Back pain can be caused by a variety of factors, including, but not limited to the rupture or degeneration of one or more intervertebral discs due to degenerative disk disease, spondylolisthesis, deformative disorders, trauma, tumors and the like. In such causes, pain typically results from compression or irritation of spinal nerve roots by reduced spacing between adjacent vertebrae, a damaged disk and/or misalignment of the spine resulting of the injury or degeneration.
Common forms of treating such pain include various types of surgical procedures in which a damaged disk may be partially or totally excised, and one or more implants is inserted between adjacent vertebrae in an effort to restore the natural spacing and alignment between the vertebrae that existed previous to the injury or degeneration, so as to relieve the compression, irritation or pressure on the spinal nerve or nerves and thereby eliminate or significantly reduce the pain that the patient is experiencing. Typically, the one or more implants are used together with substances to encourage bone ingrowth to facilitate fusion between the adjacent vertebrae. Some procedures provide implants that allow at least some limited motion between the adjacent vertebrae, even after opposite ends of the implant are fixed to the adjacent vertebrae, respectively.
Among know procedures for performing fusion are PLIF (posterior lumbar interbody fusion), ALIF (anterior lumbar interbody fusion) and TLIF (transverse or transforaminal lumbar interbody fusion). A PLIF procedure achieves spinal fusion in the low back by inserting an implant such as a cage and, typically, graft material (to encourage bone ingrowth) directly into the disc space between adjacent vertebrae. The surgical approach for PLIF is from the back of the patient, posterior to the spinal column.
An ALIF procedure is similar to the PLIF procedure), except that in the ALIF procedure, the disc space is fused by approaching the spine through the abdomen, from an anterior approach, instead of through the lower back, from a posterior approach. Although previously there was a lot of interest in perfecting an endoscopic approach for ALIF surgery, it has largely been abandoned because it placed the great vessels (aorta and vena cava) at too great a risk.
A TLIF procedure involves a posterior and lateral approach to the disc space. To gain access to the disc space, the facet joint may be removed whereby access is gained via the nerve foramen. Typically only a single implant is placed in a TLIF procedure. The implant is inserted from a postero-lateral approach, as noted, and is ultimately placed in the middle-to-anterior aspect of the disc space.
There are certain conditions where a unilateral PLIF procedure is superior to a TLIF procedure. Such conditions include those where sever spinal stenosis is present. PLIF procedures typically place a pair of implants, one on each side of the disc space. To accomplish this, a typical approach forms two access ports into the disc space, both posterior to the spinal column, with one port one side relative to midline (the spinal process) and the other on the opposite side, relative to midline. Using this approach, each implant can be delivered and placed along a substantially direct delivery pathway. However, because two ports are formed, this results in a relatively large amount of removal of tissues, and risks nerve damage on both sides of the spinal column.
Alternatively, both implants may be delivered using a unilateral PLIF technique in which only one port is formed on one side of the midline, posterior spinal column. This significantly reduces the amount of tissues that need to be removed and reduces the number of nerves at risk of being damaged by the procedure by half. A unilateral PLIF procedure requires the first implant, after being inserted into the disc space, to be laterally driven over the midline of the intervertebral disc space and into position in the opposite side of the disc space. Drawbacks to current procedures include difficulties in laterally driving the first implant from one side of the disc space to the other. During this process, when using an implant/cage that has substantially equal heights on both sides of the implant/cage the leading side of the implant often resists moving in the transverse direction towards the opposite side of the disc space, and may dig into the annulus fibrosus and resist transverse driving of the implant. Moreover, the use of standard instruments such as cage inserters, end impactors, curved curettes, curved chisels, etc. often result in breaking the implant, when used to try to drive the implant from one side of the disc space to the other. This poses a serious risk of nerve root injury and/or injury to other body structures when an instrument breaks or a cage breaks, or during the process of removing a broken cage. Additionally, there are cases were a broken cage is unable to be completely removed and this compromises a successful fusion outcome.
The use of two implants in a PLIF procedure as opposed to the use of one implant, such as in a TLIF procedure, has been noted to markedly improve interbody fusion. However, it would be further advantageous to fusion resulting from a two implant procedure if the implants could be further laterally spaced from the midline of the intervertebral disc space, compared to current two implant procedures, as this would further enhance a honeycomb formation of fusion.
There is a continuing need for implants, instruments and procedures for performing unilateral PLIF to facilitate safer and easier delivery of the first implant form one side of the disc space to the opposite side. There is a continuing need to implants instruments and procedures designed to permit placement of the implants further laterally from the midline of the intervertebral space than is possible using current implants, tools and procedures. The present invention meets at least all of the above needs.