Definition of MISS: The “6 Ts”: Target/Technology/Technique/Teaching and Training/Testing/Talent

1 Definition of MISS: The “6 Ts”: Target/Technology/Technique/Teaching and Training/Testing/Talent

Roger Härtl, Sertac Kirnaz, Juan Del Castillo-Calcáneo, and Ibrahim Hussain

Summary

This chapter provides the framework for success with minimally invasive spine surgery (MISS). To illustrate this, we developed the “6 Ts” to create a foundation for successful MISS procedures. The “6 Ts” are: target, tools, technique, training, testing, and talent. These six attributes inform one another as they develop, thus patient selection for MISS improves as mastery of the tools improves as well. MISS is an evolving field and using the “6 Ts” provides a method for reaching the main goal of MISS, which is to treat spinal pathologies with minimal invasion.

Keywords: minimally invasive spine surgery tubular retractor indirect decompression navigation muscle-sparing spine surgery over-the-top decompression

1.1 Definition of Minimally Invasive Spine Surgery

Spinal surgery that attempts to reduce the invasiveness of traditional spinal procedures is attracting considerable and growing interest worldwide. This type of surgery has been called “less invasive,” “minimal access,” or “minimally destructive” spinal surgery. For the purpose of this book, we decided to stick with the most widely used term: “minimally invasive spine surgery” (MISS). We realize and acknowledge that there is not one perfect descriptive term, as this type of surgery is evolving and surgeons in different regions have variable access to MISS-enabling technology and training. Based on the recent consensus definition by AOSpine, 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 [and] striving for better outcomes than traditional techniques.”1^,²

This definition already implies what we call as the six principles that surgeons should consider when engaging in MISS, i.e., the “6 Ts” (Fig. 1.1):

•Target: Appropriate patient and procedural selection.

•Technology: Specialized technology that enables or facilitates MISS.

•Technique: Surgical and perioperative techniques and procedures.

•Training: Adequate training and teaching of the surgeon, collaborating team, and trainees.

•Testing: Critical review and testing of surgical outcomes (research).

•Talent: Development of surgical talent.

Fig. 1.1 The “6 Ts” to success in spinal minimally invasive spine surgery (MISS). These are all interactive. For example, the results of data collection, research and outcome assessment (testing) over time will refine our surgical decision-making process (target). The tools and techniques used will determine the surgical teaching and training required to master MISS. Training and teaching are central to all innovation and are used to develop talent.

The goal of MISS is to leave the smallest possible “surgical footprint” while achieving the goal of traditional open surgery. MISS emphasizes attaining the best functional outcome for the patient, free of unnecessary iatrogenic risk exposure.

1.2 Potential of Minimally Invasive Spinal Surgery

Approximately 1.6 million instrumented spinal procedures are done in the United States each year.3 Most decompressions and approximately 50% of fusion procedures can be performed completely or partially using MISS. Therefore, an estimated 75% of all spinal surgeries could be performed completely or partially using MISS instead of conventional techniques, indicating that the full potential of MISS is yet to be recognized. The most challenging aspect for MISS is still the treatment of significant and multilevel deformities, but progress is being made in at least partially applying some of the benefits of MISS, such as percutaneous screw placement, navigation, lateral approaches, etc.

Which procedures and pathologies currently benefit most from MISS? Let us plot the complexity of thoracolumbar procedures against their invasiveness (Fig. 1.2). This is a somewhat arbitrary and subjective approach, but it effectively demonstrates the current role of MISS compared with open traditional surgery. In terms of procedure complexity, the spectrum ranges from simple lumbar disc herniation on the left to single- and multilevel lumbar stenosis decompression, single-level spondylolisthesis cases treated with MIS transforaminal lumbar interbody fusion (TLIF), multilevel lateral and then combined lateral/TLIF, and possibly anterior lumbar interbody fusion procedures for moderate deformities. All the way on the right, we find complex deformities defined as fused or rigid spines requiring more than five levels of instrumentation. Invasiveness on the Y-axis can be assessed by looking at surgical parameters such as intraoperative blood loss, infection risk, length of stay, postoperative pain levels, etc. (Table 1.1).

Fig. 1.2 Relating the complexity of the procedure to the invasiveness of the system used (see Table 1.1), complexity increases from a single-disc herniation to single-level lumbar stenosis, to multi-level instability and/or deformity requiring fusion.

Table 1.1 Factors that determine invasiveness and complexity of spinal procedures

Invasiveness factors	Complexity factors
Length of procedure	Technical demands to surgeon and staff
Blood loss	Predictability of outcome
Infection risk	Use of technology
Incision length and size of tissue exposure	Number of stages and steps in a procedure
Associated fluid shifts	Use of implants
General vs. local anesthesia	Revision surgery
Postoperative pain levels	Intradural vs. extradural
Perioperative risks	Degree of deformity correction required

