The present invention is related to spinal fixation and stabilization systems in general and to intervertebral implant systems for promoting arthrodesis in particular.
Stabilization of vertebrae relative to each other, primarily for the purposes of indirect nerve decompression and fusion (arthrodesis), is an well-accepted surgical objective. To date, most methods entail a two staged process of intervertebral distraction and then subsequent interposition of either a cortical bone graft or an inorganic implant to maintain the relative position of the vertebrae during the healing phase of arthrodesis.
Many variations of this basic surgical technique exist. Unfortunately, these systems often require considerable time and effort for successful implant placement. This is frequently due to the fact that such systems typically require both excessive surgical tissue dissection and mechanical vertebral distraction such that the various stabilization component(s) of the system can be successfully positioned in a patient""s intervertebral space.
In addition, the dimensional constraints typically imposed by access considerations are often in conflict with the desire to place the largest implant possible to support the loads transmitted across the vertebral endplates. Specifically, the larger the implant inserted, the greater the amount of resulting tissue damage both in the intervertebral space, and in the surrounding tissues.
An additional problem with many intervertebral implant devices is that they do not confer a proper lordotic relationship between the vertebrae, either as a consequence of their geometry or their insertion method.
The present invention provides an intervertebral implant system, comprising; a plurality of implants, each implant having at least one hole passing therethrough; and an elongated member dimensioned to pass through the holes in each of the plurality of implants. In a preferred method, the plurality of intervertebral implants are positioned in a patient""s intervertebral space by; introducing the elongated member into the patient""s intervertebral space; and sequentially advancing a plurality of intervertebral implants over the elongated member and into the patient""s intervertebral space.
In preferred aspects of the invention, the elongated member comprises a cord, string, tether or suture which is used to hold together the plurality of intervertebral implants such that together they form an implant assembly which is positioned between two adjacent vertebrae.
In preferred aspects, each of the intervertebral implants have ends which are angled such that when the implants are pulled or pushed together, they will tend to form a generally C-shaped assembly, which may easily be positioned between two vertebral endplates around the curved perimeter of the patient""s intervertebral space.
As will be explained, another advantage of the present system is that the degree of curvature exhibited by the C-shaped implant assembly can itself be selected by selecting implants which are dimensioned with their ends being disposed at preferred angles.
Another important advantage of the present system is that it can be deployed through a narrow operating cannula. As such, the present system advantageously permits the placement of a load supporting implant assembly over a large area between two of the patient""s vertebrae, but without requiring that a large diameter access portal pass through the patient and into the patient""s intervertebral space.
Therefore, the present system is ideally suited to be introduced into a patient in a minimally invasive surgical procedure, with minimal disturbance to the soft musculature and ligament tissue structures in the spinal region. In contrast, the placement of existing intervertebral implant systems typically compromises such tissues.
Another important advantage of the present system is that it provides an assembly (comprising a plurality of intervertebral implants) which can easily be positioned around the curved perimeter of the patient""s intervertebral surface, such that the assembly is positioned on the denser portion of the vertebral endplates (i.e.: the perimeter) to provide enhanced support between the two adjacent vertebrae.
In an optional preferred aspect, at least some of the plurality of individual intervertebral implants have top and bottom surfaces which are angled to one another such that the plurality of intervertebral implants form an assembly which tapers in a lordotic angle when the implants are abutted together end-to-end. Therefore, another advantage of the present system is that the overall implant assembly can preferably be shaped to provide a proper lordotic angle between the adjacent vertebrae when positioned therebetween.
In various optional aspects of the invention, a positioning rod can be used to position each of the separate implants. In one aspect, the separate implants are pushed tightly together, such that they form a C-shaped assembly.
In additional aspects, the elongated member passing through each of the implants can be withdrawn or tightened such that the individual implants are tightened together to abut tightly against one another end-to-end.
As will be explained, an operating cannula(e) and a surgical guideframe for positioning the operating cannula(e) may also preferably by used.
Other advantages of the present system include reduction both in the amount of vertebral distraction and tissue dissection required, thereby decreasing surgical time, complexity and trauma to the patient.