Abstract
Here is a little word association game: What do the following words have in common and what do they really mean? • Percutaneous ‘Perc’ screws • Cortical screws • Far lateral surgery • Anterior oblique surgery • Prone transpsoas surgery • Unilateral biportal endoscopy • Uniportal endoscopy • Exoscope • Machine vision • AI powered • Image guidance systems • Robotic assisted surgery • Virtual reality surgery • Machine learning • Augmented reality • Laser surgery • Enabling technologies • Levelling the playing field • Learning curve • Efficacy • Effectiveness • Efficiency
Yes, you guessed it—these are just some of terms used in conjunction with the rapid dissemination of techniques associated with the general concept of minimally invasive spine surgery (MISS). At the conclusion of this editorial we will provide you with alternative interpretations for these new catch phrases.
Since the start of the new millennium the concept of increasingly performing spinal decompression and instrumentation surgery through approaches away from the traditional posterior midline through some form of tubular retractor system has become a mainstream topic in spine surgery. The challenge seems to be more directed at what more can be performed through ever smaller surgical incisions. The actual goals of spine surgery—safe and effective decompression of compromised neural elements and mechanically sound and stable reconstruction or stabilization of (a) structurally deficient motion segment (s) in a physiologic alignment to last for a meaningful time period seems to have been subjugated to the idea that the smallest incision possible under use of an increasingly complex array of ghee whizz gadgets is the actual primary goal. This is—of course—notwithstanding to the reality that the sum of paraspinal incision scars of MISS patients is frequently longer than that of one well-placed conventional midline incision.
Undoubtedly, the idea to mimic the successes of knee and shoulder arthroscopy and less invasive hip replacement surgery by minimizing perioperative access related pain and soft tissue disruption is a meritorious undertaking and very appealing to the public. After all, who wouldn’t want an outpatient band-aid spine surgery with minimal rebound time? And for industry the advent of new access-, navigation, implant and soft tissue closure technologies has been a bonanza of new development (and income!!) opportunities. From a surgeon perspective the opportunities are also significant, as we can increasingly offer spine surgery in an outpatient setting at smaller specialized surgery centers, with the opportunity to practice more efficiently and independently from the chokehold of large hospital systems and participate in the gainsharing more directly in return for assuming some of the enterprise risk.
In terms of skills acquisition the fulminant development of MISS related technologies has brought about the challenge to try to reign in the creative entrepreneurialism by organizing scientifically based results review/reporting system and also develop a formal educational pathway into this field.
AO Spine can undoubtedly claim a center seat at the growing MISS table as an organization dedicated to regular educational and teaching efforts from the early days of this technology development onwards. Looking back, starting in 2018, “step-by-step” AO Spine MISS Curriculum constitutes a landmark accomplishment by formulating a systematic teaching effort of such exposure conscious spine surgery technologies. In terms of publications, Global Spine Journal is proud to have published well over 200 articles over the years pertaining to MISS related topics, with a highlight being the Special Issue titled “The 6T’s of Minimally Invasive Spine Surgery: Target, Technology, Technique, Training, Testing and Talent” in 2020 edited by R. Haertl.1-6 As stated in his editorial Dr Haertl postulated that perhaps as much as 75% of spine surgery done annually in the United States (from an estimated 1.2 million procedures done annually) could at one point in time in the future be done at least under partial utilization of MISS techniques, with no time point for this saturation level being given.
On the results section at this time there have been increasing voices raised by the early adopters of MISS touting the superiority of MISS over conventional “open” spine surgery.
In fact the review of larger studies in the literature is fraught with many contradictory insights, such as that of the Norwegian Spine registry, which shows no really dramatic differences in larger population groups. When there are statistically significant differences touted such as in a larger retrospective study an estimated blood loss difference of 100 – 300cc’s without differences in transfusions is clinically probably not significant. When looking at surgery times the old question emerges as to what actually constitutes surgery time—is it the beginning of actual incision or does the clock start when the far more time and radiation intensive initial imaging acquisition starts? As always looking at the raw numbers and seeing how they compare to one’s own clinical experience is a helpful real world method to go beyond pure reliance on the P-value, regardless of its significance. For instance, an inpatient length of stay of 6.5 vs 4.7 days for a traditional vs a MISS fusion cohort may be statistically significant, but is in conflict with a 1-2 day hospital length of stay expected for most single and two level fusion surgeries in United States hospitals. The most important insight of the current state of MISS publications comes from the fact that virtually all publications are from interested parties, early adopters and commercially conflicted authors.
