Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-09-02
2002-08-27
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06440168
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a spinal implant for use in intervertebral disc replacement; and more specifically relates to an articulating implant that fuses to adjacent vertebrae by bone ingrowth, thus restoring proper intervertebral spacing, and eliminating nerve root and/or spinal cord compression, while preserving spinal flexibility.
2. Description of Related Art
The spinal column is formed from a number of vertebrae, which in their normal state are separated from one another by cartilaginous intervertebral discs. These discs form a cushion between adjacent vertebrae, resisting compression along the support axis of the spinal column, but permitting limited movement between the vertebrae to provide the characteristic flexibility of the healthy spine. Injury, disease or other degenerative disorders may cause one or more intervertebral discs to shrink, collapse, deteriorate or become displaced, herniated or otherwise damaged. This can lead to compression of adjacent nerve root(s) or the spinal cord causing chronic and often disabling pain, and in advanced circumstances, irreversible paralysis of upper and/or lower limbs.
A number of devices and methods have been suggested for the replacement of damaged or dislocated intervertebral discs. One common approach is to permanently stabilize or “fuse” the adjacent vertebrae to maintain the proper intervertebral spacing and eliminate relative movement between the vertebrae. Various methods of vertebral stabilization have been developed. For example, autogenous grafts of dowel-shaped sections of bone have been implanted between the vertebrae to cause bone growth across the intervertebral space, thereby fusing the adjacent vertebrae into one bone mass. This procedure disadvantageously requires the harvest of donor bone for the graft from other parts of the patient's body, typically requiring a separate surgical procedure and resultant increases in complications and expense. An alternative source is cadaver bone, with potential complications of transmissible diseases, impaired graft incorporation, collapse or displacement. A further development to this method of vertebral stabilization involves the implantation of a perforated cylindrical bone basket between adjacent vertebrae. Bone fragments produced in preparing the vertebrae for the implantation are inserted into the bone basket to promote bone growth into, through and around the basket.
Vertebral stabilization by fusion of adjacent vertebrae has proven successful in permanently preserving intervertebral spacing, but has been found to present a number of disadvantages. Fusion of adjacent vertebrae necessarily eliminates a portion of the spine's normal range of motion, thereby reducing the subject's spinal flexibility. Additionally, fusion of the vertebrae increases the stresses imposed on adjacent mobile portions of the spinal column, often hastening the subsequent breakdown of normal joint surfaces above and below the fused vertebrae.
It has also been proposed to replace an injured intervertebral disc with a prosthesis which is “jointed” to permit relative movement between vertebrae. Previously-known devices of this type generally have been found to suffer from inadequate attachment between the prosthesis and the vertebrae. The intended movement between the components of previously-known jointed prostheses can cause relative motion between the prosthesis and adjacent bone surface(s). Because such motion would disrupt bone ingrowth, jointed prostheses have generally been considered incompatible with attachment by bone ingrowth. In addition, because the joint elements of these devices typically must occupy a substantial vertical extent in order to achieve the desired range of motion, and yet must fit within the intervertebral space, attachment of such devices generally has been by use of flat plates or surfaces provided on either side of the joint elements as points of fixation to the vertebrae. This attachment may be accomplished by compressive or friction fits, spiked projections, screws or pins, complemented in some instances with tissue ingrowth into porous surfaces. These mechanisms of attachment, however, may lack the degree and strength of fixation desired. Moreover, several such devices have used attachment flanges which extend beyond the surfaces of the vertebrae to which the device is attached. This has been found undesirable, as the extending flanges may interfere with or injure adjacent tissue. For example, it has been reported that flanges extending into immediately adjacent delicate esophageal area may interfere with swallowing and speech, or cause perforation and potentially fatal infection. An additional drawback to the use of screw and pin connections is the potential for such connectors to dislodge and cause injury.
Thus, it can be seen that a need yet exists for a spinal implant effective in permanently maintaining intervertebral spacing to prevent nerve or spinal cord compression while preserving as much of the natural range of motion between the affected vertebrae as possible. A need further exists for such a device which is capable of forming a permanent, strong attachment to the vertebrae and yet does not protrude beyond the external surfaces to which it is attached. Still another need exists for a method of replacing a damaged or displaced disc, which method maintains intervertebral spacing to prevent nerve and spinal cord compression, while preserving the natural relative motion between the vertebrae. It is to the provision of a device and method meeting these and other needs that the present invention is primarily directed.
BRIEF SUMMARY OF THE INVENTION
Briefly described, in a preferred form, the present invention comprises a spinal implant including a first element having first connection means for engaging a first vertebra. The first connection means includes a first fusion chamber having at least one opening therein for facilitating bone ingrowth into the first fusion chamber to fuse the first element to the first vertebra. The implant also includes a second element having second connection means for engaging a second vertebra. The second connection means includes a second fusion chamber having at least one opening therein for facilitating bone ingrowth into the second fusion chamber to fuse the second element to the second vertebra. The implant also includes internal articulation means, coupling the first element to the second element, for allowing relative movement between the first element and the second element. The term “internal articulation means,” is intended to mean a device that permits relative motion between components of the device, rather than between the device and an external structure such as adjacent bone or other tissue.
In specific embodiments of the subject invention, the first and second element may have either hemicylindrical or hemielliptical shaped outer surfaces. The first and second elements each having an outer wall perforated with one or more openings provided therein to allow bone ingrowth into the fusion chambers, and having abutting joint surfaces forming the internal articulation means. In a further preferred embodiment, the joint surfaces are formed as engaging concave and convex surfaces to create a ball-and-socket type joint (or groove and channel, or other such joint), which allows relative pivotal motion between the vertebrae, but resists compression therebetween.
The first and second elements can join to form a single element which can be implanted using methods similar to those followed in the implantation of previously-known non-articulating vertebral fusion implants. Temporary stabilizing means can be provided for rigidly coupling the first and second elements by interposition of bioreabsorbable elements to permit implantation and enable bone ingrowth into the fusion chambers and fusion of the first and second elements to adjacent bone during an initial stabilization period, after which said temporary means biodegrades permitting articulat
SDGI Holdings Inc.
Willse David H.
Woodard Emhardt Naughton Moriarty & McNett
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