|SYMPOSIUM - MINIMALLY INVASIVE SPINE SURGERY
|Year : 2020 | Volume
| Issue : 1 | Page : 4-10
Fundamentals of minimally invasive spine surgery
Louis Chang, Sertac Kirnaz, Juan Del Castillo-Calcaneo, Ibrahim Hussain, Roger Härtl
Department of Neurological Surgery, Weill Cornell Brain and Spine Center, New York Presbyterian/Weill Cornell Medical Center, New York, USA
|Date of Submission||29-Apr-2019|
|Date of Decision||21-Oct-2019|
|Date of Acceptance||07-Dec-2019|
|Date of Web Publication||05-Feb-2020|
Dr. Roger Härtl
Dr. Roger Härtl, Department of Neurological Surgery, New York Presbyterian/Weill Cornell Medical Center, 525 E 68th Street, New York 10021, New York.
Source of Support: None, Conflict of Interest: None
Minimally invasive spine surgery (MISS) is a set of techniques and procedures that aims to minimize local tissue damage while achieving the same goals of traditional open surgery. In this article, we will provide a brief synopsis of the current state of MISS including its advantages over open surgery and its limitations. We will also describe basic techniques and essential tools needed to perform MISS effectively. As such, we have identified six interrelated fundamental principles to achieve success in MISS. They are the six Ts: Target, Technology, Technique, Training/Teaching, Testing, and Talent.
Keywords: Indirect decompression, lateral lumbar interbody fusion, lumbar spine, minimally invasive surgery, minimally invasive, thoracic spine, transforaminal lumbar interbody fusion, extreme lateral interbody fusion
|How to cite this article:|
Chang L, Kirnaz S, Del Castillo-Calcaneo J, Hussain I, Härtl R. Fundamentals of minimally invasive spine surgery. Indian Spine J 2020;3:4-10
|How to cite this URL:|
Chang L, Kirnaz S, Del Castillo-Calcaneo J, Hussain I, Härtl R. Fundamentals of minimally invasive spine surgery. Indian Spine J [serial online] 2020 [cited 2021 Jan 19];3:4-10. Available from: https://www.isjonline.com/text.asp?2020/3/1/4/277807
| Introduction|| |
Minimally invasive spine surgery (MISS) can be defined as a “suite of technology-dependent techniques and procedures that reduces local operative tissue damage and systemic surgical stress enabling earlier return to function striving for better outcomes than traditional techniques.” In other words, the philosophy of MISS is centered around the use of techniques and technologies that can allow the surgeon to achieve the same goals of traditional surgeries with the least amount of tissue disruption and avoidance of unnecessary removal of anatomic structures.
Therefore, by virtue of limiting collateral damage to surrounding tissues, MISS has several advantages over open surgery, including reduced perioperative morbidity, reduced surgical site infections, decreased blood loss, and less iatrogenic mechanical instability. A brief overview of the history of MISS is listed in [Table 1].,,
|Table 1: Historical overview of the evolution of minimally invasive spine surgery|
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The core of MISS can be thought of in terms of six foundational pillars defined as the six Ts: Target, Technology, Technique, Training/Teaching, Testing, and Talent; (1) target refers to appropriate patient and procedural selection for MISS, (2) technology enables or facilitates a particular MISS, (3) technique, (4) training/teaching refers to interplay of both the acquisition and instruction of skills necessary for the surgeon to perform MISS, (5) testing is a critical review and examination of surgical outcomes, and (6) talent refers to the building and mastery of skills. Each of these fundamental principles of MISS will be discussed in turn; however, it is important to keep in mind that these six principles are interrelated. For example, the results of data collection, research, and outcome assessment (testing) over time will refine our surgical decision-making process (target). Another example would be the tools and techniques used will determine the surgical teaching and training required to master MISS [Figure 1].
| Potential of MISS|| |
Each year, 103,000 laminectomies and 370,000 discectomies are performed in the United States. In addition, 30%–50% of spinal fusion cases have the potential to be performed with MISS techniques, making up approximately 413,000 procedures each year. Complete or partial use of MISS techniques can be used to perform 75% of all spinal surgeries over conventional techniques, and therefore, this indicates that the full potential of MISS has yet to be achieved. The most challenging aspect for MISS is still the treatment of significant and multilevel deformities, but progress is being made to at least partially apply some of the benefits of MISS, such as percutaneous screw placement, navigation, and lateral approaches.
