Correction of Occipitocervical Malalignment Using Cervical Pedicle Screws and Plate-rod Systems: Indirect Decompression at the Craniocervical Junction in 70 Patients**

This retrospective study was conducted to analyze the clinical results in 70 patients with lesions at the craniocervical junction, and to evaluate the effectiveness of pedicle screw fixation in occipitocervical reconstructive surgery.

Methods: From February 1993 through February 2001, seventy patients with lesions at the craniocervical junction underwent reconstructive surgery using pedicle screws in the cervical spine and occipitocervical rod systems. The occipitocervical lesions were atlantoaxial subluxation associated with basilar invagination, which were caused by rheumatoid arthritis in 59 patients, os odontoideum in four, metastatic tumor in three and others in four. The lowest cervical vertebra of fusion was C2 in 49 patients, and the remaining 21 patients underwent fusion downward C3 to T2. Flexion deformity of the occipito-atlantoaxial complex was corrected by application of extensional force, and upward migration of the odontoid process was reduced by application of combined force of extension and distraction between the occiput and the cervical pedicle screws. Regarding additional surgeries, resection the posterior arch of the atlas was performed in seven patients, posterior decompression in the middle and lower cervical spine in seven, noncontiguous lower cervical fixation using pedicle screw in three, and anterior cervical fusion in two. Two patients in the initial phase of this series required Halo-vest immobilization postoperatively for dislodgement of occipital screws.

Results: Excepting three with metastatic tumors who did not receive any bone graft for fusion and one patients of postoperative early death, solid fusion was achieved in 64 of 66 patients (fusion rate: 97%). Correction of malalignment at the craniocervical junction was adequate, and postoperative MRI revealed improvement of anterior compression of the medulla oblongata. 135 degree of decreased preoperative cervicomedullary angle (normal value: 163 degree) in MRI improved to 158 degree in average. One patients sustained nerve root irritation by screw, and required screw removal. There were no other neurovascular complications by cervical pedicle screws. Two patients required elongation of the fusion level for progression of degenerative changes at the caudally adjacent segment Deep infection in two patients were successfully managed by continuous irrigation.

Discusion/Conclusions: Many patients who required occipitocervical fixation possess combined deformities in the sagittal plane. These consisted of anterior translation of the atlas on the axis, vertical subluxation of the odontoid process, and flexion deformity caused by anterior subluxation or dislocation of the occipitoatlantal complex on the axis. If atlantoaxial dislocation is irreducible and the dislocation is a causative factor of neurologic deficits, anterior decompression and fusion by a transoral or mandibullar splitting approach will be required. Occipitocervical reconstruction by the combination of cervical pedicle screws and occipitocervical rod systems provided the high fusion rate and sufficient correction of malalignment in the occipito-atlantoaxial region without serious neurovascular complications. Realignment at the craniocervical junction provided indirect decompressive effect of the medulla oblongata. Results of this series suggest that the posterior realignment procedure by pedicle screw fixation with the significant correctability of sagittal malalignment succeeds in anterior decompression of the medulla oblongata.

**The FDA has not cleared a drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed in an "off label" use).