Computer assisted screw insertion into real 3D rapid prototyping pelvis models

Objective. Show the use of computer navigation in exact screw positioning in the different pelvic bones. Background. Computer assisted pedicle screw insertion in the spine is an established procedure. Screw fixation is also used in highly difficult pelvic and hip surgery (arthroplasty revision surgery and tumor surgery). Design. Insert as long screws as possible with computer navigation into the different bones of the pelvis and compare these results with a non-computer controlled method. Methods. The computer navigation was done with the system of Medivision (Oberdorf, Switzerland), the software was SurgiGATE 2.1. Optically controlled spine instruments and a special calibrated drill were used. The screw insertion with and without computer navigation took place in seven real rapid prototyping pelvis models matched by pairs. Three screws were inserted into the Os ileum, one into the Os pubis and one into the Os ischium. The length of the inserted screws were measured and compared using routine statistic methods. Results. The mean screw length with vs. without computer navigation was 8.9 vs. 5.7 cm in the Os ileum (P=0.0001), 6.0 vs. 4.2 cm in the Os pubis (P=0.01) and 4.3 vs. 3.9 cm in the Os ischium (not significant). Conclusions. The use of computer navigation allows for the insertion of longer screws into the bones of the pelvis (more exact positioning), which requires a more precise original point of entry and direction of the drill (vector).