The current state of spine surgery teaches the technique of radical intervertebral discectomy for the purpose of providing surgical access to a pathology posterior to the disc space and or vertebral body (sometimes referred to as vertebral corpus) and anterior to the spinal cord and/or nerve roots. Removal of the spinal disc (discectomy) generally requires the final step of fusing the adjacent vertebral bodies or placing an artificial disc where the patient's natural disc previously existed. Both of these final steps to the disc removal techniques are accompanied by loss of mobility, compromises to the patient's future, and the possibility of additional surgeries. It is important to point out that the current state of spine surgery requires the radical removal of two spinal discs in the performance of a single level standard corpectomy, thus requiring multilevel fusion with permanent loss of motion at two levels of the spine. What is being emphasized is the fact that following the discectomy or corpectomy procedures the affected area of the patient needs to be reconstructed which typically requires a spinal fusion. One aspect of this invention is that the procedure that will be described herein below completely eliminates the necessity of performing a spinal fusion and in addition, the implant that is utilized in this procedure is not for the purpose of the fusion of two vertebral bodies but more importantly, it is for the purpose of restoring the bone that is used in performing the inventive procedure back to its functional condition.
The spinal disc is made up of a durable exterior called the annulus fibrosis and the soft cushioning interior called the nucleus pulpous. The spinal disc along with bony supports called facets at the posterior aspect of the spine and the ligamentous structures make up the vertebral motion segment or joint. These motion segments provide support and structural stability for the body and provide the patient with normal flexibility and the anatomically correct distribution of the biomechanical loads required of the human body.
Historically, anterior spinal surgery has been performed by gaining access to the spinal nervous anatomy and pathology by creating pathways through an intervertebral disc (discectomy) or by removing two or more intervertebral discs and one or more vertebral bodies. These techniques have required intervertebral surgical fusion at one or more levels to reconstruct the spine eliminating one or more vertebral motion segments. Recently, the performance of radical discectomy in conjunction with implantation of a total artificial disc replacement has been advocated as a means of performing anterior decompression surgery without spinal fusion. Described and disclosed here is a new method of gaining surgical access that includes a step of repairably performing intravertebral corpectomy for a vertebral body while leaving the vertebral endplates, the lateral vertebral walls, and the intervertebral disc substantially intact and which avoids an intervertebral fusion or artificial disc replacement. This newly disclosed method of operation is in stark contrast to the current state of the art of the radical corpectomy/discectomy approach which is in common use today and has been for decades for multilevel or single level decompressive surgeries in which both soft tissue and bony pathology (anatomy) have been removed in such a way to result in the need for a single or multilevel fusion surgery. The corpectomy of today, prior to this disclosure, involves the irreparable removal of the vertebral body and the vertebral endplates and intervertebral discs above and below the corpectomy. The corpectomy approach in the cervical spine includes the step of placing a bone graft and eliminating the vertebral motion segments by fusing the levels undergoing surgery similar to any of today's common disc removal and fusion techniques. The unique steps of this newly disclosed procedure will, in contrast to previous and current techniques, preserve the motion segments, also referred to as a joint, made up primarily of an intervertebral disc and ligamentous structures and leave the joint in a primarily natural state. Stated directly and clearly this disclosed technique will not fuse, eliminate, or artificially attempt to mechanically replace a patient's otherwise viable joint.
Using the current state of the art, after the surgical removal of the intervertebral disc or intervertebral discs and vertebral body, the surgeon has now gained access to the region posterior to the intervertebral disc and vertebral body and access to the epidural space and may then proceed to use normally available surgical instruments to remove any tissue which is compressing the neural elements. The impact of the typical herniation, bone spur or other pathology on the patient's life is enormous, but the actual size of the tissues needing to be removed from the cervical spine is often only a few millimeters in length.
Once the pathology has been removed the surgeon must now move on to the step of reconstructing the spine where the surgically created cavity was created during the step of exposing the pathology by removing the intervertebral disc or intervertebral discs and vertebral body. This is most commonly addressed by the surgeon performing an intervertebral fusion. This type of spinal fusion is generally augmented with a stabilization procedure that utilizes a titanium plate on the anterior aspect of the spine which is affixed to the vertebral bodies above and below the location of the decompressive surgery with titanium screws.
Bone heals best after the hard exterior shell known as the cortical layer or cortical bone has been removed revealing the softer cancellous bone within the vertebral body. For this reason the surgeon usually begins the reconstruction of the surgically created spinal defect by using a high speed drilling instrument to carve away the hard cortical layer that makes up the vertebral endplates. Once bleeding cancellous bone has been exposed on the vertebral level above and below the removed disc or discs the surgeon may begin the step of preparing an implant.
Commonly used implants that help in promoting fusion are allograft bone, autograft bone and various manufactured devices including cages. Allograft is donated bone and autograft is bone taken from the patient. Allograft is usually provided from one of the nation's tissue banks and is cut from one of the bones of a cadaver specimen that has been designated as an organ donor. To meet the standards of an organ donor, the donor must have led a lifestyle deemed to not have a likelihood of transmitting disease and the cause of death must have been determined to not affect the bones.
