Minimally Invasive Spine Surgery— Who Can it Help?
The past decade has seen a revolution in minimally invasive techniques to improve surgical outcomes, including minimally invasive spine surgery (MIS). Whereas traditional open techniques have their indications, procedural necessities including large openings, muscle attachment takedown, copious retraction, and increased operative times often stand in the way of the goals of MIS surgery. To circumvent these obstacles, MIS has emerged as an alternative form of surgical treatment, with innovations directed at restoring each of the objectives lost in large traditional operations.
Specific advancements in the field have included the development of unique methods of nerve monitoring and tissue retraction. Intraoperative nerve monitoring has offered improvements in operative safety in small corridors by avoiding direct damage or retraction injury of non-visualized neural elements.1 The virtually universal use of tubular self-retaining retractors that allow for muscle fiber spreading, rather than muscle takedown, are widely believed to be a major source of the decreased pain, reduced blood loss, earlier mobilization, and improved outcomes seen in numerous studies.2
In some cases, these tubular retractors have offered completely new corridors of surgical approach—for example, the lateral approach to the thoracic and lumbar spine. This has eliminated the widespread use of comparably morbid thoracotomies and large lumbar incisions in the effort to gain surgical access to these segments of the spine (Figure 1).
Furthermore, the development of specialized drills, delivery cannulas, and instrumentation platforms allow for safe performance of spinal decompression, as well as instrumented fusion through percutaneous placement of vertebral interbody devices, pedicle screws, fixation rods, augmenting cement, and numerous other therapeutic measures (Figure 2).
These rapid advances in techniques, instruments, and indications have led to the successful implementation of MIS for the treatment of a diverse group of pathologies. Indeed, MIS procedures are now applied to all arenas of surgical disease including the treatment of trauma, spinal deformity, tumor, and degenerative disease.
This article will review the advancements in MIS, as well as outline which patients may benefit from MIS.
Over the last decade, the number of tools in the MIS surgeon’s armamentarium has increased dramatically. In the next section, we will discuss the implementation of MIS surgery in a number of commonly encountered disorders. But first, we will briefly introduce a few of the newer and commonly used techniques available. This is not an exhaustive list, as new technologies emerge in this arena daily.
Lateral Lumbar Interbody Fusion
Since its publication in 2006 by Ozgur et al, this procedure has revolutionized thoracolumbar spine surgery.3 Using a lateral approach to the spine via fluoroscopy and serial dilation of the iliopsoas muscle, surgeons are able to perform a near total discectomy and placement of a large interbody cage in order to facilitate fusion. The cages in this procedure are on average 3 to 4 times larger than the traditional posterior or transforaminal lumbar interbody, which improves rates of fusion and diminishes cases of pseudarthroses, or failed fusion of the spine (non-union) (Figure 3).
Opponents of lateral lumbar interbody fusion (LLIF) claim that the indirect neuroforaminal decompression accomplished with placement of a large interbody graft is not as effective as direct decompression from the posterior approach. However, Kepler et al4 recently reported a 35% average increase in foraminal area in LLIF (P<0.01), which theoretically provides mechanical relief of nerve root compression in the foramen.
Injury to the lumbar plexus is also possible; however, the use of neuromonitoring during these cases provides a tool against injury (Figure 4). Other benefits of this technique include less muscular dissection/trauma, decreased operative time, decreased hospital stays, less blood loss, and overall improved patient satisfaction.5-8 The lateral approach also lends itself to other uses besides interbody fusion, such as lateral corpectomy for trauma and tumor. It has also been used recently in restoration of coronal and sagittal balance in cases of spinal deformity.
Percutaneous Spinal Screw Fixation
Posterior pedicle screw fixation of the lumbar spine in combination with interbody graft placement provides an internal bracing system to allow fusion across the interbody space. When performed bilaterally, it provides mechanical stability in all axes of rotation (Figure 5). Recent industry advances in screws and screw systems give surgeons the opportunity to place pedicle screws percutaneously, or through the skin, with minimal muscle dissection (Figure 6). Using fluoroscopy and muscle dilation rather than electrocautery (which is a source of significant postoperative pain), the surgeon can place pedicle screws with more lateral to medial angulation than is possible in open cases, which leads to improved pullout strength. Placement of percutaneous pedicle screws can also be done in the lateral position after an interbody cage has been inserted, thus saving steps such as removing the drapes, repositioning the patient, and redraping (Figure 7). Another advancement is placement of transfacet screws in a percutaneous nature (Figure 8). This may be useful in cases where pedicle screws are not possible.
Axial Lumbar Interbody Fusion
Discogenic disease at the L5/S1 level of the spine is unable to be treated through a lateral interbody fusion due to anatomic constraints, such as the iliac crest and lumbar plexus. However, a technique named AxiaLIF (lumbar interbody fusion) (TranS1, Raleigh, North Carolina) allows surgeons access to this level percutaneously. It is accomplished through a small paracoccygeal incision and finger dissection along the presacral plane that allows for docking of a retractor and placement of a screw from the vertebral body of S1 up into L5 after using wire brushes to clear the disc space. It is generally recommended that this be backed up with posterior fixation due to the unstable nature of the construct. Patients are pretreated with a bowel regimen, as injuries to the bowel, though rare, are a possibility. This technique takes on average 40 to 60 minutes.