Michael Y. Wang, Yi Lu, D. Greg Anderson and Praveen V. Mummaneni (eds.)Minimally Invasive Spinal Deformity Surgery2014An Evolution of Modern Techniques10.1007/978-3-7091-1407-0_38

38. The Future of MIS Spine Surgery

Richard G. Fessler¹

(1)

Department of Neurosurgery, Northwestern University, Chicago, IL, USA

Richard G. Fessler

Email: rfessler@rush.edu

Abstract

So many factors affect where minimally invasive spine surgery (MISS) will go in the immediate and near future that it is hazardous, and probably foolhardy, to make predictions. Many of these factors, if not most, have little to do with surgery, medicine, or even health care. To consider this issue systematically, however, let’s first define what we mean by “minimally invasive spine surgery” and then consider the question of “Where should MISS surgery go, in a perfect world?” Then let’s examine the question, “What factors could alter the pathway of where MISS should go?” Finally, by combining the information learned from the answers to both of those questions, let’s consider the final question, “Where is MISS likely to go in the future?”

38.1 Introduction

38.2 What Is MISS?

Recently, there has been great debate over exactly what surgery qualifies as MISS and what doesn’t. Is a 2 cm skin incision MISS? 3 cm? 4 cm? 25 cm? Or is the size of the skin incision irrelevant? Does MISS require complete sparing of the muscles and other soft tissues? Must it be done through a tubular retractor? Must you use an endoscope? Does a procedure in which only a limited paraspinal muscle dissection is performed qualify as MISS? [1, 2] If a vertebrectomy is performed through a small incision using soft tissue sparing technique, is that MISS? Clearly, the variety of operations proposed as MISS, and the variability of pathology approached (from a small disc herniation to intradural tumors and major scoliosis), complicates attempts to establish a firm definition. I would propose, however, that every MISS procedure be judged upon the equivalent operation if performed open. Thus, one possible definition for a MISS operation is:

a spine surgical procedure which produces significantly reduced, approach related, soft tissue destruction when compared to the equivalent open surgical procedure

Note that this does not define any specific type of equipment, approach, amount of blood loss, skin incision, etc. Moreover, it is still somewhat vague in specifics. However, in some ways, the question here seems a little like the question regarding the definition of obscenity. As proclaimed by Justice Potter Stewart in 1964, “I shall not today attempt further to define {obscenity}; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it…” [3]. The above definition at least gives you the tools to “know it when you see it.”

38.3 Where Should MISS Go in the Future?

Several years ago, while writing a chapter conjecturing on this same topic, I made the statement: “MISS MUST progress and become the mainstream technique of performing spinal surgery” [4]. I based that statement on the belief that MISS would most closely achieve the “goals” of spine surgery. Thus, where MISS needs to “go” is that place where it most successfully achieves the desired surgical result, with the least possible pain, anatomical destruction, complications, and cost. That is the ideal but will vary depending upon the specific surgical procedure involved. In this text, we have considered surgery for spinal deformity; therefore, let’s consider the ideal future for deformity surgery. The “ideal” goal of deformity surgery includes (1) perfect correction of sagittal, coronal, and axial deformity, (2) 100 % fusion rate, (3) 0 % complications, (4) relief of pain, (5) maintenance of normal paraspinal soft tissue anatomy, (6) minimal blood loss, and (7) immediate return to normal activities of daily living with excellent quality of life.

Is this an achievable goal? There is now an accumulating literature demonstrating that spinal surgery performed with MISS technique has similar long-term outcomes compared to open equivalents but results in less pain and less use of pain medicine [5, 6], less blood loss [7, 8], lower infection rates [9], less requirement for intensive care [10], and less hospitalization [7, 8]. Physiologic stress is reduced [11]. Complication rates are lower [12]. Muscle atrophy is reduced [13] and normal motion is more accurately preserved [14]. Fusion rates are reported in the 80–95 % range [8, 15]. So, is the “ideal” suggested above achieved? No. But, significant improvements are evident in many areas, such as complications, relief of pain, soft tissue anatomy and blood loss, and rate of return to normal activities.

Progress is also being made in the ability to correct deformity using MISS techniques. Anand et al. reported 12 patients in whom coronal Cobb angle was corrected from a mean of 18.93° (SD 10.48) to 6.19° (SD 7.20) [16]. More recently, Wang reported on a “hybrid” MISS technique in which he reported correction of preoperative coronal Cobb angles from 29.2° to 9.0°, improvement of lumbar lordosis from 27.8° to 42.6°, and improvement of spinal vertebral angle (SVA) from 7.4 to 4.3 cm [1]. Clinical outcomes, as measured by visual analog scale (VAS) and Oswestry Disability Index (ODI), were similar to those achieved with open correction of deformity.

