Is This the Future Minimally Invasive Spine Surgery

Figure 1. Intraoperative photo showing a tubular retractor placed over a series of muscle dilators to approach the spine. With the evolution of modern spine surgery, the use of minimally invasive surgical techniques for the treatment of spinal pathologies has experienced exponential growth. The term minimally invasive spine surgery can be defined as techniques that attempt to limit approach-related morbidity by reducing iatrogenic trauma to normal anatomical structures of the spine. Common to many of these minimally invasive procedures is the use of muscle splitting approaches using a series of muscle dilators and small portals that minimize injury to the muscular, ligamentous and bony structures of the spine (Figure 1).

Minimally invasive procedures now have been successfully applied to the cervical, thoracic, and the lumbar spine. They can be preformed via posterior, anterior and lateral approaches. Preliminary data on reduced postoperative pain, length of hospital stay and recovery time as well as improved patient outcomes have been reported by a number of investigators.

Some Techniques Come and Go
Within the field of spine surgery, several procedures have been introduced to surgeons with considerable fanfare only to be abandoned after a few years in the clinical arena. This can be due to a number of factors including initial reports of excellent clinical results in multicenter trials where the technique is preformed by “the experts” or “inventors,” but the initial hyperbole that accompanies announcement of a new technique or technology is short-lived. With time the technique is either adopted because of its true worth or abandoned because it fails to yield the expected outcomes. Examples of technologies and techniques that spine surgeons have seen come and go include cylindrical cages (the “cage rage”), intradiscal electrothermal therapy, and laser discectomy. Although these technologies are still used, they have not gained the widespread acceptance that was anticipated. On the other hand, techniques and technologies that are successful and used by most spine surgeons include anterior cervical discectomy, fusion and plating, interbody fusion, and pedicle screw fixation. Time is the great equalizer for any new surgical technique and will ultimately determine its value. So how will minimally invasive spine surgery fare?

Figure 2. Intraoperative photo showing the use of a microscope that can enhance visualization while a minimally invasive spine procedure is performed through a tubular retractor

Despite the rapid growth of minimally invasive spine technologies, universal acceptance and adoption of these techniques by spine surgeons have been slow and intermittent. This is in part because of the initial lag time in receiving related surgical training, the learning curve needed to master these techniques, and surgeons’ general penchant for prudent adoption of new technologies. Microscope visualization can facilitate the learning of some of these techniques (Figure 2). Nevertheless, patients are interested in treatments that reduce postoperative pain and recovery times, and a driving force in the adoption of minimally invasive spine surgery is patient-requested referral to surgeons who can perform these procedures safely and effectively. Other factors that promote the use of minimally invasive spine techniques include increased efficiency of healthcare delivery, industry involvement in development of minimally invasive devices, and the desire of surgeons to remain on the leading edge of treatment options. Examples of minimally invasive spine techniques that have significantly reduced cost of treatment while improving patient outcomes are percutaneous techniques such as vertebroplasty, kyphoplasty [Kyphon, Sunnyvale, Calif.] and more recently, OptiMesh [Spineology Inc., St. Paul, Minn.] reconstruction for treatment of osteoporotic compression fractures.

A review of minimally invasive spine techniques reveals that they can be preformed to address a wide variety of spinal conditions and pathology, thus making these techniques attractive to those surgeons wanting to specialize in this particular area of spine surgery. Though data are preliminary, results are comparable to or better than open techniques. A number of potential benefits that can be seen in minimally invasive compared to open techniques include less scar formation and fewer subsequent reoperations, while maintaining the normal spine architecture.

Figure 3. Intraoperative lateral fluoroscopic image showing percutaneous pedicle screw placement over k-wires, thus eliminating the need to expose the bony anatomy of the spine.

Figure 4. Postoperative axial T2-weighted MRI scan after a minimally invasive interbody fusion and percutaneous instrumentation. Note preservation of posterior lumbar musculature with minimal scar formation

New Minimally Invasive Techniques
A wide range of minimally invasive technologies that reduce approach-related morbidity has only recently been introduced. The development of percutaneous pedicle screw systems reduces the need to strip the paraspinal musculature off the spine for pedicle screw placement (Figure 3). Instead fluoroscopic or, in some cases, image guidance navigation can direct pedicle screw placement. This technique can significantly affect patient outcomes by preventing many of the problems encountered with open techniques, namely injury to the paraspinal musculature and adjacent facet joints and excessive scar formation (Figure 4). Successful fusion rates can potentially be enhanced since less of the supporting architecture of the spine is disrupted.

However, caution needs to be exercised. Similar to the advent of rigid spinal fixation, there are few class I and class II studies that definitively establish the advantage of minimally invasive procedures over that of open ones. For the moment, the rationale for choosing minimally invasive over open procedures lies in the underlying assumptions and beliefs of the surgeon and patient. For example, when shown the difference between the incisions of an open versus a percutaneous pedicle screw instrumentation operation, many surgeons believe that the benefit of the minimally invasive approach is obvious. For others, this visceral response is not enough to justify the initial learning curve required to adopt minimally invasive techniques. Further, prospective randomized controlled class I studies of minimally invasive procedures will need to be completed to ultimately prove their benefits.

In my experience, minimally invasive techniques are extremely effective in a variety of spine conditions including spondylolisthesis and associated stenosis as well as for surgeries in patients for whom previous open procedures have failed. Time will ultimately determine if minimally invasive techniques are a lasting part of the future of spine surgery. In my opinion they will be.

Mick Perez-Cruet, MD, MS, is director of the Minimally Invasive Spine Surgery and Spine Program, Michigan Head and Spine Institute, Detroit, Mich. Disclosure: The author is a consultant for Abbott Spine and Spineology Inc. and has received research support from Abbott Spine.

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