The present invention relates to medical devices, methods and systems. More specifically, the invention relates to devices, methods and systems for promoting fusion of and/or stabilizing a facet joint of a spine.
Approximately 80% of Americans experience at least a single episode of significant back pain in their lifetime. For many people, back pain is a chronic, often debilitating disorder. The direct costs of treating back pain, as well as the indirect costs, such as lost wages and decreased productivity, are staggering.
Although back pain may be caused by a number of different factors, many cases of back pain are caused by conditions related to the spinal (or “vertebral”) column. The vertebral column is made up of bones (vertebrae) and intervertebral discs that reside in the joint spaces between the vertebral bodies of the vertebrae. Three joints reside between every two adjacent vertebrae—one larger intervertebral joint between the two intervertebral bodies and two facet joints located posterolaterally relative to the vertebral bodies. These three joints share the load applied between every set of two vertebrae. Many spinal ailments are caused by degeneration, injury or deformity of these vertebral joints and/or intervertebral discs.
Treatment of spinal pain typically begins with conservative, non-surgical methods, such as rest, heat, analgesics, physical therapy and manipulation. Unfortunately, however, conservative treatments fail in a significant number of spinal pain patients, and surgery is often required. Current surgical procedures for treating intervertebral disc and joint maladies include decompressive surgery, in which all or part of an intervertebral disc and/or the spinal laminae and facets are removed, decompression with fusion of the joint (or “arthrodesis”), and arthrodesis alone. Intervertebral joint arthrodesis involves fusing two adjacent vertebrae to stop the motion between those vertebrae.
Decompression (removal of structures compressing the spinal nerves including laminae, facet joints and/or intervertebral discs) is a very common surgical procedure that is very effective in promptly relieving significant pain derived from pressure on spinal nerve roots (“radicular” pain). The overall success rates for decompression alone, however, range from 48% to 89%. Spinal fusion is sometimes needed in combination with decompression to more successfully treat spinal pain.
Intervertebral fusion is designed to stop the motion at a painful vertebral joint, which in turn should decrease pain generated from the joint. It is also performed to stabilize an unstable intervertebral segment, which if left unfused, could cause recurrent compression of the spinal nerves. Fusion procedures involve adding bone graft to an area of the spine to set up a biological response that causes the bone graft to grow between the two vertebral elements and thereby stop the motion at that segment. Often, some type of support structure is attached to the two vertebrae being fused, to hold the vertebrae in a stable position relative to one another while the bone graft material causes fusion. Typical support structures, for example, include bone screws (or “pedicle screws”) attached to rods. Discectomy combined with fusion has been the most common surgical treatment for symptomatic cervical spondylosis for over 40 years. Good to excellent results have been reported in 52-100% of anterior lumbar interbody fusions and 50-95% of posterior lumbar interbody fusions.
A number of different spinal fusion surgical procedures are currently in use. The most common fusion procedure performed in lumbar surgery is posterolateral intertransverse fusion. Although the technique is often quite successful, the standard procedure often causes significant trauma to the paraspinous muscles. These muscles must be stripped from the transverse processes and retracted for an extended period of time to expose the underlying bone, which can result in denervation, devascularization, and ischemia of these important muscles, leading to atrophy and necrosis. Significant spasm in the short term and atrophy and necrosis in the long term contribute to the morbidity and sequelae of fusion. The clinical effect of this muscle morbidity can be significant postoperative pain and functional impairment in the convalescent period, as well as permanent impairment of paraspinal lumbar muscular function.
Other surgical techniques for performing spinal fusion are associated with similar and/or additional risk factors. For example, posterior lumbar interbody fusion (“PLIF”) achieves fusion by inserting bone grafts, titanium threaded cages, bone dowels, or carbon fiber spacers filled with bone graft into an intervertebral disc space. All PLIF techniques require removal of the posterior bone of the spinal canal (laminectomy), retraction of the nerves and removal of the disc material from within the disc space, any of which may cause complications. Another procedure, anterior lumbar interbody fusion (“ALIF”), is similar to PLIF, except that in ALIF the disc space is fused by approaching the spine through the abdomen instead of through the back. An additional, and potentially significant, risk of ALIF is potential damage to abdominal structures, such as the large arteries that supply blood to the legs.
As mentioned above, with many spinal fusion procedures, some type of support structure, such as screws, rods, pins, cages and/or the like, is used to hold the adjacent vertebrae in place while they are fusing together with the help of the bone graft, bone adhesive, or the like. One of the primary risks of fusion surgery is that a solid fusion will not be obtained (“nonunion”), thus requiring further surgery. One of the main challenges of intervertebral fusion surgery is to stabilize the vertebrae long enough, using the support structure(s), so that they have time to fuse. Another challenge is actually applying the support structure properly. Pedicle screws, for example, may often be effective at providing support during intervertebral fusion, but they can be difficult to place properly, and if misplaced may cause nerve root and/or vascular injury.
As the population continues to age, surgical procedures for fusing and/or stabilizing vertebrae will become ever more common. Therefore, a need exists for improved techniques, devices and systems for performing such procedures. Such improved methods and devices should ideally facilitate and/or enhance intervertebral fusion, while preventing or reducing the prevalence of complications or sequelae. Ideally, minimally invasive procedures would be developed that would provide stabilization of an intervertebral joint for a sufficient period of time to allow the vertebrae to fuse. Also ideally, such procedures would be relatively simple to use. At least some of these objectives will be met by the present invention.