Overcoming the Learning Curve

Efrem M. Cox, David J. Hart, and Mick J. Perez-Cruet

Abstract

There is a learning curve to mastering minimally invasive spinal surgery approaches, techniques, and technology safely and effectively. This can be achieved through class study, cadaveric labs, fellowships, and experience in the operative arena with an accomplished minimally invasive spine surgeon. However, careful patient work-up and selection is also critical to providing effective minimally invasive spine surgery care. This chapter will discuss not only the evolution of minimally invasive spine surgery but also the various modalities used to teach surgeons how to perform these procedures safely and effectively. In learning these techniques, we recommend starting with straightforward cases such as lumbar microdiscectomy and advancing to more complex cases as each stepped approach and technique is mastered.

Keywords: minimally invasive, approaches, technique, technology, safety, complication avoidance, cadaver training, operative experience

7.1 Introduction

Minimally invasive spinal surgery (MISS) encompasses modifications of techniques and procedures to allow for decreased morbidity from exposure and dissection, as well as new techniques for treatment of spinal disease. The recent past has seen a significant increase in the volume and breadth of MISS procedures. Some believe that the increasing use of MISS represents a natural and logical progression of the field of spine surgery. As patients continue to learn more about MISS procedures through advertisements and patient testimonials, there will be further demand for practicing physicians to garner the skills to perform these newer techniques. MISS represents a shift away from the traditional surgical paradigm of maximal exposure, with the expected benefits of improved outcomes and decreased morbidity, operative time, length of hospitalization, and, ultimately, cost. The techniques of MISS aim to achieve the goals of proven open surgical techniques with less associated short-term morbidity and decreased hospital stays. MISS in combination with newer intraoperative navigational tools also offers potentially reduced radiation exposure and more accurate placement of instrumentation.¹

MISS generally requires the use of unique or modified tools and the acquisition of new skills. Minimally invasive surgery further represents a departure from traditional surgery with regard to operative view and approach to the anatomy. As a result, operative times may increase initially compared with traditional surgeries. Those with experience in minimally invasive techniques caution that significant investment by the surgeon is required before the benefits of MISS may be realized, as the learning curve is steep.² A proper understanding of the fundamental differences and similarities between MISS and traditional surgery serves as the basis to overcome the learning curve. With focused attention to the novel aspects of MISS, similar or improved surgical outcomes can be achieved with less operative time, decreased hospital stay, and decreased postoperative analgesia requirements.

7.2 Evolution of Minimally Invasive Spine Surgery

While MISS is considered by many to be fairly new, attempts to develop less invasive spinal procedures can be found as far back as the mid-20th century with Dr. Smith’s percutaneous injection of chymopapain for the treatment of sciatica.³ In the 1960s, Gazi Yasargil⁴^,⁵^,⁶ worked with R. Peardon Donaghy, developing microsurgical instrumentation and techniques best known for the their impact on cerebral microsurgery. These same principles were later applied to spinal surgery. The use of the microscope for microsurgical techniques, pioneered by Drs. Yasargil, Williams, and Caspar⁷^,⁸ in the late 1970s, served as the foundation for MISS. The first publication of a microsurgical discectomy was in 1978.⁹ Dr. Williams⁹ popularized the procedure with his results described on 532 patients. His impression of its benefits with regard to decreased incision size and cosmesis, reduced blood loss, and decreased morbidity was confirmed in numerous subsequent studies. Percutaneous procedures were then developed. Percutaneous discectomy and laser discectomy were attempted in the 1980s prior to the 1993 Mayer and Brock¹⁰ paper detailing the use of the endoscope for spine surgery. Shortly thereafter, Drs. Smith, Foley, Fessler, and Perez-Cruet¹¹ designed modified operative spinal instruments for endoscopic tubular-access microdiscectomy and expanded the “tubology” applications. Incorporation of endoscopic techniques refined in other surgical disciplines served to further broaden the scope of MISS.

