OTA 1997 Posters - Pelvic & Acetabular Fractures

*Evaluation of a Computer-Assisted Surgical Technique for Percutaneous Internal Fixation in a Transverse Acetabular Fracture Model

David M. Kahler, MD, Robert Zura, MD, K. Mallik, MD

Dept. of Orthopaedic Surgery, Univ. of Virginia Health Sciences Center, Charlottesville, Virginia, USA

Introduction: Certain minimally displaced acetabular fracture patterns are amenable to treatment with computed tomography (CT) assisted percutaneous fixation using cannulated screws. This technique appears to avoid many of the complications associated with formal open surgical exposure of the acetabulum. Although the early results have shown promise in the treatment of selected 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 patient specific CT image of the pelvis in a computerized surgical navigation system. This integrated system consists of an array of three digital cameras, LED-equipped optically-tracked surgical instruments, and a computer workstation on a rolling cart.

Methods: Ten simulated high transverse acetabular fractures were created in cadaver specimens. An external array consisting of spherical aluminum fiducials affixed to carbon fiber rods was attached to the iliac wing of each specimen with two 4.5 mm Schanz pins. The fiducials are readily visible on CT, and provide fixed reference points on both the virtual model and the specimen. Digitized CT scans of the specimens were loaded onto the computer workstation, and ideal pin placement and length for fracture fixation were then planned on the virtual model. Registration and orientation were performed using a probe with a concave hemispherical tip that mates with the fiducials. Using percutaneous technique, an optically tracked drill guide was used to direct a 2.8 mm guide wire perpendicular to the fracture cephalad to the joint surface, followed by a second wire crossing the fracture into the anterior column. Intraoperative radiographic imaging was not utilized during passage of the guide wires.

Results: Plain radiographs and specimen dissection were performed after fixation for evaluation of the accuracy of pin placement. In each case, accurate placement of the guide wires was possible without direct visual or radiographic feedback. 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. All ten anterior column guide wires were successfully placed without violating the confines of the column.

Conclusion: Computer integrated percutaneous fixation of transverse acetabular fractures in vitro provides comparable accuracy to CT-guided procedures without the need for intraoperative radiographic imaging. This technique offers substantial operative time savings and may decrease the need for formal open surgical exposure in selected fractures. Computer assisted surgery may also prove a useful adjunct to conventional internal fixation using standard surgical approaches. Case reports will be used to demonstrate clinical application of this technique in acetabular fractures and iliosacral disruption.