With the excitement of growth fueled by enthusiastic “early adopters” in the field comes a growing responsibility. Speaking from the vantage point of a more seasoned spine surgeon raised in the “open” era there is a growing number of consistent subjective observations appearing in connection with MISS treated patients showing up in the daily clinical practice of a busy tertiary/quaternary traditional surgeon. Before going into a listing of some of these it should be clearly stated that the field of Spine care in general and in all its incarnations is a study of imperfection, frustrations and setbacks—and ideally presents an ongoing learning and opportunity for continuous self-improvement. That said here is a listing of some of the more common themes of MIS surgery patients:
For decompressions common themes are missed or underdecompressed neural elements, “patched” dural tears, iatrogenic pars defects. For fusions there is a growing trend of multilevel fusions, usually covering the L3-5, sometimes L2-5 levels, commonly without or insufficient lordosis and deficient sagittal balance and/or imbalanced coronal alignment. There are more and more patients with complex arrays of multiportal anterior, anterolateral and then percutaneous posterior access scars commonly combined with an inexorable march up the lumbar spine with annual rostral progression to the point of the thoracolumbar junction, when the referral to a “traditional” “open” spine surgeon finally occurs. This is aside from the question of non-/delayed-/mal-/nonunions with settled small interbody cages and loosened or cutout screws. And relative to anterolateral and far lateral tubular-based spine surgeries the question of plexopathies, neuropathies, hip flexion and knee extension weakness and visceral organ injuries (blood vessels, ureters, bowels) has emerged as a feared (but reportedly very rare) complication entity with pseudohernias (paralysis of the obliqui musculature) being one of the more benign but poorly understood emerging postoperative phenomena previously almost unheard of in the era of more conventional anterior thoracolumbar approach surgeries.
Again complications, set-backs and unanticipated developments are firmly part of all spine surgeries regardless of approach techniques. This spurious listing of complications, however, is to serve as a reminder that we are still in an era of discovery and early consolidation as we are witnessing the conversion of emerging MISS technologies, as practiced by dedicated early adopters, into a mainstream practice pattern. As we are witnessing this mainstreaming effect, it would be helpful to reflect that although surgeons applying the impressively evolving “suite of enabling technologies” (Haertl) should still adhere to the core principles of spine surgery—meaning applying the least invasive surgery relative to the patient and their disease process. Just because a fusion can be performed with less invasive access technology should not mean that this is the new standard of care for degenerative conditions that could be equally—if not better—served with a well performed decompression or stabilization surgery only. The statement that ‘decompressions don’t work as well as fusion surgeries’ in the treatment of a mechanically stable lumbar spinal stenosis surgery, for instance, is a worrisome quote increasingly seen at national conferences by surgeons employing MISS fusion techniques. The true essence of “less invasive spine surgery” might be better served by considering the magnitude of biomechanical intervention such as a decompression surgery vs a fusion surgery. Such a methodology might be more inclusive of motion preserving non-fusion techniques anatomically conscientious of non-destabilizing decompression techniques, even if applied with a conventional midline approach and not through a tubular retractor. With this in mind here is a “tongue in cheek” decoding of the lexicon of MISS words presented in the introduction. • Percutaneous ‘Perc’ screws: Why work hard on getting a fusion if I can put in screws through a muscle? • Cortical screws: Marginal screws for marginal fixation • Far lateral surgery: Psoas – who needs a psoas? • Prone transpsoas surgery: See above, just upside down. • Anterior oblique surgery: There sure are a lot of tubular structures running across that space. • Unilateral biportal endoscopy: Shoulder surgery reinterpreted for the spine • Uniportal endoscopy: Wow! All in one! • Exoscope: Magnum view through a tiny camera. • Machine vision: The camera that sees it all – provided there is good hemostasis • AI powered: Whoever programmed this algorithm is telling you what to do – thanks Hal! • Image guidance systems: Could be better than a night-time C-arm tech – if the program works today • Robotic assisted surgery: Yeah - No more carpal tunnel! • Virtual reality surgery: Am I really seeing what I’m seeing or is it just an illusion? • Augmented reality: Reality as it might be. (don’t leave your proprioceptive skills at home) • Machine learning: Hopefully the machine will be willing to learn from its administrators’ mistakes • Laser surgery: Burning up tissues is so much more gratifying than drilling and picking away at them • Enabling technologies: Everybody can do this • Levelling the playing field: No more need for star surgeon experts – see above • Learning curve: Euphemism for how many otherwise avoidable complications are acceptable? And finally the big three E’s, as applied to Spine surgery: • Efficacy • Effectiveness • Efficiency 1. Efficacy means to see if under idealized circumstances a certain procedure performed by true experts can work in very well selected patients under carefully curated conditions. 2. Efficiency means that a procedure is assessed for its results under real world circumstances as practiced by the average surgeon for regular patients. 3. Efficiency means that a certain procedure also works in the most economical way.
Seen under the guise of the three E’s, MISS has arrived at the inflection point of the second E phase—efficiency. This is an undeniable credit to the pioneers of the technique—certain early adopters who are not blindly jumping on a bandwagon but are willing to critically reflect on wins and losses and openly share their experiences with their peers and the public. To make it into the third E phase—the efficiency eVALUEation– will be a critical hurdle to pass on the road to Dr Haertls 75% utilization prediction and only become realistic if MISS with all its direct and indirect add-on costs makes it through the Efficiency phase with more population based assessments performed over longer durations of time. Until such time MISS remains an interesting care option but is far from being a new “standard of care.”