Vertebral interbody spacer

1. An interbody spacer adapted for placement between a pair of spaced and facing vertebrae of a spine; said spacer comprising:

a) a body having upper and lower abutment surfaces adapted to engage respective vertebrae during use and a front surface and a rear surface; said front and rear surfaces having substantially equal widths and being substantially flat and vertically aligned in use; said upper and lower abutment surfaces being generally convex from front to rear formed by a front planar facet, a middle planar facet, and a rear planar facet, wherein the middle planar facet includes opposed planar lateral bevels sloping outwardly wherein said abutment surfaces have a maximum height at a point closer to a body midline than to both said front and rear surfaces so as to be adapted to conform to the curvature of facing surfaces of the vertebrae and so as to facilitate insertion;

b) said body having a pair of opposed concave lateral side surfaces that extend from the front to the rear thereof and include at least one tool-engagement formation wherein each of said side surfaces cooperate with said planar lateral bevels so as to facilitate rotation of the spacer during installation; and

c) a first width of a first intersection of said front surface with each of the upper and lower abutment surfaces being substantially equal to a second width of a second intersection of said rear surface with each of the upper and lower abutment surfaces so as to resist subsidence of said body into the facing surfaces of the vertebrae; a third width of each of the upper and lower abutment surfaces being greater than the first and second widths at a location spaced from both the first and second intersections; and

d) said body having a solid core located between said side surfaces.

2. The interbody spacer according to claim 1 wherein:

a) said lateral side surfaces have a generally constant radius therealong about an axis that is parallel to a front to rear central axis of said body.

3. The interbody spacer according to claim 2 wherein:

a) each of said lateral side surfaces has an innermost region; and

b) said solid core is located between vertical planes tangentially engaging the innermost region of respective lateral side surfaces; said core being further positioned between said upper and lower abutment surfaces and between said front and rear surfaces.

4. The interbody spacer according to claim 1 wherein:

a) said solid core is free of pass through apertures.

5. The interbody spacer according to claim 1 wherein:

a) said lateral side surfaces open laterally outward in opposite directions and each lateral side surface is partially cylindrical in shape about an axis that is parallel to a central front to rear axis of said body.

6. The interbody spacer according to claim 1 wherein:

a) said body has a central front to rear axis; and

b) said core at any cross section thereof that is perpendicular to said body axis is free of pass through voids.

7. The interbody spacer according to claim 1 wherein:

a) said lateral side surfaces in conjunction with the intersection thereof with said upper and lower surfaces form upper and lower arches on each side of said spacer; and

b) said arches cooperate with said central core to provide a strong stable support structure.

8. The interbody spacer according to claim 1 wherein:

a) said upper and lower abutment surfaces are substantially smooth.

9. The interbody spacer according to claim 1 wherein:

a) said body includes a plane of convexity; and

b) said plane of convexity is associated with said point closer to a body midline.

10. An interbody spacer having opposed concave side surfaces comprising:

a) a solid central core located between said side surfaces; the central core having upper and lower surfaces that are generally convex from a front to a rear of the spacer and are formed by a front planar facet, a middle planar facet, and a rear planar facet; the core having front and rear surfaces that are generally flat and vertical in use and that intersect at opposite ends with the upper and lower surfaces at intersections; all of the intersections are of generally equal width and each of the upper and lower surfaces are wider than the intersections at a location spaced from both of the intersections;

b) each of said upper and lower surfaces having opposed planar lateral bevels sloping outwardly and cooperating with side surfaces and being adapted to facilitate rotation of the spacer during installation; the upper and lower surfaces having a maximum height spaced nearer to a center of the spacer than to any of the intersections; and

c) said side surfaces open laterally outward and have a generally uniform radius therealong; said side surfaces extending from near the upper surface to near the lower surface of said core; said side surfaces having an axis that is generally paralleled to a central front to rear axis of said core; and said side surfaces having at least one tool-engagement formation, wherein said at least one tool-engagement formation extends laterally from said side surface in a direction selected from the group consisting of inward and outward.

11. A method of promoting fusion between a pair of spaced and facing vertebrae comprising the steps of:

a) providing an interbody spacer having a body with a solid central core located between a pair of opposed and concave lateral side surfaces that extend from a front to a rear of the body and having a pair of upper and lower convex surfaces that are convex between the front and the rear of the body formed by a front planar facet, a middle planar facet, and a rear planar facet and that are adapted to conform to the curvature of facing surfaces of the facing vertebrae; the body having front and rear surfaces that are generally flat and vertical in use and that intersect with the upper and lower surfaces at intersections that are all substantially equal in width; said central core having a maximum height near a midpoint thereof and spaced from each of the intersections; the upper and lower surfaces being widest at a location spaced from opposite ends thereof and each of said side surfaces having at least one tool-engagement formation extending inwardly therefrom and being adapted to cooperatively engage engagement pins of an installation tool;

b) providing laterally positioned bevels on opposed sides of the middle facet of each of the upper and lower surfaces;

c) placing said spacer in a sideways position between said vertebrae;

d) rotating said spacer to an upright position so that the bevels facilitate rotation of the spacer and so that the upper and lower surfaces are aligned after rotation with and in touching relationship with similarly shaped facing surfaces of the vertebrae; and

e) thereafter supporting one of said vertebrae relative to the other with said spacer so as to encourage fusion of bone between said vertebrae.

