Variation of craniocervical junction volume as an effective parameter for basilar invagination treatment

The major pathological change in basilar invagination (BI) is represented in the decrease of craniocervical junction (CVJ) volume resulting from abnormal bone protrusion around the foramen magnum. The diagnosis and clinical evaluation of BI is mainly based on the clinical manifestations and radiographic measurements by means of calculation of the scan lines of CVJ in X-ray, CT and MRI. With the transoral decompression atlantoaxial reduction plate (TARP III) system, the decompression, reduction and fixation can be achieved to decompress and stabilize medulla spinalis change the position of the dens in CVJ, thus expand the CVJ relative volume, relieve the compression on medulla spinalis and the nerve injury. However, the correlation between the dens position change and the variation of CVJ has not been established previously. This study focused on the clinical significance of the variation of craniocervical junction (CVJ) volume caused by the dens position change for the treatment of BI.

We've performed an analysis of data from 62 BI patients admitted from January 2008 to May 2013, who were treated by TARP III system. The data include preoperative, postoperative JOA scores (Japanese Orthopaedic Association scores, 17 points method), preoperative and postoperative X-ray, thin-slice CT scan with three-dimensional reconstruction and MRI scan to measure the cervicomedullary angle (CMA). We have analyzed the preoperative and postoperative three-dimensional CT data by means of MIMICS 10.01 software system according to the Box volume (BV) method to determine the changes of CVJ volume resulting from preoperative and postoperative dens position change, assessed the correlation between the CVJ volume changes and the JOA scores with correlation between CMA change and the JOA scores. All data were analyzed by paired t-test and Pearson correlation analysis.

In all 62 patients, JOA scores were recovered from preoperative 9.26 ± 1.66 to postoperative 13.02 ± 1.44, CMA change rate was 21%, and CVJ volume change rate was 36%. The CMA change rate and the JOA score recovery rat exhibited relevance, as Pearson's correlation coefficient was 0.46 (p < 0.005). The Pearson's correlation coefficient between CVJ volume change rate and JOA score recovery rate was 0.63 (p < 0.005), and the CVJ volume change rate was significantly different while compared with the correlation between CMA change rate and JOA score (p < 0.005).

the CVJ volume change rate is a sensitive and reliable parameter for the evaluation of neurological function improvement in patients with BI. It can be used as a predictor to evaluate the postoperative neurological recovery.