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10 Articles in Volume 12, Issue #7
August 2012 Pain Research Updates
Cash Patient: A Clinical Dilemma
Common Opioid-Drug Interactions: What Clinicians Need to Know
Compliance in Pain Patients: Balancing Need to Test With Need to Treat
Cytochrome P450 Testing In High-dose Opioid Patients
Discharging a Patient Suspected of Diversion
Examining the Safety of Joint Injections In Patients on Warfarin
Genomic Medicine
Letters to the Editor from August 2012
Minimally Invasive Spine Surgery— Who Can it Help?

Minimally Invasive Spine Surgery— Who Can it Help?

Outcomes of minimally invasive spine surgeries now rival, or even outperform, traditional open procedures.

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).

Figure 1. Traditional open posterior wound for segmental fixationFigure 2. minimally invasive spine surgery with percutaneous pedicle screw fixation

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.

Techniques
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.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).

Figure 3. LLIF comparison

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.

Figure 4: use of directional neuromonitoring during an XLIF

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.

Figures 5-8

Tubular Microdiscectomy
Herniated nucleus pulposus, or a herniated disc, is a common cause of radicular pain. Although herniated discs commonly resolve on their own, many times patients are so incapacitated after maximizing nonoperative therapies that they opt for surgical intervention. In the case of a patient with primarily leg pain, rather than axial back pain, who has a corresponding herniated disc at the appropriate level, a tubular microdiscectomy is an excellent minimally invasive option. It involves a 2 to 3 cm posterior incision just off the midline, and placement of dilators and a retractor under fluoroscopic guidance. Once in place, a high-speed drill and bayoneted instruments are used to do a partial laminectomy/mesial facetectomy to access the disc herniation. This is usually done on an outpatient basis with the majority of patients experiencing immediate pain relief.

Microendoscopic Discectomy
Another MIS option for the management of a lumbar herniated disc is microendoscopic discectomy (MED). First described in 1997 by Foley and Smith,9 MED allows surgeons to decompress a symptomatic lumbar nerve root reliably using a minimally invasive endoscopic approach.9-12 Although seemingly a more attractive option given the subcentimeter incision, more surgeons are familiar with tubular microdiscectomy technique for lumbar disc herniations. However, given the recent advances in camera optics and 3D imaging, endoscopic approaches likely will play an important role in the future of spine surgery.

Illustrative Cases

Case 1: Degenerative
The patient is a 72-year-old man with chronic low back pain and radicular pain down the outside and back of both legs. He has tried and failed every nonoperative measure, including opioids and non-steroidal anti-inflammatory drugs, injections (epidurals and facet blocks with lidocaine and steroids), rhizotomies (destruction of nerve roots), physical therapy, chiropractic manipulation, and acupuncture. The patient feels his life is significantly impaired and is not worth living since he has many grandchildren and was previously active.

After discussing his surgical options, as well as the significant risks associated with surgery, he decided to undergo an extreme lateral interbody fusion (XLIF, NuVasive Inc, San Diego, California) at L2-L5 with anterior longitudinal ligament (ALL) release to correct sagittal balance and percutaneous pedicle screw fixation (Figure 9). This was separated into two stages with the patient’s total hospitalization lasting 5 days, total blood loss for both procedures of 100 mL, and early ambulation with near total pain relief.

Figures 9-11

Case 2: Trauma
A 19-year-old man was involved in a motor vehicle collision. The patient (the driver) had been restrained by his seat belt. He never lost consciousness and, on examination, was found to be neurologically intact. However, the patient suffered an L1 burst fracture involving significant spinal canal compromise from a retropulsed fragment. He was cleared by the trauma team and taken directly to the operating room for a lateral retropleural L1 corpectomy and fusion, with placement of an expandable cage and lateral plate (Figure 10). The patient awoke from surgery with no neurological deficits and continues to do well in follow up (Figure 11).

Case 3: Tumor
A 47-year-old nurse with no medical history was referred to a neurosurgeon after she was found to have a pathologic T11 fracture with spinal cord compression during a workup for back pain and gait instability. She was taken immediately to the operating room for a lateral retropleural corpectomy with placement of an expandable cage with a wide footprint to prevent subsidence. This was all done through a 5 cm lateral midaxillary incision (Figures 12 and 13). This procedure was intended to treat the neural elements, compression, and impending paralysis. Pain was controlled with routine postoperative pain medications.

Figures 12-14

Case 4: Deformity
The patient is an elderly 75-year-old woman with a history of untreated scoliosis. The patient complained of chronic low back pain and leg pain that is worse on the left than the right side. She feels she has lived with this pain (scoliosis) long enough, and that the pain is getting worse to the point where she is incapacitated. The patient elected to have minimally invasive multilevel lateral lumbar interbody fusions with ALL release for restoration of sagittal balance. The second stage of the surgery entailed placement of percutaneous pedicle screws from T10-S1. Postoperative imaging showed excellent correction of sagittal and coronal alignment (Figure 14). The surgical treatment in this group of patients is challenging. The morbidity is significant with “conventional” surgical procedures. In this case, the outcome was successful with a combination of MIS techniques.

Conclusions
In this climate of evidence-based medicine and cost-effectiveness analyses, it will be ever more challenging to advance surgical disciplines with new technologies and techniques. However, as we have shown through technical explanations and case illustrations, MIS procedures can rival or even outperform some of the more morbid open procedures. In addition, these techniques allow for surgical intervention in the elderly and those previously deemed unfit for surgery, with excellent radiographic and clinical results. For this reason, it is extremely important that we as clinicians record outcome data as we push the boundaries of our self-imposed limitations.

Last updated on: October 26, 2012
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