Selection strategy of occipito-C2 angle and posterior occipitocervical angle in patients with basilar invagination during occipitocervical fusion

English Keywords:Occipitocervical fusion  Occipito-C2 angle  Posterior occipitocervical angle  Basilar invagination

English Abstract:

  【Abstract】 Objectives: To explore the proper selection strategy of occipito-C2(OC2A) and posterior occipitocervical angle(POCA) in in patients with basilar invagination during occipitocervical fusion(OCF). Methods: Data of 42 patients with basilar invagination(BI) who underwent OCF from January 2012 to January 2017 were reviewed. 15 males and 27 females with an average age of 47.6±10.7 years were included. And the height of patients was 164.8±11.5cm, weight was 61.5±8.8kg, and body mass index(BMI) was 22.6±3.1kg/m2. Among them, BI combined with atlantooccipital fusion in 13 cases, atlas dysplasia in 8 cases, odontoid malformation in 5 cases, and atlantooccipital fusion + Klippel-Feil syndrome in 16 cases. Eighty-four healthy subjects were selected according to the baseline matching of gender and age of patients with BI, 30 males and 84 females with an average age of 50.6±9.5 years were included. The height of healthy subjects was 166.1±12.4cm, weight was 63.8±9.6kg, and BMI was 22.1±3.9kg/m2. OC2A and POCA of the healthy subjects were measured. OC2A, POCA, cervical spinal angle(CSA), and theheight ratio of lower cervical intervertebral disc to vertebral body (S value) were measured preoperatively, immediately after surgery, and at the final follow-up in patients with BI. The mean value and 95% confidence intervals(95% CI) of OC2A and POCA in the healthy subjects were obtained. The patients with BI were divided into normal angle group (OC2A and POCA both in 95%CI of healthy group) and abnormal angle group according to the value of OC2A and POCA immediately after surgery. The difference of OC2A(d-OC2A) and POCA(d-POCA) from post-operation immediately to pre-operation were obtained.The preoperative and final follow-up visual analog scale(VAS), Japanese Orthopedic Association score(JOA), neck disability index(NDI), and dCSA/dS (CSA/S from immediately after surgery to the final follow-up) were recorded. Results: The values of OC2A and POCA were 14.8°±4.5° and 108.1°±8.6° in the healthy, respectively, and the respective 95% confidence intervals(CIs) were 8.6°-21.1° and 91.2°-121.8° as the normal range. The preoperative OC2A, POCA and CSA of patients were 5.6°±4.3°, 123.8°±10.4° and 25.7°±9.5°, respectively. The values of OC2A and POCA immediately after surgeryin normal angle group(n=26) were 12.9°±3.2°, 111.9°±7.2°. In abnormal angle group(n=16), the postoperative OC2A and POCA were 6.1°±2.4° and 120.4°±9.4°, respectively. The d-OCA and d-POCA of normal angle group were 10.6°±3.5°(6.5°-18.8°) and -8.8°±5.2°(-24.0°-5.5°), and those values of the abnormal angle group were 3.8°±4.1°(-4.5°-9.5°) and -6.4°±4.2°(-18.0°-7.8°), respectively. And the difference of postoperative OC2A, POCAand d-OC2A between the two groupswere statistically significant(P<0.05). The VAS, JOA, and NDI of abnormal angle group at the final follow-up were significantly better than those in the normal angle group (P<0.05), and the normal angle group showed statistically greater dCSA and dS than those in the abnormal angle group(P<0.05). Conclusions: Preoperative OC2A and POCA in BI patients are different from those in the normal population. Based on the values of OC2A and POCA in patients before surgery, the selection of OC2A is lower than the normal range and closer to the biomechanical environment of occipitocervical region and lower cervical spine before operation which can reduce the postoperative compensatory abnormal activities and degeneration of the lower cervical spine and improve the clinical efficacy of patients.