Laterally expanding intervertebral fusion device

Details Laterally expanding intervertebral fusion device Laterally expanding intervertebral fusion device

2000-10-25

2003-09-02

Shaver, Kevin (Department: 3732)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

C623S011110

Reexamination Certificate

active

06613089

ABSTRACT:

BACKGROUND OF THE INVENTION
In general, this invention relates to intervertebral spacers and their use in orthopedic treatment. More specifically, the present invention is directed to intervertebral spacers composed of a shape memory polymeric material. The intervertebral spacers can be deformed and induced to recover their original configuration as desired to facilitate orthopedic treatment of spinal defects.
Removal of damaged or diseased discs and implantation of intervertebral spacers into the disc space are known medical procedures used to restore disc space height, and to treat chronic back pain and other ailments. The spacers can be formed of a variety of materials—both resorbable and non-resorbable materials—including bone-derived material, metallic, ceramic, and polymeric materials. Typically, spacers are pre-formed into a general configuration that is easy to fabricate or, in selected examples, spacers are pre-formed to a generalized configuration that resembles idealized vertebral endplates. During surgery, the vertebral endplates must be prepared to receive the spacers. This typically involves either partial or full discectomy to remove the damaged or diseased disc. Thereafter the bone tissue of the vertebral endplates is cut in preparation to receive the spacer. It is also desirable to promote fusion between the vertebral bodies that are adjacent to the damaged or diseased discs. The endplates are often shaved, exposing the cancellous bone tissue in the vertebral body, to enhance the fusion between the vertebrae. Additionally, an osteogenic material is combined with a spacer—typically packed inside the spacer body and in the disc space around the space—to further promote bone growth. Current surgical techniques approach the disc space from a variety of directions, including anteriorly, posteriorly, posterior-laterally and anterior-laterally. Regardless of the direction of approach, the surgery is extremely difficult, and several organs, vessels and nerve structures must be avoided. From the posterior approach, surgeons must be very careful to avoid the spinal cord and associated nerves. An oblique approach, such as from a posterior lateral or anterior lateral direction, offers many advantages. However, the oblique approaches only afford access to one side of the disc space. Obviously, it is desirable to avoid multiple incisions into the patient. Further smaller incisions and narrow passageways into the targeted disc space decrease the patients post surgical pain and recovery time. Further complicating the situation, the exposed cancellous bone tissue central to the vertebral body is spongy and an implanted spacer can subside into the tissue.
Therefore, it would be desirable to provide a spacer capable of withstanding the biomechanical loads exerted by the spinal column without subsiding into the spongy cancellous bone tissue. The spacer should also bear against strong cortical bone around the periphery of the endplates. Yet the space should be capable of being inserted into the disc space via a minimally invasive route.
Thus, in view of the above-described problems, there continues to be a need for advancement in the relevant field, including spacers for treatment of spinal defects and methods of treating spinal defects. The present invention is such an advancement and provides a wide variety of additional benefits and advantages.
SUMMARY OF THE INVENTION
The present invention relates to intervertebral spacers, the manufacture and use thereof. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.
In general, this invention provides an expandable spacer for implantation between adjacent vertebrae to treat spinal defects. The spacer can be formed of a shape member polymer (SMP) and molded into a pre-selected configuration. Fabrication of the spacer using a shape memory polymeric material imparts novel and particularly advantageous characteristics to the intervertebral space. In a preferred embodiment, the spacer fabricated from a SMP can be molded into a desired configuration. However, when the spacer body is heated above a deformation temperature (T
d
)—which is usually equivalent to the glass transition temperature (T
g
) of the polymeric material, the polymeric material becomes elastic. When heated to a temperature equal to or above T
d
, the spacer body can be deformed to a wide variety of configurations by applying pressure or forcing it into a mold. The spacer body can be “frozen” into the deformed configuration by cooling it below the T
d
while the body is maintained in the deformed configuration. Thereafter the deformed spacer body retains the deformed configuration until it is heated above T
d
. When the spacer body is reheated above T
d
, the SMP again becomes elastic; and in the absence of any applied pressure, the spacer body automatically reverts to its original molded configuration. This process can be repeated any number of times without detrimental effect on the SMP or the spacer itself.
In one form, the present invention provides a fabricated. intervertebral spacer molded to a desired shape and/or size. The spacer comprises a body composed of a polymeric material that exhibits a shape memory defect above a deformation temperature. Above the deformation temperature, the body can be deformed to a first configuration. Preferably, the first configuration provides a reduced external volume or cross-sectional area. Cooling the deformed spacer to a temperature below the deformation temperature effectively freezes the spacer body in the first configuration. The deformed spacer can then maintain the first configuration until it is desired to cause the body to revert to its original, molded configuration. It should be understood that a spacer can be deformed/conformed to a desired configuration and/or allowed to recover to its original configuration at any time—either before or after implantation into the disc space. Since the deformed spacer can be smaller than the molded spacer, the deformed spacer can be more readily inserted into the disc space. In a particularly preferred form, after implantation the deformed spacer is heated above its deformation temperature, which permits and allows it to revert to its original configuration or a second configuration substantially equivalent to the original configuration. The resulting implanted spacer can essentially fill the disc space, if desired, while only requiring a small entrance incision.
In one form the present invention provides an intervertebral spacer for implantation into a disc space between adjacent vertebrae. The spacer comprises a deformable body formed to include a shape memory polymeric material. The body comprises a first bearing surface, an opposite second bearing surface, and a peripheral sidewall positioned therebetween. The body has a lateral axis extending therethrough and positioned to lie substantially parallel the first bearing surface. The body deforms in a direction along said lateral axis upon application of selected stimuli. In one preferred embodiment, after the spacer is implanted into a disc space, the body expands laterally in the disc space. In other preferred embodiments, the selected stimuli include heating the body to a temperature equal to or greater than about 38° C.
In another form, the present invention provides a spacer for insertion into the spine. The spacer is formed of a material comprising a shape memory polymer and provided in an original configuration and deformable to a second configuration, wherein the spacer reverts to the original configuration by action of the shape memory polymer.
In yet another form, the present invention provides a method of orthopedic treatment. The method comprises: preparing a disc space between adjacent vertebrae to receive an intervertebral spacer

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