The application and clinical significance of a new occipitocervical distance measurement method in the operation of basilar invagination

English Keywords:Basilar invagination  Occipitocervical distance  Cervical spine X-ray  Occipitocervical fusion

English Abstract:

  【Abstract】 Objectives: To measure the occipitocervical distance of patients with basilar invagination(BI) through the method of measuring the vertical distance from the center of C4 vertebral body to McGregor line, and to explore the feasibility and clinical significance of such method in evaluating the longitudinal reduction of occipitocervical area during the occipitocervical fusion(OCF). Methods: The clinical data of 82 patients with BI treated at our hospital from January 2014 to January 2019 was collected, including 23 males and 59 females, aged 50.3±9.6 years. 56 patients underwent OCF surgery(17 males and 39 females), Among them, 3 patients developed low cranial nerve palsy symptoms such as dysphagia, dysphagia, reduced pharyngeal reflex and other intolerant symptoms after OCF operation, which was considered to be related to the patients' excessive longitudinal occipitocervical region distraction during operation, and revision surgery was performed to reduce the distance their longitudinal occipitocervical region distraction. The vertical distance between the center of C4 vertebral body and the McGregor′s line(OC4D) of each patient was measured on neutral radiograph of lateral cervical spine in standing position and hyperextension and hyperflexion radiograph before operation. The OC4D values on lateral radiographs of cervical spine in natural standing position of 56 patients during hospitalization after surgery were measured(53 patients with improved symptoms after OCF and 3 patients underwent revision surgery after OCF), and the OC4D values of the 3 patients who underwent revision surgery after OCF were obtained before revision on cervical lateral radiographs in natural standing position. The vertical distance of tip of the odontoid to the McRae line(McRL) was measured on CT scans of the cervical spine on admission in 56 surgical patients and during hospital admission after OCF(3 patients after revision surgery). The longitudinal reduction distance of the occipitocervical in 53 patients who routinely recovered after OCF and 3 patients who underwent revision surgery after OCF was calculated(postoperative OC4D value-preoperative OC4D value). The Japanese Orthopaedic Association(JOA) score(17 points) was recorded at preoperation and 12 months follow-up. The reduction rate of occipitocervical area and the improvement rate of neurological function were calculated. Results: The OC4D of the 82 patients with basilar invagination on admission was 49.1±7.6mm in the neutral position, 49.0±7.5mm in the hyperflexion position, and 49.0±7.7mm in the hyperextension position, showed no statistically significant difference(P>0.05). The inter-observer ICC values of OC4D measurements in neutral, hyperextension, and hyperflexion positions were 0.951, 0.963, and 0.949(P＜0.05), and the intra-observer ICC values were 0.977, 0.982, and 0.971(P＜0.05), respectively. Among the 56 patients underwent surgery, 3 patients underwent revision surgery, and the symptoms of low cranial nerve palsy were significantly relieved after revision. The lower cranial nerve palsy symptoms of the patients were significantly relieved, and there were statistically significant differences in OC4D values before and after revision surgery(P＜0.05). The MCRL value decreased from 6.3±2.8mm preoperatively to 1.8±1.2mm postoperatively. The neutral OC4D values of 56 patients increased from 48.9±6.0mm before operation to 53.5±6.6mm after operation. The occipitocervical longitudinal reduction distance was 4.8±1.2mm, and the 95% reference value range was 2.4-7.2mm. JOA score was increased from 11.84±2.70 points before surgery to 14.88±1.74 points after surgery at 12 months follow-up, with statistically significant differences(P<0.05). The average reduction rate of occipitocervical region was 65.8%. The average neurological improvement rate was 70%. The correlation coefficient between longitudinal distraction distance and reduction rate and neurological improvement rate was 0.831 and 0.725(P<0.001), respectively. Conclusions: OC4D measurement is a simple and effective occipitocervical distance measurement method, it can be used to estimate the longitudinal distraction distance in the occipitocervical region of patients, before posterior occipitocervical fusion for BI. It can be used to evaluate the longitudinal distraction of the occipitocervical region, intraoperatively, while ensuring adequate decompression reduction of the occipitocervical area, it can avoid related postoperative complications caused by excessive longitudinal occipitocervical extension.