In my own personal series of patients with at least 2-year follow-up (i.e., my first deformity patients done with pure MISS technique), preoperative coronal Cobb angle improved from 25.9° to 8.3°. Lumbar lordosis slightly improved from 27.9° to 33.6°. Pelvic tilt improved from 25.7° to 18° and SVA minimally worsened from 5.1 to 5.7 cm. Thus, although coronal deformity significantly improved, lumbar lordosis, pelvic tilt, and SVA were minimally altered. However, as techniques and technologies have evolved, data collected on more recent patients is markedly better. In the last five patients operated on, coronal Cobb angle improved from 33.1° to 9.3°, lumbar lordosis improved from 14° to 34.9°, pelvic tilt improved from 29.6° to 19.1°, and SVA improved from 8.1 to 4.0 cm. Thus, even in a short period of time, results of MISS correction of sagittal plane deformity have dramatically improved. It seems highly likely that as experience, techniques, and instrumentation continue to improve, these results will likewise continue to improve. Finally, it should be noted that even in the early patients, in whom radiographic results were not as acceptable as patients operated on using open technique, results of VAS, OSI, and SF-36 were not significantly different between the groups (unpublished data) and the classical advantages of MISS techniques were still maintained with significantly shorter hospitalization, blood loss, CSF leaks, wound infections, and interestingly junctional kyphosis!

38.4 What Factors Could Alter the Pathway of Where MISS Should Go?

38.4.1 Patient Demand

As public awareness increases, demand for MISS procedures will increase. This is particularly true for traditionally “large” operations associated with prolonged and severe pain, high complication rates, and lengthy recoveries, such as scoliosis correction. This is going to be compounded by patients becoming increasingly more informed via the Internet. Furthermore, as more and more patients who have received MISS procedures are available to give testimony to their friends and neighbors, public awareness will increase, as will requests for MISS technique.

38.4.2 Skill Level and Education

The success of any surgical procedure depends upon the ability of surgeons to perform it safely and successfully. That, in turn, depends upon the inherent difficulty of the operation and the skill level of the surgeon. Thus, education and training are of paramount importance for increasing the use of MISS technique in deformity. Currently, surgeons versed in the techniques of MISS are not experienced in performing correction of scoliosis and vice versa. For surgeons bringing either skill set, to excel at performing MISS correction of deformity, it will be necessary to acquire the skills of the “other” group as well. For MISS surgeons, this means understanding the pathobiology of the causes and natural history of kyphoscoliosis, as well as the detailed biomechanics of occipital-spinal-sacral/pelvic balance, and the surgical techniques necessary to achieve spinal axis balance. For scoliosis surgeons, it means becoming comfortable with an entirely new set of instruments, perhaps learning the visual and proprioceptive skills necessary to operate in a two-dimensional visual field (i.e., endoscopic), learning to work in the restricted space of expandable tubular working channels (therefore working in parallel rather than triangulation), and performing complex procedures such as hemostasis and dural closure in very restricted spaces.

In general, new technologies take one to two generations to become widely adopted. This is partly a result of what must be learned but is also influenced by the nature of graduate and postgraduate education. Surgical residents, who are being trained in programs in which MISS deformity surgery is already being practiced, will simply learn these skills as part of their armamentarium. As more and more institutions have skilled faculty, this will become standard of care, similar to the way in which spinal instrumentation was adopted in the United States over the last 25–30 years. Given this rate of adoption, it is likely that spinal surgeons approaching the end of their active career will never need to learn these techniques. However, that leaves a group of surgeons who were not trained in MISS deformity during residency, but who have long careers ahead of them, and will need to learn the techniques to continue to perform “state-of-the-art” surgery. Since this is not the type of surgery that can be adequately learned in a weekend course, the question is: How do these surgeons learn these techniques?

Current recommendations to acquire this training include a series of educational steps. First, trained deformity surgeons should attend one or more didactic courses to learn the indications, contraindications, theory, and basic techniques for MISS procedures. Similarly, trained MISS surgeons should do the same to learn the basics of deformity surgery. Second, hands-on training, on both foam bone models and cadavers, should be completed. Although early in its development and implementation, computer simulation might also play a role in this training. Third, the student-surgeon should observe several procedures being performed by an experienced MISS deformity surgeon. Finally, if the opportunity exists, it would also be reasonable for the lesser experienced MISS deformity surgeon to “scrub” on several cases for proctoring prior to independently engaging in the procedures. It is the later suggestion that is particularly problematic for surgeons, as few centers are available where this is actually possible. In addition to the traditional industry and professional society educational courses, the Society for Minimally Invasive Spine Surgery (SMISS) is specifically creating a defined curriculum to teach both basic and advanced MISS procedures.

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