By plotting the complexity of thoracolumbar procedures against their invasiveness, the current benefit of MISS can be illustrated [Figure 2]. Although this is a somewhat arbitrary and subjective approach, it effectively shows the current role of MISS vis-a-vis open traditional surgery. In terms of procedure complexity, the spectrum progresses from simple lumbar disc herniation on the left to single and multilevel lumbar stenosis decompression, to single-level spondylolisthesis cases treated with minimally invasive surgery (MIS) transforaminal lumbar interbody fusion (TLIF), to multilevel lateral, and then combined lateral or TLIF and possibly anterior lumbar interbody fusion (ALIF) procedures for moderate deformities. All the way on the right, we find complex deformities defined as fused or rigid spines requiring >5 levels of instrumentation. Invasiveness on the Y axis can be assessed in terms of surgical parameters such as intraoperative blood loss, infection risk, length of stay, and postoperative pain levels.
|Figure 2: Comparison between level of complexity and invasiveness in minimally invasive spine surgery versus open surgery|
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Literature and experience show that with the very low level complexity cases, no major difference is observed between MISS and open traditional surgery when it comes to outcome and with many of the factors associated with invasiveness. The more we move to the right, the more complex and “less minimally invasive” treatment interventions become. Such is the case for rigid curves requiring >5-level surgery including L5/S1, rigid deformities requiring >10-level fusion, or previously instrumented multilevel fusions . The downsides of MISS currently outweigh the potential benefits.
On the basis of these thoughts, it is our understanding and belief that the zone of greatest benefits with MISS currently lies within the treatment of pathologies ranging from lumbar disc herniation to moderate deformities up to approximately five levels. This benefit zone for MISS, however, is constantly being expanded with the increasing incorporation of MISS components into more complex surgical pathologies. Examples of this would include the use of lateral anterior column release procedures with hyperlordotic cages combined with more traditional open osteotomy procedures. Other examples include the potential use of three-dimensional (3D) navigation and robotic surgery in multilevel deformity correction procedures, preoperative 3D planning, and virtual augmentation, which may contribute to overall less invasiveness.,,,
These considerations show that MISS has already gained a significant role in spinal surgery that will become even more prominent as technology and techniques evolve over time. Indeed, a future of spinal surgery without an adoption of MISS techniques and principles does not seem to be possible.
| The Six Ts of MISS|| |
Target is choosing the right procedure for the patient and the presenting pathology. Often within spinal surgery, there are several possible surgical avenues that can be used to address a patient’s surgical issue. In MISS, it is important to select a procedure that is both personalized and meets the needs of the patient.
Surgical decision-making involves a combination of careful consideration of accurate diagnosis, an understanding of the natural history of the underlying pathology and the likely impact of surgery on the disease process. Accurate diagnosis will require the understanding and classification of different types of pain patterns and presentations such as radicular pain, axial back pain, myelopathy along with the synthesis of a careful clinical examination and history taking, review of imaging studies, and sometimes additional testing such as electromyography, nerve conduction studies, or diagnostic injections. This can be best accomplished in a team-based approach with other subspecialists such as pain anesthesiologists, physiatrists, and neurologists all involved in the workup. Careful review of imaging studies with a radiologist with advanced expertise in spinal pathology in more complex cases is also helpful.
Second, other factors have to be taken into account during the surgical decision-making process such as the natural history of the disease, age, functional status, and comorbidities including obesity and osteoporosis. Finally, surgical decision-making in MISS must take into consideration the patient’s expectations, lifestyle, as well as social factors. For example, if the patient is an avid athlete and wishes to return to an active lifestyle, the surgical decision may be different than in a patient who lives a sedentary lifestyle and desires nothing more than to be able to carry out daily activities without issues. Social network and support systems also play an important role. Patient expectations have to be considered, and if not realistic, would need to be addressed before making a final decision.
Lastly, it is important to have an understanding of the natural history of the underlying pathology and the likely impact of surgery on the disease process. For example, in a case of degenerative scoliosis, it would be important to understand its natural history over time and how likely is the curve to worsen over time versus the impact and unwanted side effects that surgical intervention can have over time. For instance, will surgery worsen the patient’s current biomechanics and accelerate the disease process? Another example would be in patients with lumbar stenosis and spondylolisthesis—will a decompression alone cause instability that will worsen the slip and require a fusion at a later time?