Over the past decade, there have been further advancements in MISS treatment options ranging from instrumentation (e.g., tubular and expandable retractors) to intraoperative imaging to neuronavigation. Many of these advancements in MISS have centered on the goal of improvement in exposure for surgical approaches, yet minimizing soft-tissue destruction and compromise of the posterior paraspinous musculoligamentous complex. Tubular retractor systems have undergone various modifications that have expanded the role of MISS approaches in accomplishing lumbar fusion techniques (e.g., transforaminal lumbar interbody fusion [TLIF]) for treatment of spondylolisthesis, degenerative disc disease, spinal deformity, and trauma. In comparison to open procedures, MISS has demonstrated comparable outcomes to open techniques, but with decreased complications, blood loss, narcotic pain medication usage, return to work time, and hospital length of stay.¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²⁰^,²¹^,²² Intraoperative imaging has commonly been used in spinal instrumentation; however, complications of malpositioned screws are variably reported throughout the literature.²³^,²⁴^,²⁵ Some surgeons using open approaches have utilized free-hand methods to limit radiation exposure. On the contrary, MISS is dependent on intraoperative imaging for proper localization of the operative site and placement of instrumentation. This does, however, provide a certain degree of radiation exposure to the surgeon, patient, and operating room personnel. Recently, there has been an evolution of intraoperative imaging/navigation and robotic modalities (e.g., plain fluoroscopy, 2D, 3D, and intraoperative computed tomography (CT)-guided robotics) with the aim to increase the accuracy of spinal instrumentation placement and decrease radiation exposure ²⁶^,²⁷ ( Fig. 7.1).

Nevertheless, general acceptance and incorporation of minimally invasive techniques have been a slow process. Chymopapain nucleolysis and the automated percutaneous lumbar discectomy were part of the growing pains of MISS. The chymopapain studies, while serving as a platform for the development of further minimally invasive therapies, also brought attention to the learning curve associated with these new procedures. Proponents of chymopapain indicated that lack of familiarity and training, and application with poor indications were significant factors contributing to the high rate of complications. Indeed, the severe complication of hemiparesis and paraplegia resulting from intrathecal injection as well as anaphylaxis resulting in death from intrathecal injection may have been avoidable. Further developments in MISS have been coupled with improved clinical studies, many published since the turn of the 21st century, and a focused attention on the differences in surgical technique with the resultant need for appropriate training to overcome the learning curve.

MISS represents a departure from traditional spine surgery with regard to use of intraoperative image guidance, hand–eye dissociation with endoscopy and microscopy, increased working distance, different surgical view, and a narrow working channel with modified instrumentation. Attention to these unique aspects of MISS and their advantages as well as limitations is paramount to overcoming the learning curve.

Fig. 7.1 Surgeon learning robotic Mazor X (Mazor Robotics Inc., Orlando, FL) system for placement of percutaneous pedicle screws.

For practicing physicians, the novelty of the different instrumentation and operating through a narrow corridor may cause some to be less comfortable initially, when transitioning from open procedures. In a systematic review, Sclafani and Kim ²⁸ report that the learning curve of performing MISS procedures could be overcome within performing 30 consecutive cases. There is considerable variation in the level of difficulty of different MISS procedures (e.g., laminectomy, microdiscectomy, percutaneous instrumentation, TLIF, posterior cervical decompression). Proficiency with MISS techniques will progress with one’s increasing comfort with the instrumentation and familiarity with operative corridors.

7.2.1 Cadaveric Training

Cadaveric training under the tutelage of expert minimally invasive spine surgeons remains the standard to learning minimally invasive spinal procedures. These cadaveric labs can be developed to mimic the operative environment and improve mastery of various minimally invasive spinal techniques ( Fig. 7.2). These labs are being conducted by various industry leaders, national and state surgical organizations, and smaller focused organizations such as the Minimally Invasive Neurosurgical Society (MINS) ( Fig. 7.3). These labs provide an excellent venue for small group or one-on-one training with the experts and include focused didactic sessions.

7.2.2 Operative Training

Training surgeons in the operative suite is an invaluable method to learn minimally invasive spine surgery. Training in the operative suite effectively shows surgeons how to set up the operative arena, position the patient, and perform the procedure. This exposure is critical and can be conducted as a visiting surgeon, medical student, resident, or fellow. Residency and fellowship training of minimally invasive spinal techniques remains a critical learning venue to improving patient care and outcomes. Additionally, participation in the preoperative clinic evaluation and work-up of these patients as well as postoperative follow-up can lead to mastery of these techniques.

