The human spine is a complex arrangement of connective tissue, vertebrae, intervertebral discs, the spinal canal, the spinal cord, nerves, and the like. A plurality of vertebrae are stacked upon one another into four regions, the cervical, thoracic, lumbar, and sacrum regions. Intervertebral discs are located between stacked vertebra and abut the spinal cord, which runs through the spinal canal of the vertebrae.
Healthy intervertebral discs make the spine remarkably strong and flexible, being able to bend with ease when under heavy loads. The intervertebral discs have several functions, one of which is serving as shock absorbers for the spine. Each disc resembles a jelly donut, having a relatively tough outer layer, called the annulus fibrosis, that surrounds a gel-like inner layer, called that nucleus pulposus. The annulus fibrosis is composed of concentric layers of intertwined fibrocartilage forming annular bands, which are arranged to resist forces placed upon the spine. The vertebrae's cartilaginous endplate, also a part of the disc space, separates the nucleus pulposus and annulus fibrosis from the adjacent vertebrae.
The nucleus pulposus is composed of cells from the primitive notochord and contains significant amounts of substances capable of exciting, or increasing the excitability of, sensory nerves. These substances include prostaglandin E, histamine-like substances, potassium ions, lactic acid, and several polypeptide amines.
Although the spine is resilient, trauma or osteo-degenerative diseases can cause injury to vertebrae or intervertebral discs, particularly about the lumbar region of the spine. This is a source of chronic lower back pain for millions of people. Tears to the intervertebral discs can lead to herniated disc disease, where the nucleus pulposus migrates into the outer areas of the intervertebral disc space and presses against the spinal cord or possibly collapses vertebral bodies onto one another. Herniated discs or tears in the annulus fibrosis can make the slightest movements very painful.
There are many ways to treat intervertebral disc problems. Current methods focus on fusing adjacent vertebrae together or using partial or total prosthetic disc implants. In a spinal fusion procedure, some or all of the disc material is removed from the level to be fused. In particular, for interbody fusion procedures such as posterior lumbar interbody fusions (PLIF) or transforaminal lumbar interbody fusions (TLIF), a hole is made in the annulus and the interior portion of the disc is removed. Cartilaginous endplates are abraded to induce bleeding bone. In the place of disc material, an interbody fusion device is implanted. The fusion device is intended to maintain the height of the disc space and help stabilize the segment while fusion occurs. Fusion is achieved by implanting either bone harvested from another site in the patient (autograft) or an autograft replacement into the disc space.
Autograft replacement implants are associated with osteo-inductive factors and other bio-active agents that help promote osteoblastic formation. The ultimate goal of these implants is to promote bone growth that will connect vertebrae endplates to limit motions associated with the patient's lower back pain.
There are potential drawbacks to these sorts of spinal procedures. The surgically made hole in the outer band of the annulus fibrosis, if not properly closed or shielded, could act as a door for bone tissue and osteo-inductive agents to migrate from the intervertebral disc space into the area about the spinal canal. These migrations could eventually lead to pain in the patient associated with bone tissue protruding through the annulus fibrosis and pressing against spinal nerves.
Another possibility is bone tissue forming about the spinal canal due to osteo-inductive agents that have passed through the outer bands of annulus fibrosis. Depending on the type and amount of osteo-inductive agent used in the procedure, one could have bone or cartilage forming about the spinal cord, nerve roots, and surrounding muscles that can cause severe pain.
The prior art discloses methods or devices dealing with closing surgically prepared holes in the annulus fibrosis. U.S. Pat. No. 7,094,258 discloses methods of reinforcing the annulus fibrosis. The '258 patent further discloses inserting a barrier into the interior of an annular defect to seal it after an implant procedure. This patent prefers that the barrier be flexible in nature, being made from woven material such as Dacron™ fabric, Nylon™ fabric, collagen, synthetic polymers, and the like.
U.S. Pat. No. 6,371,990 discloses an apparatus and method for controlling vertebral motion. The '990 patent discloses reinforcing the inner walls of annulus fibrosis to support a prosthetic disc implant. The opening in the annulus fibrosis, referred in the '990 patent as flaps, is sewn shut and supported by a wire mesh that is screwed into adjacent vertebrae separated by the targeted disc space.
U.S. Pat. No. 6,454,804 discloses using a mixture of living annulus fibrosis tissue and the same obtained from a recently deceased person or animal donors to augment damaged annulus fibrosis in a patient. The '804 patent generally refers to gluing or suturing this annulus mixture to the inside or the outside of a patient's annulus.
Despite these procedures, there remains a need for a method that uses a tissue inhibiting matrix to ease complications associated with cell and osteo-inductive agent migration in the early phases of spinal repair.