[Computer-assisted screw osteosynthesis of the posterior pelvic ring. Initial experiences with an image reconstruction based optoelectronic navigation system].

Injuries of the posterior pelvic with combined anterior and posterior instability require the stabilisation of both the anterior and posterior pelvic ring. If the injury only involves the ligamental connections, then a transileosacral osteosynthesis with screws is the minimal invasive and biomechanically suitable method of choice. The difficulty with this approach is the correct placement of the screws. Their position must be monitored intraoperatively in 3 planes (inlet, outlet and lateral viewing). This denotes that conventional methods involve high radiation dosages for the patient and the surgical staff. Having the system readily available and being able to perform updates during the operation, fluoroscopically supported navigation for the treatment of fresh injuries becomes possible. Between October 1999 and December 2000 7 patients with traumatic instability of the posterior pelvic ring were treated by computer assisted percutaneous transileosacral screw osteosynthesis. In each case the osteosynthesis of the ileosacral joint was performed with two cannulated AO 7.3 mm titanium screws. After the operation the screw position was controlled by CT scanning and compared to the data acquired intraoperatively. No patients had infection, and there were no postoperative neurological defects. The postoperative CT scans showed no intraspinal or intraforminal malplacement of the screws. In two cases a slight tangential screwthread penetration through the ventral sacrum was found. Our first experiences with this novel technology are encouraging and clearly demonstrate the advantages of fluoroscopic supported passive navigation systems for the optimal placement of ileosacral screws.