As these techniques continue to evolve, robotic simulation training will take on an increasing role ( Fig. 7.4). These techniques can result in improved patient outcomes in those patients suffering from complex spinal pathologies such as difficult-to-approach thoracic apex tumors ( Fig. 7.5).

7.3 Indications and Contraindications

The necessity of a thorough understanding of the indications and contraindications cannot be overstated. While the indications and contraindications for the individual minimally invasive techniques are described in detail in other chapters, we would like to speak to some general principles in this chapter.

Fig. 7.2 (a–c) Operative suites mimic the operative environment of the surgeon and facilitate learning and mastery of minimally invasive spinal techniques.

Fig. 7.3 Cadaveric minimally invasive laboratory held at the Beaumont Simulation Learning Center, Royal Oak, MI, and sponsored by the Minimally Invasive Neurosurgical Society (MINS, Royal Oak, MI). (a,b) Course registrants learn through cadaveric training held in state-of-the-art operative suites. (c) Didactic sessions taught by MIS experts in the field. (d) Image guidance laboratory for learning percutaneous pedicle screw placement. (e) MINS organizers Mick Perez-Cruet, MD, MS (President and Founder, center), and administrators Jennifer Harris (left) and Joe Edwards (right).

7.3.1 Patient Selection

Each patient should receive a thorough history and physical examination. Available nonsurgical options should always be considered and discussed with the patient. Relevant imaging should be obtained. The surgeon should consider both traditional surgical options and minimally invasive ones that are indicated to treat the patient’s pathology. Patients who are not good surgical candidates in general are usually also not good candidates for MISS. Patients who have severe osteoporosis may not be appropriate for instrumented fusion surgery, whether open or MISS. The advantages of MISS approaches become truly evident in patients with morbid obesity or severe degenerative changes (particularly in the lumbar spine, and/or when anatomic variation such as hypertrophied facets affect exposure) that can lead to a significant amount of retraction and muscle disruption to achieve adequate exposure. In contrast, MISS techniques decrease the amount of exposure one needs, thus lessening the length of incision and subsequently decreasing the “dead space” within the wound. This is particularly beneficial in patients with risk factors for poor wound healing, such as those with diabetes, obesity, and poor nutritional status.

Fig. 7.4 (a) Mimic training station. (b,c) Teaching minimally invasive assisted robotic spine surgery (MARSS).

Fig. 7.5 Once mastered, these techniques can be used to remove complex tumor pathology using the da Vinci robot. (a,b) Surgeon at the da Vinci robotic console used to robotically remove an apically located thoracic tumor (c) seen on the right-side coronal CT (d).

The surgeon must weigh the risks and benefits of all options and should factor in his or her own level of comfort and experience with the surgical techniques under consideration. For example, an elderly, medically frail patient with multiple (> 2) levels of lumbar canal stenosis would typically be treated in our practice with a traditional open approach. The benefits of MISS in this patient, such as smaller incision and decreased soft-tissue injury, might be outweighed by the increased surgical time needed to treat three or more levels with MISS, thus increasing time under general anesthetic and increasing perioperative morbidity risk. In this case, we would elect to treat the patient in an open manner. Hence, patient selection is of utmost importance in surgical decision making, whether open or MISS.

While there may be significant controversies regarding the use of MISS in degenerative spinal conditions, treatment of spinal deformity with MISS is even more problematic. Some studies, and many experts in surgical correction of spinal deformity, suggest that MISS approaches for deformity may undercorrect sagittal spinal parameters resulting in suboptimal outcomes.²⁹^,³⁰^,³¹^,³² There have been several algorithms developed. Most recently, the minimally invasive spinal deformity (MISDEF) algorithm, developed by the International Spine Study Group,³³ provides three classifications. The algorithm categorizes patients based on radiographic parameters such as sagittal vertebral axis, pelvic tilt, lumbar lordosis to pelvic incidence mismatch, degree of listhesis, thoracic kyphosis, and coronal Cobb angle. Based on the criteria, classes I and II are amenable for MISS. Class III patients who have a sagittal vertebral axis greater than 6 mm, pelvic tilt greater than 25 mm, a lumbar lordosis to pelvic incidence mismatch greater than 30 degrees, and thoracic hyperkyphosis greater than 60 degrees are more appropriate candidates for an open approach, due to potential need for osteotomies to achieve adequate correction of the deformity.³³ However, many authors are currently developing and testing MISS strategies to accomplish osteotomies and major curve corrections, with data on these techniques expected soon after this writing.

