A leading cause of lower back pain arises from lumbar intervertebral disc pathology caused by degeneration of the intervertebral disc. As a disc degenerates, the nucleus and annulus functions are compromised. The nucleus becomes thinner and unable to handle compression loads. The annulus fibers become redundant as the nucleus shrinks. The redundant annular fibers are less effective in controlling vertebral motion. The disc pathology can result in the bulging of the annulus into the spinal cord or nerves, narrowing of the space between the vertebra where the nerves exit, tears of the annulus under abnormal loads caused by excessive motion between the vertebra, and disc herniation. Additionally, lower back pain may be caused by collapse of the disc and the dysarthrosis of an unstable or degenerative vertebral facet joint. A technique for managing these problems is to remove the problematic disc and replace it with a porous intervertebral fusion device that restores disc height and allows for bone growth therethrough for the fusion of the adjacent vertebra.
In general, delivery of conventional intervertebral fusion devices requires significantly invasive implantation procedures. In some configurations, the intervertebral implants are not adjustable by the surgeon during an open surgical procedure. Therefore, the surgeon must choose the size that most closely matches the desired height, length, and width dimensions, and then make the implant fit. Because these implants are of a predetermined size and shape, the implant site must correspond to the implant configuration. This can require extensive site preparation to complete implantation. Fusion devices with parallel superior and inferior surfaces either fit tightly posteriorly and loosely anteriorly, or require removal of vertebral bone in order to fit posteriorly. Extensive site preparation such as this can compromise the success of the implantation procedure by causing excessive damage to the receiving vertebral elements. In addition, open surgical implantation of posterior implants requires excision of stabilizing muscles, ligaments, tendons, and bony structures such as facet joints. The implants must therefore overcome the destabilization caused by the surgery, as well as provide additional stabilization to promote bony fusion. In addition, open anterior surgery in the lumbar spine can present risks due to the close proximity of the aorta and bifurcation of the aorta.
To combat some problems associated with open anterior surgeries, minimally invasive procedures have been developed. Current implants, or inner body cages, used in minimally invasive procedures, however, are still unable to conform to the necessary lordotic angle between adjacent vertebra. In addition, surgeons must rely on high manual forces to distract (dilate) the disc space. Finally, current cages do not have a shape that is optimal in terms of support.
Accordingly, there is a need for instrumentation and techniques that allow for a self-distracting, self-leveling, and adjustable inner body cage that can be easily inserted and positioned.