Artificial functional spinal unit assemblies

Abstract

An artificial functional spinal unit is provided comprising, generally, an expandable artificial intervertebral implant that can be placed via a posterior surgical approach and used in conjunction with one or more artificial facet joints to provide an anatomically correct range of motion. Expandable artificial intervertebral implants in both lordotic and non-lordotic designs are disclosed, as well as lordotic and non-lordotic expandable cages for both PLIF (posterior lumber interbody fusion) and TLIF (transforaminal lumbar interbody fusion) procedures. The expandable implants may have various shapes, such as round, square, rectangular, banana-shaped, kidney-shaped, or other similar shapes. By virtue of their posteriorly implanted approach, the disclosed artificial FSU's allow for posterior decompression of the neural elements, reconstruction of all or part of the natural functional spinal unit, restoration and maintenance of lordosis, maintenance of motion, and restoration and maintenance of disc space height.

Description

PRIORITY CLAIM [0001] This application is a continuation of U.S. patent application Ser. No. 10 / 634,950 entitled “ARTIFICIAL FUNCTIONAL SPINAL UNIT ASSEMBLIES” filed on Aug. 5, 2003, the disclosure of which is hereby incorporated by reference.BACKGROUND [0002] 1. Field of the Invention [0003] The present invention generally relates to functional spinal implant assemblies for insertion into the intervertebral space between adjacent vertebral bones and reconstruction of the posterior elements to provide stability, flexibility and proper biomechanical motion. More specifically, the present invention relates to artificial functional spinal units comprising an expandable artificial intervertebral implant that can be inserted via a posterior surgical approach and used in conjunction with one or more artificial facet joints to provide a more anatomically correct range of motion. [0004] 2. Description of Related Art [0005] The human spine is a complex mechanical structure composed of altern...

AI Technical Summary

Benefits of technology

"The patent describes an artificial spinal unit that can be placed via a posterior surgical approach and used in conjunction with natural facet joints to provide anatomically correct range of motion. The expandable artificial implant has a concave upper body and a recessed channel lower body that can be compressed to fit between the vertebral bodies. The implant restores disc height and promotes bone growth to securely hold the prosthesis in place. The invention provides a two-step procedure that allows for the placement of an interbody device and replacement of one or both facet joints, avoiding the need for anterior exposure and reducing risks and morbidity. The artificial FSU is designed to restore natural spinal elements and maintain stability for the anteriorly located interbody device."

Problems solved by technology

However, genetic or developmental irregularities, trauma, chronic stress, and degenerative wear can result in spinal pathologies for which surgical intervention may be necessary.

Such events cause the height of the disc nucleus to decrease, which in turn causes the anulus to buckle in areas where the laminated plies are loosely bonded.

Such practices are characterized by certain disadvantages, most important of which is the actual morbidity of the procedure itself.

Placement of rigid cages or structural grafts in the interbody space either requires an anterior surgical approach, which carries certain unavoidable risks to the viscous structures overlying the spine (intestines, major blood vessels, and the ureter), or they may be accomplished from a posterior surgical approach, thereby requiring significant traction on the overlying nerve roots.

The interval between the exiting and traversing nerve roots is limited to a few millimeters and does not allow for safe passage of large intervertebral devices, as may be accomplished from the anterior approach.

Alternatively, the anterior approach does not allow for inspection of the nerve roots, is not suitable alone for cases in which the posterior elements are not competent, and most importantly, the anterior approach is associated with very high morbidity and risk where there has been previous anterior surgery.

Another significant drawback to fusion surgery in general is that adjacent vertebral segments show accelerated deterioration after a successful fusion has been performed at any level.

Other drawbacks include the possibility of “flat back syndrome” in which there is a disruption in the natural curvature of the spine.

Finally, there is always the risk that the fusion attempt may fail, leading to pseudoarthrosis, an often painful condition that may lead to device failure and further surgery.

As previously discussed, however, cages that would be placed from the safer posterior route would be limited in size by the interval between the nerve roots.

Ultimately though, it is important to note that the fusion of the adjacent bones is an incomplete solution to the underlying pathology as it does not cure the ailment, but rather simply masks the pathology under a stabilizing bridge of bone.

This bone fusion limits the overall flexibility of the spinal column and artificially constrains the normal motion of the patient.

This constraint can cause collateral injury to the patient's spine as additional stresses of motion, normally borne by the now-fused joint, are transferred onto the nearby facet joints and intervertebral discs.

Placement of posterior devices that maintain mobility in the spine have been limited due to the relatively small opening that can be afforded posteriorly between the exiting and transversing nerve roots.

Additionally, placement of posterior interbody devices requires the removal of one or both facet joints, further destabilizing the spine.

Thus conventional posteriorly placed interbody devices have been generally limited to interbody fusion devices.

Also, the anterior approach does not offer the surgeon an opportunity to view the posterior neural elements and thereby does not afford an opportunity for decompression of those elements.

Once an anterior exposure had been utilized a revision procedure is quite risky and carries significant morbidity.

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