34th Annual Scientific Meeting proceedings

The goal of minimally invasive surgery (MIS) is to perform a specific procedure with minimal surgical trauma, while still achieving the goal of the procedure. For spine, MIS has become a common choice for various procedures in humans at all spinal levels, including decompressive and certain stabilization procedures. Retrospective reviews on MIS for spine in humans report shorter surgery times, decreased intraoperative blood loss, shorter hospital stays and decreased complications. Comparative prospective human studies between MIS and open approaches are fewer in numbers but uniformly support the just mentioned benefits, except for surgery time, which for some procedures was longer in the MIS group compared to open surgery group. There appears to be a difference in study results when MIS is used for single site versus major multilevel procedures. Unfortunately, prospective randomized clinical trials are limited, and evidence of clear superiority of MIS over open approach in human spine is limited.

It should be a common surgical goal to reduce trauma by surgical approaches and protect surrounding soft tissues. This reduction in iatrogenic trauma can be pursued by limited open or true MIS approaches. Important requirements must be met when applying MIS to the spine, such as absolute need for magnification and illumination as well specialized instrumentation and implants. Due to its minimally invasive nature, intraoperative imaging and/or navigation are an additional pillar of MIS. Once these requirements have been met, the remaining important consideration is access strategy to the desired spinal location. A great variety of human spinal MIS retractors are available and can broadly be divided into rigid (such as tubular retractors) or adjustable (with moveable retractor blades). The cost of these retractors varies greatly and can reach over €100,000 for a complete instrument set. Considerations must also be given to the availability of equipment such as fluoroscopy, surgical microscope or endoscopic magnification, illumination, and potentially even cone beam CT and surgical navigation.

Published veterinary studies on MIS in spine are limited and almost all are based on cadaveric studies and a few clinical studies with a small number of patients. They cover various aspects of the requirements for MIS in spine, especially access strategies and magnification. Various studies describe the use of video-assistance to improve visualization of neuroanatomic structures. The use of tubular retractors has been described to successfully reduce the dimensions of the soft tissue approach, while still being able to perform decompressive procedures. As proof of concept, spinal navigation was evaluated and found to be accurate and safe in one large breed dog.

The emergence and availability of 3D printed patient-specific guides (PSG) offers unique opportunities for veterinary spinal MIS. There has been an increased use of 3D PSGs as drill guides for open approach instrumented spinal surgery in cats and dogs. Recently, the use of 3D printed PSGs as spinal MIS retractors has been described for targeted approaches for spinal decompression canine cadavers. These guides act as tubular retractors and are fixed to the planned anatomic location with screws placed into adjacent vertebrae. Human MIS retractors are often dimensionally and anatomically ill-fitting for our veterinary patients, leading, among other issues, to soft tissue obstruction by excessive muscle creep or slippage of the retractor from the intended location. While veterinary 3D PSGs have specific imaging/planing requirements and must be correctly applied and used, they allow us to produce appropriately fitted tubular guides that might solve many of the reported issues when using human instruments.

As with any emerging technique, MIS approaches and specialized equipment require refinement, and new technologies need to be assessed. And importantly, clinical studies are needed to confirm the proposed benefits of MIS spine surgery in veterinary patients.

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