Some surgeons feel donor bone does not heal as well as autograft bone. Also, some patients are uncomfortable with the idea of placing the bones of a deceased person into their bodies. For these reasons among others, surgeons will sometimes harvest a portion of a bone from the patient having spine surgery. The step of harvesting bone from a patient requires a separate simultaneous surgery on another area of the body to remove healthy bone. Many patients have reported that the harvesting of healthy bone from their bodies creates as much or more short, medium, and long term pain as the spinal surgery itself causes.
The next surgical step is to cut or machine the bone selected by the patient and surgeon to be used as an implant into a shape and size similar to the void created in the steps of removing the intervertebral disc or intervertebral discs and vertebral body and cutting away the adjoining vertebral endplates' cortical shells.
This shaping step is done in the operating room, usually by the attending surgeon using grinding or cutting tools. This is a critical step in the rebuilding process as an implant too deep could compress and injure the spinal cord. If the implant is too short it will not have proper contact with the bleeding cortical bone and will have undo motion not allowing for proper healing (union or fusion) which will likely prompt additional surgeries to repair the non union. If an implant is too tall, the spine can be over distracted potentially resulting in pain and structural instability. The combination of the intraoperatively shaped and cut vertebral cortical endplates and the custom formed bone implant are often referred to as parts of a construct.
In an additional effort to avoid post operative deformation of the spine and in a step to decrease the chances of the bone implant migrating to an undesirable location as well as for other reasons, another implant is usually added to the construct. This implant is typically called a cervical plate.
A cervical plate is most often made of titanium and is accompanied by screws of the same material. This plate is affixed to the anterior aspect of the spine by placing screws through the plate and into the vertebrae above and below the surgically created defect. Sometimes after the patient heals, another surgery is performed to remove the plate. Post operative complications including screw breakage, screw back out, screw displacement, plate breakage, plate migration, and other complications, can necessitate the removal of the spinal instrumentation. Other times the patient is reluctant to undergo additional surgeries and the plate is left in place.
The disadvantages of the removal of the intervertebral disc or intervertebral discs and vertebral body, and the following intervertebral fusion, by the placement of intervertebral fusion devices are many. Several of these disadvantages can lead to additional surgeries. A fused vertebral motion segment eliminates any movement the patient had previously at that level. This elimination of movement can lead to sore muscles, a reduction in normal activities and additional loading at the adjacent vertebral levels. This additional loading can cause adjacent intervertebral discs to prematurely collapse or wear out. The collapse of adjacent levels can require additional spinal fusions at those now affected levels.
The risk of adjacent level disc disease is great enough that often times a surgeon will suggest going ahead and fusing several levels of the spine during the first surgery if some of the adjacent levels look questionable, as it is possible that the adjacent asymptomatic levels will become symptomatic under the new postoperative conditions.
These costs, risks and unintended consequences are common enough and are thoroughly recognized to the point that many attempts have been made to find substitutes to the fusion procedure.
One of the latest attempts and possibly the most expensive is the artificial disc. Several companies have introduced or conducted clinical trials on various designs of artificial discs. Some are experimenting with augmenting or supplementing the disc, others are experimenting and trialing various designs of partial or complete artificial discs.
The placement of an artificial disc still requires the complete removal of the intervertebral disc to gain access to the surgical target. With the intervertebral disc removed a normal biologically and anatomically intact vertebral joint or motion segment postoperatively is not possible.
Artificial discs have only been available clinically for a short time and many of the pending designs are not yet complete. Therefore, the long term outcomes and potential problems with these devices are still an unknown. Some experts feel the artificial disc or supplemented disc will provide at a minimum an alternative to the definitive and generally considered non beneficial intervertebral union or fusion. Many of those experts also feel the likely result will be additional surgeries down the road for the patient as the artificial discs and or augmented discs wear out. Others also state that the changes provided by the artificial disc will alter the anatomical loading of the posterior facet joints leading to arthritis.
In accordance with this invention, after the surgeon has performed an incision in the skin of the patient in proximity to the pathology, the surgeon will next remove either mechanically with the use of a high speed bone dissecting instrument or by other means, such as using a laser or other instrument, the corpous portion of the vertebrae leaving but a shell defined by the lateral walls and end plates of the bone. The portion of the bone being removed preferably is beginning anteriorly or anterolaterally and extending inwardly toward the anterior or anterolateral epidural space and proximal to the dura.
The opening associated with this intravertebral corpectomy serves two alternate purposes. 1) The removal of the bone if in proximity to the pathology can in the process of removal also remove the pathology, or 2) it provides a space that allows the surgeon to perform a surgical procedure that is directed to remove the pathology or treat the surgical target. In either process, the intravertebral corpectomy allows the procedure for removing or treating the pathology without the necessity of providing an intervertebral fusion. Obviously, the elimination of the fusion, provides to the patient the mobility that was evidenced before the operation occurred. Hence, the intravertebral corpectomy affords a medical procedure that obviates the fusion required when other types of medical procedures, like discectomy or cervical corpectomy, are performed.