Technology refers to surgical instrumentation, tools, and imaging systems used to conduct or facilitate an MISS procedure. In MISS, the outcome of surgery is significantly impacted by access to special tools. In cases the necessary tools are not available, it may be a safer alternative to perform conventional open surgery. The fundamental tools/technologies frequently needed to perform MISS techniques include the following:
Access: Tubular or specular retractors and endoscope
Visualization and illumination: Microscope and endoscope
Special implants (e.g., expandable cages, hyperlordotic cages, stand-alone cages, cannulated screws, and percutaneous single-step pedicle screw system)
Curved, bayoneted, and extended instruments
Intraoperative imaging system with two-dimensional and 3D navigation and robotic guidance systems
Surgical planning and augmented reality software
One particularly important tool for MISS is the surgical microscope, which has become a mainstay tool in the field of MISS. The surgical microscope gives the surgeon the depth resolution and illumination when working in small surgical fields with limited exposure. Current surgical microscopes can have high-definition video documentation systems and integrated navigation technology, allowing individuals to easily edit and transfer videos to any handheld devices.
Imaging is essential in spine surgery to accurately localize the pathology, avoid wrong-level surgery, and insert implants properly. More importantly, anatomic reference points that may be needed for orientation and the instrumentation placement may not be openly visualized in MISS procedures, highlighting the need for proper imaging. For example, the Airo CT scanner (Brainlab, Feldkirchen, Germany) has expanded from a tool for instrumentation navigation to one used for intraoperative planning and guidance during the entire procedure. This has allowed navigation to be used for the entirety of the procedure, which is also known as total navigation, from the localization of pathology and planning of incisions to instrumentation placement, tubular decompression, and the measurement of rods without fluoroscopy. 3D navigation has improved the MISS workflow through increased accuracy of localization and hardware implantation and decreased radiation to the surgical staff. With total navigation, surgical workflows are more efficient and reproducible; thereby, making spine surgery more accurate and safer.
The paradigm shift from open surgery to MISS was achieved gradually with the development of new technologies. The trajectory of the progress of MISS in its earlier stages involved mini-open, percutaneous tubular approaches. Currently, MISS procedures can be performed through tubular retractors that are less than 20mm in diameter.
Technique is related to the surgeon’s training, operative capabilities, and experiences in MISS. For most individuals beginning MISS, many surgeons go through a learning curve to become more comfortable and to improve on MISS techniques. The basis of MISS is built on several key techniques including:
Tubular decompression to minimize tissue disruption and preserve stability
This principle comes from the widely accepted custom in MISS that fusion is not indicated in all patients with lumbar spinal stenosis and spondylolisthesis. Unlike open laminectomies, this approach typically spares bone and supporting structures. At our institution, 54% of 110 cases presented with spondylolisthesis and underwent a MISS laminectomy. Over the next 2 years, 3.5% of the patients needed a reoperation and fusion. This greatly differed from the work of Blumenthal et al., which reported that of 40 patients who had undergone open surgery, 37.5% needed a reoperation after 3 years. Our department reviewed 37 studies, totaling 1156 patients, in a meta-analysis and concluded that there was a lower rate of reoperation and fusions in the future, decreased slip progression, and higher patient satisfaction with the MISS laminotomy over open surgery.
The slalom technique is a strategy used to reduce destabilization for multilevel decompressions. In this technique, the side of the approach alternates on a level-to-level basis. This technique serves as an example of how a bilateral decompression is achievable through a unilateral approach.
MISS can also be used in combination with other techniques. If a single level is unstable, whereas several other levels require decompression, the surgeon can perform a fusion at the unstable level with MISS decompressions at the more stable levels. In this setting, our cadaveric studies showed that MISS decompressions were superior to open laminectomies.
Unilateral approach for bilateral decompression
This approach refers to achieving a bilateral decompression and contralateral foraminotomy via a unilateral minimally invasive incision. Foley described microendoscopic discectomy as a treatment for herniated lumbar disc disease in 1997. This approach gained in popularity with surgeons in various institutions and was eventually established as one of the first MISS techniques. Approximately 77% patients who had undergone this procedure had favorable outcomes and decreased postoperative hospitalization stays, averaging 7.7h. As the microendoscopic discectomy technique became more well-known, innovation increased, and the first case series on bilateral decompression via a unilateral approach was published in 2002 and had excellent results. The exposure achieved with this approach is similar to that of open surgery and provides a clear view of neural structures in the spinal canal.
For degenerative spinal disorders such as lumbar stenosis, foraminal narrowing, disc herniations, and facet joint cysts of up to two levels, decompression with tubular retractors has become the more favored approach at our institution. In 2014, we published a case series of 32 patients with foraminal compression that were operated by a facet-sparing contralateral tubular approach. This approach had excellent outcomes in 95.2% of the patients.
