Aim: Of Calveston (USA) and Crete (HELLAS). We studied immediate and long-term outcome of 50 patients who underwent subaxial lateral mass fixation of the cervical spine between January 1997 and March 2001.

Patients and Methods: Intraopeartive fluoroscopy and somatosensory evoked potential monitoring were employed in all patients. Immediate postoperative CT scans were performed to determine screw trajectory and placement. Follow up ranged from 1 to 5 years.

Results: Postoperative CT scans showed that 113 of 210 screws (54%) had unicorticate and 46% had bicorticate purchase. Forty-five screws (31 %) had suboptimal trajectory, but only 7 of these screws minimally penetrated the foramen transversarium without resultant vascular or neurological sequelae.

The overall fusion success rate in our series was 90%, while pseudoarthrosis occurred in 5 patients (10%), with screw breakage in 1 patient (2%). Two of these patients had bone graft supplementation and in other 2 patients was done anterior fusion.

Conclusions: Results of this study show that the recommended drilling technique and trajectory (15–25 degrees postal to the sagital plane, 20–30 degrees lateral I the axial plane), supplemented bone grafting and intraoperative SEP monitoring are all associated to good screw placement, fusion and neurological outcome and are recommended for all lateral mass fusion procedures.