Feasibility of Minimally Invasive Sacropelvic Fixation Percutaneous S2 Alar Iliac Fixation

Study Design. A cadaveric study with postoperative computed tomography scan to evaluate instrumentation placement. Objective. To successfully place percutaneous sacropelvic instrumentation. Summary of Background Data. S2 iliac fixation has been in use clinically at some centers. Recently, anatomic data have been presented on the technique. The purpose of this study is to determine the feasibility of percutaneous placement of S2 iliac sacropelvic fixation (1) without damage to vital structures and (2) with in-line placement with S1 pedicle screws. Methods. Eight cadaveric spines were used in this study. Percutaneous pedicle screws were placed from L3-S1 in 4 and from L2-S1 in the remainder. Percutaneous S2 iliac screws were placed using a modification of the open technique. Rods were placed using minimally invasive techniques. All specimens were CT scanned. Trajectory of the screws was measured from CT scans. Maximal length was judged by a k-wire left in the S2 iliac screw. CT scans were critically evaluated for risks to visceral and neurovascular structures as well as cortical breaches. Results. Average length of the screws was 92.5 mm (range, 69-120 mm). No screw was intrapelvic or risked any visceral or neurovascular structure. No screws violated the cortex of the ilium. All S2 iliac screws were in-line with the S1 pedicle screws. The average cephalo-caudad trajectory was 29 caudal from direct lateral. The average anterior-posterior angulation was 42 from a horizontal line connecting the PSIS. Conclusion. Use of the S2 iliac technique may be a viable option in minimally invasive thoracolumbar deformity surgery. The screws were all in-line and connected easily to the cephalad instrumentation. On average, a length of approximately 90 mm was attained. No visceral or neurovascular structure was injured. Visualization of the first dorsal foramen and a standard anteroposterior and inlet radiograph were used for placement.