[A strategy of combining posterior occipitocervical angle with occipital-C 2 angle for adjustment of occipitocervical fixation angle in posterior instrumented occipitocervical fusion].

Objective: To assess the application and the effectiveness of a strategy of combining posterior occipitocervical angle (POCA) with occipital-C 2 (O-C 2 ) angle for adjustment of occipitocervical fixation angle in posterior instrumented occipitocervical fusion.

Methods: The clinical data of 22 patients undergoing posterior instrumented occipitocervical fusions between March 2013 and January 2016 were retrospectively analysed, and all patients were performed by using a strategy combining with POCA and O-C 2 angle for adjustment of occipitocervical fixation angle. All patients suffered from occipitocervical instability, including 7 males and 15 females with an average age of 44.4 years (range, 20-63 years). The patients were diagnosed as skull base depression with atlantoaxial dislocation in 20 cases and rheumatoid arthritis in 2 cases. The preoperative Japanese Orthopaedic Association (JOA) score was 13.2±2.0, and the visual analogue scale (VAS) score was 6.3±0.9. The POCA was first used to guide the pre-bending of the nail-rod system during the operation, so that POCA of 12 patients with abnormal preoperative POCA could be restored to the normal range; then intraoperative fluoroscopy was used to confirm whether the O-C 2 angle was within the normal range (4 cases were abnormal and 2 cases needed intraoperative adjustment); finally, POCA and O-C 2 angles were within normal range after adjustment. The postoperative complications were recorded, and the JOA and VAS scores were used to evaluate the recovery of spinal nerve function and the degree of pain relief after operation. The radiological data were collected to evaluate the bone graft fusion, the changes of postoperative POCA, O-C 2 angle, and lower cervical curvature (Cobb angle).

Results: All 22 patients were followed up 12-48 months, with an average of 24 months. No serious complications and reoperation occurred. At last follow-up, the VAS score and JOA score were 2.9±0.8 and 15.4±0.9 respectively, which were significantly improved when compared with preoperative ones ( t =15.870, P =0.000; t =6.587, P =0.000). Imaging examination showed that 22 patients had occipitocervical osseous fusion, good position of internal fixator without loosening or fracture, and good occipitocervical stability. The POCA and O-C 2 angles were within the normal range at 3 days after operation and at last follow-up, and there were significant differences when compared with preoperative ones ( P <0.05); but no significant difference was found in POCA and O-C 2 angles between at 3 days after operation and at last follow-up ( P >0.05). There was no significant difference in Cobb angle of lower cervical spine between before and after operation ( P >0.05).

Conclusion: The strategy of combination POCA and O-C 2 angle for adjustment of occipitocervical fixation angle during operation can ensure a better effectiveness.