Patients that experience chronic discomfort in their backs often require remedial surgery in order to correct structural problems such as disc degeneration. This degeneration may come in many forms, but invariably results in an unacceptable variance in the alignment and/or spacing of one or more portions of the spine. It is acknowledged that maintenance of the normal curvature of the lumbar spine is preferable, and so when corrective surgery is required, it is important to re-establish the normal biomechanical arrangement, and to restore the profile of the spine.
A wide variety of prior art techniques have been used to correct spinal posture and the placement and spacing of the individual vertebrae. One common technique where disc degeneration has occurred is to remove the degenerated disc, distract the disc space, and fuse the adjacent vertebrae together. These interbody fusions attempt to address the instability caused by degenerative discs and facet joints by using implants to restore the natural arrangement of the spine and stabilizing screws, and rods to anchor the spine in place while the fusion of bones is accomplished. In particular, most of these methods require the insertion of metal cages packed with bone or ortho-biological compounds (osteoinductive/osteoconductive) within the disc space that serve to fuse the adjacent vertebrae.
Again, there are innumerable techniques and surgical approaches to accomplish this interbody fusion. Traditional techniques use either a posterior or anterior approach (see, FIGS. 1a & 1b). In a posterior technique, such as Posterior Lumber Interbody Fusion (PLIF), it is necessary to dissect and retract the back muscles, bones, vessels, ligaments and nerves, which causes a great deal of trauma to the supporting muscles and ligaments of the back. Meanwhile, in an anterior approach, such as Anterior Lumber Interbody Fusion (ALIF), it is necessary to proceed through the abdominal musculature and cavity. This creates the risk of major injury associated with trauma to important vascular structures and/or the genitourinary structures. More recently minimally invasive techniques have been proposed that use a trans-lateral approach, such as Transforaminal Lumber Interbody Fusion, or a trans-sacral approach, such as Axial Lumbar Interbody Fusion (AxiaLIF®). (See, e.g., U.S. Pat. No. 6,899,716 and U.S. Pat. Pub. No 2011/0112373, the disclosures of which are incorporated herein by reference.).
All of these methods have drawbacks, either with regard to the invasiveness of the technique, or, in the case of the trans-sacral approach, the limited area of the spine on which they can be implemented. Now a trans-psoas approach has been proposed that gives access to the disc space from L-1 to L-5. This approach is being increasingly employed to treat common spinal disorders including disc degeneration, spinal deformity and trauma. However, the technique has not been extended to the L-5/S-1 disc space because the anatomy of the pelvis, the lumbarsacral plexsus and the iliac vessels make the standard trans-psoas approach extremely dangerous. In addition, the tools to work with this approach are still quite limited and, primarily being borrowed from more traditional techniques, are not well-suited to exploit the minimally invasive nature of the trans-psoas approach. Therefore, a need exists to provide surgical tools and methods adapted for use in a trans-psoas approach to spinal fusion.