Evaluation of a computer integrated surgical technique for percutaneous fixation of transverse acetabular fractures

Abstract

Certain minimally displaced acetabular fracture patterns are amenable to treatment with computed tomography (CT) assisted percutaneous fixation using cannulated screws (Kahler DM, et al. Presented at AAOS Annual Meeting, Feb. 1996). Although the early results have shown promise in the treatment of transverse, anterior column, and anterior column/posterior hemitransverse fractures, there remain concerns regarding radiation exposure to the patient, operative time averaging 45 minutes per screw, and the questionable sterility of the CT suite. A feasibility study was therefore undertaken to evaluate a new technique of percutaneous acetabular fracture fixation utilizing a stored CT image of the pelvis in a computer integrated surgical system, consisting of an array of three CCD cameras and a computer workstation. Five human cadaver pelvis specimens with intact external soft tissues were obtained, and simulated transverse acetabular fractures with roof arcs of approximately 30 degrees were created bilaterally. An external fiducial array consisting of aluminum spheres affixed to carbon fiber rods was attached to the iliac wing of each specimen with two 4.5 mm Schanz pins. Computed tomography was performed to allow segmentation of the specimens and fiducial arrays. The digitized scans were then loaded onto a computer workstation, and ideal pin placement and length were planned. The fiducial arrays were registered using a probe to allow orientation of the pelvis, and the specimen and drill guide were then optically and dynamically tracked during the procedure. Internal fixation was simulated by the percutaneous placement of a 2.8 mm guide wire perpendicular to the fracture cephalad to the joint surface, and a second wire crossing the fracture into the anterior column. Plain radiographs and specimen dissection were performed after fixation for evaluation of the accuracy of pin placement. There was no sign of penetration of the hip joint or the cortical bone of the pelvic brim along the entire path of the wires. It was found that computer integrated percutaneous fixation of transverse acetabular fractures in vitro provides comparable accuracy to CT-guided procedures without the need for intraoperative CT or a formal surgical exposure. Additionally, operative time is greatly reduced in comparison with CT-guided technique, and the computer integrated surgical system allows greater variability in the angle of screw placement to compensate for variations in pelvic anatomy. Computer integrated surgery may allow accurate percutaneous placement of cannulated screws in acetabular fracture surgery, and may prove a useful adjunct to conventional internal fixation using standard surgical approaches.