Spacerless artificial disc replacements
Spacerless artificial disc replacements (ADRs) are disclosed. One preferred embodiment includes two saddle-shaped components to facilitate more normal spinal flexion, extension, and lateral bending while limit axial rotation, thereby protecting the facet joints and the annulus fibrosus (AF). Either or both the superior and inferior components are made of a hard material such as chrome cobalt, titanium, or a ceramic including alumina, zirconia, or calcium phosphate. The articulating surfaces of the ADR are also preferably highly polished to reduce friction between the components. Metals, alloys or other materials with shape-memory characteristics may also prove beneficial.
This application claims priority from U.S. Provisional Patent Application Serial No. 60/372,520, filed Apr. 12, 2002, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTIONThis invention relates generally to artificial disc replacements (ADRs) and, more particularly, to devices that operate without softer spacer materials such as polyethylene.
BACKGROUND OF THE INVENTIONPolyethylene spacers are common in some artificial joint situations, including total knee replacements (TKRs). Polyethylene spacers are also used between metal plates in many artificial disc replacement (ADR) designs.
Complications arising from poly debris are well documented, however, including fracture of the spacer once it becomes too thin, absorption and migration of poly particles throughout the body, and loosening of the bone metal junction as a reaction of the poly debris.
Metal-on-metal and ceramic-on-metal surfaces have much lower wear characteristics. In fact, metal-on-metal surfaces demonstrate 400 times less wear than polyethylene on metal surfaces.
While there have been attempts to limit the use of poly in ADR designs, all existing approaches constitute ball-and-socket configurations which do not inherently limit axial rotation. Instead, axial rotation is limited through the use of multiple ball-and-socket joints or an elongated ball-and-socket joint, which complicates the design.
SUMMARY OF THE INVENTIONThe present invention replaces polyethylene artificial disc replacement (ADR) spacers with harder, more wear-resistant materials. In the preferred embodiments, an ADR according to the invention includes opposing saddle-shaped components to facilitate more normal spinal flexion, extension, and lateral bending. Preferably, the ADR allows at least 10 degrees of movement in the flexion to extension direction and at least 5 degrees of movement in the lateral bending direction. The saddle-shaped articulating surfaces also limit axial rotation, thereby protecting the facet joints and the annulus fibrosus (AF).
According to the invention, either or both the superior and inferior components are made of a hard material such as chrome cobalt, titanium, or a ceramic including alumina, zirconia, or calcium phosphate. The articulating surfaces of the ADR are also preferably highly polished to reduce friction between the components. Metals, alloys or other materials with shape-memory characteristics may also prove beneficial.
The vertebral surfaces of the components may be treated to promote bone ingrowth. For example, the vertebral surfaces of the components may have plasma spray or beads. Alternatively, one or both components may be cemented to the vertebrae. The vertebra-facing surfaces may also include projections such as keels that fit into the vertebrae. In embodiments adapted for cementation, one of the components could be made of polyethylene or other softer material.
BRIEF DESCRIPTION OF THE DRAWINGS
Claims
1. An artificial disc replacement (ADR), comprising:
- an inferior component;
- a superior component; and
- a smooth, continuous interface between the inferior component and superior components, the interface including at least one convex surface articulating with at a corresponding concave surface.
2. The ADR of claim 1, wherein both components are metallic or ceramic.
3. The ADR of claim 1, wherein the components are physically configured to facilitate flexion, extension, and lateral bending while limiting axial rotation.
4. The ADR of claim 1, wherein the components are saddle-shaped.
5. The ADR of claim 1, wherein the vertebral surfaces of one or both of the components are treated to promote bone ingrowth.
6. The ADR of claim 1, wherein one or both of the components are cemented to a respective vertebral endplate.
7. The ADR of claim 1, wherein one or both of the components include projections adapted to fit into a respective vertebral endplate.
8. The ADR of claim 1, wherein one the components is made of polyethylene.
Type: Application
Filed: Apr 14, 2003
Publication Date: Jan 31, 2008
Inventors: Bret Ferree (Cincinnati, OH), David Thompkins (Milford, OH)
Application Number: 10/413,028
International Classification: A61F 2/44 (20060101);