This invention relates generally to artificial disc replacements (ADRs) and, more particularly, to devices that operate without softer spacer materials such as polyethylene.
Polyethylene 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, absorptions 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 the poly in ADR designs, all existing approaches constitute call-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.
The 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 on 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 fibrosis (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.
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/372,520, filed Apr. 12, 2002 and this application is a continuation of U.S. application Ser. No. 10/413,028, filed on Apr. 14, 2003, the disclosures of which are incorporated herein by reference.
Number | Date | Country | |
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60372520 | Apr 2002 | US |
Number | Date | Country | |
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Parent | 10413028 | Apr 2003 | US |
Child | 11194786 | Aug 2005 | US |