Coorelation analysis between early postoperative center of gravity line (W-line) and proximal junctional failure after adult spinal deformity correction

English Keywords:Adult spinal deformity  W-line  Proximal junctional failure  Receiver operating characteristic curve analysis  Long-fusion surgery

English Abstract:

  【Abstract】 Objectives: To explore the correlation between the early postoperative center of gravity line of the human body, namely W-line in this study, and the proximal junctional failure(PJF) developing in adult spinal deformity(ASD). Methods: We retrospectively analyzed the data of 99 adult spinal deformity(ASD) patients(male: 19; female: 80) who received surgery operation in our single institution from June 2014 to March 2019. All of the patients underwent posterior long-segments(≥4 vertebras) fusion with instrumentation, and were followed up for a minimum of 24 months. The spinopelvic parameters before operation, at 3 months after operation and the final follow-up were measured and recorded. On the lateral full-spine X-ray radiographs, the vertical line through the external auditory canal was defined as the W-line, according to which, all the patients were divided into three groups: group A, group B, group C. The horizontal distance between W-line and S1 was defined as WSD, and the horizontal distance from W-line to the midpoint of the central line of the femoral head was defined as WHD. WSD and WHD were measured at 3 months after operation, and the position of W-line was converted into numeric value of W-line(N-W-line): N-W-line=WHD/WSD. The value of WSD/WHD was recorded as positive if W-line was in front of the reference point, and vice versa. The optimal location of W-line was deduced using receiver operating characteristic(ROC) curve analysis. A Kaplan-Meier curve and Log-rank were used to analyze the differences in PJF-free survival. Results: ROC curve analysis determined the optimal threshold of N-W-line at the 3rd month postoperatively was ±0.78 [sensitivity=75.0%, specificity=75.9%, the area under the curve (AUC)=0.736, P=0.003]. Then, three groups were defined as group A: the N-W-line>0.78, group B: -0.78≤N-W-line≤0.78, and C: N-W-line<-0.78, respectively. The pelvic incidence of patients in group A was the smallest among the three groups(P<0.05), and the sagittal vertical axis (P<0.001), T1 pelvic angle (P<0.001) and mismatch of pelvic incidence minus lumbar lordosis(P<0.001) at the 3rd month postoperatively were smaller than the other two groups significantly. Yet, of groups A, B and C, the number of patients occurring PJF was 12, 3, and 1, respectively, and the patients in group A suffered the highest incidence of PJF comparing with groups B and C （12/32 vs 3/49 vs 1/18, P<0.001）. Moreover, PJF-free survival was the lowest in the group A(P=0.005, Log-rank test). In groups C and B, the W-line position gradually moved forward, and the sagittal spinopelvic parameters increased gradually, while the incidence of PJF decreased significantly. Conclusions: The early postoperative W-line could be an effective predictor for PJF in ASD patients after deformity correction. ASD patients with W-line behind the sacrum or deviating away from the hip forwardly at the early post-operation would be vulnerable to PJF-developing. Those ASD patients with mildly inclination forwardly may have the optimal spinopelvic alignment after surgery.