Analysis of Associating Radiologic Parameters With Clinical Outcomes After Posterior C1–2 Fusion

OBJECTIVE: To evaluate which radiologic parameters affect clinical outcomes in patients underwent posterior C1–2 fusion for atlantoaxial dislocation. METHODS: From January 2014 to December 2017, among 98 patients underwent C1–2 posterior fusion, patients with previous cervical surgery or extending to subaxial spine or basilar invagination were excluded. Finally, 38 patients were included. O–C2, C1–2, C1–C7, C2–C7 cobb angle (CA), T1 slope, C1–7, C2–7 sagittal vertical axis (SVA), and posterior atlantodental interval (PADI) were measured at preoperative and postoperative 1 year. The difference between postoperative and preoperative values for each parameter was designated as Δvalue. Postoperative subaxial kyphosis (PSK) was defined to decrease ≥ 10° at subaxial spine. Visual analogue scale (VAS), Japanese Orthopedic Association (JOA) score, Neck Disability Index (NDI) were used to evaluate clinical outcomes. RESULTS: Mean age was 54.4 ± 15.9. Male to female was 14 to 24. Of radiologic parameters, C1–7 SVA and PADI were significantly changed from 26.4 ± 12.9 mm, 17.1 ± 3.3 mm to 22.6 ± 13.0 mm, 21.6 ± 3.4 mm. ΔC1–2 CA was correlated with ΔC1–7 CA and ΔC2–7 SVA. ΔPADI correlates with ΔO–C2 CA. VAS correlates with ΔC1–7 CA (p = 0.03). JOA score also correlates with ΔC2–7 SVA (p = 0.02). NDI was associated with ΔPADI (p < 0.01). The incidence of PSK was 23.7%, and not significant with clinical outcomes. CONCLUSION: ΔC1–2 CA was correlated with ΔC1C7 CA, ΔC2–7 SVA. ΔC1–7 CA, ΔC2–7 SVA, and ΔPADI were the key radiologic parameters to influence clinical outcomes. Postoperative C1–2 angle should be carefully determined as a factor affecting clinical outcomes and cervical sagittal alignment.