BACKGROUNDSacroiliac (SI) screw fixation is a demanding technique, with a high rate of screw malposition due to the complex pelvic anatomy. TiRobot™ is an orthopedic surgery robot which can be used for SI screw fixation. This study aimed to evaluate the accuracy of robot-assisted placement of SI screws compared with a freehand technique.

METHODSThirty patients requiring posterior pelvic ring stabilization were randomized to receive freehand or robot-assisted SI screw fixation, between January 2016 and June 2016 at Beijing Jishuitan Hospital. Forty-five screws were placed at levels S1 and S2. In both methods, the primary end point screw position was assessed and classified using postoperative computed tomography. Fisher's exact probability test was used to analyze the screws' positions. Secondary end points, such as duration of trajectory planning, surgical time after reduction of the pelvis, insertion time for guide wire, number of guide wire attempts, and radiation exposure without pelvic reduction, were also assessed.

RESULTSTwenty-three screws were placed in the robot-assisted group and 22 screws in the freehand group; no postoperative complications or revisions were reported. The excellent and good rate of screw placement was 100% in the robot-assisted group and 95% in the freehand group. The P value (0.009) showed the same superiority in screw distribution. The fluoroscopy time after pelvic reduction in the robot-assisted group was significantly shorter than that in the freehand group (median [Q1, Q3]: 6.0 [6.0, 9.0] s vs. median [Q1, Q3]: 36.0 [21.5, 48.0] s; χ2 = 13.590, respectively, P < 0.001); no difference in operation time after reduction of the pelvis was noted (χ2 = 1.990, P = 0.158). Time for guide wire insertion was significantly shorter for the robot-assisted group than that for the freehand group (median [Q1, Q3]: 2.0 [2.0, 2.7] min vs. median [Q1, Q3]: 19.0 [15.5, 45.0] min; χ2 = 20.952, respectively, P < 0.001). The number of guide wire attempts in the robot-assisted group was significantly less than that in the freehand group (median [Q1, Q3]: 1.0 [1.0,1.0] time vs. median [Q1, Q3]: 7.0 [1.0, 9.0] times; χ2 = 15.771, respectively, P < 0.001). The instrumented SI levels did not differ between both groups (from S1 to S2, χ2 = 4.760, P = 0.093).

CONCLUSIONSAccuracy of the robot-assisted technique was superior to that of the freehand technique. Robot-assisted navigation is safe for unstable posterior pelvic ring stabilization, especially in S1, but also in S2. SI screw insertion with robot-assisted navigation is clinically feasible.