordance with the present invention.[0013]
• FIG. 2 is a front elevational view of the device.[0014]
• FIG. 3 is a side elevational view of the device.[0015]
• FIG. 4 is a side elevational view of the device on a reduced scale shown positioned between a pair of vertebrae.[0016]
• FIG. 5 is a front elevational view on a reduced scale of a pair of the devices joined by the bar and positioned between a pair of vertebrae.[0017]
• FIG. 6 is a perspective view of the device mated with a tool for installing the device.[0018]
• FIG. 7 is a perspective view of the device being installed with the tool between the vertebrae.[0019]
DETAILED DESCRIPTION OF THE INVENTION
• As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.[0020]
• The reference numeral[0021]1 generally designates an interbody spacer or device. Normally the device1 is utilized in pairs and connected with abar4 for placement between a pair of adjacentspinal vertebrae6 and7.
• The device[0022]1 has a generally partial cylindrical shape with equal opposed side portions or sectors removed. In particular, the device1 has abody10 with anupper surface11 and alower surface12. The upper andlower surfaces11 and12 are semi-cylindrical in shape, elongate and are typically generated from a radii of the same length. The upper and lower surface also have athread15 that is wound helically about the device1 in a pattern that is discontinuous between the upper andlower surfaces11 and12. The illustratedthread15 is a V-shaped thread, although other types of thread forms, such as square or step forms, may be utilized in accordance with the invention.
• As is seen in FIG. 3, the[0023]thread15 has a major diameter and minor diameter forming the peaks and valleys of the thread. As the thread approaches the anterior or front end (to the right of FIG. 3) of the device1 in aregion16 the thread depth reduces progressively with each consecutive turn or 360° pass about the device1. That is, each time thethread15 passes once around the device1 in a turn, the thread depth becomes less and the minor diameter of the thread becomes greater.
• Near the very front of the device[0024]1 the minor thread depth and major thread depth are generally equal so as to produce a generally smoothsemi-cylindrical region17. Thesemi-cylindrical region17 provides greater support to an anteriorharder bony region18 of thevertebrae6 and7 so as to oppose subsidence during usage. Theupper surface11 has opposedparallel edges20 and21 and thelower surface12 has similarparallel edges22 and23.
• The[0025]body10 also has a pair of side surfaces30 and31. The side surfaces30 extends between thetop surface edge20 andbottom surface edge22, whereas theside surface31 extends between thetop surface edge21 and bottom surface edge23. The side surfaces30 and31 are curved, arcuate or crescent shaped, as is seen from the front in FIG. 2. Preferably, the side surfaces30 and31 each have a radius of generation which is approximately equal. In some embodiments of the invention, the radius of generation of each of the side surfaces30 and31 will be equivalent to the radii of generation of theupper surface10 andlower surface11, except the side surfaces30 and31 will be concave in nature and the upper andlower surfaces10 and11 are convex. In this manner the side surfaces30 and31 are the reverse of the surface that would be generated by either the upper orlower surfaces10 or11 being continued with the same arc about the exterior of the device1. Also, the device has an axis of rotation A. Any plane passing through the device1 that is perpendicular to the axis A has an intersection with any of thesurfaces10,11,30 and31 which is semi-circular.
• The[0026]body10 also has a generally flatrear surface39 and afront surface40. Thefront surface40 has a vertically centrally locatedrecess43. Therecess43 has an anterior rectangularly shaped portion45 and anouter portion46 which is also centrally rectangular in shape, but has semi-circular upper andlower extensions48 and49. A threaded bore50 passes coaxially trough thefront surface40 and is centered on therecess43.
• The[0027]bar4 is elongate with rounded opposite ends. Thebar4 has a pair ofapertures51 and52. Thebar4 has a cross-section which is sized and shaped to snugly fit in the recess rectangular portion45 of each device1. In this manner, thebar4, when in therespective recesses43 functions as a lever arm to prevent inadvertent rotation of the devices1.
• A pair of[0028]set screws54 are sized and shaped to be received throughrespective apertures51 or52 in thebar4 and subsequently, into and threadably received inrespective bores50 of one of the devices1. Eachset screw54 has ahead55 that is preferably externally threaded and received in a similar thread in the semi-circular shapedportions48 and49 of therecess43. Theset screw head55 also has a coaxially alignedaperture58 which is sized and shaped to receive a driving tool (not shown) such as an alien wrench. When an allen wrench is to be utilized, theaperture58 has a hexagonal shaped opening.
• In use, a pair of devices[0029]1 are positioned between a pair ofvertebrae6 and7 such as is shown in FIG. 5. Atool60 havingside panels61 and62 includes ahandle63 for turning and is used to insert the devices1. Theside panels61 and62 mate with thesides30 and31 of each device1 to complete a cylinder and haveexternal threads64 and65 that mate with thethread15 to complete thethread15. The device1 is placed in thetool60 in the manner shown in FIG. 6 and then inserted between thevertebrae6 and7 in the manner shown in FIG. 7. Thebar4 is joined by a pair ofset screws54 to each of the devices1. Bone chips and the like for promoting growth of bone and fusion between thevertebrae6 and7 may be placed between the devices1, if desired by the surgeon.
• It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.[0030]