Indirect neural decompression
This technique is most commonly used to treat degenerative spinal disorders in the lumbar spine. To achieve neural decompression and stabilization, the approaches for indirect decompression include extreme lateral interbody fusion (XLIF), oblique lateral interbody fusion (OLIF), and ALIF. Of these approaches, XLIF is the most common, and our institution has focused on determining procedural and patient factors critical to achieving a successful indirect decompression after an XLIF surgery. In our study of 23 patients presenting with foraminal stenosis and unilateral leg pain, using an XLIF technique for a single level showed excellent results at 1-year follow-up. Several factors must be taken into consideration during the application of indirect decompression techniques [Figure 3]. A retrospective study that focused on radiological and clinical outcomes after an XLIF procedure found that the most significant factor in determining the success of indirect decompression was the cage width (i.e., a larger width had a smaller risk of subsidence).
|Figure 3: Potential patient-related and procedure-related factors that determine the success of indirect decompression (modified from Del Castillo-Calcaneo et al.)|
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Percutaneous screw placement
When instrumentation with pedicle screws is required, the ability to place them through a percutaneous method obviates the need to make a long incision with extensive muscle stripping and retraction to gain access as is the case of traditional pedicle screw insertion. This technique of pedicle screw placement adheres to the mindset in MISS of limiting surrounding tissue injury and unnecessary exposure of the adjacent levels. Avoiding manipulation of the adjacent facet joints could mitigate the development of adjacent level disease. This is also another example of how techniques and technology are intricately related in the advancement of MISS as the development of cannulated screws, extended screw tabs or towers, and navigation has allowed this technique to be a major part of an MIS surgeon’s armamentarium.
As with all new techniques, the process of attaining surgical proficiency involves a learning curve. The learning curve can have an impact on intraoperative tissue trauma, blood loss, and complication rates.,, For surgeons who have never performed MISS or have not yet reached the plateau of the learning curve, the first two Ts, target (i.e., appropriate patient selection) and technology (i.e., having the appropriate instruments available) are critical to training and overcoming the challenges inherent to learning a new technique.
One of the best ways to become proficient is to teach others. Therefore, teaching and training are intricately interwoven and they go both ways—teaching yourself and teaching others. For those who are already experts in MISS, the desire to train colleagues, residents, and fellows, may be equally important to them. Recently, surgical simulation using realistic models has become available allowing surgeons to train in the basic skills and procedures of MISS. In addition, attending courses focused on teaching surgeons about MISS procedures is of high value.
Residents are exposed to MISS techniques earlier in their training as it becomes more prominent in the field of spine surgery. They may even graduate from their institutions with a competency in MISS techniques; thereby, eliminating the learning curve that many spine surgeons may face when they are new to MISS. The advancement of the MISS field is highly dependent on providing proper education to the future generations of surgeons.
Testing: research and outcomes
Continuous outcome tracking and research are essential, especially for the novice MISS surgeon. Following your outcomes closely will allow you to identify deficiencies and strengths and will allow you to focus your time and attention on areas that may need improvement. It will also affect all other aspects of the six Ts. For example, your surgical decision-making process may evolve over time and determine whether you decide to invest in a certain technology, such as the case to invest in a 3D navigation system if one has less than desirable screw placement accuracy or concerns about radiation exposure. These decisions are best made with objective data. Outcome tracking will also help in the counseling of patients. MISS is an evolving field so inputs from a broad pool of surgeons who practice it are vital for evolving techniques. As a surgeon you may decide to join one of the larger organizations and engage in research and clinical studies to advance the field of MISS.
Finally, it is important for any surgeon considering the nervous plunge into an unfamiliar set of skills and techniques in MISS to understand that no one was born with the innate ability to perform a laminectomy through a tube that is roughly half an inch in diameter. As Daniel Coyle put forth in his book,The Talent Code: Greatness Isn’t Born. It’s Grown. Here’s How, creating skill is a biologic, molecular response to certain signals and can be developed to high levels with optimal training. Of course, this can be applied to any facet of life including learning and performing MISS.
| Conclusion|| |
MISS is an advancing field, which has rapidly progressed in the past decade and will continue to expand its role in treating complex spinal pathology. The six Ts are the essential ingredients for successful MISS. The field of MISS develops in parallel to technological development, impacting both imaging and surgical implementation. Its ultimate goal is to provide spinal health via the least invasive manner while also avoiding overtreatment. With MISS, patients are given the best opportunity for favorable outcomes while having a short recovery course with minimal iatrogenic spinal instability.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]