The Future of Minimally Invasive Spine Surgery

Abstract

The field of minimally invasive spine surgery (MIS) has enjoyed a staggering rate of advancements in techniques and technologies over the last 15 years. Even though innovation in this domain has not reached its apogee, the rate of change is likely slowing. Therefore, in considering the future of MIS, it seems most appropriate to honestly assess prior developments (MIS evolution), what techniques in MIS appear to be most effective (MIS present), and what efforts hold the most promise for the future (MIS future). MIS DEFINITIONS MIS has become a fundamental part of spinal surgical practice for a variety of reasons, including the promise of decreased morbidity and faster recovery times. A combination of better surgeon training and education and the wide availability of the necessary operative equipment has made most MIS techniques readily accessible. Furthermore, there has been an increased demand from patients seeking MIS treatment for their spinal diseases. This demand has been driven, in part, by advertising and product vendors. New technologies emerge each year, including recent devices that offer percutaneous approaches for central lumbar stenosis,1 foraminal stenosis,2 and sacroiliac joint dysfunction.3 However, this onslaught of new devices and techniques can produce as much confusion as enthusiasm because the evidence base for their use lags behind their introduction. The resultant poor understanding of the effectiveness and clinical role for various “MIS” procedures has even led to a threat to payment for services. Indeed, the BlueCross/BlueShield subsidiary Anthem has had a long-standing negative coverage decision against percutaneous and endoscopic spinal surgery as being “investigational and not medically necessary.”4 In 2009, United Healthcare declined to cover MIS direct lateral interbody fusion techniques but chose to cover “laser spine surgery.”5 All this serves to underscore the need for better clarity in the classification of MIS procedures. In response to these pressures, the American Association of Neurological Surgeons/Congress of Neurological Surgeons Section on Disorders of the Spine and Peripheral Nerves in 2011 elaborated a framework for better understanding of MIS procedures. Specifically, we set forth procedural definitions based primarily on the method of access and modality of visualization. This framework seeks to differentiate those procedures that achieve the same anatomic surgical objectives as existing open procedures from uniquely novel approaches. Therefore, the techniques are broken down into 3 broad categories: percutaneous, endoscopic, and minimal access. Percutaneous procedures are those that gain access via a percutaneous needle or cannula and for which the only mode of visualization is fluoroscopy. Endoscopic procedures also gain access via a percutaneous cannula, use solely the endoscopic camera for visualization, and require specialized instruments. Minimal-access techniques, on the other hand, rely on a tissue-sparing approach with tubular dilators and retractors that allow visualization of the anatomic structures with the naked eye with or without the use of adjunctive magnification (eg, loupes or microscope). Minimal access also permits the use of either conventional or specialized surgical instruments. It is this final category of procedures that have the most surgical relevance and can therefore be best compared with and equated to their typical open counterparts. The remainder of this article focuses largely on the minimal-access category of techniques when referring to MIS. MIS EVOLUTION The primary goal of MIS surgery is to reduce approach-related tissue injury and complications and thereby reduce postoperative pain, blood loss, and recovery time while still achieving the same clinical objectives.6 Preclinical, histological, serological, radiological, and clinical outcome data have shown the often profound iatrogenic tissue injury associated with typical open posterior spinal ap