Values of spino-cranial angle in sagittal balance reconstruction in occipitocervical fusion

English Keywords:Spino cranial angle  Atlantoaxial spine  Occipitocervical fusion  Sagittal balance  Cervical parameters

English Abstract:

  【Abstract】 Objectives: To explore the application value of spino-cranial angle(SCA) in sagittal balance regulation during occipitocervical fusion(OCF) surgery and sagittal balance assessment after surgery, as well as its relationship with other cervical sagittal parameters. Methods: A total of 55 patients with instability in the occipitocervical junction region were included in this study, all of whom were treated with OCF and were followed up ≥12 months. There were 30 males and 25 females, aged 18-70 years, with a mean of 45.2±11.9 years. On the preoperative and final follow-up X-rays, cervical sagittal parameters were measured, such as SCA, O-C2 angle(O-C2A), T1 slope(T1S), cervical lordosis(CL), cervical sagittal vertical axis(cSVA), and T1S-CL. The relationships between SCA and other sagittal parameters were analyzed. Setting T1S-CL=20° as sagittal balance， the patients were divided into balance group and imbalance group, and the optimal SCA cut-off value for sagittal balance before operation was confirmed to be 86.65° using receiver operating characteristic(ROC) curve analysis. According to the optimal SCA cut-off value, the patients were divided into low SCA group(SCA<86.65°, n=35) and high SCA group(SCA≥86.65°, n=20). There was no significant difference between the two groups in age, gender, operative time, operative segment, and blood loss(P>0.05). The sagittal parameters before operation and at final follow-up were measured and compared between the two groups, meanwhile, clinical outcome scores including Japanese Orthopaedic Association(JOA) scores and neck disability index(NDI) were also compared to evaluate the relationship between SCA and clinical outcomes. Results: There was a significant correlation between SCA and CL(r=-0.74), T1S-CL(r=0.61), T1S(r=-0.54) and cSVA(r=0.35)(P<0.05). However, the relationship between SCA and O-C2A was poor(r=0.23, P=0.19). The low SCA group had higher O-C2A, T1S, and CL compared to the high SCA group before operation, and at final follow-up, the low SCA group had greater values of change except for O-C2A(5.86°±14.76° vs 14.13°±8.86°). Regarding clinical outcomes, both groups demonstrated significant postoperative improvements in JOA scores and reductions in NDI scores compared to preoperative levels. However, the high SCA group exhibited lower preoperative JOA scores and higher NDI scores, with smaller improvements in JOA scores and smaller reductions in NDI scores at final follow-up compared to the low SCA group. Conclusions: The SCA with an optimal cutoff value of 86.65° can effectively predict cervical sagittal balance and clinical prognostic outcomes after OCF. It serves as a high-quality sagittal parameter for evaluating the surgical efficacy. Specifically, patients with low preoperative SCA exhibit more significant improvements in postoperative sagittal alignment and better clinical outcomes, whereas high SCA can act as an early warning signal for poor preoperative quality of life. Notably, the correlation between SCA and O-C2A is weak, making it difficult to directly provide a reference for the individualized planning of preoperative fixation angles in OCF.