12. An interbody spacer adapted for placement between a pair of spaced and facing vertebrae of a spine; said spacer comprising:

a) a body having upper and lower abutment surfaces adapted to engage respective vertebrae during use and a front surface and a rear surface; said front and rear surfaces being generally vertical and flat during use; said upper and lower abutment surfaces being generally convex from front to rear wherein said abutment surfaces are formed by a front planar facet, a middle planar facet, and a rear planar facet and have a maximum height at a point closer to a body midline than to both said front and rear surfaces so as to be adapted to conform to the curvature of facing surfaces of the vertebrae and so as to facilitate insertion, said body including an intersection between each of said upper and lower abutment surfaces and each of said front and rear surfaces, each of said intersections including a width, said widths being substantially equal to one another and being spaced from the maximum height; both of the upper and lower abutment surfaces being wider at a location spaced from both of the intersections than at the intersections;

b) at least one lateral facet joined to and sloping laterally away from the middle facet of at least a respective one of the upper and lower abutment surfaces;

c) said body having a pair of opposed concave lateral side surfaces that extend from the front to the rear thereof and include at least one tool-engagement formation; and

d) said body having a solid core located between said side surfaces.

13. An interbody spacer adapted for placement between a pair of spaced and facing vertebrae of a spine; said spacer comprising:

a) a body having upper and lower abutment surfaces adapted to engage respective vertebrae during use and a front surface and a rear surface the front and rear surfaces being substantially flat and vertical in use; said front and rear surfaces intersecting with the upper and lower abutment surfaces at intersections; said upper and lower abutment surfaces being generally convex from front to rear wherein said abutment surfaces have a maximum height at a point closer to a body midline than to said front surface and being substantially spaced from both the front and rear surfaces so as to be adapted to conform to the curvature of facing surfaces of the vertebrae and so as to facilitate insertion; each of the upper and lower abutment surfaces being formed by a front planar facet, a middle planar facet and a rear planar facet wherein the middle planar facet includes opposed planar lateral bevels sloping outwardly;

b) said body having a pair of opposed concave lateral side surfaces that extend from a front to a rear thereof and include at least one tool-engagement formation wherein each of said side surfaces cooperate with said planar lateral bevels so as to facilitate rotation of the spacer during installation; and

c) a width of the intersection of said front surface with each of upper and lower abutment surfaces being substantially equal to a width of the intersection of said rear surface with each of upper and lower abutment surfaces so as to resist subsidence of said body into the facing surfaces of the vertebrae; both of the upper and lower abutment surfaces being wider at a location spaced from both of the intersections than at the intersections; and

d) said body having a solid core located between said side surfaces.

14. An interbody spacer adapted for placement between a pair of spaced and facing vertebrae of a spine; said spacer comprising:

a) a body having upper and lower abutment surfaces adapted to engage respective vertebrae during use and a front surface and a rear surface; the front and rear surfaces being substantially flat and vertical in use and intersecting the upper and lower abutment surfaces respectfully at intersections; said upper and lower abutment surfaces being generally convex from front to rear wherein said abutment surfaces have a maximum height at a point closer to a body midline than to said front surface and where the maximum height is substantially spaced from each intersection so as to be adapted to conform to the curvature of facing surfaces of the vertebrae and so as to facilitate insertion; the upper and lower abutment surfaces each comprising a front planar facet, a middle planar facet and a rear planar facet joined so as to be convex; the upper and lower abutment surfaces each having opposed side bevels located between the front and rear surfaces to facilitate turning of the body during installation;

b) said body having a pair of opposed concave lateral side surfaces that cooperate with said side bevels, extend from the front to the rear thereof and include at least one tool-engagement formation; the side surfaces extend between the upper and lower abutment surfaces and are concave having an axis of curvature that extends from front to rear; and

c) a first width of a first intersection of said front surface with each of upper and lower abutment surfaces being substantially equal to a second width of a second intersection of said rear surface with each of upper and lower abutment surfaces so as to resist subsidence of said body into the facing surfaces of the vertebrae; each of the upper and lower abutment surfaces having a third width spaced from the first and second widths that is wider than the first and second widths; and

d) said body having a solid core located between said side surfaces.