Claims (15)

What is claimed and desired to be secured by Letters Patent is as follows:

1. An interbody device for placement between a pair of adjacent vertebrae; said device comprising:

a) a body having an axis and upper and lower elongate surfaces that are generally coaxially located with respect to said axis; said upper and lower surfaces having elongate sidle edges;

b) said body also having inwardly arced side surfaces; said side surfaces extending between respective side edges of said upper and lower surfaces.

2. The device according toclaim 1 wherein:

a) said side surfaces have a semi-circular cross-section in a plane passing perpendicular to said axis.

3. The device according toclaim 1 wherein:

a) both of said side surfaces have a common radius of generation.

4. The device according toclaim 3 wherein:

a) said upper and lower surfaces have a radius of generation approximately equal to said side surfaces common radius of generation.

5. The device according toclaim 1 wherein:

a) said upper and lower surfaces have a helically wound discontinuous thread located thereon.

6. The device according toclaim 1 wherein:

a) said thread extends from a rear to near a front of said device.

7. The device according toclaim 1 wherein:

a) said thread has a generally uniform thread depth except near a front of said device whereat said thread depth is reduced.

8. The device according toclaim 7 wherein:

a) said thread has a maximum and minimum diameter therealong and said minimum diameter approximately equals said maximum diameter in two forward turns of said thread so as to provide a generally smooth cylindrical surface for anterior bone support.

9. The device according toclaim 1 wherein:

a) said device has a front wall; and

b) said front wall includes a centrally located recess adapted to receive a bar for connecting together a pair of said devices.

10. The device according toclaim 9 in combination with said bar.

11. The combination according toclaim 10 wherein:

a) said recess has upper and lower walls and;

b) said bar is sized and shaped to snugly abut against said recess walls when placed in said recess so as to resist relative rotation between said bar and said device.

12. The combination according toclaim 11 wherein:

a) said bar includes a bore and said device includes a threaded bore such that both of said bores align when said bar is received in said slot.

13. The combination according toclaim 12 including:

a) a set screw sized and shaped to be received through said bar bore and threaded to be matingly received in said device threaded bore to operably secure said bar to said device.

14. In a threaded interbody device for placement between a pair of adjacent vertebrae having an axis of rotation with upper and lower outer surfaces adapted to operably engage respective vertebrae and a pair of side surfaces joining respective outer edges of said lower and upper surfaces; the improvement comprising wherein:

a) each of said side surfaces have a concave circular cross-section in a plane perpendicular to said axis.

15. In a generally cylindrical threaded interbody device for placement between a pair of adjacent vertebrae; the improvement comprising:

a) open spaced cylindrical sectors on opposite sides of said device so as to produce side walls that are spaced, concave and that join outer edges of upper and lower surfaces of said device.

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