Both free hand and robotic-guided S2 alar-iliac (S2AI) screw placement prove to be safe, accurate and reliable techniques for achieving spinopelvic fixation. This is the finding of Jamal Shillingford (Department of Orthopaedic Surgery, Columbia University Medical Center, The Spine Hospital, New York Presbyterian, New York, USA) and colleagues, initially published in Spine.
This is the first study in the literature comparing free hand technique and robotic-assisted guidance for S2AI screw placement at a single centre.
The authors found a 97.9% accuracy for robotically guided S2AI screws. There was only one moderate to severe breach, and no major neurovascular or visceral complications. When comparing the free hand group and the robotically guided group, there were no significant differences in overall accuracy rates (94.9% vs. 97.9%, p=0.630), breach grade, breach direction, or overall complications between the groups.
Comparing data specifically on breaches: there were five cortical breaches in the free hand group, versus two in the robotically guided group (p=0.463); the number of moderate to severe breaches was three in the free hand group compare to one in the robotically guided group (p=0.630); and the average breach distance was similar between the two groups (3.9±2.2mm vs. 7.9±4.8mm, p=0.160).
A total of 51 patients (105 screws) who underwent spinopelvic fixation between 2015–2016 were propensity matched based on preoperative characteristics: 28 patients (59 screws) in the free hand group, and 23 patients (46 screws) in the robot group. There was one three-screw and one four-screw construct in the free hand group. The mean ages in the free-hand group and the robotically guided group were 57.9±14.6 years and 61.6±12.0 years (p=0.342), respectively. Despite matching, there was a greater proportion of women in the free hand group (71.4%) than in the robotically guided group (43.5%).
Shillingford and colleagues say, “The ability to achieve rigid spinopelvic fixation has plagued deformity surgeons for decades. Allen and Ferguson [both Section of Pediatric Orthopaedic and Spine Surgery, University of Texas Medical Branch, Galveston, USA] were the first to specifically address pelvic fixation with the Galveston technique, which incorporated the ilium into fixation constructs, paving the way for the spinopelvic instrumentation techniques utilised today.”
Allen and Ferguson first described the Galveston technique in 1984, before writing in 1988 the advantages of the procedure as “avoidance of postoperative casting or bracing, maintenance of secondary spinal contours, secure pelvic fixation when needed, and anterior thoracoplasty in a majority of patients”. Iliac screws are an alteration to the original Galveston technique, “but still require extensive sub-fascial dissection, making them prone to complications from implant prominence”, according to the present study authors.
Shillingford et al explain that the S2AI technique achieves lumbopelvic fixation through a midline incision with minimal subperiosteal dissection, less screw prominence, and subsequently, fewer wound complications. They add, “Additionally, the S2AI screws align with the cephalad S1 screws, obviating the need for offset connectors.”
Free hand S2AI screw placement circumvents the need for intraoperative fluoroscopy. Fluoroscopic guidance assists with accurate screw placement, but also exposes both surgeon and patient to increased levels of radiation, in addition to increased logistical considerations such as increased equipment and staff requirements. Therefore, robotic guidance—a recent technological advancement—has been proposed as a method of improving screw accuracy while potentially reducing operative time and radiation exposure to the surgeon.
The study authors acknowledge certain limitations to their study, explaining in Spine, “Aside from the inherent limitations of retrospective studies, our study did not include a fluroscopically guided cohort. Moreover, the free hand placement performed by a single, experienced senior surgeon may not be generalisable to the average spine surgeon. Additionally, there is a learning curve for placement of S2AI screws with robotic-assisted guidance that we did not objectively discern with the study. The safety of screw placement again may not be generalised to the average spine surgeon new to the use of robotic assistance when compared to the experienced surgeons in this study that utilised this technique. Lastly, although we were able to confirm the S2AI screws within the confines of the ilium, the resolution of the images obtained from the O-arm were limited when compared to conventional CT.”
For future work on robotically assisted versus free hand S2AI screw placement, prospective randomised trials are needed to “more rigorously evaluate” the difference between these insertion techniques, Shillingford et al conclude. They add, “Ultimately, multiple other factors, including cost, equipment availability, and surgeon experience, contribute to the decision regarding the various S2AI screw insertion techniques.”
Speaking to Spinal News International about the use of robotics in surgery, Shillingford comments, “Robotic-guidance is increasingly utilised in both simple and complex spine surgery. Since its FDA approval, robots have been used to place over 100,000 screws in over 15,000 spine cases. Potential advantages advocating use of robot-guidance in previous studies have included improved accuracy, less intraoperative radiation, the ability to choose implants preoperatively, and optimal planning of screw location to facilitate rod placement. Three of the most beneficial cases for using robotic assisted spine surgery include: 1) revision cases with prior fusion masses 2) placement of S2AI screws and 3) minimally invasive spine surgery (MIS).”
“There are, however, some potential disadvantages of robotic-assistance including the cost, availability, learning curve and the impact on resident/fellow training. Additionally, current robotic systems often require a computed tomography (CT) study to register the system while ensuring accuracy. It is our duty to develop a greater understanding of the biomechanics and advancements associated with this technology, so that we can balance safety for both the patient and surgeon. We also must remain conscious of both equipment costs and availability of these technologies (robotics and navigation) to ensure optimal outcomes for patients undergoing spine surgery.”
“Our study proved that both the free hand and robotic-guided techniques for S2-Alar-Iliac (S2AI) screw placement were safe and reliable for achieving spinopelvic fixation. Both techniques had comparable accuracy (98% robotic-guided vs. 95% free hand), even with the inclusion of surgeons at various levels of training (senior residents to senior spine surgeons). Additionally, there were no intraoperative or postoperative neurovascular or visceral complications resulting from either technique. The free hand technique relies heavily on the use of both palpable and visible pelvic anatomic landmarks for screw placement accuracy.”
“Currently, some robotic systems incorporate an advanced surgical planning software tool, thereby allowing surgeons to classify curve patterns, preoperatively determine implant positioning and size, decide on osteotomy planning and correction mechanics, and assist with realigning the spine in the coronal and sagittal plane.”