7.4 Preoperative Planning

Preoperative work-up should include routine laboratory studies and further imaging as indicated. Evaluation and appropriate work-up of any and all comorbidities should be performed. If possible, the surgical plan should be reviewed in advance with anesthesia with attention to special considerations as necessitated by various MISS procedures. For example, thoracoscopic procedures requiring mainstem bronchus intubation and single-lung ventilation may necessitate preoperative pulmonary function testing and cardiac work-up.

7.4.1 Instrumentation

Acquisition of necessary tools and equipment should be arranged with the operating suite staff in advance. In particular, necessary imaging tools, such as X-ray, fluoroscopy equipment, or CT scanner, should be reserved. In addition, an endoscope with video tower and lighting source or microscope should be pretested and reserved. If electrophysiologic monitoring is indicated, arrangements with the appropriate technician should be made in advance. Additionally, appropriate minimally invasive instrumentation should be selected along with appropriate hemostatic agents.

7.4.2 Patient Positioning

Patient positioning is of paramount importance in MISS. Careful attention should be paid to placing the patient in the ideal position for the planned surgical procedure and any special bed or positioning equipment required should be reserved in advance.

Once a patient is positioned properly, it is imperative to assure that anatomic alignment is correct before proceeding. One should check alignment of the spinous processes in relationship to the pedicles as well as the orientation of the end plates with fluoroscopy (C-arm). If navigational tools are to be employed, care should be taken to ensure that the patient or the reference instruments are not moved once 3D imaging has been acquired.

Specific details of different instrumentation types, neuronavigation, and intraoperative imaging will be covered in detail elsewhere in this book.

7.5 Surgical Approach

We will defer specific discussion of individual MISS techniques, as those are covered in detail elsewhere in this book, but in general, fascial incision is key for almost every procedure. In thin patients, one may dissect with a Kelly clamp and monopolar cautery, strip fat with a sponge, and directly visualize the fascial incision. In obese patients, we generally rely on tactile feel of scalpel against the fascia. Avoid cutting deeply—muscle bleeding will be problematic. Palpate with a finger before proceeding to ensure adequate incision length (should be at least as long as skin incision, no shorter).

7.5.1 Surgical Technique

The operative techniques for the individual procedures are discussed in other chapters of this work. In this section, we will elucidate the unique aspects of MISS that form the basis of operative differences between MISS and traditional surgery. Minimally invasive surgery presents several unique and novel challenges to the surgeon. A unique operative field view with decreased overall exposure is the first major difference noted by most surgeons upon their first experience with MISS. A smaller incision, generally off midline, or several small incisions, represents a departure from the traditional midline incision associated with posterior cervical or lumbar procedures. Hand–eye dissociation, lack of depth perception, increased distance from the operative field, modified instrumentation, increased use of intraoperative imagine guidance, and a narrow working channel constitute the other major challenges. Each of these aspects, however, can be mastered with due diligence.

The Incision

The most obvious difference for both the surgeon and the patient is a smaller incision or a set of small incisions ( Fig. 7.6). Attention to incision placement is of utmost importance for nearly all MISS procedures. For both percutaneous procedures and those utilizing narrow tubular working channels, the trajectory to the desired location is paramount. As such, increased use of intraoperative image guidance is a must. For most minimally invasive posterior procedures, we position the C-arm fluoroscopy machine (or two machines for procedures requiring biplanar fluoroscopy, such as percutaneous pedicle screws or kyphoplasty) and mark the appropriate level with a Kelly clamp or K-wires prior to surgical field preparation and sterile draping ( Fig. 7.7). CT guidance for screw placement has also been described. Depending on the procedure to be undertaken, the incision is drawn at various distances lateral to the spinous process at the appropriate level. For example, endoscopic laminectomy with a 16-mm working channel would necessitate a 1.8-cm incision roughly 2 cm lateral to the spinous process. The exact location of the incision would be slightly adjusted depending on whether a hemilaminectomy or complete laminectomy was going to be performed and depending on the patient’s body habitus. Kyphoplasty would require a stab incision from a more lateral position. Percutaneous pedicle screw instrumentation would require a slightly longer incision at roughly the same position as for kyphoplasty.