Literature and experience show that with the very-low-level complexity cases, there is no big difference between MISS and open traditional surgery when it comes to outcome and invasiveness (Fig. 1.3). For example, patients with simple lumbar disc herniation for the most part will do equally well whether treated by a well-trained endoscopic spine surgeon, via tubular surgery, or by open microdiscectomy.⁴^,⁵ However, when we move to a slightly more complex operation, such as a decompression for severe lumbar spinal stenosis, there is already a clear advantage for MISS. Studies show that performing this decompression through tubes or specular retractors using a unilateral laminectomy for bilateral decompression (ULBD) is associated with multiple benefits to the patient, including earlier return to work, less pain, and lower risk of infection⁶^,⁷^,⁸^,⁹^,¹⁰ when compared with traditional open surgery. When it comes to patients with lumbar stenosis and spondylolisthesis, the difference between MISS and traditional open surgery is even more pronounced because open surgery will frequently be performed by combining a decompression with fusion, whereas with MISS a fusion can be avoided if the spondylolisthesis is stable.¹¹ For patients with unstable spondylolisthesis, studies have shown that MIS TLIF is associated with benefits over open fusion and/or TLIF, including reduction in length of stay, decreased infection rates, and decreased costs.¹²^,¹² Further to the right, we move toward mild and moderate deformity pathologies that can frequently be treated by taking advantage of less invasive lateral, oblique, or anterior indirect decompression and fusion procedures, all of which provide excellent clinical results while minimizing complications and invasiveness. As we move to the right, even the MISS treatment interventions become more complex and less “minimally invasive”. This is mainly based on the increase in operative time, number of different access sites, and number of MISS procedures required to achieve the overall surgical goal. Finally, for rigid curves requiring more than 5-level surgery including L5/S1, rigid deformities requiring more than 10-level fusion, or previously instrumented multilevel fusions, the downsides of MISS currently outweigh the potential benefits. Based on the work by the International Spine Study Group, a recommendation was developed for the treatment of adult degenerative scoliosis¹³ and recently updated. Compared to the previous algorithm from 2014,¹³ the introduction of new technology, such as expandable cages, lateral techniques, anterior column release (ACR), and other technologies and procedures, has expanded the indications for MISS for deformity correction to now include patients with deformities and even with significant lumbar lordosis–pelvic incidence (LL-PI) mismatch.¹⁴

Fig. 1.3 Comparison of surgical approach and bony removal between minimally invasive spine surgery (left) and open spine surgery (right).

Based on these thoughts, it is our belief that the greatest benefits of MISS are currently for the treatment of pathologies ranging from lumbar disc herniation to moderate deformities up to approximately five levels, which can be considered as the “benefit zone” for MISS. However, this benefit zone for MISS is constantly being expanded with the expansion of MISS components into more complex surgical pathologies. Examples of this would include the use of lateral ACR procedures with hyperlordotic cages combined with more traditional and open osteotomy procedures performed posteriorly (Chapters 27 and 28). Other examples include the adoption of three-dimensional (3D) navigation and robotic surgery in multilevel deformity correction procedures and preoperative 3D planning and virtual augmentation in, for example, complex tumor resections, which may contribute to overall less invasive surgery.

These considerations demonstrate that MISS has already gained a significant role in spinal surgery that will become even more prominent as technology and techniques evolve. Indeed, a future of spinal surgery without an adoption of MISS techniques and principles does not seem to be possible.

1.3 The “6 Ts” to Success in MISS: Components for a Successful MISS Practice

The “6 Ts” of MISS represent a concept that references the key elements determining the success of MISS and the MISS surgeon over time, these are: target, technology, technique, teaching and training, testing, and talent. We will further describe each of the “Ts” in relation to MISS. It is important to realize that these are all interactive. For example, over time the results of data collection, research, and outcomes assessments (testing) will refine our surgical decision-making process (target) which in turn will influence the next generation of MISS surgeons (teaching and training). The tools and techniques used will determine the surgical teaching and training required to master MISS. As research shows, talent is highly dependent on the correct teaching and training methodology.

1.3.1 Target

“Target philosophy” is described as choosing the right operation for the appropriate patient and pathology. This decision-making process is one of the most complex problems in spinal surgery because there is very little science to guide the surgeon and patient. Spinal surgical decision-making is based to a large extent on the surgeon’s experience and background, training level, and patient expectations and beliefs which are not always clear or measurable. By including the target philosophy in our “6 T” concept of the key elements for success, we try to shed some light on the difficult decision-making process in spinal surgery. The classic dilemma with spinal surgery is the poor correlation between patient’s signs and symptoms, imaging findings, patient expectations, and ultimately patient outcome. If in doubt, a conservative approach may be sometimes the best option: The “least invasive” MISS operation is the one not performed because of a lack of correlation between patient signs and symptoms, imaging findings, and expected outcome. On the other hand, if there is a correlation, we struggle as MISS surgeons to balance treating only the patient’s current signs and symptoms versus more extensive surgery that anticipates future deterioration as a result of the natural history, as a result of the surgical intervention, or both. This highlights the challenge we have with defining the natural history of untreated or minimally treated degenerative spinal disease; at what point should we treat abnormal imaging findings even though the patient may not be (yet) symptomatic?

Take, for example, an elderly patient who presented without mechanical back pain but with a significant right-sided L3 radiculopathy. Imaging demonstrated a significant degenerative scoliosis with single-level foraminal compression in the concavity of the curve (Fig. 1.4). This patient was treated successfully with an ambulatory single-level translumbar discectomy and fusion. However, several perioperative questions arise: Should this patient have undergone a bigger surgery that addresses the deformity? Will the one-level fusion accelerate the deformity progression above and below? A clear answer cannot be provided at this time, and surgical decision-making will therefore be guided by the patient’s expectations, the surgeon’s recommendation and experience, and a comprehensive discussion between both parties.

Fig. 1.4 Imaging of an elderly patient who presented with significant right-sided L3 radiculopathy without mechanical back pain. Imaging demonstrates significant degenerative scoliosis with single-level foraminal compression in the concavity of the curve. Patient had pain resolve 15 weeks post operation.

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